ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V002T00A001. doi:10.1115/FEDSM2018-NS2.

This online compilation of papers from the ASME 2018 5th Joint US-European Fluids Engineering Division Summer Meeting (FEDSM2018) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

2nd Symposium on Development and Applications in Computational Fluid Dynamics

2018;():V002T09A001. doi:10.1115/FEDSM2018-83013.

The Eulerian methods are susceptible to generate the nonphysical spurious currents in the multiphase flow simulations near the interfaces. This paper presents a new Eulerian method to accurately simulate the velocity fields, especially near the multiphase flow interfaces and prevents the numerical results from generating the nonphysical currents. A Eulerian central difference finite-volume scheme equipped with the suitable numerical dissipation terms is used to simulate incompressible multiphase flows. The interface is captured by Flux Corrected Transport-Volume of Fluid method (FCT-VOF). Increasing the accuracy near the sharp gradients, such as interface, the conservative form of incompressible Navier-Stokes equations is solved to locally conserve the properties. The main feature of this algorithm is its ability to control the pressure gradient oscillation and also spurious currents near the interface; two common problems in multiphase flow simulations, and as a result improves the accuracy of the simulation by artificial numerical dissipations. The results show the FCT-VOF is able to precisely calculate the interface, and the numerical dissipation terms are the powerful device to prevent the spurious currents.

Commentary by Dr. Valentin Fuster
2018;():V002T09A002. doi:10.1115/FEDSM2018-83018.

Unsteady numerical investigations of flow past a partially rotating stepped cylinder have been performed. The objective of the study was to investigate whether the wake characteristics could be controlled with rotation of one cylinder while the other remains stationary and how partial rotation impacts the aerodynamic forces. The stepped cylinder was 2 m in length where the first meter was a round cylinder 5 cm in diameter followed by a 2:1 step down cylinder. Two round end plates, 0.1 cm thick and 40 cm in diameter, were placed at each end. The end plates were positioned at 5 degrees with respectto the incoming flow to remove the end effect on vortex shedding. All simulations were performed using the Siemens PLM STAR-CCM+ CFD software with K-ω turbulence model. The time step was 0.00083 second to resolve the flow for each 10 degrees rotation. 1200 time steps were used. The investigations were performed with one cylinder rotating while the other remains stationary. Four cases were investigated. When either cylinder was rotating, the RPM was maintained at either 2000 or 4000 while the free stream velocity was maintained at 10 m/sec. The Reynolds number for the large and small cylinders were approximately 32,258 and 16,129, respectively. The corresponding velocity ratios λ for the large cylinder rotating were 0.5 and 1.0, and 0.25 and 1.0 for the small cylinder.

Previous investigations have classified vortical structure in the wake of a step cylinder in terms of L-cell (for large cylinder), S-cell (for small cylinder) and N-cell (the region in between). When the large cylinder is rotating, at λ = 1.0, the velocity and vorticity in the wake of the large cylinder is increased. The N-cell initially has a larger velocity than the L-cell and is at a slanted angle. A suction effect was observed in the near wake region, causing the flow in the L-cell to coalesce near its midsection. The vortices originated at the step were connected to the S-cell at a lower speed. The overall lift to drag ratio (L/D) for this case was 1.14. When λ = 0.5, vortex structures were maintained through the three different cells with increased variations in cell frequency across the large cylinder, the L/D was reduced to 0.36.

When the small cylinder was rotating, at λ = 0.5, vortex shedding was suppressed within the S-cell and considerable distortion was observed in the vortical structure in the wake of the large cylinder. However, the N-cell had similar structure as when large cylinder was rotating, but connecting to the L-cell at a larger slanted angle. When λ was reduced to 0.25, shedding was observed across the length of the cylinder with increased variations. The corresponding L/D ratios for these cases were both at 0.2.

Commentary by Dr. Valentin Fuster
2018;():V002T09A003. doi:10.1115/FEDSM2018-83050.

Due to global demand for energy, there is a need to maximize oil extraction from wet reservoir sedimentary formations, which implies the efficient extraction of oil at the pore scale. The approach involves pressurizing water into the wetting oil pore of the rock for displacing and extracting the oil. The two-phase flow is complicated because of the behavior of the fluid flow at the pore scale, and capillary quantities such as surface tension, viscosities, pressure drop, radius of the medium, and contact angle become important. In the present work, we use machine learning algorithms in TensorFlow to predict the volumetric flow rate for a given pressure drop, surface tension, viscosity and geometry of the pores. The TensorFlow software library was developed by the Google Brain team and is one of the most powerful tools for developing machine learning workflows. Machine learning models can be trained on data and then these models are used to make predictions. In this paper, the predicted values for a two-phase flow of various pore sizes and liquids are validated against the numerical and experimental results in the literature.

