ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V01CT00A001. doi:10.1115/FEDSM2017-NS1C.

This online compilation of papers from the ASME 2017 Fluids Engineering Division Summer Meeting (FEDSM2017) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

15th International Symposium on Gas-Liquid Two-Phase Flows

2017;():V01CT14A001. doi:10.1115/FEDSM2017-69022.

Models and simulations are employed to analyze the motion of a spring-supported piston in a vibrated liquid-filled cylinder. The piston motion is damped by forcing liquid through a narrow gap between a hole through the piston and a post fixed to the housing. As the piston moves, the length of this gap changes, so the piston damping coefficient depends on the piston position. This produces a nonlinear damper, even for highly viscous flow.

When gas is absent, the vibration response is overdamped. However, adding a little gas changes the response of this spring-mass-damper system to vibration. During vibration, Bjerknes forces cause some of the gas to migrate below the piston. The resulting pneumatic spring enables the liquid to move with the piston so as to force very little liquid through the gap. Thus, this “Couette mode” has low damping and a strong resonance near the frequency given by the pneumatic spring constant and the total mass of the piston and the liquid. Near this frequency, the amplitude of the piston motion is large, so the nonlinear damper produces a large net force on the piston.

To analyze the effect of this nonlinear damper in detail, a surrogate system is developed by modifying the original system in two ways. First, the gas regions are replaced by upper and lower bellows with similar compressibility to give a well-defined “pneumatic” spring. Second, the upper stop against which the piston is pushed by its lower supporting spring is replaced with an upper spring, thereby removing the nonlinearity from the stop.

An ordinary-differential-equation (ODE) drift model based on quasi-steady Stokes flow is used to produce a regime map of the vibration amplitudes and frequencies for which the piston is up or down for conditions of experimental interest. These results agree fairly well with Arbitrary Lagrangian Eulerian (ALE) simulations of the incompressible Navier-Stokes (NS) equations for the liquid and Newton’s 2nd Law for the piston and bellows.

A quantitative understanding of this nonlinear behavior may enable the development of novel tunable dampers for sensing vibrations of specified amplitudes and frequencies.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2017;():V01CT14A002. doi:10.1115/FEDSM2017-69023.

We develop an idealized experimental system for studying how a small amount of gas can cause large net (rectified) motion of an object in a vibrated liquid-filled housing when the drag on the object depends strongly on its position. Its components include a cylindrical housing, a cylindrical piston fitting closely within this housing, a spring suspension that supports the piston, a post penetrating partway through a hole through the piston (which produces the position-dependent drag), and compressible bellows at both ends of the housing (which are well characterized surrogates for gas regions). In this system, liquid can flow from the bottom to the top of the piston and vice versa through the thin annular gaps between the hole and the post (the inner gap) and between the housing and the piston (the outer gap). When the bellows are absent, the piston motion is highly damped because small piston velocities produce large liquid velocities and large pressure drops in the Poiseuille flows within these narrow gaps. However, when the bellows are present, the piston, the liquid, and the bellows execute a collective motion called the Couette mode in which almost no liquid is forced through the gaps. Since its damping is low, the Couette mode has a strong resonance. Near this frequency, the piston motion becomes large, and the nonlinearity associated with the position-dependent drag of the inner gap produces a net (rectified) force on the piston that can cause it to move downward against its spring suspension. Experiments are performed using two variants of this system. In the single-spring setup, the piston is pushed up against a stop by its lower supporting spring. In the two-spring setup, the piston is suspended between upper and lower springs. The equilibrium piston position is measured as a function of the vibration frequency and acceleration, and these results are compared to corresponding analytical results (Torczynski et al., 2017). A quantitative understanding of the nonlinear behavior of this system may enable the development of novel tunable dampers for sensing vibrations of specified amplitudes and frequencies.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2017;():V01CT14A003. doi:10.1115/FEDSM2017-69086.

Energetic valorization of thermoplastic wastes (High-density polyethylene (PE) and Polypropylene (PP)) to produce fuel using pyrolysis process is presented in this paper. HDPE and PP pyrolysis experiments were carried out in a lab-scale batch reactor under an inert atmosphere. Nitrogen gas was used as carrier before and during the experiments. The temperature was varied from 293 K to approximately 773 K. The viscosities of HDPE, PP and the mixture 50% HDPE & 50 % PP pyrolysis liquids are respectively equal to 1.08 cP, 0.67 cP and 0.8 cP. Its densities are respectively equals to 0.735, 0.751 and 0.759 (at 20 °C–30 °C). The high calorific value (the heating Value) is respectively equals to 45.235 ± 0.641 MJ/kg, 46.151 ± 1.33 MJ/kg and 45.393 ± 0.87 MJ/kg. The liquids obtained have approximately the same Kerosene (Coal Oil) high calorific value (46 MJ/kg). The flash points are respectively equal to 32 °C, 31 °C and lesser than 25 °C for the mixture. They are lesser than coal oil and Diesel values which are equal to 38 °C for Kerosene and between 38 °C and 58 °C for Diesel.

The mixture of two polymers decreases the viscosity values comparing to coal oil (1.7 cP) and Diesel (3.35 cP).

Commentary by Dr. Valentin Fuster
2017;():V01CT14A004. doi:10.1115/FEDSM2017-69145.

An experimental study of the inclination angle (±2° from horizontal) effects on high viscosity oil and gas two-phase flow has been conducted, and the available multiphase flow models/correlations have been evaluated using the acquired data.

The effect of pipe inclination on the slug flow characteristics of highly viscous oil-gas two-phase flow was studied based on 1,040 data points covering a wide range of experimental conditions and liquid viscosities in a 50.8-mm-ID pipe at 2° downward and upward inclinations from horizontal. The oil viscosity ranged from 155 cP to 587 cP. Superficial liquid and gas velocities varied from 0.1 m/s to 0.8 m/s and from 0.1 m/s to 5 m/s, respectively. The basic two-phase flow parameters and slug flow characteristics have been analyzed and compared with the past studies conducted for near horizontal pipes.

Commentary by Dr. Valentin Fuster
2017;():V01CT14A005. doi:10.1115/FEDSM2017-69184.

The proton exchange membrane fuel cell (PEMFC) system is becoming one of the most potential power systems for automotive applications in the future. Though the efficiency of PEMFC is high, almost half of the hydrogen energy is taken away by coolant without being utilized. Organic Rankine Cycle (ORC) could be used for the waste heat recovery of PEMFC. The working fluid of ORC flows directly into the fuel cell stack and cool the stack as the same time. In this paper, the feasibility of R245ca as the coolant of PEMFC and working fluid of ORC is studied. A simulation model of the fluid flow and heat transfer of R245ca in PEMFC cooling plates is set up with the CFD software package FLUENT. The Volume of Fluid (VOF) model is used to simulate the two-phase flow. Results show that R245ca can efficiently remove the waste heat and ensure uniform temperature distribution in PEMFC.

Commentary by Dr. Valentin Fuster
2017;():V01CT14A006. doi:10.1115/FEDSM2017-69276.

Two-phase flows are commonly found in the extraction and production of petroleum and the separation process involving the liquid gaseous phases has great importance. The separators used for this purpose have usually high separation efficiency, however their large dimensions make difficult the construction, installation and maintenance of these equipment in offshore applications. An alternative to reduce the dimensions of these systems is to use a distribution method that can divide the flow, making it possible to use more than one separator. This distributor ideally will produce flow rates equitably distributed across all outlets. The distribution system proposed in this work has a cyclonic chamber, where a vertical ascendant liquid film flow occurs under the action of centrifugal and gravitational fields. This study aims to analyze the development and behavior of the liquid film flow and the efficiency of the distribution system as a function of the liquid and gas flow rates, using an experimental setup and CFD simulations performed with the software ANSYS-CFX 15.0. For the experimental setup a Wire-mesh sensor with 12×12 wires and two others with 8×8 wires were used in order to analyze the variation of the thickness of the liquid film formed in the cyclonic chamber and evaluate the flow pattern at the inlet of the system. In the numerical study, a three-dimensional hybrid mesh was constructed, using the Eulerian-Eulerian two fluid model coupled with the compressive discretization scheme to capture the liquid-gas interface, the Shear Stress Transport (SST) turbulence model and the finite volume based on finite elements. It was possible to carry out a numerical model validation through a comparison with the experimental data. The development of this numerical model might help the advance of new technologies applied in the petroleum industry and this study is focused on area that lacks more studies related to vertical ascendant liquid film flows under centrifugal and gravitational field effects.

Commentary by Dr. Valentin Fuster
2017;():V01CT14A007. doi:10.1115/FEDSM2017-69413.

The Gas-Liquid Cylindrical Cyclone (GLCC©1) is a simple, compact and low-cost separator, which provides an economically attractive alternative to conventional gravity based separators over a wide range of applications. More than 6,500 GLCC©’s have been installed in the field to date around the world over the past 2 decades. The GLCC© inlet section design is a key parameter, which is crucial for its performance and proper operation. The flow behavior in the GLCC© body is highly dependent on the fluid velocities generated at the reduced area nozzle inlet. An earlier study (Kolla et al. [4]) recommended design modifications to the inlet section, based on safety and structural robustness. It is important to ensure that these proposed configuration modifications do not adversely affect the flow behavior at the inlet and the overall performance of the GLCC©. This study is carried out for a specific GLCC© field application, separating light oil, steam flooded wells in Minas, Indonesia. Computational Fluid Dynamics (CFD) software is used to analyze the hydrodynamics of flow with the proposed modifications of the inlet section for GLCC© field applications.

Commentary by Dr. Valentin Fuster
2017;():V01CT14A008. doi:10.1115/FEDSM2017-69451.

We present a method to simulate surface tension between immiscible materials within an inviscid compressible flow solver. The material interface is represented using the volume of fluid technique with piecewise-linear interface reconstruction. We employ the continuum surface force model for surface tension, implemented in the context of the MUSCL-Hancock finite volume method for the Euler equations on an adaptively refined Eulerian mesh. We show results for droplet verification test cases.

Commentary by Dr. Valentin Fuster
2017;():V01CT14A009. doi:10.1115/FEDSM2017-69483.

The dynamics of gas jets expelled into liquid are investigated utilizing Computational Fluid Dynamics (CFD). Results are analyzed with respect to changes in external liquid velocity and mass flow rate of the gaseous jet. In order categorize the complicated nature of the gas-fluid interactions coupled with the many physical dependencies, a flow-regime map is created. The majority of the regimes result in the formation of gaseous cavities encasing the jet, of which forms several cavity types. The internal flow structure of the categorized regimes are then studied with respect to the jet interactions with surrounding liquid and formed cavities. The results show major regions of recirculation and that the jet acts as a confined jet.

Topics: Flow (Dynamics) , Jets
Commentary by Dr. Valentin Fuster
2017;():V01CT14A010. doi:10.1115/FEDSM2017-69557.

This work presents simulations of a heavy gas, SF6, immersed within a light gas, air, under the effect of a converging shock wave. Upon interaction of the shock wave with the perturbed interface between air and SF6, Richtmyer-Meshkov instability (RMI) and, later, Rayleigh-Taylor instability (RTI) take place. More precisely, a succession of RMI and RTI occurs due to multiple shock and rarefaction waves, and gives rise to mixing between the heavy and light fluids. The problem of hydrodynamic instability-induced mixing in converging geometry is particularly relevant to engineering applications such as the process of nuclear fusion by the inertial confinement approach. This study is motivated by the need to better understand the relation between the initial perturbations at the interface between the fluids and the development of the instabilities and mixing in a converging geometry. Using the Flash Code, a PPM hydrodynamic solver developed by the ASC center at the University of Chicago [1], this study focuses on the growth rate of instabilities and the subsequent mixing associated with various carefully designed initial interfacial perturbations in the implosion configuration described above. In cylindrical geometry, comparisons between the growth of high and low frequency single mode perturbations are presented. It is found that at later times, after RMI and RTI take place, the width of the mixing layer is the largest for the low-wavenumber initial interface perturbation. Also, simulations show that the SF6 target with the highest wavenumber perturbation presents the most mixing at the later times but the lowest wavenumber initial interface perturbation presents the most mixing before reshock.

Commentary by Dr. Valentin Fuster

15th International Symposium on Gas and Liquid-Solid Two-Phase Flows

2017;():V01CT15A001. doi:10.1115/FEDSM2017-69126.

There has been a growing public health issue concerning the regulation of indoor air quality (IAQ) and the human exposure to particulate matter (PM). Today, this exposure is a major worldwide concern because ambient PM concentrations in many cities exceeded the limits set by the European air quality directive. Underground airborne particles are mainly generated by the mechanical abrasion of rail tracks, wheels and brake pads produced by urban railways transportation. For that reason, understanding the transport mechanism of particles with various size distribution is essential and crucial for understanding and accurately predicting the behavior of the main high particle concentration areas. In this framework, a simple case of particles emission inside a viscous flow in a channel has been investigated both experimentally and numerically. The suspended particles used experimentally are molybdenum solid particles with a broad size distribution (in diameter) from 1 to 80 μm (size similar to cases such as in braking systems). The experimental tests are conducted for a flow in a channel at a horizontal steady inflow velocity of uf = 0.15m/s. The solid particles are injected transversely to the horizontal bottom wall with an injection steady velocity of ui = 0.95m/s. Measurements and analysis are carried out using shadowscopy technique to determine the particles concentration fields. Finally, experimental results are compared to numerical ones predicted by a continuum computational fluid dynamics (CFD) approach using the SBM (Suspension Balance Model) implemented in “OPENFOAM” (via the Finite Volume Method).

Commentary by Dr. Valentin Fuster
2017;():V01CT15A002. doi:10.1115/FEDSM2017-69188.

Optical methods for investigating multiphase flows are reviewed and discussed in the scope of the development of apparatus convenient for nuclear fuel reprocessing. Indeed, the various processes implemented (e.g. leaching, solvent extraction, filtration, crystallization, etc.) involve either liquid/gas, liquid/liquid and/or liquid/solid flows. Besides the adaptation of classical techniques, such as PIV and image processing, that have been used to quantify velocity fields and particles size distribution in flat-tank reactors, a typical design used in the nuclear industry to mitigate criticality issues, more innovating techniques are currently developed. The latter open the way to the measurement of less usual, although equally important measurements, such as the droplet composition in a liquid-liquid extraction column, and mass transfer rate in multiphase flows.