Commentary by Dr. Valentin Fuster
2018;():V002T09A004. doi:10.1115/FEDSM2018-83058.

This article describes a CFD engineering application developed to investigate numerically the multiphase, non-isothermal, turbulent flow physics within the suspension preheater of a dry-process rotary cement kiln. The multi–stage cyclone preheater is a counter-current heat exchanger.

We used the CFD flow solver ANSYS-Fluent R18.1. to accomplish this task. The hybrid Eulerian multiphase-dense discrete phase model is a coupled Eulerian-Lagrangian technique. The primary carrier-phase is treated as a continuum by solving the Navier-Stokes equations, while the secondary discrete dispersed-phase is solved by tracking the particle parcels through the calculated flow field. The multiphase turbulence of the carrier-phase is modeled using the Reynolds stress transport model. The dispersed-phase interactions are modeled through the specific collisions models provided by the kinetic theory of granular flow and/or discrete element method. The Eulerian multiphase-DDPM method provided a quiet stable solution for a medium/high mass loading (solid to gas mass ratio 0.89:1).

The four-stage cyclone suspension preheater is analyzed for its operating performance i.e. overall pressure drop and global collection efficiency of cyclone stages, calcination degree at bottom cyclone stage, flue gas temperature at 1st. cyclone stage and availability to get more insight of very complex multi-phase flow patterns within this equipment. The set of industrial measurements, collected during a heat and mass balance of a dry process rotary cement kiln, were used to verify and to validate part of the simulation results.

Commentary by Dr. Valentin Fuster
2018;():V002T09A005. doi:10.1115/FEDSM2018-83060.

Adjoint based sensitivity studies are effective means to understand how flow quantities of interest and grid quality could affect the flow simulations. However, applying an unsteady adjoint method to three-dimensional complex flows remains a challenging topic. One of the challenges is that the flow variables at all previous time steps will be needed when solving the unsteady adjoint equation backwards in time. The straightforward treatment of storing all the previous flow solutions could be prohibitive for simulations with a large number of grid points and time steps. To avoid storing the full trajectory, the checkpointing method only stores the flow solutions at some carefully selected time steps called checkpoints, and re-computes the flow solutions between checkpoints when they are needed by the adjoint solver. However, the re-computation increases the computational cost by multiple times of the cost of solving the flow equations, which may be unacceptable for some applications. Alternatively, in this study, several data compression algorithms with much less extra cost were considered for alleviating the storage problem. In these data compression algorithms, the full flow solutions were projected onto a small set of bases which were either generated by the proper orthogonal decomposition (POD) method or by the Gram-Schmidt orthogonalization. Only a small set of bases and corresponding expansion coefficients need to be stored and they could recover the flow solutions at every time step with reasonable accuracy. The data compression algorithms were implemented in the numerical test cases, and the computed adjoint solutions were compared with that obtained by using full flow solutions. The comparisons demonstrated that the data compression algorithms were able to greatly reduce the storage requirements while maintaining sufficient accuracy.

Commentary by Dr. Valentin Fuster
2018;():V002T09A006. doi:10.1115/FEDSM2018-83061.

In the present work, thermal effects induced in the hydrodynamics of heavy oil transport in pipelines are analyzed. Here, the thermal dependence of the dynamic viscosity and the mechanical heating caused by viscous dissipation are taking into account; therefore, the mathematical models that represent the study are solved in a coupled manner, evaluating at the same time both, the flow field inside of the pipeline, as well as, its corresponding heat transfer processes with respect to the environment. In order to conduct the analysis properly, numerical solutions are obtained in dimensionless way, and three main dimensionless parameters are defined; namely, β, Λ and Br, which represent the ratio of the internal radius to the length of the pipeline, the thermal conductivity for the diffusive heat transfer process in the conjugated system pipeline-thermal insulation (soil), and the Brinkman number associated to the mechanical heating, respectively. The main results reveal that, when heavy oils (extra-viscous fluids) are transported in pipelines, until a small reduction in their temperature generate substantial increment in the dynamic viscosity, and consequently, the flow rate is reduced in comparison with predictions considering a full thermal insulation condition (adiabatic process). Hence, we can conclude that during the transport of heavy oil the heat transfer and its effects over the flow field have to be estimated and controlled, this with the aim of having an efficient transport.