Topics: Multiphase flow
Commentary by Dr. Valentin Fuster
2017;():V01CT15A003. doi:10.1115/FEDSM2017-69234.

Hydrocyclone separators are widely used in various industrial applications in the oil and mining industries to sort, classify and separate solid particles or liquid droplets within liquid suspensions. Often, studies in the literature have investigated idealized and simplified geometries, which are also typically scaled down to very small sizes. In this study, the two phase flow system inside a transparent acyclic model with actual milling circuit cyclone hydraulics was investigated computationally and experimentally. The diameter and height of the hydrocyclone are 12.7 cm and 94 cm, respectively. In many industrial applications, a single phase flow system in a hydrocyclone is a rarity, since nearly all cyclones have an underflow which is open to atmosphere, and therefore an air core is present along the central axis. In this study, the flow field with an air core present has been investigated. The computational modelling was conducted using Star CCM+, a commercial Computational Fluid Dynamics (CFD) software package. Large Eddy Simulation (LES) and the Volume of Fluid multiphase model was used. Additionally, the computational studies also focused on the prediction of the dimensions of the air core, which were measured experimentally. The tests were conducted in the Reynolds number range of 20,000–150,000 and 9000–67,800 for the water and NaI solution respectively. The model hydrocyclone was made of optically transparent acrylic plastic with flat, smooth outer surfaces so that there were no reflections, distortions, or obstructions. Refractive index matching, to minimize refraction effects, between the test fluid and acrylic test piece was achieved using a test liquid of sodium iodide aqueous solution (63.3% NaI by weight). Images of the flow field with the air core were taken using a Canon DSLR camera. A comparison between the experimental data and the computational results were made in the r-z plane. The experimental results and the computational results will be discussed in this paper.

Topics: Circuits , Milling
Commentary by Dr. Valentin Fuster
2017;():V01CT15A004. doi:10.1115/FEDSM2017-69240.

For the purpose of Computational Fluid Dynamic (CFD) simulations, the broad particle size distribution (PSD) encountered in industrial slurries is classified into a discrete number of size classes. Since mono-size simulations consume much less computational time, especially in 3D simulations, it would be advantageous to determine an equivalent single particle size representation which yields the same wear distribution predictions as the multi-size simulations. This work extends the previous two-dimensional study [1], which was for a specific PSD slurry flow through three selected pumps, to determine an effective equivalent mono-size representation. The current study covers two-dimensional simulations over a wide range of pumps of varying sizes (40 pumps), 2 inlet concentrations and 4 different particle size distributions. Comparison is made between the multi-size wear prediction and different possible representative mono-size particle wear predictions. In addition, a comparison of multi-size and different mono-size results using three dimensional simulations is also shown for a typical slurry pump as a sample case to highlight that the conclusions drawn for two dimensional simulation could hold good for three dimensional simulations as well. It is observed that by using a mono-size equivalent, the computation time is 20–25% of the computation time for multi-size (6-particle) simulation.

Commentary by Dr. Valentin Fuster
2017;():V01CT15A005. doi:10.1115/FEDSM2017-69243.

Coriolis and impact wear testers are commonly used in the slurry industry to determine the sliding and impact wear coefficients (respectively) for a given combination of slurry and wear substrate material. In these experiments, the mass loss of wear specimens, and the easily-measured bulk concentration, flow rate and angle of the impact wedge are correlated to determine estimates of wear coefficients. In CFD-based wear prediction in slurry pump casings and impellers, these experimentally determined coefficients are used in combination with such near-wall computed quantities as particle concentration, velocity, and angle of impact, with a potential inconsistency between the bulk quantities of the wear experiments and the local CFD-based flow field.

This paper uses finite element CFD to obtain the slurry flow field in the Coriolis and impact wear testers. The ratio of the wear-related bulk quantities to the local quantities is evaluated for both impact and sliding wear. It is observed that this ratio for the impact wear coefficient is of the order of 2.0 for the flow conditions studied. In the Coriolis wear tester experiment, it turns out fortuitously that for certain operating conditions, the wear coefficient determined using bulk flow quantities would be nearly the same as the wear coefficient determined using local quantities.

Commentary by Dr. Valentin Fuster
2017;():V01CT15A006. doi:10.1115/FEDSM2017-69317.

Fluidized beds are widely used in industry for combustion, gasification, catalytic cracking and several other purposes. Pneumatic conveying of air is popularly used in industry to transport materials such as pulverized coal through pipelines. A common observation in gas-solid flow dynamics in both of the above systems is the formation of high concentration regions of particles; known as clusters in fluidized beds and rope like structures in pipe bends and ducts. Both the clustering and roping phenomenon were clearly observed in some experiments and in simulations of both fluidized beds and gas-solid flows in pipe bends. It has been found from these simulations that there is a strong correlation between vorticity and concentration. The high particle concentration regions are bounded by vortices of clockwise and counter clockwise direction of roughly the same order of magnitude and there is very low vorticity at the high concentration regions.

The goal of this study is to find the cause and effect relation between the gas vorticity and the high particle concentration regions; in particular whether the gas vorticity causes particle agglomeration into clusters or vice-versa. Numerical study has been performed on a vertical pipe by creating a vortex field. In this regard, very large eddy simulations with Lagrangian Discrete Phase model have been performed using Ansys FLUENT and MFIX software packages. The influence of particles on the vorticity has been studied. Influence of several factors such as particle size, injection velocity etc. have also been studied. Correlations among turbulent kinetic energy, vorticity, and particle clustering and/or roping are illustrated.

Commentary by Dr. Valentin Fuster
2017;():V01CT15A007. doi:10.1115/FEDSM2017-69350.

Sand particles entrained in fluids can cause erosive wear and damage to piping materials by impacting their surfaces which could result in failure of the piping system. Several parameters have been determined to affect the erosion behavior and mechanism of solid particle erosion. Some of these parameters include surface material, particle impact speed and angle, and particle size, shape and hardness. However, the effect of particle size on the total erosion rate and local erosion pattern has not been thoroughly investigated. It has been observed that sand particles with various sizes cause different slurry erosion patterns. Changing the particle size alters the Stokes number and consequently produces different erosion patterns and magnitudes. Thus, the effects of particle size on total erosion rate and erosion pattern in a submerged slurry jet are investigated for different impingement angles. Experiments are performed on 316 stainless steel specimens for average particles sizes of 25, 75, 150, and 300 μm. The jet angle is varied to 45, 75 and 90 degrees, and the slurry jet velocity is set to 14 m/s. The erosion pattern of the specimen is examined by obtaining the 3D microscopic profile of the eroded specimen by means of an optical profiler. It is found that the erosion profile changes as the jet angle varies. It is also observed that erosion profile is significantly different for smaller particles as compared to the larger particles. Moreover, these differences become more pronounced as the jet angle decreases. The present work discusses the differences of erosion patterns produced by both large and small particles. Computational Fluid Dynamics (CFD) is also used to study the effect of particle size on particle trajectories, impact speed, and impact angle. Also, CFD results help in explaining the differences observed in the erosion profiles caused by different particle sizes.

Commentary by Dr. Valentin Fuster
2017;():V01CT15A008. doi:10.1115/FEDSM2017-69355.

Many industrial processes involve high concentration particulate multiphase flow in which the carrier phase is continuous and the solid particles are dispersed in the carrier phase. Although much research has been directed toward modeling of solid particle erosion, very few have presented a generalized approach for erosion modeling under high concentration slurry impact. Experimental and numerical studies have shown that when particles are transported by liquid or dense gas, the particle impact angles are very low. The impact angles in these cases are sometimes less than the smallest angle that can be obtained in a direct impingement erosion test. Moreover, particle-particle interaction is significant when particle loading is high, and the effect should be accounted for in the numerical simulation. In this work, a mechanistic erosion equation that includes an abrasion term for low angle impacts is implemented in CFD simulation of submerged slurry impinging jet with ANSYS Fluent. The Eulerian-Lagrangian method is used to model the carrier fluid flow and particle tracking, respectively, while the particle-particle interaction is resolved statistically through a two-fluid Eulerian-Granular model. In this approach, particle-particle interaction is modelled through solid stresses acting on the particles in a dense flow by an additional acceleration in the particle force balance for the Lagrangian phase. The CFD erosion predictions are compared with experimental data from a previous work in the literature. It is shown that by including the abrasion term, the total mass loss of the specimen agrees better with experimental data, and the obtained erosion pattern is more comparable to the data collected by 3D profilometry. It was found that the combined two-fluid model is capable of capturing the decrease in the erosion ratio (defined as the ratio of material loss to the particle throughput) with increase in particle loading which can be ascribed to a shielding effect caused by particles moving close to the wall.

Commentary by Dr. Valentin Fuster
2017;():V01CT15A009. doi:10.1115/FEDSM2017-69374.

Computational Fluid Dynamics (CFD) based erosion prediction procedures are carried out to predict erosion for a submerged liquid jet impingement geometry. 2-D axisymmetric modeling with different near wall treatments are employed to model the wall bounded turbulent jet flow. Discrete Phase Model (DPM) is applied to track particles and obtain particle impact characteristics. Erosion is calculated using a typical Finnie-Bitter model [1]. In this paper, two categories of near wall modeling approaches (wall functions and near wall models) are presented and examined. Erosion prediction results for 300 μm large particles and 25 μm small particles are compared with experimental data to evaluate different near wall models with application to erosion prediction. Near wall trajectories are extracted to explain prediction results and reveal particle near wall behaviors. It is shown that appropriate selection of meshes and near wall models is capable of yielding good erosion prediction regardless of particle size.

Commentary by Dr. Valentin Fuster
2017;():V01CT15A010. doi:10.1115/FEDSM2017-69409.

Unconsolidated reservoirs are notorious for production of sand with crude oil and natural gas. Bed formation in production pipelines poses several operational problems, such as partial or complete pipeline blockage, which decreases production rate and increases frictional pressure losses. Equipment failure may occur as well as erosion/corrosion and formation of corrosive cells under the sand beds. In this study, solid transport in horizontal stratified gas-liquid flow is investigated for a high concentration of 20,000 PPM, leading to sand bed formation. The experiments are conducted with air and water along with glass bead with particle sizes of 45–90 μm and 425–600 μm. The sand bed formation is studied by conducting experiments with gas-slurry flow. The experimental results confirm that the height of the bed decreases with increasing superficial gas velocity, and increases with increasing superficial liquid velocities. It is also observed that the height of the bed created with smaller diameter particles is larger than the one created by the bigger. The acquired experimental data shed more light on the formation of sand beds. It also serves as a basis for theoretical mechanistic models to enable prediction and design of stratified gas-liquid-solid flow.

Commentary by Dr. Valentin Fuster
2017;():V01CT15A011. doi:10.1115/FEDSM2017-69412.

The Gas-Liquid Cylindrical Cyclone (GLCC©1) is a simple, compact and low-cost separator, which provides an economically attractive alternative to conventional gravity based separators over a wide range of applications. The GLCC© inlet section design is a key parameter, which is crucial for its performance and proper operation. An in-depth evaluation of specific design modifications and their effectiveness on safety and structural robustness are carried out in this study using Finite Element Analysis. Fluid-Structure Interaction (FSI) analysis is also carried out utilizing the results of Computational Fluid Dynamics (CFD) aimed at investigating the effect of fluid flow on the inlet section structural integrity. The selected design modifications are based on feasibility of GLCC© manufacturing and assembly for field applications. Different case studies incorporating sustained GLCC© internal pressure, dead weight loading, forces generated because of slug flow and high temperatures are evaluated and presented. The concept of holes cutout in baffle have been proven effective with no stresses or deformation in the baffle area. FSI simulation of slug flow have proved that FEA direct loading case studies are far more conservative.

Commentary by Dr. Valentin Fuster
2017;():V01CT15A012. doi:10.1115/FEDSM2017-69444.

Here we present and benchmark an analytical model to describe the radial extent of erosion of settled particle beds by radial wall jets as a function of time. The extent of erosion is an essential measure of the performance of vessels mixed by arrays of radial wall jets because portions of vessel floors not cleared of settled particles may accumulate undesirable constituents. We derive a model of the cleared radius as a function of time scaled so that fits may be described using only two free parameters. We find remarkably good agreement between experimental data and the model upon fitting. Extracted fitting parameters are shown to be reasonable. The influence of nozzle transience on erosion transience has also been evaluated. We find that nozzle transience explains the initially slower rate of erosion and decreases the final extent of erosion by one to three nozzle diameters for the cases considered. Future work remains to evaluate the dimensionless groups from conservation laws and account for vessel curvature.

Commentary by Dr. Valentin Fuster
2017;():V01CT15A013. doi:10.1115/FEDSM2017-69462.

A slurry jet driller is a novel drilling method, which delivers an abrasive slurry and supercritical gas mixture, to an expander nozzle. The expanded fluids flowing out of the nozzle, energize the particles, which hit the target material and erode it, achieving drilling. The expansion of the gas from a super critical state to in situ pressure and temperature conditions is the driving mechanism of the drilling operation. The primary objective of this paper is to evaluate the feasibility of the novel slurry jet drilling system.

An experimental program is carried out for testing the performance of a slurry jet driller. The slurry is formed by mixing water with garnet particles, and a super critical carbon dioxide as the gas phase. The purpose of experiments is to evaluate the erosive nature of garnet rocks and to test the cutting efficiency of the nozzle. The acquired data show that the material removal rate increases with increase in the gas-slurry flow ratio, until a ratio of 1.5. A further increase in the flow ratio results in a reduction of the rate of material removal.

Improved nozzle geometry was obtained using a program written in MATLAB. Criteria used for geometry improvement was the force applied to the bottom of the drilled bore. A rudimentary model is developed for the prediction of material removal rate utilizing a slurry jet driller, which is presented in a dimensionless form. The model incorporates the important variables affecting the jet driller system performance, including fluid and target material properties, and particle velocity. A fair agreement is observed between model predictions and experimental data, exhibiting a 20% deviation.

Topics: Drilling , Slurries
Commentary by Dr. Valentin Fuster

17th International Symposium on Numerical Methods for Multiphase Flow

2017;():V01CT16A001. doi:10.1115/FEDSM2017-69051.