Commentary by Dr. Valentin Fuster
2018;():V002T09A007. doi:10.1115/FEDSM2018-83065.

Phase separation using swirling flows is a technique used in inline separators. In the present study, an existing separator device generates a swirling flow which interacts with a conical hollow bluff body to where the air phase is collect. We use the commercial CFD code Fluent to simulate and investigate the characteristics of single-phase turbulent swirling flow interaction with a solid conical bluff body on a laboratory-scale model. The simulation work employed different RANS turbulence models; namely, RNG k-ε, SST k-ω and RSM. A constant velocity was imposed at the inlet of the computational domain while a constant pressure was prescribed at the outlet. The results are validated against experimental measurements. The effect of flow rate was investigated. The resulting flow is investigated around the bluff body and within the whole outlet pipe downstream of the swirl generator because the separation depends strongly on the flow behavior in this extended region. The core flow reversal persists up to the bluff body at high flow rates. This is significant in terms of phase behavior in the separation application in addition to the loads on the bluff body. The profiles of the tangential velocity corresponded to a Rankine vortex swirling flow type along the whole axial distance. The results show that the RSM gives the best accuracy among the three RANS models compared with the experimental data. The rate of swirl decay decreases as the flow rate increases. For the lowest flow rate, the swirl decay followed an exponential trend which becomes almost linear for the highest flow rate considered. At low swirl intensities, the pressure peaks are observed on the bluff body apex while, at high swirl intensities, the reversal flow generates the lowest pressure at the centerline affecting the cone as well.

Commentary by Dr. Valentin Fuster
2018;():V002T09A008. doi:10.1115/FEDSM2018-83090.

In order to study the relationship between the cavitation flow and energy conversion, based on the continuity equation, Renault N-S equation and RNG k-ε turbulence model, the whole flow field cavitation numerical simulation on unclear main pump model under design condition is carried out. Through the variation of pressure and velocity on the streamlines, combined with the basic equation of the pump, the dynamic and hydrostatic head of the nuclear main pump under different cavitation conditions are studied. The results show that the energy of fluid of nuclear main pump is provided by posterior segment of impeller, and the energy of the fluid decreases gradually from the shroud to the hub. Cavitation interferes with the flow of liquid in the impeller, which leads to the relative velocity increases and the pressure decreases in cavitation region, and the work capacity of blades is almost zero in bubble areas. At the same time, in non-cavitation region along with streamlines the dynamic head increases and the hydrostatic head decreases with the development of cavitation, and the decrease of the hydrostatic head is greater than the increase of the dynamic head, which results in the decrease of pump head and efficiency. In addition, in the cavitation region, with the development of cavitation, the sudden change of the dynamic and hydrostatic head increases, which increase the flow loss in the impeller and results in the decrease of pump head and efficiency moreover.

Commentary by Dr. Valentin Fuster
2018;():V002T09A009. doi:10.1115/FEDSM2018-83091.

Planing hard-chine hulls are often employed on fast boats to ensure high lift and moderate drag in high-speed regimes. Although such boats are usually designed for relatively light loadings, occasionally they may need to operate in overloaded conditions with reduced speed. The focus of this study is on planing hull hydrodynamics in such pre-planing, high-lift regimes. A numerical tool based on a finite-volume viscous solver is applied to simulate a compact planing hull in a speed range from the displacement to planing modes. Numerical results for the model-scale hull resistance, trim and sinkage are compared with experimental data. Additionally, an overloaded condition of this hull is simulated. The resulting variations of hydrodynamic parameters are discussed.

Topics: Hull
Commentary by Dr. Valentin Fuster
2018;():V002T09A010. doi:10.1115/FEDSM2018-83131.

The anode baking process is developed and improved since the 1980s due to its importance in Aluminium industry. The process is characterized by multiple physical phenomena including turbulent flow, combustion process, conjugate heat transfer, and radiation. In order to obtain an efficient process with regards to quality of anodes, soot-free combustion, reduction of NOx and minimization of energy, a mathematical model can be developed. A mathematical model describes the physical phenomena and provides a deeper understanding of the process.

Turbulent flow is one of the important physical phenomena in an anode baking process. In the present work, isothermal turbulent flow is studied in detail with respect to two turbulence models in COMSOL Multiphysics software. The difference between wall boundary conditions for these models and their sensitivity towards the boundary layer mesh is investigated. A dimen-sionless distance in viscous scale units is used as a parameter for comparison of models with and without a boundary layer mesh. The investigation suggests that the boundary layer mesh for both turbulence models increase the accuracy of flow field near walls. Moreover, it is observed that along with the accuracy, the numerical convergence of Spalart-Allmaras turbulence model in COMSOL Multiphysics is highly sensitive to the boundary layer mesh. Therefore, development of converged Spalart-Allmaras model for the complete geometry is difficult due to the necessity of refined mesh. Whereas, the numerical convergence of k-ε model in COMSOL Multiphysics is less sensitive to the dimen-sionless viscous scale unit distance. A converged solution of the complete geometry k-ε model is feasible to obtain even with less refined mesh at the boundary. However, a comparison of a developed solution of k-ε model with another simulation environment indicates differences which enhance the requirement of having converged Spalart-Allmaras model for complete geometry.

Commentary by Dr. Valentin Fuster
2018;():V002T09A011. doi:10.1115/FEDSM2018-83132.

The stall margin and choke margin of centrifugal compressor could be increased by using Self-Adaptive Casing Treatment (SACT). The previous numerical research mainly focuses on making parametric optimization rather than the selection of turbulence model and flow field analysis of the compressor with SACT. In this work, the 3D steady state simulations were carried out to obtain the performance and flow field of the Krain impeller with and without SACT by ANSYS-CFX. Four turbulence models including k-Epsilon turbulence model, RNG k-Epsilon turbulence model, Shear Stress Transport (SST) turbulence model and BSL Reynolds Stress (BSL) turbulence model were used to simulate the Krain impeller with a vaneless constant area diffuser. The numerical data were validated by the experimental data in reference. The results of this study showed that different turbulence models led to differences in performance predictions and flow field characteristics, and the overall performance and flow field features could be predicted more accurately by using SST turbulence model. The bypass flow and reinjected flow were respectively observed in the hole when the Krain impeller with SACT worked at large and small mass flow rate conditions. And the stable working range of the Krain impeller was expanded by using SACT. In addition, the development of the low-velocity fluid at the blade tip region was restrained with the application of SACT.

Topics: Impellers
Commentary by Dr. Valentin Fuster
2018;():V002T09A012. doi:10.1115/FEDSM2018-83141.

Natural ventilation is the process of supplying and removing air through an indoor space by natural means. Windcatcher has been used over centuries for providing natural ventilation using wind power, it is an effective passive method to provide healthy and comfortable indoor environment by decreasing moisture content in the air and reducing pollutants concentration. The windcatcher’s function is based on the wind and on the stack effect resulting from temperature differences. Generally, it is difficult for wind to change its direction, and enter a room through usual openings, the windcatcher is designed to overcome such problems since they have vertical columns aimed at helping wind to channel down to the inside of a building. The efficiency of a windcatcher is maximized by applying special forms of opening and exit. The openings depend on the windcatcher’s location and on its cross sectional area and shape such as square, rectangular, hexagonal or circular. In this study the effect of the inlet design is investigated to achieve better air flow and increase the efficiency of windcatchers. To achieve this, CFD (computational fluid dynamics) tool is used to simulate the air flow in a two dimensional room fitted with a windcatcher based on different inlet designs such as a uniform inlet, a divergent inlet and a bulging-convergent inlet.

Commentary by Dr. Valentin Fuster
2018;():V002T09A013. doi:10.1115/FEDSM2018-83149.

Computers are crucial to nearly every endeavor in the modern world. Some computers, particularly those used in military applications, are required to endure extreme conditions with limited maintenance and few parts. Units such as these will hereafter be referred to as “rugged computers.” This series of experiments aims to produce improvements to rugged computers currently in service. Using heat pipes and finned heat sinks on an enclosed box, a computer’s Central Processing Unit (CPU) is able to reject heat without suffering contamination from unforgiving environments. A modular prototype was designed to allow for three distinct cases; a case with no heat pipes and fins, a cast with heat-pipes mounted internally with exterior fins and a case with heat-pipes extended externally with exterior fins. Each case was tested at three different heat loads, with a copper plate heated by a silicone heat strip simulating the heat load generated by a CPU. Each case/load combination was run many times to check for repeatability. The aim of this research is to discover the ideal case for maximum heat transfer from the CPU to the external environment. In addition to the experiments, numerical simulation of these modular prototypes with different designs of heat pipes were conducted in this research. Creating an accurate model for computer simulations will provide validation for the experiments and will prove useful in testing cases not represented by the modular prototype. The flow and heat transfer simulations were conducted using Autodesk CFD. The aim here is to create a model that accurately reflects the experimentally-verified results from the modular prototype’s cases and loads, thereby providing a base from whence further designs can branch off and be simulated with a fair degree of accuracy.