The objective of this work is to analyze fluid flow in horizontal pipes with three phase gas-liquid-solid Newtonian fluid by our developed CFD simulation model and validate the simulation with experimental works. Air as gas, water as liquid and silica sand as solid particle is used for this work. ANSYS fluent version 16.2 is used to do the simulation. Eulerian model with Reynolds Stress Model (RSM) turbulence closure is adopted to analyze multiphase fluid flow. Length of pipe is 2.9 m and diameter is 0.0416 m, which are selected from experimental works to validate the simulation and after a good agreement with experimental data, sensitivity analysis is conducted to observe the three phase fluid flow characteristics through horizontal flow. Pressure gradient (pressure drop per unit length) is used as primary parameter to analyze. Effect of in situ concentration of solid in slurry, diameter of pipeline, roughness of wall material and viscosity of water in slurry are analyzed throughout this paper. This article provides validity of our proposed model. After that we tried to perform some parametric studies, changing variables of three phase fluid flow through horizontal pipeline with ours validated model. The main approach here is to demonstrate our CFD model in different ways to researchers and industries related to multiphase pipeline flow fields and make it acceptable to them. Also, Fluid Structure Interaction (FSI) is introduced at the end of this study to explain the goal of this project.

Commentary by Dr. Valentin Fuster
2017;():V01CT16A002. doi:10.1115/FEDSM2017-69098.

In this paper, the investigation on dynamics of high-speed micron-sized droplet impact on textured surfaces is carried out through computational fluid dynamics (CFD) simulations. An open-source code Gerris has been adapted to address the challenging issues facing simulations of high-speed impact of microdroplets on the rough surface, such as thin spreading lamella, secondary droplet breakup, and small features of rough surfaces. Validation is first presented to evaluate the accuracy of the simulation code for modeling high-speed droplet impact on the microstructured surface. Then, we carry out 3D simulations of a 10 μm diameter water droplet impact on different textured surfaces with different impact velocities. We find that a large portion of the thin lamella actually surfs over the top of pillars during spreading with only center area of impact saturated with liquid. Our simulations indicate that both impact velocity and surface morphology play an important role in the splashing phenomenon. Increasing pillar spacing makes droplet impact more prone to splashing. Splashing on surfaces of larger pillar spacing is characterized by the breakup of high-speed jets. Larger impact velocity results in more intensified splashing. For a given impact velocity, densely packed pillars (i.e., smaller pillar spacing) can reduce or even suppress the splashing due to viscous drag effect from pillars in wetted region. The existing splashing threshold models that depend only on surface roughness fail in the prediction of the critical speed for splashing on textured surfaces.

Commentary by Dr. Valentin Fuster
2017;():V01CT16A003. doi:10.1115/FEDSM2017-69102.

Recently, attention has been given to indoor air quality due to its serious health concerns. Clearly the dispersion of pollutant is directly affected by the airflow patterns. The airflow in indoor environment is the results of a combination of several factors. In the present study, the effects of thermal plume and respiration on the indoor air quality in a ventilated cubicle were investigated using an unsteady computational modeling approach. The person-to-person contaminant transports in a ventilated room with mixing and displacement ventilation systems were studied. The effects of rotational motion of the heated manikins were also analyzed. Simulation results showed that in the cases which rotational motion was included, the human thermal plume and associated particle transport were significantly distorted. The distortion was more noticeable for the displacement ventilation system. Also it was found that the displacement ventilation system lowered the risk of person-to-person transmission in an office space in comparison with the mixing ventilation system. On the other hand the mixing system was shown to be more effective compared to the displacement ventilation in removing the particles and pollutant that entered the room through the inlet air diffuser.

Commentary by Dr. Valentin Fuster
2017;():V01CT16A004. doi:10.1115/FEDSM2017-69113.

The presence of near wall bubbles may reduce the skin friction drag. This phenomenon has been studied by well designed experiments and combined computational fluid dynamics (CFD) and population balance model (PBM) simulations in this paper. Drag reductions and bubble distributions over a flat plate have been implemented in cavitation tunnel experiments at various flow speeds and air injection rates. CFD-PBM modeling for bubble drag reduction (BDR) has been modified and validated by the flat plate experiments. Drag and lift forces are fully modeled, and bubble breakup and coalescence are calculated. A wide range of bubble sizes are well captured base on the aforementioned numerical consideration. And this modeling work can be further used to design full-scale BDR ships and to discover detailed BDR mechanisms. The predicted drag reductions and bubble distributions are in reasonable accordance with the experimental results. Approximately 30% of BDR is achieved both in the numerical and experimental results. The influence of flow speeds and air injection rates on drag reductions and bubble distributions is discussed. In particular, the mechanism of BDR is analyzed based on the detailed flow filed profiles from numerical simulations. Higher air injection rates generally lead to thicker bubble layer thickness from the rear-part of buffer region (20 < y+ < 30) to turbulent region (y+ > 30). And noticeable increases of air volume fraction in the laminar region (y+ < 5) and forepart of buffer region (5 < y+ < 20). The change of the velocity gradient in the near wall region is considered to be directly related to drag reduction.

Commentary by Dr. Valentin Fuster
2017;():V01CT16A005. doi:10.1115/FEDSM2017-69128.

Two-phase turbulence is studied using DNS of upward turbulent bubbly flows in a plane channel. Fully deformable monodispersed bubbles are tracked by the Front-Tracking algorithm implemented in TrioCFD code on the TRUST platform. Two sets of fluid properties are used. Firstly, two simulations are performed with virtual fluids at a low void fraction of 3% and for a Reynolds friction number of 127 to benchmark our code against [1]. Good agreements are obtained for both deformable and spherical cases. A third simulation closer to pressurized water reactor (PWR) conditions was performed at higher void fraction and Reynolds number to push the limits of DNS capabilities.

DNS results are averaged (i) to provide reference profiles for an up-scaling methodology towards RANS two-fluid models and (ii) to analyze the equilibrium between buoyancy, surface tension, viscous and turbulent shear at statistically steady-state. Surface tension forces and turbulence are essentials to capture the equilibrium. Their accurate modeling is the key to velocities and void fraction predictions in averaged codes. Our analysis reveals the important role of surface tension, not only in the determination of the bubble shapes, but also as a source of local imbalance of the momentum transfer between phases. More advanced models considering interfacial energy are necessary to predict these flows.

Commentary by Dr. Valentin Fuster
2017;():V01CT16A006. doi:10.1115/FEDSM2017-69139.

Buoyancy driven motion of a single droplet in another quiescent fluid was simulated by a Front-Tracking method. The rising velocity and the projected area of the droplet were obtained in spherical, ellipsoidal, and wobbling regimes. Form and skin drag forces were calculated by integrating pressure distribution and velocity profiles along the interface of the droplet. Drag coefficient was obtained from those values when the rising velocity reached the terminal velocity. The scaling for drag of a liquid droplet was compared with the theoretical model. When the viscosity of the droplets was lower than that of the surrounding fluid, the drag coefficients can be predicted by the model for the limiting case of gas bubbles. When the viscosity of the droplets was larger than that of the surrounding fluid, on the other hand, the drag coefficients can be predicted by the model when solid particles are assumed.

Topics: Buoyancy , Drops , Computation
Commentary by Dr. Valentin Fuster
2017;():V01CT16A007. doi:10.1115/FEDSM2017-69190.

The most part of two-phase flows relevant to industrial applications is characterized by high density ratios that make numerical simulations of such kind of flows still challenging in particular when the interface assumes complex shape and is distorded by high shear. In this paper a new strategy, to overcome the numerical instabilities induced by the large densities/shears at the interface, is described for staggered cartesian grids. It consists in a consistent mass-momentum advection algorithm where mass and momentum transport equations are solved in the same control volumes. The mass fluxes are evaluated through the Volume-of-Fluid color function and directly used to calculate momentum convective term. Two and three-dimensional high-density test cases (the density ratio goes from 103 to 109) are presented. The new algorithm shows signifcantly improvements compared to standard advection methods therefore suggesting the applicability to the complete atomization process simulations.

Commentary by Dr. Valentin Fuster
2017;():V01CT16A008. doi:10.1115/FEDSM2017-69206.

As one of the main types of dropshaft structure, vortex dropshaft is commonly used in hydropower stations, urban drainage systems and other water conservancy projects. Many scholars have conducted researches into hydraulic characteristics of this type of dropshaft. However, its flow patterns and mechanisms are still not clear. Consequently, a 3-D, steady, two-phase numerical model of vortex dropshaft is developed through FLUENT software, using volume of fluid (VOF) method to track the interface of air and liquid water. Four cases sharing the same geometry domain and boundary conditions with different inlet velocities have been studied. The specific flow patterns and formation mechanisms in the four cases are discussed in this study, and the influences of inlet velocity are investigated as well. The results show two negative pressure zones appearing at inlet and outlet connections threatening the structural safety, and it is important to optimize the structure design and control the inlet flow.

Commentary by Dr. Valentin Fuster
2017;():V01CT16A009. doi:10.1115/FEDSM2017-69242.

Advancement in the experimental techniques have brought new insights into the microscale boiling phenomena, and provide the base for a new physical interpretation of flow boiling heat transfer. A new modeling framework in Computational Fluid Dynamics has been assembled at MIT, and aims at introducing all necessary mechanisms, and explicitly tracks: (1) the size and dynamics of the bubbles on the surface; (2) the amount of microlayer and dry area under each bubble; (3) the amount of surface area influenced by sliding bubbles; (4) the quenching of the boiling surface following a bubble departure and (5) the statistical bubble interaction on the surface. The preliminary assessment of the new framework is used to further extend the portability of the model through an improved formulation of the force balance models for bubble departure and lift-off.

Starting from this improved representation at the wall, the work concentrates on the bubble dynamics and dry spot quantification on the heated surface, which governs the Critical Heat Flux (CHF) limit. A new proposition is brought forward, where Critical Heat Flux is a natural limiting condition for the heat flux partitioning on the boiling surface. The first principle based CHF is qualitatively demonstrated, and has the potential to deliver a radically new simulation technique to support the design of advanced heat transfer systems.

Commentary by Dr. Valentin Fuster
2017;():V01CT16A010. doi:10.1115/FEDSM2017-69258.

The present paper aims to predict the separation efficiency and pressure drop of a vertical geothermal cyclone type separator using CFD (Computational Fluid Dynamics) simulations, for optimizing the design of such separator. A benchmark study was firstly performed for a single phase flow in a Stairmand design cyclone using four different turbulence models, in order to verify the prediction accuracy of flow velocity distribution by comparison with experimental data in literature. The investigated turbulence models include (1) Renormalization Group (RNG) k-ε, (2) Realizable k-ε, (3) Reynolds stress turbulence model (RSM) and (4) Large eddy simulation (LES). Results show that RNG k-ε and Realizable k-ε models are not capable of reproducing the experimental data while the RSM and LES models reproduce the flow velocity distribution very well. Then, CFD simulations of two-phase flow in a steam-water cyclone separator were carried out for different stream inlet velocities applying the RSM model. This is based on the consideration that steady state analysis can be done for the RSM model, and however, transient analysis is needed for the LES model, and hence, more expensive and time-consuming for engineering applications. The CFD results for outlet steam quality and pressure drop were obtained under different stream inlet velocities. The separation efficiency and outlet steam quality decreases a little when the inlet velocity increases from 34.5m/s to 72m/s. However, the outlet steam quality predicted in the present CFD analysis is close to that of Lazalde-Crabtree.

Commentary by Dr. Valentin Fuster
2017;():V01CT16A011. doi:10.1115/FEDSM2017-69335.

The slug flow regime is probably the prevailing pattern in the oil and gas industry, appearing in the nuclear industry as well. As a consequence, several studies have been conducted in order to understand the physics of this flow regime and to obtain a model to predict its properties. This work presents a transient hybrid methodology to simulate the gas-liquid slug regime in pipes with a change of direction from horizontal to downward inclined flow. The simulation initiates with a slug tracking model assuming the pipe to be filled with liquid, and follow the unit cells while they flow through the horizontal section; the information about the unit cells entering the pipe are obtained from experimental data. Near the elbow and beyond, the unit cells are simulated by a simplified two-fluid Lagrangian model, capable of providing flow details with the change of direction, and the dissipation of the slug flow to the stratified regime in a descendent slope. Simulations for a 4.862-m pipe were carried out, with the change of direction from horizontal to −3° and −5°. The results were compared to experimental data, showing that the model can successfully predict the flow behaviour for the given conditions.

Commentary by Dr. Valentin Fuster
2017;():V01CT16A012. doi:10.1115/FEDSM2017-69370.

In the multiphase simulation of material handling and filtration processes the coupling between the fluid phase, which imposes aero- or hydrodynamic forces onto the particles, and the particulate matter, which in turn impose momentum into the fluid, is of major importance. Conventional simulation methods such as CFD-DEM-coupling are based upon empirical and analytical drag models. Moreover, they have the degradation of particles to point masses in common. Thus empirical modeling neglects the microscopic details that are essential to a profound understanding of micro scale processes and accurate macro scale simulation results.

A new simulation model which is built upon numerical simulation methods like CFD and the immersed boundary method is developed for OpenFOAM®. It is capable of fully discretizing the geometry of arbitrarily shaped bodies.

This work demonstrates the application of our simulation model to the multiphase flow in the near wall shear flow field of centrifugal separators. The validation of the model regarding particle drag and spin of variously shaped particles in the shear flow shows that the particle shape determines essentially the process of settling, separation and resuspension.

Commentary by Dr. Valentin Fuster
2017;():V01CT16A013. doi:10.1115/FEDSM2017-69555.

A framework is developed to integrate MFiX (Multiphase Flow with Interphase eXchanges) with advanced linear solvers in Trilinos. MFiX is a widely used open source general purpose multiphase solver developed by National Energy Technology Laboratories and written in Fortran. Trilinos is an objected-oriented open source software development platform from Sandia National Laboratories for solving large scale multiphysics problems. The framework handles the different data structures in Fortran and C++ and exchanges the information from MFiX to Trilinos and vice versa. The integrated solver, called MFiX-Trilinos hereafter, provides next-generation computational capabilities including scalable linear solvers for distributed memory massively parallel computers. In this paper, the solution from the standard linear solvers in MFiX-Trilinos is validated against the same from MFiX for 2D and 3D fluidized bed problems. The standard iterative solvers considered in this work are Bi-Conjugate Gradient Stabilized (BiCGStab) and Generalized minimal residual methods (GMRES) as the matrix is non-symmetric in nature. The stopping criterion set for the iterative solvers is same. It is observed that the solution from the integrated solver and MFiX is in good agreement.

Commentary by Dr. Valentin Fuster
2017;():V01CT16A014. doi:10.1115/FEDSM2017-69562.

A numerical experiment studying the gas-particle variant of the Richtmyer-Meshkov instability is presented. Using an Eulerian-Lagrangian approach, namely point particle simulations, we track trajectories of computational particles composing an initially corrugated particle curtain, after the curtain’s interaction with a shock wave. We solve the compressible multiphase Euler equations in a two-dimensional planar geometry and use state-of-the-art particle force models, including unsteady forces, for the gas-particle coupling. However, additional complexities associated with compaction of the curtain of particles to random close packing limit and beyond are avoided by limiting the simulations to relatively modest initial volume fraction of particles. At a fixed Mach number, we explore the effects of the initial perturbation amplitude, initial particle volume fraction and initial shape on the dispersal of the particle curtain. For this shock strength, our simulations suggests that the amplitude of the initial perturbation does not play a significant role in the late time particle dispersal, contrary to the volume fraction. Higher initial particle volume fraction tend to faster particles dispersal. Finally, higher frequency initial perturbations seem to be absorbed by lower frequency initial perturbations.

Commentary by Dr. Valentin Fuster

8th International Symposium on Turbulent Flows: Issues and Perspectives

2017;():V01CT18A001. doi:10.1115/FEDSM2017-69066.

Effects of roughness on the near-bed turbulence characteristics in oscillatory flows are studied by means of particle-resolved direct numerical simulations (DNS). Two particle sizes of diameter 375 and 125 in wall units corresponding to the large size gravel and the small size sand particle, respectively, in a very rough turbulent flow regime are reported. A double-averaging technique is employed to study the nature of the wake field, i.e., the spatial inhomogeneities at the roughness length scale. This introduced additional production and transport terms in double-averaged Reynolds stress budget, indicating alternate pathways of turbulent energy transfer mechanisms. Budgets of normal components of Reynolds stress reveal redistribution of energy from streamwise component to other two components and is attributed to the work of pressure in both flow cases. It is shown that the large diameter gravel particles significantly modulate the near-bed flow structures, leading to pronounced isotropization of the near-bed flow; while in the sand case, elongated horseshoe structures are found as a result of high shear rate. Effect of mean shear rate on the near-bed anisotropy is significant in the sand case, while it is minimal for the gravel-bed. Redistribution of energy in the gravel case showed reduced dependence on the flow oscillations, while for the sand particle it is more pronounced towards the end of an acceleration cycle.

Commentary by Dr. Valentin Fuster
2017;():V01CT18A002. doi:10.1115/FEDSM2017-69316.

The paper investigates the destruction-of-dissipation tensor εεij in low-Reynolds number turbulent plane channel flow. This tensor, which represents the destruction of the dissipation tensor εij (appearing in the budgets of the covariances of fluctuating velocities rij) by molecular viscosity, exhibits specific near-wall anisotropy and is not 2-C at the wall. The budgets of εεij (turbulent and viscous diffusion, pressure-term, various production mechanisms, and destruction by molecular viscosity εεεij) are studied and various scaling relations are examined.

Commentary by Dr. Valentin Fuster
2017;():V01CT18A003. doi:10.1115/FEDSM2017-69521.

The phenomenon known as Toms effect can impart viscoelasticity to a water flow when a small amount of water-soluble polymer is added. The resulting viscoelastic fluid generates viscoelastic stress in the flow, dramatically reducing the turbulent stress.

In this study, the spatial distribution of velocity is measured using a stereo-PIV method in the streamwise-spanwise plane parallel to the wall. Modification of the near wall turbulence by the polymer solution blown slowly from a permeable wall was investigated by analyzing the velocity distribution acquired by stereo-PIV measurements.

Experimental results reveal that streamwise local mean velocity decreases as the dosed polymer concentration increases. The skewness factor at this height shifts from 0 to positive by adding the polymer, which indicates intensified turbulent coherent structure. Moreover, the spatial two-point correlation function calculated from streamwise velocity fluctuations maintains its high correlation with the streamwise direction. It is consistent with the finding from the instantaneous velocity distribution, which shows that the flection of low-speed streaks is suppressed. Next, it is revealed that the normal velocity at the wall for low-speed fluid is decreased dramatically by polymer additives. Moreover, applying the quadrant analysis, it is confirmed that ejection events are suppressed with decreasing normal velocity at the wall. Suppression of ejection motion affects to the turbulence in the log law layer. We conclude that this is one reason that turbulence is suppressed in a wide range of the shear layer by polymer additives present only in the vicinity of the wall.

Commentary by Dr. Valentin Fuster
2017;():V01CT18A004. doi:10.1115/FEDSM2017-69533.

Turbulent surfactant solution flows dramatically suppress turbulent scalar and momentum transports with changes to turbulent structures near the wall. In this study, particle image velocimetry and planar laser induced fluorescence concentration measurement method were used simultaneously to analyze turbulent mass transfer experimentally in surfactant channel flows at high Reynolds number. When compared against the instantaneous flow fields of the water case, the results showed a decrease in the magnitude of elementary vortices in the near-wall region. Momentum and scalar transports are caused by the combination of elementary vortices that are irregularly arranged at the outer edge of the shear layer. A conceptual vortex model is proposed for turbulent scalar transfer that provides a partial explanation for the turbulence statistics of a surfactant solution flow, such as the Reynolds shear stress, turbulent mass flux, and mean concentration distribution.

Commentary by Dr. Valentin Fuster
2017;():V01CT18A005. doi:10.1115/FEDSM2017-69558.

The addition of a small amount of surfactant into water induces viscoelasticity. In turbulent channel and pipe flows, the wall friction significantly decreases with the surfactant additive, but a heat-transfer reduction also occurs. On the other hand, a phenomenon is reported that the instantaneous main flow broadly meanders in space and time under a certain condition in the surfactant solution flow past a backward-facing step (BFS); thus, the mean Reynolds shear stress remarkably increases. The influence of such a phenomenon cannot be neglected in thermal fluid equipment with usually complicated configurations. Therefore, understanding this phenomenon in detail is important both academically and industrially. In this study, particle image velocimetry measurements were carried out in a viscoelastic BFS flow with meandering phenomenon at high Reynolds number. We focused on the turbulent structures in the flow fields and investigated the interrelationship among the spatial scales of the eddy structures, Reynolds shear stress, and meandering motion using a spatial two-point correlation function or conditional averaging. In the meandering condition, we revealed that the Reynolds shear stress due to the low-speed fluid that departs from the upper wall opposite the step across the main flow contributes the largest to the mean Reynolds shear stress value. Then, a secondary recirculation region appears near the upper wall, in addition to the primary recirculation region. A reverse flow is apt to occur when rapid deceleration and pressure rise happens due to the sudden expansion of the channel cross section. Therefore, flow separation occurs at the upper wall, and a large-scale circulation appears there. Such flow is caused by the relationship between the pressure rise and the momentum transfer between the flow and the wall. We can conclude that the condition where an unstable motion occurs is influenced by the concentration of the surfactant solution because the surfactant additive acts on the shear stress.

Commentary by Dr. Valentin Fuster

11th International Symposium on Flow Applications in Aerospace

2017;():V01CT19A001. doi:10.1115/FEDSM2017-69117.

Evolution of wing tip vortex has been widely studied by many researchers. Winglet, jet, and suction devices have been implemented close to the wing tip to passively or actively mitigate the tip vortex effects. This study aims to investigate the effects of employing a synthetic jet at the tip of a half wing model. The flow was assumed to be incompressible, low speed and the Reynolds number based on chord length with aspect ratio equal to two for half wing was 1.8 × 105. Different reduced frequencies and momentum coefficients were applied. A Detached Eddy Simulation by considering Spalart-Allmaras as the turbulence model for subgrid scale zone and near the walls was employed to simulate the flow field study. Results showed large diffusivity in vortex core. Also, a reduction in longitudinal and total velocity magnitude has observed at vortex core region in the near wake.

Commentary by Dr. Valentin Fuster
2017;():V01CT19A002. doi:10.1115/FEDSM2017-69238.

The aerodynamic performance of an oscillating pitching and plunging foil operating in the energy harvesting mode is experimentally investigated. Experiments are conducted in a closed-loop recirculating wind tunnel at Re of 24,000 to 48,000, and reduced frequencies (k) of 0.04 to 0.08. Foil kinematics are varied through the following parameter space: heaving amplitude of 0.3c, pitching amplitudes of θ0 = 45° to 75°, as well as phase lag between sinusoidal pitching and heaving motions of Φ = 30° to 120°. Aerodynamic force measurements are collected to show the energy extraction performance (power coefficient and efficiency) of the foil. Coupled with the force measurements, flow fields are collected using particle image velocimetry. The flow field characteristics are used to supplement the force results, shedding light into flow features that contribute to increased energy extraction at these k values. In addition, inertia-induced passive chord-wise flexibility at the leading edge (LE) of the foil is investigated in order to assess its feasibility in this application. Results indicate that favorable performance occurs near θ0 = 45°, Φ = 90° and k = 0.08. When k is decreased (through increased U) to 0.04, overall extraction performance becomes insensitive to θ0 and Φ. This is supported by the flow field measurements, which show premature leading edge vortex (LEV) evolution and detachment from the foil surface. Although overall performance was reduced with the passive LE flexibility, these results indicate that a proper tuning of the LE may result in a delay of the LEV detachment time, yielding increased energy harvesting at this otherwise inefficient operating parameter space.

Commentary by Dr. Valentin Fuster
2017;():V01CT19A003. doi:10.1115/FEDSM2017-69361.

In this work, a Sequential Decision Process (SDP) is applied to perform fuselage design using Computational Fluid Dynamics (CFD). The SDP uses models to provide two-sided estimates that attempt to bound the exact solution, ultimately converging to an optimal design space to be analyzed with models of increased fidelity. The present work proposes the use of laminar and turbulent physics in CFD models to form lower and upper bounds on drag calculations, respectively. These bounding models are then used in a formal SDP to cull the design space, focusing the region of interest for increased fidelity modeling and analysis. Increasing mesh resolution is used to increase fidelity, creating a multi-fidelity approach to aerodynamic shape design. In this work the SDP-CFD design approach is applied to two design problems: (1) drag minimization of a fairing with a defined thickness and (2) drag per unit volume minimization of a fairing. The results of this study demonstrate that the SDP-CFD approach can accurately and quickly improve the fuselage design.

Commentary by Dr. Valentin Fuster
2017;():V01CT19A004. doi:10.1115/FEDSM2017-69365.

Ice-shape prediction results are shown wherein Discrete-Element Roughness Method (DERM)-based CFD solutions are coupled with LEWICE to supplement the built-in heat transfer prediction module. This coupling produces multi-step ice-shape predictions. The effect of using the newer roughness-height distribution model of Han and Palacios rather than the roughness-height prediction of LEWICE is also gauged. DERM is used in an attempt to improve heat transfer predictions beyond the capability of a sand-grain-roughness model while only slightly increasing the computation time. LEWICE is the industry-standard ice growth prediction tool maintained by NASA. LEWICE is known to predict ice shapes very accurately within its validation envelope, but suffers lowered accuracy for icing conditions in the glaze regime. The predictions that result from the DERM-LEWICE coupling are compared with ice shapes generated in experiments from the Penn State Adverse Environment Rotor Test Stand (AERTS). It is observed that ice-shape predictions in the glaze-icing regime can be highly sensitive to the convective heat-transfer predictions.

Commentary by Dr. Valentin Fuster
2017;():V01CT19A005. doi:10.1115/FEDSM2017-69501.

When a shock wave is incident on an obstacle, it is not only reflected back but also transmitted into the obstacle itself. The transmitted shock wave has not been fully investigated so far, compared with the reflected shock wave. In actual situations, the behavior and the characteristics of the transmitted shock wave are also of importance. In battlefields, human bodies are often subject to explosions and resulting shock waves. In particular, severe damage can be caused when a shock wave is transmitted into the human brain.

In the present study, we conducted experiments to investigate the behavior and intensity of a shock wave, after it is transmitted into various materials. The materials used were sintered metal, silicone, and polyethylene foam. They were fixed on a specially devised model with a cavity, by which the resulting wave after a shock wave is transmitted could be observed. In order to understand what is happening in sintered metal, a 2-D model made of straws was devised and used.

Topics: Shock waves
Commentary by Dr. Valentin Fuster
2017;():V01CT19A006. doi:10.1115/FEDSM2017-69583.

In this study, a non-linear fluid-solid interaction (FSI) methodology is uniquely developed to simulate the aerodynamic interaction and disturbance of flow along a high-bypass propulsion system subjected to foreign object ingestion (FOI). For the analysis, a time explicit finite element analysis is applied with an advanced computational scheme, Arbitrary Lagrangian-Eulerian (ALE). The advanced finite element formulation is able to successfully demonstrate the interaction between air and the high-bypass jet engine subjected to a soft body FOI by solving both solid and fluid continua simultaneously. As a result, the proposed damage modeling methodology simulates the progressive failure caused by the exertion of aerodynamics over the damaged and undamaged components.

Commentary by Dr. Valentin Fuster

17th International Symposium on Fluid Power

2017;():V01CT20A001. doi:10.1115/FEDSM2017-69014.

For the axial flow fans NACA profiles have been well explored. However, the development and production of NACA profiles are also very expensive. Due to their lower cost of production circular arc blades are also applied to axial flow fans. But there is few information in the open literature focusing on flow loss and behavior of circular arc blades. Therefore, one question remains: how much is the difference of flow loss and behavior between NACA profiles and circular arc blades. In this paper NACA 65 profile and circular arc blade are examined by numerical method. The paper shows the flow loss of both blades in dependence of incidence, Reynolds number and spacing ratio. The occurrence of flow behavior, such as separation bubbles on the leading edge and flow structure on the sidewall is examined and discussed. The flow structure is given on basis of numerical flow picture. Additionally, the flow loss in the sidewall region of both investigated blades are worked out and compared.