Commentary by Dr. Valentin Fuster
2018;():V002T09A014. doi:10.1115/FEDSM2018-83155.

A breakwater is a structure used to reduce the energy of waves. When used properly, they can protect coasts from being affected by waves. One such application is to lessen erosion along Louisiana’s coastlines, where wave action is strong and is the main source of the erosion. Additionally, the breakwater can change how sediments are transported, and allow for the deposition and accumulation of sediment at target areas. This research aims to give a numerical comparison of the effectiveness of three different breakwater designs, and reveal the turbulence characteristics downstream of the breakwaters. Three breakwaters are examined: a solid panel without any holes, another panel with one hole, and a third panel with three holes. These breakwaters are expected to be placed on the banks of various water bodies in coastal Louisiana, to protect the surrounding wetlands from coastal erosion and land losses. The designs aim to reduce the wave action from the water bodies, while the holes on them allow the sediments to pass through and deposit on the wetlands downstream. To run the simulations, the CFD software ANSYS FLUENT was used. The numerical results were compared to experimental data, and the good agreement proves the accuracy of the results. The effects of different wave patterns on the downstream turbulence were also analyzed and discussed in this study.

Commentary by Dr. Valentin Fuster
2018;():V002T09A015. doi:10.1115/FEDSM2018-83206.

An efficient cooling method for the turbine inner casing is essential with the increasing of the turbine inlet temperature. The heat transfer and flow characteristics of a coupled cooling system in the turbine inner casing part, i.e., three rows of impingement jets and film holes, have been studied numerically according to the real turbine operating conditions. Seven inclined angles of the film holes along the mainstream direction (90°, ±60°, ±45°, ±35°) and the impingement jets arrangements have been researched. The positive inclination is that the angle between the fluid flow from the film holes and the mainstream is less than 90°. Otherwise, it would be negative. The numerical validation reveals that the selected computational method can provide a good prediction of the reported experimental results of the impinging-film cooling system. Then the method has been applied in the investigation of the local/average temperature, film-cooling effectiveness, and the flow patterns on the film-cooled surface.

The results show that the inclined angle can achieve a significant improvement in the film cooling performance. With the positive inclination of film holes, the average temperature of the interaction surface between the mainstream and the turbine inner casing can decrease 50K compared with that of 90°. And the average temperature on the interaction surface with the negative inclined angle can even be reduced by more than 100K. Additionally, the average film-cooling effectiveness can be increased by up to 31.79%. Such results prove that decreasing the value of inclined angle can achieve a better heat transfer performance. Moreover, the negative inclination of film holes can improve the uniformity of the film-cooling effect. On the other hand, the influence of impingement jets arrangements on the film cooling behavior is negligible. Further analysis of the flow streamline illustrates that the coolant jet from the inclined film holes can attach to the interaction surface more firmly, which will achieve a better protection away from the high-temperature turbine gas. The research will provide direct guidance for the cooling design of the turbine inner casing and improve the thermal efficiency of the gas turbine system.

Commentary by Dr. Valentin Fuster
2018;():V002T09A016. doi:10.1115/FEDSM2018-83207.

The flow and spray parameters can have noticeable roles in heavy fuel oil (HFO) spray finesse. As known, the interaction between droplets and cross flow should be considered carefully in many different industrial applications such as the process burners and gas turbine combustors. So, it would be so important to investigate the effect of injecting HFO into a crossflow more subtly. In this work, the effects of various flow and spray parameters on the droplet breakup and dispersion parameters are investigated numerically using the finite-volume-element method. The numerical method consists of a number of different models to predict the droplets breakup and their dispersion into a cross flow including the spray-turbulence interaction one. An Eulerian–Lagrangian approach, which suitably models the interaction between the droplets and turbulence, and also models the droplets secondary breakup is used to investigate the interactions between the flow and the droplet behaviors. After validating the computational method via comparing them with the data provided by the past researches, four test cases with varying swirl number, air axial velocity, droplet size, and fuel injection velocity are examined to find out the effects of preceding parameters on some spray characteristics including the droplets path, sauter mean diameter (SMD), and dispersed phase mass concentration. The results show that the droplets inertia and the flow velocity magnitude have significant effects on spray characteristics. As the droplets become more massive, the deflection of spray in flow direction becomes less. Also, increasing of flow velocity causes more deflection for sprays with the same droplet sizes.