Topics: Blades
Commentary by Dr. Valentin Fuster
2017;():V01CT20A002. doi:10.1115/FEDSM2017-69158.

Vortex cutting imposes significant forces on blades in applications such as wind turbines operating in the wake of upstream turbines, helicopter rotor vortex impingement on the tail rotor, intake vortex interaction with a pump impellor, and streamwise vortex ingestion into a submarine propeller. The transient lift on a blade during orthogonal cutting of a vortex with non-zero axial flow was examined in the current paper using a combination of scaling theory, an analytical solution for instantaneous cutting and full Navier-Stokes simulations. The paper focuses on two distinct forces that occur during vortex cutting — the transient lift force that occurs during penetration of the blade leading edge into the vortex core and the steady-state lift force associated with the difference in vortex core radius over the blade surface. We show that the maximum value of the lift coefficient for the transient blade penetration force is proportional to the impact parameter and inversely proportional to the axial flow parameter. This observation is used to collapse predictions of the full Navier-Stokes simulations for lift coefficient over a wide range of values of the governing dimensionless parameters.

Commentary by Dr. Valentin Fuster

8th Symposium on Bio-Inspired Fluid Mechanics

2017;():V01CT21A001. doi:10.1115/FEDSM2017-69221.

Sharks, dolphins and butterflies swim and fly in different flow regimes, yet the structure of their surfaces interacting with the surrounding fluid all appear to contain very important microscopic features that lead to reduced drag and increased flying or swimming efficiency. Sharks have moveable scales (approximately 200 microns in size) that act as a passive, flow-actuated dynamic roughness for separation control. Water tunnel experiments with real shortfin mako shark skin samples mounted to models have shown significant control of flow separation in both laminar and turbulent boundary layer scenarios. Dolphins have sinusoidal-shaped millimeter-sized transverse grooves covering a large percentage of their body. Experiments show that similar geometries embedded in a turbulent boundary layer can lead to separation control at the slight expense of increased friction drag. Alternatively, butterfly scales (100 microns in size covering the wings in a roof shingle pattern) appear to fundamentally alter the local skin friction drag depending on flow orientation for what is dominantly a laminar boundary layer interacting with the wings. However, in this case the surface may also slow the growth and formation of the leading-edge vortex and these effects shown in experiments may help explain a mean decrease in climbing efficiency (joules per flap) of 37.8% for live butterflies once their scales were removed. An overview of these results is discussed for these three cases, bringing out the importance of finding solutions in nature for essential engineering problems.

Commentary by Dr. Valentin Fuster
2017;():V01CT21A002. doi:10.1115/FEDSM2017-69264.

The study of highly unsteady wing flapping includes the large scale vortices, complicated locomotion/dynamics and deformable wing structures. When flapping insects/birds approach or perch on some objects, such as ground, wall or obstacle, the solid boundary dissipates, absorbs and bounces the leading edge, trailing edge and wing tip vortices, which are generated and shed during the flapping flight. Such phenomenon creates a high pressure area, leads to cushion effect and influences the aerodynamics, stability and maneuverability significantly. This paper uses immersed boundary method (IBM) to numerically study the aerodynamic performance of flapping wing in proximity of obstacles, investigate the distance, flapping motion and wing flexibility effects and relevant symmetric/asymmetric flow patterns, research the influence of vortex generating and shedding to the lift/drag change, explore the key distance and reveal the mechanism how insects/birds adjust the flapping motion to achieve ideal flight. Such research could theoretically support the development of micro-bionic flapping wing vehicle.

Topics: Wings
Commentary by Dr. Valentin Fuster
2017;():V01CT21A003. doi:10.1115/FEDSM2017-69285.

A typical example of the flow field around a moving elastic body is that around butterfly wings. Butterflies fly by skillfully controlling this flow field, and vortices are generated around their bodies. The motion of their elastic wings produces dynamic fluid forces by manipulating the flow field. For this reason, there has been increased academic interest in the flow field and dynamic fluid forces produced by butterfly wings. A number of recent studies have qualitatively and quantitatively examined the flow field around insect wings. In some such previous studies, the vortex ring or vortex loop formed on the wing was visualized. However, the characteristics of dynamic forces generated by the flapping insect wing are not yet sufficiently understood. The purpose of the present study is to investigate the characteristics of dynamic lift and thrust produced by the flapping butterfly wing and the relationship between the dynamic lift and thrust and the flow field around the butterfly. We conducted the dynamic lift and thrust measurements of a fixed flapping butterfly, Idea leuconoe, using a six-axes sensor. Moreover, two-dimensional PIV measurement was conducted in the wake of the butterfly. The butterfly produced dynamic lift in downward flapping which became maximum at a flapping angle of approximately 0.0 deg. At the same time, the butterfly produced negative dynamic thrust during downward flapping. The negative dynamic thrust was not produced hydrodynamically by a flapping butterfly wing because a jet was not formed in front of the butterfly. The negative dynamic thrust was the kicking force for jumping and the maximum of this kicking force was about 6.0 times as large as the weight. On the other hand, the butterfly produced dynamic thrust in upward flapping which was approximately 6.0 times as large as the weight of the butterfly. However, the attacking force by the abdomen of the butterfly was included in the dynamic thrust and we have not yet clarified quantitatively the dynamic thrust produced by the butterfly wing.

Topics: Wakes
Commentary by Dr. Valentin Fuster
2017;():V01CT21A004. doi:10.1115/FEDSM2017-69460.

Thunniform swimmers are known to travel at high speeds for long periods of time and at high hydrodynamic efficiency. Thus, there is a great deal of interest in their swimming physics. In order to better understand these physics, a newly designed robotic tuna was constructed that allows for interchangeable caudal fins. This robot was put in a water tunnel and tested at tail beat frequencies ranging from 0.5 to 1.0 Hz and at freestreams of 0, 0.2, and 0.4 m/s. A lever assembly was used to transmit thrust force to a load cell, and power was calculated using data from current sensors. Preliminary results suggest that swept caudal fins produce more thrust and are more efficient than trapezoidal fins at higher freestreams while the opposite is true at lower freestreams. However, several induction factors need to be resolved before more confident assertions can be made.

Topics: Thrust , Robotics , Shapes
Commentary by Dr. Valentin Fuster
2017;():V01CT21A005. doi:10.1115/FEDSM2017-69470.

Currently, the surgical procedure followed by the majority of cardiac surgeons to address right ventricular dysfunction is the Fontan procedure, which connects the superior and inferior vena cava directly to the left and right pulmonary arteries bypassing the right atrium. However, this is not the most efficient configuration from a hemodynamics perspective. The goal of this study is to develop a patient-specific 4-way connector to bypass the dysfunctional right ventricle and augment the pulmonary circulation. The 4-way connector is intended to channel the blood flow from the inferior and superior vena cava directly to the right and left pulmonary arteries. By creating a connector with proper hemodynamic characteristics, one can control the jet flow interactions between the inferior and superior vena cava and streamline the flow towards the right and left pulmonary arteries. In this study the focus is on creating a system that can identify the optimal configuration for the 4-way connector for patients from 0–20 years of age. A platform is created in ANSYS that utilizes the DOE function to minimize power-loss and blood damage propensity in the connector based on junction geometries. A CFD model is created to simulate the blood flow through the connector. Then the geometry of the bypass connector is parameterized for DOE process. The selected design parameters include inlet and outlet diameters, radius at the intersection, and length of the connector pathways. The chosen range for each geometric parameter is based on the relative size of the patient’s arteries found in the literature. It was confirmed that as the patient’s age and artery size change, the optimal size and shape of the connector also changes. However, the corner radius did not decrease at the same rate as the opening diameters. This means that creating different sized connectors is not just a matter of scaling the original connector to match the desired opening diameter. However, it was found that power losses within the connector decrease and average and maximum blood traversal time through the connector increased for increasing opening radius. This information could be used to create a more specific relationship between the opening radius and the flow characteristics. So in order to create patient specific connectors, either a new more complicated trend needs to be found or an optimization program would need to be run on each patient’s specific geometry when they need a new connector.

Topics: Hemodynamics
Commentary by Dr. Valentin Fuster
2017;():V01CT21A006. doi:10.1115/FEDSM2017-69471.

A single ventricular physiology of the human heart caused by a dysfunctional right ventricle is usually treated with the three-stage Fontan operation. The outcome of this operation is an extra-cardiac total cavopulmonary connection (TCPC) which supplies the deoxygenated blood from the body to the lungs by directly connecting the inferior and superior vena cava (IVC and SVC) to the left and right pulmonary arteries (LPA and RPA). However, the situation is worsened due to non-physiologic flow conditions and pressure loss inside the cavopulmonary track, which ultimately calls for a heart transplantation. A modest pressure rise of 5–6 mm Hg will help to regain the normal physiology of the patient. In order to achieve this, a conceptual design of a dual propeller pump inside a flared TCPC is developed and studied.

In order to provide a modest pressure rise, a blood pumping device was inserted inside the flared TCPC connection which consisted of two propellers, each placed in the SVC and the IVC and connected by a single shaft. The IVC and the SVC propellers were designed to rotate at the same rotational speed, having the same pressure rise but different blood inflow rate. The equal pressure rise across both the propellers was necessary at the design speed and flow rate to prevent any blood flow into the opposite vena cava. The TCPC-dual propeller conjunction was examined for the hydraulic performance and the flow pattern inside the TCPC using the 3D-CFD simulations on Ansys-CFX. The effect of axial distance between the two propellers on the blood flow interference and energy loss was also studied to select an optimal separation distance between them.

The introduction of dual propeller pump inside the flared TCPC led to a pressure rise of 2–15 mm Hg at a total flow rate of 4.5 lpm (63% from IVC and 37% from SVC) with the rotational speed ranging from 6000–12000 rpm. It was seen that an axial separation of 70 mm between the two propellers provided the best performance in terms of flow interference and energy loss.

A dual propeller pump assembled with an optimized TCPC could provide the required pressure rise for a particular age group of patients with univentricular Fontan physiology. The ability of dual micro-propeller pump to provide the required pressure rise will help to augment the cavopulmonary flow and hence help to regain the normal flow physiology as that witnessed by a human with biventricular circulation.

Commentary by Dr. Valentin Fuster
2017;():V01CT21A007. doi:10.1115/FEDSM2017-69559.

Bioinspired swimming methods have become highly attractive due to the potential for low environmental impact and high efficiency. However, although the efficiency has been quantified for select robotic and theoretical models, this paper explores more directly how requisite power consumption of an undulatory fin is affected by desired swimming speed. It further introduces and quantifies a method for recovering energy from the flow. First, CFD was used to simulate a cross-section of a fish fin with a wave number of 1.2 and a linearly increasing amplitude envelope. Flow speed and fin wave frequency were varied to determine interactive effects on force production and power requirements. The data from these simulations was fitted with polynomial functions over the range used for the study. To determine the potential for power regeneration from the flow, the fin was augmented with a mathematical model of a DC motor and shaft driving it. By incorporating the motor model into the fin analysis, the authors analyzed the amount of power input, or power regeneration, into the system from a constant velocity fluid flow, and developed a relationship between flow velocity and power regeneration. This relationship provides insight into both the level of power regeneration for the fin if held fixed in constant flow, and the minimum flow speed to regenerate energy at a desired rate. The determination of the relationships between efficiency and mode of operation will provide insight into the energetic efficiency of robotic designs using this method. Furthermore, the possibility of power recovery could pave the way for longer lasting underwater robots in extended missions. The determination of both efficiency and power regeneration capability will provide insight into the energetic feasibility of using, and improving on, the current capabilities of bioinspired underwater propulsion.

Topics: Biomimetics
Commentary by Dr. Valentin Fuster
2017;():V01CT21A008. doi:10.1115/FEDSM2017-69566.

This paper presents an empirical approach for flapping-wing aerodynamics using a servo-driven towing tank and a dynamically scale-up robotic manipulator. Time-varying aerodynamic force and moment were measured, and digital particle image velocimetry in multiple cross-sections were conducted. Three case studies showed that the towing tank experiment could be an effective way to investigate the aerodynamic characteristics in detail, which are difficult to be predicted by other conventional approaches. The force and moment measurements clarified that an advance ratio has significant role in governing the LEV behavior and consequent aerodynamic performance of flapping wings. Results for moving sideways showed the effects of the wing-wing and wing-body interaction, and the usefulness of the towing tank experiments for analyzing the flight dynamic characteristics. It was also shown that the towing tank experiments can be applicable to realistic wing motions; test results using the wing kinematics of a living insect in forward flight were well compatible with the trim condition of the insect.

Commentary by Dr. Valentin Fuster
2017;():V01CT21A009. doi:10.1115/FEDSM2017-69573.

Bees sustain flight at extremely low Reynolds Numbers (500<Re<10,000) using three degrees of freedom and a flap frequency between 100 and 200 Hz. These combined mechanics create a complex vortex field that results in extraordinary agility and flight efficiency. In addition to agility and efficiency, bees are able to carry loads up to 80% of their body weight for miles making bee flight a very interesting subject area for drone and UAV related development. In order to better understand these complex fluid dynamics, Fluent is utilized to resolve the flow fields during forward flight for 4 anatomically accurate cross-sections of the bee wing at a speed of 1 m/s in two-dimensional flow. Each of the four cross-sections are taken at regular 1/6th wingspan intervals from the anatomically accurate bee wing model. The bee wing model was generated from a μCT scan of Bombus pensylvanicus with generalized bee kinematics presented in the literature. The kinematics applied to each cross-section are adjusted for the change in radial distance from the wing base. The presented analysis and discussion investigates the effects of the variation in cross-section and kinematics over the wing on vortex-shedding dynamics, and instantaneous aerodynamic forces.

Commentary by Dr. Valentin Fuster
2017;():V01CT21A010. doi:10.1115/FEDSM2017-69579.