Topics: Fuel oils
Commentary by Dr. Valentin Fuster
2018;():V002T09A017. doi:10.1115/FEDSM2018-83218.

Sea-based aviation operations, such as carrier launch / recovery of aircraft, can be limited or interrupted by ship motion. Such operations may benefit from real time ship-motion forecasting, particularly in sea states above SS6, as unanticipated large motions may suddenly occur. Ship motion forecasting was optimized using an autoregressive moving average vector (ARMAV) model. The forecasting was accurate for approximately 25 seconds with accuracy evaluated using either correlation coefficient or root mean square error metrics. The ship motion data evaluated was simulation data generated by a ship motion prediction program for a generic CVN hull.

Topics: Ships
Commentary by Dr. Valentin Fuster
2018;():V002T09A018. doi:10.1115/FEDSM2018-83258.

Liquid metal infiltration consists of infusing liquid metal into a porous media or a packed bed of boron carbide powder to react and create ultimately a metal or ceramic matrix embedded with boride-carbide precipitates. The purpose of the study is to model the liquid flow into the capillaries of the packed bed by using machine learning algorithms from an open source available as TensorFlow library created by Google Brain. The library has a variety of algorithms including training and inference algorithms forming deep neural network models to predict the wetting dynamics, flow resistance, and the depth/rate of penetration into the capillaries of the packed bed. In the present work, the results from the machine-learning python code based on the TensorFlow library is compared against the experimental data obtained for molten Hf-Ti-Y-Zr alloys infiltrating into a packed bed of boron carbide at temperatures up to 2300°C. A summary of the techniques used to tweak the machine learning algorithms to predict the infusion behavior will be presented.

Topics: Metals
Commentary by Dr. Valentin Fuster
2018;():V002T09A019. doi:10.1115/FEDSM2018-83273.

Fragmentation of molten metal droplets is an important process in steam explosions caused by melt-coolant interactions. Ciccarelli and Frost (1994) found the formation of melt jets (or spikes) in hot melt drops immersed in water. In order to gain insight into this mechanism, they carried out experiments where melt jets were formed in a stratified water/liquid metal system with local generation of high-pressure vapor at the interface. This paper is dedicated to investigating how melt jets are formed in this mechanism when a stratified water/liquid metal system is analyzed. Also, a study of the most significant parameters in this process is performed. A 2D computational fluid dynamics (CFD) simulation is carried out using ANSYS Fluent software to study these phenomena by having water above hot liquid metal, a vapor film in between and a pressure pulse in the vapor film. The results show that the larger the pressure or density, the greater the melt jet length. In order to confirm this, deep neural network algorithm created by TensorFlow library was implemented to facilitate the understanding of the studied phenomena. The formation of melt jets observed in Ciccarelli and Frost’s experiments is also observed in current simulation.

Commentary by Dr. Valentin Fuster
2018;():V002T09A020. doi:10.1115/FEDSM2018-83281.

Advances in nanotechnology allows for electrodeposition and fabrication of micro/nano electrodes between substrates of microfluidic channels which later can be used as electrodes to apply DC or AC voltage. Microchannels taking advantage of this technology have shown promising results in flow cytometry [1,2], and cell sorting applications [3–6].

In this paper, first we study the influence of electric potential on particle sorting in a microchannel. For this purpose, a two dimensional computational fluid dynamics (CFD) model is created, meshed and solved in STAR-CCM+ which is a commercial simulation tool. Two type of spherical solid particles with different diameter are introduced through an injector from particulate flow inlet. These solid particles are treated as Lagrangian phase. The simulations are conducted in transient mode and the particle injection is occurred once the flow regime became steady state. The proposed model is based on finite volume approach and confirms the effectiveness of dielectrophoresis on particle sorting.

In the second part of this work, we focus on optimizing the separation efficiency of microchannel by implementing Siemens exclusive automated design exploration technology named SHERPA. Through this hybrid and adaptive strategy we investigate 4 key parameters including electric potential, flow velocity at two inlets, and particle mass flow rate. The objective is to minimize the electric potential while maximize the efficiency of device, measured by amount of particles separated at the outlet. In total 40 designs are evaluated. The results show that by adjusting the flow rate ratio between inlets, and applying a low voltage such as 5 V, you can increase the mass flow rate of segregated particles by approximately 100 times.

The proposed model not only can help shortening the time to market for new dielectrophoresis based channels, but also be used to optimize the overall device performance to achieve the best separation efficiency at optimal condition.