Bioinspired designs offer a viable solution to the design challenges of micro air vehicles (MAVs) desired to operate in the same size region under similar conditions as flying vertebrates and insects. Inspired by our previous studies of tethered live dragonflies, here, a quantitative characterization of the unsteady aerodynamic features of a live, freely flying dragonfly under well-established level flight condition will be presented. In particular with regard of the span-wise features of vortex interactions between the fore- and hind-pairs of wings, that highly contributes to the flight agility and efficiency of dragonflies. Flow fields of free flying dragonflies in still air have been measured by time-resolved stereo particle image velocimetry (TRS_PIV). A specifically designed dark flight chamber has been built, where hand hold dragonflies (Pantala flavescens) were released and made to fly nearly parallel to the measurement plane toward a guiding light. Realistic kinematics of the dragonfly wings in free flight were measured by filming with 2 synchronized high-speed video cameras. Using the recorded images, several dozens of landmarks on the fore- and hind-wing surfaces and several landmarks on the body were traced with high precision and the three-dimensional coordinates were then reconstructed with a direct linear transformation (DLT) method. Using the reconstructed wing-body model, Navier-Stokes-based computational fluid dynamics (CFD) analyses, with wing shapes prescribed based on the experimental measurement, dynamically moving multi blocked, and an overset-grid system were conducted. The numerical results are in overall agreement with the PIV data, and the combined numerical and experimental approach offers valuable insight into aerodynamic analyses. The results show that the interaction with the forewing leading edge vortex (LEV) strongly influences the flow structures around the inner spanwise region of the hindwing, while aerodynamic enhancement via vortex capture in the outer span is observed. The interaction depends not solely on wing phasing, geometrical arrangement, but also the flight mission.

Topics: Vortices
Commentary by Dr. Valentin Fuster

12th Symposium on Flow Manipulation and Active Control

2017;():V01CT22A001. doi:10.1115/FEDSM2017-69046.

A numerical study is conducted to explore the unsteady nature of fluidic oscillators which is responsible for generating sweeping jets for effective flow control of large-scale applications. Two- and Three-dimensional (2D and 3D) Unsteady Reynolds-Averaged Navier-Stokes (URANS) and 3D Improved Delayed Detached Eddy Simulation (IDDES) are employed to simulate and resolve the flow structures in the internal flow passages of a fluidic oscillator and external flow field in a quiescent flow condition. The predicted flow generated by an enlarged actuator with an outlet diameter of 25 mm using air as a working fluid is validated against measurements at various supply rates. Comparison of current computational results using 2D and 3D URANS with experiments indicates a reasonable agreement in the jet oscillation frequency. However, a significant discrepancy in the streamwise velocity field is observed between the 2D URANS and experimental data. The 3D URANS also under-predicts the jet width and consequently over-predicts the extension of the jet in the axial direction downstream of the actuator exit. Excellent agreement in the jet oscillation frequency and internal and external flow field is obtained at two supply rates between 3D IDDES and measurements.

Commentary by Dr. Valentin Fuster
2017;():V01CT22A002. doi:10.1115/FEDSM2017-69060.

Analysis of the experimental results of separation control with a dielectric barrier discharge plasma actuator over a NACA0015 airfoil and an Ishii airfoil, which is practical airfoil and gains better aerodynamic performance than NACA0015 airfoil at low Reynolds number, is conducted to investigate the relationship between the parameters (i.e. nondimensional burst frequency: F+, input voltage: Vpp, angle of attack: AoA) and the improvement of the aerodynamic performance. Time-averaged pressure distributions are measured at Reynolds number of 62,000 around the airfoils. In this study, scatter plot matrix (SPM) is used as the data mining technique to extract the correlation between parameters. Results indicate that for both NACA0015 and Ishii airfoils, F+ = 6 and 1 are effective for low and high AoA, respectively. Also SPM plots show that the pressure coefficient at the trailing edge and lift-to-drag ratio (L/D) are well related each other.

Commentary by Dr. Valentin Fuster
2017;():V01CT22A003. doi:10.1115/FEDSM2017-69226.

This study proposes separation control investigation using a Dielectric Barrier Discharge (DBD) plasma actuator on a NACA0015 airfoil over a wide range of Reynolds numbers. The airfoil was a two dimensional NACA0015 wing model with chord length of 200mm. Reynolds numbers based on the chord length were ranged from 252,000 to 1,008,000. A plasma actuator was installed at the leading edge and driven with AC voltage. Burst mode (duty cycle) actuations, in which nondimensional burst frequency F+ was ranged in 0.1–30, were applied. Time-averaged pressure measurements were conducted with angles of attack from 14deg to 22deg. The results show that initial flow fields without an actuation can be classified into three types; 1) leading edge separation, 2) trailing edge separation, and 3) hysteresis condition between 1) and 2), and the effect of burst actuation is different for each above initial condition.

Commentary by Dr. Valentin Fuster
2017;():V01CT22A004. doi:10.1115/FEDSM2017-69246.

This paper experimentally investigates the effectiveness of a closed-loop flow control method using a DBD plasma actuator for a NACA0015 airfoil, in which the surface pressure fluctuation is fed back to the system; the actuator was driven when the pressure fluctuation exceeds the setup threshold. The Reynolds number based on the chord length is set to 63,000 and the angle of attack is in the range from 12 to 15 degrees. The actuator was installed on the surface at 5% of the chord length from the leading edge. The results show that the closed-loop control worked better than the continuous operation. In the angle of attack of 12 and 14 degrees, the complete attached flow was attained by setting the appropriate threshold value of the pressure fluctuation. On the other hand, in 15 degrees, although the complete attached flow was not attained, the flow separation was partially suppressed.

Commentary by Dr. Valentin Fuster
2017;():V01CT22A005. doi:10.1115/FEDSM2017-69272.

We experimentally control the turbulent flow over backward-facing step (ReH = 31500). The goal is to modify the internal (Xr) and external (Lr) recirculation points and consequently the recirculation zone (Ar). A model-free machine learning control (MLC) is used as control logic. As benchmark, an optimized periodic forcing is employed. MLC generalizes periodic forcing by a multi-frequency actuation. In addition, a sensor-based control and a non-autonomous feedback, open- and closed-loop laws, were use to optimize the control. The MLC multi-frequency forcing outperforms, as expected, periodic forcing. The non-autonomous feedback brings a further improvement. The unforced and actuated flows have been investigated in real-time with a TSI particle image velocimetry (PIV) system. The current study shows that a generalization of multi-frequency forcing and sensor feedback significantly reduces the turbulent recirculation zone, far beyond optimized periodic forcing. The study suggests that MLC can effectively explore and optimize new feedback actuation mechanisms and we anticipate MLC to be a game changer in turbulence control.

Commentary by Dr. Valentin Fuster
2017;():V01CT22A006. doi:10.1115/FEDSM2017-69461.

Aerodynamic investigation of tandem airfoil configuration has so many applications in different industries that has become a topic of scientific interest since many years ago. One can name a lot of applications in this field such as the aerodynamic interaction between a wing and a tail or a wing and a flap of an aircraft, blades of a rotor and a stator in a compressor or turbine, the tandem blades in the rotor of a compressor, wings of an MAV, to name but a few. The primary objective of this research is to investigate the effect of active flow control (AFC) on two airfoils in tandem configuration, in which the upstream airfoil undergo pitching motion and the downstream airfoil is stationary. In the first place, the aerodynamic characteristics of airfoils in tandem configuration such as lift and drag coefficient is obtained when there is no flow control on the airfoils (clean case). Following this, the mentioned quantities are calculated for the airfoils when AFC has been applied on the forefoil. In order to analyze the effect of AFC and tandem configuration aerodynamic characteristics, the lift and drag coefficient of clean case is compared to those of the controlled case. The result suggests that AFC has caused the amount of CL to grow significantly. It was also observed that the tandem configuration had little influence on the forefoil. On the other hand, the vortices coming from the upstream airfoil generated thrust on the hindfoil. In case of AFC, our results suggest that fluctuations of both lift and drag forces decrease in the hindfoil. It is worth mentioning that this research is among the firsts studying the effect of AFC on tandem airfoils and will pave the way for those who are interested in this field.

Commentary by Dr. Valentin Fuster
2017;():V01CT22A007. doi:10.1115/FEDSM2017-69569.

The size of wind turbine blades has been continuously increased for better aerodynamic efficiency. However, the large scale blades induce loud noise and vibration as well as the increased difficulty in maintenance; all of these eventually causes the increase in the cost of energy. The vibration of wind turbines is mainly caused by wind turbulence, wind shear, and tower shadow. These causes change in local angle of attack of wind turbine blades and create mostly periodic vibration.

In this work, a flow control device is applied for vibration reduction of wind turbine blades. The conventional role of flow control devices is to increase lift coefficient and to reduce drag coefficient by flow separation delay. In this research, flow control device is used to make a flat slope of lift coefficient in specific angle of attack range for vibration reduction; lift coefficient is not always increased but also decreased, too.

To manipulate the lift coefficient slope, several types of flow separation controller are considered. Finally, a plasma actuator is selected because the minimal structural modification is necessary while providing sufficient lift coefficient control. The plasma actuator is attached to an airfoil to blow the jet upwind to decrease the lift. Computational fluid dynamics simulation is conducted to estimate the flow control performance of the plasma actuator. Experiments are conducted on a DU35-A17 airfoil to verify the lift coefficient manipulation performance of the plasma actuator.

Commentary by Dr. Valentin Fuster

21st Symposium on Fundamental Issues and Perspectives in Fluid Mechanics

2017;():V01CT23A001. doi:10.1115/FEDSM2017-69091.

Contact angle is an important parameter that characterizes the degree of wetting of a material. While for a static case, estimation and measurement of contact angle has been well established, same can not be said for the dynamic case. There is still a lack of understanding and consensus as to the fundamental factors governing the microscopic dynamic contact angle. With the aim of understanding the physics and identifying the parameters that govern the actual or microscopic dynamic contact angle, we derive a model based on first principles, by performing a force balance around the region containing the contact line. It is found that in addition to the surface tension, the microscopic dynamic contact angle is also a function of surface tension gradient and the jump in normal stress across the interface. In addition to having a significant contribution in determining the microscopic dynamic contact angle, surface tension gradient is also a key cause for contact angle hysteresis.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A002. doi:10.1115/FEDSM2017-69127.

Vortex induced vibration of a circular cylinder with low mass ratio in vicinity of a wall boundary is investigated experimentally in a water tunnel facility. Simultaneous measurements of the flow field via planar Particle Image Velocimetry and amplitude response have been carried out across a wide range of reduced velocities and cylinder-wall gap ratios (S* = S/D). For S* ≥ 3, both the amplitude response and the wake development are not significantly affected by the presence of the wall boundary. As S* is decreased below 3, the amplitude response decreases until S* ≈ 0.5, where the cylinder begins to periodically impact the wall. For all S* ≤ 0.5, the cylinder continues to impact the wall in a periodic fashion, and the reduced velocity range over which this occurs increases. Mean field and RMS field statistics revealed strong asymmetric wake development for S* < 3. Proper Orthogonal Decomposition of the velocity data was used to investigate the energy distribution in the coherent wake structures, and to filter the incoherent fluctuations via construction of a Reduced Order Model. Reconstructions of instantaneous vorticity fields obtained from the ROM illustrate the changes in vortex shedding patterns with the cylinder response.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A003. doi:10.1115/FEDSM2017-69136.

Much research has been devoted to incestigating the relationship between Knudsen number and slip velocity using different lattice Boltzmann methods. However, these models are complex to implement for simulations in continuum regime, and have shown to diverge when compared with Direct Simulation Monte Carlo (DSMC) simulations at high Knudsen numbers. In this study, a molecular dynamics (MD)-based Knudsen number is presented, and the relationship between Knudsen number and slip velocity is presented. The proposed slip model directly correlates the Knudsen number with the slip velocity. The model is implemented on a shear-driven MD simulation of a Couette flow, and curve fitting is used to get an exponential solution for the slip velocity. The solution obtained from the proposed model as well as the solutions from the literature are compared with a DSMC simulation. The results show that the proposed exponential solution agrees well with DSMC simulations in comparison with the models from the literature. The exponential solution can serve as boundary conditions for simulating flows at different Knudsen numbers in continuum regime.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A004. doi:10.1115/FEDSM2017-69237.

Even Newtonian liquids are now known to slip past suitably engineered surfaces, such as those exhibiting super-hydrophobicity. Through friction reduction, such surfaces have potential to significantly reduce the required the motive power to drive confined flows. Studies of unconfined shear flows over such surfaces have revealed that patterned slipping surfaces are intrinsically inferior to the less realizable uniformly slipping surfaces in terms of the fluid slip velocity generated per unit pattern-averaged shear stress. In this study, a spectrally accurate semianalytical approach is used to assess the friction-reduction performance of several alternate ways of confining the flow over a patterned surface. Fluid permeates by pressure differential through a channel with plate-like walls. One of the plates forming the channel is kept fixed throughout the study to have a sinusoidal slip pattern, while the second plate can be non-slipping, uniformly slipping and patterned identically to the first surface. The gap between the plates, the degree of slip and pattern waveform parameters can be varied between limits not restricted by the model. Significantly different behaviours in permeability and the effective degree of slip of the first plate arise from the differences in patterning on the second plate.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A005. doi:10.1115/FEDSM2017-69280.

The impact of inflow conditions on the flow structure and evolution characteristics of annular flows of Newtonian and shear-thinning fluids through a sudden pipe expansion are studied. Numerical solutions to the elliptic form of the governing equations along with the power-law constitutive equation were obtained using a finite-difference scheme. A parametric study is performed to reveal the influence of inflow velocity profiles, annular diameter ratio, k, and power-law index, n, over the following range of parameters: inflow velocity profile = {fully-developed, uniform}, k = {0, 0.5, 0.7} and n = {1, 0.8, 0.6}. Flow separation and entrainment, downstream of the expansion plane, creates central and a much larger outer recirculation regions. The results demonstrate the influence of inflow conditions, annular diameter ratio, and rheology on the extent and intensity of both flow recirculation regions, the wall shear stress distribution, and the evolution and redevelopment characteristics of the flow downstream the expansion plane. Fully-developed inflows result in larger reattachment and redevelopment lengths as well as more intense recirculation, within the central and corner regions, in comparison with uniform inflow conditions.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A006. doi:10.1115/FEDSM2017-69299.

Wheel aerodynamics has a major impact on the overall aerodynamic performance of a vehicle. Different vortex excitation mechanisms are responsible for the induced forces on the geometry. Due to the high degree of complexity, it is difficult to gain further insight into the vortex structures at the rotating wheel. Therefore, wheel aerodynamics is usually investigated using temporally averaged flow fields. This work presents an approach to apply a recently introduced low-memory variant of Dynamic Mode Decomposition (DMD), namely Streaming Total DMD (STDMD), to investigate temporally resolved simulations in greater detail. The performance of STDMD is shown to be comparable to conventional DMD for a rotating generic closed wheel simulation test case. By creating a Reduced-Order Model (ROM) using a comparably small amount of DMD modes, the amount of complexity in the flow field can be drastically reduced. Orthonormal basis compression, amplitude ordering and a newly introduced amplitude weighting method are analyzed for creating a suitable ROM of DMD modes. A combination of compression and ordering by eigenvalue-weighted amplitude is concluded to be best suited and applied to the Delayed Detached Eddy Simulation (DDES) of the rotating generic closed wheel and a production vehicle rim wheel. The most dominant flow structures are captured at frequencies between 18Hz and 176Hz. Leading modes for both geometries are found close to the wheel rotation frequency and multiples of that frequency. The modes are identified as recirculation modes and vortex shedding.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A007. doi:10.1115/FEDSM2017-69314.

The transient flow field near the surface of a substrate impacted by a pulsating supersonic jet emerging from a long tube is investigated using a simplified axially symmetric numerical approach. In the system being modeled, the pulses are created using a rotary valve located at the tube entrance. This flow situation approximates the conditions existing in the Shock-Induced Cold Spray process for coating surfaces with metallic particles. Previous numerical studies of transient supersonic jets either focused on jets emerging from orifices or did not give details of the complex supersonic flow field in the jet impact region. The current approximate numerical method considers the flow within the long tube and in the jet impact region. The procedure involves two stages. The upstream pressure variation with time is first determined using a one-dimensional compressible flow approximation of the entire tube and rotary valve arrangement. The resulting pressure versus time curve serves as the transient inlet boundary condition for an axially symmetric computational fluid dynamic solution of the flow through the tube and region of jet impact on the substrate. The numerical solutions of substrate pressure on the jet centerline versus time are compared with available experimental results and predict certain general features of the substrate pressure traces. Although the simplified model is only in fair agreement with some aspects of the experimental curves, it is shown to be useful in explaining certain peculiar flow features. With the aid of the numerical solution, an explanation for the movement and instability of the bow shock wave which forms ahead of the substrate is described.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A008. doi:10.1115/FEDSM2017-69343.

An experimental investigation is conducted to study the leading edge vortex (LEV) evolution of a simultaneously heaving and pitching foil operating in the energy harvesting regime. Two dimensional particle image velocimetry measurements are collected in a wind tunnel at reduced frequencies of k = fc/U = 0.05–0.20. Vorticity flux analysis is performed to calculate the constant C in the vortex formation number equation proposed by J. O. Dabiri [1], and it is shown that for a flapping foil operating in the energy harvesting regime, this constant is approximately equal to 1.33. We demonstrate that the optimal LEV formation number (T̂max ≈ 4) is achieved at k = 0.11, which is well within the range of optimal reduced frequency for energy harvesting applications (k = 0.1–0.15). This suggests that the flow energy extraction is closely related to the efficient evolution process of the LEV.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A009. doi:10.1115/FEDSM2017-69345.

An isotropic elastic porous structure whose pore geometry is regular (periodically uniform) will experience non-uniform deformation when a viscous fluid flows through the matrix under the influence of an externally applied pressure difference. In such a case, the flow field will experience a non-uniform pressure gradient whose magnitude increases in the direction of bulk flow. In this study, a method is presented that predicts local losses of the flow through a porous matrix whose geometry varies in the direction of flow. Employing an asymptotic expansion about the variation in geometry provides an expression relating local hydraulic permeability to local pore geometry. In this way the pressure field is able to be determined without requiring the explicit solution of the flow field. In this study a test case is presented showing that the local pressure losses are predicted to be within 0.5% of the losses determined from the solution to the Navier-Stokes Equations. The approach can be used to simplify the coupled fluid-solid problem of flow through elastic porous media by replacing the need to explicitly solve the flow field.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A010. doi:10.1115/FEDSM2017-69372.

Wing selection plays a crucial role for race cars as it generates the most downforce. This is essential to maintain traction which leads to faster lap timings, and maintain efficiency in the performance of the race car. In this paper, the numerical simulation of a Formula SAE (FSAE) Car is performed. The FSAE car is restricted by regulations in terms of the geometry of the front and rear wing configuration. Hence, it becomes necessary to optimize the selection of airfoils in order to get the best out of the wing configuration. It is also essential to observe the tradeoff between the downforce generated and the drag produced in a racecar for optimal performance. This serves as the primary motivation of this research paper. The focus is on Benzing airfoils, which show considerably better performance in terms of downforce production in a race car than conventional airfoils. The wing configuration utilized in this research paper consists of a single mainplane and two flaps.. The freestream velocity of the flow is in the range of 0–60mph (0–26m/s). The 122 series of Benzing airfoils is utilized for the mainplane and the 153 series of Benzing airfoils is utilized for the flaps for manufacturing reasons. Nine different combinations of Benzing airfoils were utilized wherein it was noticed that an appropriate selection of the airfoils for the mainplane and flaps with a fixed angle of attack difference, leads to a 12–15% increase in downforce amongst the Benzing airfoils itself. Similarly, it was also observed that an optimal configuration would lead to a 12–15% decrease in drag in comparison too poor performing airfoil. The Be 153-055 airfoil acts as an excellent flap within the limits of computational error. Data from an on-track test is used in order to verify the approach utilized in this paper in order to validate if the approach used in this paper would be feasible. It is observed that the Benzing airfoil does improve the average cornering speed of the car by around 10% in comparison to the previous configuration of S1223 airfoil as the main plane and the goe 477 airfoil as the flap.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A011. doi:10.1115/FEDSM2017-69389.

In many industrial applications such as oil and gas production systems and heat exchangers, annular flow is a frequently observed flow regime. A lot of experiments and analysis have been carried out in the last decades in order to determine the thickness of the liquid film in annular flow and in straight pipes; however, published liquid film thickness models and experimental data in bends are scare. This paper presents a model for predicting average liquid film thickness in bends according to the correlations obtained for calculating dimensionless interfacial friction factor as well as dimensionless liquid film thickness in bends. Correlations were obtained based on analysis carried out using a control volume of gas core and utilizing experimental data available in the literature for liquid film thickness in bends. Furthermore, liquid film thickness distribution at the inner and outer bends of elbows were investigated, and a simple analytical model has been developed for predicting film thickness at the outer and inner radii of a bend. It is shown that, the average film thickness calculations from the current model agree with experimental data and results show that the model can predict the film thickness changes based on the flowrates and properties of liquid and gas phases.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A012. doi:10.1115/FEDSM2017-69398.

Drafting is commonly utilized in cycling, particularly during competitions. According to the literature, in a racing environment, the riders can expend 90% of their energy on overcoming drag, and can save about 30% of their energy by riding behind another rider in the absence of cross-wind. In the presence of a strong cross-wind, competitive cyclists form echelons by placing themselves about halfway behind each other, while being slightly offset sideways. Although forming an echelon is a common practice, the formation has not been sufficiently studied in the literature. To address this, the drag and side forces on a model cyclist were studied experimentally. A simplified 3D model was built based on the outline of a competitive cyclist. Two 1:11 scale models were rapid-prototyped and tested in a wind tunnel. The drafting effects on a cyclist were investigated for different yaw angles — the angles of the apparent wind with respect to the direction of cyclist motion. The effects of wind-stream-wise position and wind-off-stream-wise position were studied for each angle by measuring the drag and side-force on a model placed in the wake of another identical model. The results suggest that there is a significant decrease in both drag and side force when a cyclist is riding in the wake of another cyclist. Although a smaller wind-stream-wise offset generally results in smaller forces, this effect is not significant for most configurations. The offset in the wind-off-stream-wise direction has a noticeable effect on the forces — no off-stream-wise offset results in the lowest drag and side force, except for low yaw angles at which it may be beneficial for the drafting cyclist to be slightly forward with respect to the in-line (no offset) position.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A013. doi:10.1115/FEDSM2017-69408.

During a severe accident, contact of the molten corium with the coolant water may cause an energetic steam explosion which is a rapid increase of explosive vaporization by transfer to the water of a significant part of the energy in the corium melt. This steam explosion has been considered as an adverse effect when the water is used to cool the molten corium and could threaten reactor vessel, reactor cavity, containment integrity. In this study, TROI TS-2 and TS-3 experiments as part of the OECD/SERENA-2 project were analyzed with TEXAS-V. Input parameters were based on actual TROI experiment data. In mixing simulations, calculated results were compared to melt front behavior, void fraction in trigger time and other parameters in experiment results. In explosion simulations, corresponding to TROI experiments an external triggering was employed at the moment that melt front reached heights of 0.4 m. Calculated results of peak pressure and impulse at the bottom were compared with TROI experiment results. Melt front behaviors of the melt was different from the experimental results in both TS-2 and TS-3. Void fraction in triggering time in TS-2 was in good agreement with the experiment results and in TS-3 was slightly overestimated. The peak pressure and impulse at bottom were successfully predicted by TEXAS-V. These calculations will allow establishing whether the limitations and differences observed in the simulations of the experiments are important for the reactor case.

Topics: Explosions , Steam
Commentary by Dr. Valentin Fuster
2017;():V01CT23A014. doi:10.1115/FEDSM2017-69417.

The common peat moss, Sphagnum, is able to explosively disperse its spores by producing a vortex ring from a pressurized sporophyte to carry a cloud of spores to heights over 15 cm where the turbulent boundary layer can lift and carry them indefinitely. While vortex ring production is fairly common in the animal kingdom (e.g. squid, jellyfish, and the human heart), this is the first report of vortex rings generated by a plant. In other cases of biologically created vortex rings, it has been observed that vortices are produced with a maximum formation number of L/D = 4, where L is the length of the piston stroke and D is the diameter of the outlet. At this optimal formation number, the circulation and thus impulse of the vortex ring is maximized just as the ring is pinched off. In the current study, we modeled this dispersal phenomenon for the first time using ANSYS FLUENT 17.2. The spore capsule at the time of burst was approximated as a cylinder with a thin cylindrical cap attached to it. They were then placed inside a very large domain representing the air in which the expulsion was modeled. Due to the symmetry of our model about the central axis, we performed a 2D axisymmetric simulation. Also, due the complexity of the fluid domain as a result of the capsule-cap interface, as well as the need for a dynamic mesh for simulating the motion of the cap, first a mesh study was performed to generate an efficient mesh in order to make simulations computationally cost-effective. The domain was discretized using triangular elements and the mesh was refined at the capsule-cap interface to accurately capture the ring vortices formed by the expulsed cap. The dispersal was modeled using a transient simulation by setting a pressure difference between inside of the capsule and the surrounding atmospheric air. Pressure and vorticity contours were recorded at different time instances. Our simulation results were interpreted and compared to high-speed video data of sporophyte expulsions to deduce the pressure within the capsule upon dispersal, as well as the formation number of resulting vortex rings. Vorticity contours predicted by our model were in agreement with the experimental results. We hypothesized that the vortex rings from Sphagnum are sub-optimal since a slower vortex bubble would carry spores more effectively than a faster one.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A015. doi:10.1115/FEDSM2017-69418.

An experimental investigation was conducted to study the effects of Reynolds number on mixing characteristics and turbulent transport phenomena in the near and intermediate regions of free equilateral triangular and round jets issuing from modified contoured nozzles (nozzles with sharp linear contractions). Detailed velocity measurements were made using a particle image velocimetry at Reynolds numbers of 6000, 10000, 13800 and 20000. Computational fluid dynamics (CFD) was also applied to understand the flow behaviors in different Reynolds numbers. We applied standard k-ε turbulence model in an axisymmetric domain to conduct the numerical simulation of the round jet cases. The potential core length was the system response quantity to evaluate our simulation against the experimental results. The geometrical comparative study shows enhanced mixing in the near field of the triangular jets compared to the round jets, regardless of Reynolds number. This conclusion is supported by shorter potential core length and faster growth of turbulence intensity on the centerline of the triangular jets. The obtained data in the round jets exhibit that the jet at the lowest Reynolds number has the most effective mixing with the ambient fluid, while increase in Reynolds number reduces the mixing performance. In the triangular jets almost there is no Reynolds number effect on the measured quantities including the length of the potential core, the decay rate and the axis-switching locations. The results revealed that the asymptotic values of the turbulence intensities on the jet centerline are not only independent of the Reynolds number but also they are the same for both the round and triangular jets. Due to the specific shape of the triangular nozzle, a skewed flow pattern is observed in the near field region in the major plane while the jet is absolutely symmetric in the minor plane. The turbulence structures in all the jets studied become larger as streamwise distance increases, while there is no considerable Reynolds number or nozzle geometry effects on the size of the structures on the jet centerline.

Topics: Turbulence , Jets
Commentary by Dr. Valentin Fuster
2017;():V01CT23A016. doi:10.1115/FEDSM2017-69419.

An experimental study was conducted to investigate nozzle geometry effects on mixing characteristics and turbulent transport phenomena in the near and intermediate regions of free jets issuing from modified contoured nozzles (contoured nozzle with a sharp linear contraction). The cross-sections examined were round, square, equilateral triangle as well as ellipse and rectangle with aspect ratio of 2. For each nozzle shape, detailed velocity measurements were made using particle image velocimetry at a Reynolds number of 10000. It was observed that noncircular jets have shorter potential cores than their round counterparts and their lengths are comparable with those of orifice jets. In addition, the spread and decay rates and the levels of turbulence intensities are the highest in the jets issuing from the elliptic and rectangular nozzles, implying enhanced mixing in these jets. The results from the swirling strength analysis revealed that the rotational motions induced by vortices within the minor planes of the elliptic and rectangular jets are more intense than those observed in the other jets. Furthermore the obtained data indicate distinctly different flow characteristics in the major and minor planes of elliptic, rectangular and triangular jets due to their asymmetric shapes. The size of turbulence structures in all the jets studied increases with streamwise distance and the elliptic and rectangular jets contain the largest structures.