Commentary by Dr. Valentin Fuster
2018;():V002T09A021. doi:10.1115/FEDSM2018-83368.

Membrane desalination is a pressure driven process which is being employed on a large scale in areas which do not have an easy access to fresh water resources. The large energy consumption of this process has encouraged researchers to explore the different spacer designs for maximizing permeate per unit of energy consumed. Computational fluid fynamics (CFD) was used to simulate the mass transfer enhancement in a reverse-osmosis desalination unit employing spiral wound membranes lined with zigzag spacer filaments of alternating diameters. Finite Volume based open source software OpenFoam was used to resolve the flow properties in a two-dimensional model by varying the Reynolds number until the onset of instability. Diamters of alternate strands were varied between ratios of 1, 1.5 and 2. The research provides guidelines based on comprehensive data set of velocity contours, pressure distribution, wall shear stresses and steady state vortex systems for using alternating strand design in zigzag configuration for maximum mass transfer and least pressure drop taking into account the concentration polarization.

Commentary by Dr. Valentin Fuster
2018;():V002T09A022. doi:10.1115/FEDSM2018-83408.

Cerebral aneurysms are abnormal dilations of blood vessels within the skull that, in some cases, may rupture and bleed. The rupture of an aneurysm can cause significant bleeding into or around the brain (a stroke). Flow diverters are specially designed low porosity stents that are deployed into the parent artery to cover the neck of the aneurysm. The dense mesh-like structure of flow diverters aims at redirecting flow from the aneurysm to the parent artery and vice versa, resulting in flow stasis in the aneurysm and promoting thrombus formation conditions. The thrombosed aneurysm is then resorbed by the body’s wound healing mechanisms-the end result of which is a remodeled vessel returned to its normal physiological state. Most previous studies have been focused on correlating the hemodynamic conditions with the outcome of the flow diverters. On the other hand, the effects of the location of the stents have not been addressed. In this study, a numerical simulation of an idealized side wall aneurysm model is used to predict the hemodynamic conditions for different flow diverter stent locations. The CFD model of the aneurysm is developed based on data from the literature and the geometrical parameters are set according to the test data. Pulsatile boundary conditions are chosen according to the normal physiological conditions. The entire stent geometry is used to model the effect of the stent on the flow characteristics. The hemodynamic conditions in the aneurysm corresponding to different stent locations are compared. The results show that the average velocity and vorticity are significantly different depending on different stent locations. Marked reduction in average velocity, average vorticity, and mean wall shear stress within the aneurysm sac have been observed even in malposition cases. The results of this study can be further used to guide the deployment of the flow diverter stent in clinical application.

Commentary by Dr. Valentin Fuster
2018;():V002T09A023. doi:10.1115/FEDSM2018-83431.

In this paper, the turbulent reacting flow in an industrial furnace is numerically simulated using the RANS equations. The two-equation standard k-ε and the eddy dissipation models are used respectively to close the turbulent closure problem and to consider the turbulence-chemistry interaction. The radiation transfer equation is solved using the discrete ordinates method (DOM). To calculate the radiation absorption coefficient in participating combustion gases, we use the spectral line-based weighted sum of grey gases (SLW) model and compare the achieved results with famous gray-based model, i.e., the weighted-sum-of-gray-gases (WSGG) model. The results of this research show that using the SLW model, the predicted heat transfer from the flame to the furnace walls is reduced due to the thermal radiation. So, the predicted temperature filed increases up to 5% near the outlet of furnace in comparison with the results of WSGG model, which is in more agreement with the experimental data. These results indicate that if one wishes to accurately predict the temperature field and the temperature sensitive quantities such as the NOx emission, one should use the spectral-based models to calculate the radiation absorption coefficient. The details are discussed in the results section.

Commentary by Dr. Valentin Fuster
2018;():V002T09A024. doi:10.1115/FEDSM2018-83436.

The strength of an oil carrier is generally checked using static load or equivalent load of wave action in accordance with relevant specifications. In order to accurately calculate the stress and the deformation of an oil carrier under wave action, the fluid-structure interaction system in the platform Workbench is used in this work. And, the pressure-based solver, the two-phase flow model and UDF (User Defined Function) in the software FLUENT are used to compile the three-order Stokes Wave so as to simulate ocean waves. Forces acting on the surface of the oil carrier are obtained by calculating the flow field, and the structural strength of the carrier is then investigated under sagging and hogging conditions. The results show that: the three-order Stokes Wave matches well with the theoretical result, and it is feasible to research the strength of the oil carrier by generating waves using this numerical method. In addition, the method of fluid-structure interaction is applied to investigate the structural strength of the fully-loaded carrier under sagging and hogging conditions.