Topics: Turbulence , Jets , Nozzles
Commentary by Dr. Valentin Fuster
2017;():V01CT23A017. doi:10.1115/FEDSM2017-69420.

While many theoretical and numerical studies have been carried out to study blast induced traumatic brain injury (bTBI), validation of simulation results is still a concern due to moral issues and experimental constraints. Shock-tubes are one of the major means for replicating blast waves in a controlled medium. North Dakota State University Shock-tube (NDSUST) has been designed to simulate the blast shockwaves in an attempt to study and investigate bTBI. However, accurate replication of a blast profile in terms of the impulse and overpressure is highly dependent on the geometrical features of the shock-tube. To this end, numerical methods such as computational fluid dynamic (CFD) analysis can help to evaluate and increase the efficiency of the current shock-tubes. The NDSUST contains three major parts, namely, driver (the high pressure container), driven cone, and the chamber to setup the head model. The driver and driven cone are separated by layers of Mylar membrane. Shockwaves are defined by three pressure-time characteristics; positive phase (positive impulse), negative phase (negative impulse), and maximum pressure (overpressure). While the current NDSUST simulated most shockwave characteristics accurately, the negative impulse was observed to be considerably long. The diameter of Mylar membrane interface, the volume of the deriver, and the chamber room cross-section connected to the driven cone, were considered as possible parameters affecting the efficiency of the shock-tube. Accordingly, NDSUST was modeled in ANSYS CFX using its actual dimensions. A transient CFD analysis was carried out using ANSYS CFX to simulate the turbulent, supersonic, and compressible flow upon rupture of the Mylar membrane in order to study the pressure wave propagation inside the shock-tube. No-slip boundary conditions were chosen for the shock-tube walls. Driver and driven sections were considered as two separate domains connected using an interface. The shockwave was generated by setting the driver and driven sections at high and low pressures, respectively and running the simulation for a total time of 1 second. The primary results revealed that the current cross-section at the interface of the driven cone and the square chamber caused the pressure disruption (pressure oscillation) upon entrance of the pressure waves into the chamber room. In addition, it was concluded that the driver volume would affect the negative impulse’s duration and the negative peak pressure.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A018. doi:10.1115/FEDSM2017-69448.

Blast waves are generated upon release of a large amount of energy in few milliseconds. Upon release, these high pressure waves propagate rapidly and interact with human head and lead to severe traumatic brain injury (TBI). Understanding the mechanics of blast flow would allow us to develop effective tools to protect the head against these shockwaves. Military helmets are known as the most effective tool for protecting the soldier’s head against blast threats. However, due to the complicated nature of the shockwave development and propagation, as well as its interaction with head and helmet, the efficiency of helmets is still in question. The major problem with using helmets under blast loading is the entrapment of blast shockwaves inside the helmet gap and its reflection from the interior of the helmet’s shell. Moreover, development of an amplified pressure region at the opposite side of the incoming blast waves, referred to as the underwash effect of helmets has raised some concerns. To this end, we performed a computational fluid dynamics (CFD) analysis to better understand the mechanism of the blast shockwave interaction with head, as well as the effect of the helmet on the alteration of flow mechanics. The compressible, turbulent blast flow was simulated in ANSYS CFX by releasing the air from a high-pressure domain into the low-pressure one (at ambient pressure). The un/protected heads were exposed to an identical blast overpressure of 520 kPa in a frontal open blast scenario. Pressure contours and velocity profiles were recorded at several time instances for both unprotected and helmeted heads. Our primary results revealed that the change of the flow momentum inside the helmet gap, the reunion of the blast flow inside the gap as well as the development of adverse pressure gradient (and hence recirculating flow region) at the rear side of the head are the major reasons leading to this adverse phenomenon.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A019. doi:10.1115/FEDSM2017-69469.

The impact of flow inertia on flow and heat transfer in suddenly expanding annular pipe flows of a shear-thinning non-Newtonian fluid is studied within the steady laminar flow regime. The equations governing conservation of mass, momentum, and energy, along with the power-law constitutive model are numerically solved using a finite-difference numerical scheme. The influence of inflow inertia, annular-nozzle-diameter-ratio, k, power-law index, n, and Prandtl numbers, is reported for: Re = {50, 100}, k = {0, 0.5}; n = {1, 0.6}; and Pr = {1, 10, 100}. Heat transfer augmentation, downstream the plane of expansion, is only observed for Pr = 10 and 100. The extent and intensity of recirculation in the corner region, increases with inflow inertia. Higher Reynolds and Prandtl numbers, power-law index values, and annular diameter ratios, in general, reflect a more dramatic heat transfer augmentation downstream of the expansion plane.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A020. doi:10.1115/FEDSM2017-69502.

In this study, we conducted experiments using a shock tube to investigate how the thickness of soft reflecting material affects the reflected shock wave of oblique shock reflection. Results indicated that transition to Mach reflection (MR) is delayed when the reflecting surface is silicone, compared with that when the surface is rigid. Regarding the influence of reflecting material thickness, no remarkable difference was observed between 1mm and 10mm thickness, due to the trade-off of reflecting wedge angle and material thickness. No significant difference was observed regarding the influence of silicone on wave configuration.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A021. doi:10.1115/FEDSM2017-69503.

When a flat plate falls freely in periodic oscillating motion regime, unsteady fluid forces create additional lift force contributions due to the rotational behaviour. Computational fluid dynamics is used to simulate the free fall behaviour of a flat plate with aspect ratio β = 20 falling in two-dimensional flow with Reynolds number Re ≈ 10,000 and non-dimensional moment of inertia I* = 0.115. To validate the free fall trajectory obtained by computational fluid dynamics, video recordings are used. Based on the validated free fall computational fluid dynamics simulation, the instantaneous fluid forces and torques on the plate are obtained.

The validated simulations show significant deviations in per-pendicular and tangential force coefficients at the same angle of attack depending on the trajectory history of the plate. At low angles of attack below 5 deg, the tangential force differs significantly. Oppositely, the difference in the perpendicular force is most pronounced at high angles of attack. During a free fall, the angle of attack is below 5 deg in 70 % of the time. Furthermore, the angle of attack is only above 45 deg in less than 5 % of the time. Therefore, effort must be put into a more detailed description of the tangential force component, in order to improve the existing modelling framework for non-spherical particles.

Topics: Flat plates
Commentary by Dr. Valentin Fuster
2017;():V01CT23A022. doi:10.1115/FEDSM2017-69549.

Theory of molecular Taylor-Aris dispersion (TAD) is an accepted framework describing tracer dispersion in suspension flows and determining effective diffusion coefficients. Our group reported a pseudo-Lagrangian method to study dispersion in suspension flows at FEDSM-2000. Tracer motions were studied in a steadily moving inertial reference frame (SMIRF) aligned with the flow direction; increments of change of axial position of individual tracers were collected to demonstrate how the tracer moved as they, individually, interacted with similar collections of other bodies brought to and from the region. First, individual tracers with no apparent axial velocity component (NAAVC) were identified; they exhibited fixed positions in video recordings of images collected in the SMIRF. Then, time increments were measured for tracers to pass at least 5, but usually 10 pre-selected, nested distances in the up- or downstream direction laid out with respect to the zero-site in the SMIRF. Such data were richer than measurements of tracer spread over time because stations along each path were serial first-passages (FP) with probabilistic meaning. Dispersion of various types of suspension and two transformation rules for combining velocity components are discussed herein.

Traditional low-speed continuum theory and particle dynamics use Galilean transforms. Yet, to recognize the limited speed in laws for channel flows, Lorentzian transformations may be appropriate. In a four-space, deterministic paths would begin at NAAVC sites and continue in time-like conical regions of four-space. Distances in this space are measured using Minkowski’s metric; at the NAAVC site and on the boundary of the space-time cone, this metric has the format of the Fürth, Ornstein, and Taylor (FOT) equation when only terms to order t2 are used. Data shown at FEDSM-2000 can be reinterpreted as “prospective paths” in time-like regions that were consolidated in normalized cumulative probability distributions to provide retrospective descriptions. The ad hoc sign alteration of the FOT equation to fit the data of FEDSM-2000 is now taken as a part of measuring lengths using a Minkowski metric, which signifies a hyperbolic geometry, for which an inherent scaling constant is a negative curvature. The space also has an intrinsic distance of ℓ = Sτ, obtained from fitting parameters (S, τ) for the FOT equation. Integrals of the area under the FOT curve have units of volume, which are considered as describing an average volume of dispersion on S3, the 3-sphere. Path motion through this volume was kinematic dispersion, S2τ, which was the form for effective diffusivity in continuum theory used in FEDSM-2000. Weiner and Wilmer describe transformations in four-spaces in terms of commutating rotations on orthogonal planes, a concept readily linked to symmetries in the hyperbolic space typical of Lorentzian transformations; they also describe a second order ODE like the FOT equation.

Commentary by Dr. Valentin Fuster
2017;():V01CT23A023. doi:10.1115/FEDSM2017-69554.

The present study experimentally investigates the effect of plasma discharges on the ignition of a laminar methane jet diffusion flame in a stream of co-flow air. The Reynolds number of the jet flame, based on the nominal jet velocity and the nozzle diameter, is approximately Re = 2000. The plasma discharge, a corona type, is produced between two tungsten wires with a diameter of 0.5 mm and a gap of 15 mm. Results show that the application of plasma discharge in a near-nozzle region can ignite the flame. A non-reacting free jet similarity solution is applied to examine the ignition locations and it shows that many of the locations are outside the jet boundary, where the mixture is leaner than stoichiometry. The minimum input power required for flame ignition is seen to increase with radial distance away from the nozzle and decrease with downstream locations. A high input power required for ignition is found to be close to the nozzle exit, where a high strain can be expected. Spectroscopic study confirms the emission spectra in non-thermal air plasma and shows the intensity difference in spectra between discharges that ignite and do not ignite flames.

Commentary by Dr. Valentin Fuster

10th Symposium on Transport Phenomena in Energy Conversion From Clean and Sustainable Resources

2017;():V01CT24A001. doi:10.1115/FEDSM2017-69009.

Recently there have appeared multiscale lotus-leaf-like superhydrophobic surfaces that can enhance dropwise condensation in well-tailored supersaturation conditions. However, designs of most biomimetic surfaces were not driven by the understanding of underlying physical mechanisms. We report energy-based analysis of growth dynamics of condensates from surface cavities. As observed in condensation experiments, these textured surfaces with two tier roughness are superior to flat or solely nanotextured surfaces in spatial control of condensate droplets. To understand the role of condensate state transition in enhancing condensation heat transfer, we considered adhesion energy, viscous dissipation and contact line dissipation as the main portion of resistant energy that needs to be overcome by the condensates formed in surface cavities. By minimizing the energy barrier associated with the self-pulling process, we optimized first tier roughness on the hierarchically textured surfaces allowing condensates to grow preferentially in the out-of-plane direction. The nano-roughness of the second tier plays an important role in abating the adhesion energy in the cavities and contact line pinning. From the perspective of molecular kinetic theory, the dual scale engineered surface is beneficial to remarkably mitigating contact line dissipation. This study indicates that scaling down surface roughness to submicron scale can facilitate self-propelled condensate removal.

Commentary by Dr. Valentin Fuster
2017;():V01CT24A002. doi:10.1115/FEDSM2017-69485.

A numerical study is performed for the fluid flow, heat and mass transfer in a ventilated enclosure where a thermally and solutally activated square block is placed for heat and solute exchanges. The block is maintained with higher temperature and concentration than that of inlet flow and the walls are impermeable and adiabatic to heat and solute. Cold fluid is entered through a slot of left vertical wall and flushes out at the different slots of opposite wall to study the mixed air distribution due to the thermosolutal source present in the core of the enclosure. The dynamic, thermal and solutal transport phenomena are computationally visualized through the streamlines, isotherms and iso-concentration lines. The efficient cooling activities are studied by changing the locations of inlet and outlet ports with the variation of Richardson number (Ri) and Reynolds number (Re) for a fixed Prandtl number (Pr = 0.71).

Topics: Fluid dynamics , Heat
Commentary by Dr. Valentin Fuster

16th Symposium on Transport Phenomena in Materials Processing and Manufacturing Processes

2017;():V01CT25A001. doi:10.1115/FEDSM2017-69249.

When products requiring careful handling such as semiconductor wafers and food (hereinafter called “workpieces”) are transported in manufacturing processes, problems can occur due to malfunctions that degrade sanitary conditions during the transport of workpieces through contact. An excellent device for transporting workpieces is a pneumatic non-contact holder (hereinafter called “cup”). This device holds a workpiece without contact by using pneumatic pressure, and so a workpiece doesn’t suffer damage or contamination. The purpose of this paper is to propose a method for overcoming the weaknesses in vortex-type non-contact holders, which is a cup that can hold a workpiece by using the negative pressure generated by the centrifugal force of a swirling flow, and propose a shape of cup which will generates a larger holding force from the point of view of energy saving. Specifically, we changed the shape of the chamfer in the swirling chamber exits and the number of the nozzles, and measured the holding force characteristics and the pressure distribution of the cup, thereby examining the performance of the cups. The experimental results indicate that the holding force is strongly related to both the shape of the chamfer in the swirling chamber exits and the number of the nozzles.

Topics: Swirling flow
Commentary by Dr. Valentin Fuster
2017;():V01CT25A002. doi:10.1115/FEDSM2017-69270.

Manufacturing companies have a need for performance and life test equipment to improve the detection of leakage and damage on the seat of valve discs. In the present study, in order to develop such equipment, we first obtained failure data information from the fields, analyzed failure modes based on field data collected from customers, and then obtained our own field data using measuring equipment. Second, we designed and manufactured specific performance and life test equipment. The concept used to fabricate this equipment can be adapted for use with other valves, for example, ball valves and gate valves of various sizes, ranging from 400 mm to more than 2,000 mm. Although increasing the pressure is not difficult in small-sized valve systems, large-sized valve systems require the use of super-large pumps to increase the valve’s internal pressure. Therefore, in this study, the impulse pressure reappearance technique was developed to solve flow shortage during durability test.

Commentary by Dr. Valentin Fuster

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