Topics: Waves , Tankers
Commentary by Dr. Valentin Fuster
2018;():V002T09A025. doi:10.1115/FEDSM2018-83440.

Despite their low efficiency compared with centrifugal pumps, jet-pumps are highly reliable robust equipment with modest maintenance which is ideal for many applications, mostly in the oil & gas industry. For example, jet-pumps could result attractive compared to other multiphase pump systems in terms of reactivating transport lines of heavy crude oil. Nevertheless, their design method and performance analysis are rarely known in the literature and keep a high experimental component like most of the pumping equipment. Starting with a pump designed by a traditional method, this paper aims to evaluate the effect of multiple geometrical and operational variables that influence the jet-pump performance combining CFD (Computational Fluid Dynamics) simulation and optimization algorithms using commercials software (ANSYS CFX® and PIPEIT® tool). Automatically, the geometric parameters are modified according to the rules of the optimization routines seeking to maximize the flow capacity, respecting restrictions such as energy consumption.

A case study is presented for the preliminary design of a pump to boost flow capacity in a trunk line of a heavy oil field. As preliminary design all simulations were carried out using single phase water flow. With this method, it was possible to quickly evaluate around 400 geometries of jet-pumps. The geometry of the optimum final pump is consistent with other pumps reported by other works. This pump enhances the fluid capacity of the line in 17% over the traditional design for the same parameters of power or consumed energy.

Commentary by Dr. Valentin Fuster
2018;():V002T09A026. doi:10.1115/FEDSM2018-83441.

Nowadays, under unstable prices scenarios, the oil and gas industry is looking for improvement in its production processes, either by increasing the production and/or lowering the operational costs. Aircoolers, particularly, are key equipments in the natural gas industry, and are frequently the bottleneck of gas conditioning processes.

To improve air cooling efficiency and increase their gas volume capacity, several solutions are commonly implemented such as: fan blade angle change, air inlet section modification, fogging cooling system, among others.

The present study shows the CFD (Computational Fluid Dynamics) analysis of an air cooler, under an air flow with an evaporative cooling system, in order to quantify the effect of this cooling process on its overall equipment performance.

Simulations were carried out using sing the ANSYS CFX v-14® software, in a simplified multidomain which consider fluid and solid blocks:

1.- External two-phase flow (air + water droplets) with heat and mass transfer

2.- Heat transfer through the pipe wall

3.- Single phase natural gas flow inside the tubes

In order to stablish an operational range of the fogging system, the influence of parameters like: inlet temperature and relative humidity of the air, water flow rate, water droplets mean diameter, water injection position, were studied [9, 10].

The results show a good agreement (around 5%) respect to the reported values on the literature. The best performance for the equipment was reported with a droplet diameter of 20 μm and for low relative humidity (less than 65%), which guarantees the complete evaporation of the droplets within the studied domain. For the analyzed operating conditions, a reduction of the gas outlet temperature of up to 1.5°C can be achieved.

Commentary by Dr. Valentin Fuster
2018;():V002T09A027. doi:10.1115/FEDSM2018-83442.

Quifa is one of the largest heavy-oil fields in Colombia with a total fluids production of 1,320 KBPD with a water cut of 96.7% through 272 active wells, approximatively. Facilities to handle such amounts of water, have to deliver crude oil under market specifications and clean up the water prior to its reinjection, require several stages of oil-water separation. The first phase in oil water separation process is Free Water Knock Out vessels (FWKO), which are in charge of extracting to extract most of the water, frequently assisted by heat or chemical products which help gravity to perform the separation. The treated water (which contain still some oil) is then directed to the following stage separation carried out by the big tanks called skimmers, which are designed to clean the water down to a few ppm of oil. Nowadays, even though the advance on computational calculations has increased, these tanks are frequently designed using only the concept of time of residence and considering the internal velocities to be as low as possible, so that improve separation. For these last considerations, FWKOs and Skimmers could have internal components like manifold or baffles.

The present work explains a CFD (Computational Fluids Dynamics) study of different internal manifolds configurations, which aimed to improve the fluid distributions and velocities inside the tanks of Quifa field. Simulations were performed by CFX commercial software under two-phase flow eulerian-eulerian homogeneous model.

The optimum manifold configuration, achieves uniform static pressure and flow distribution across the entire main pipe, reducing secondary internal flows and hydraulic losses.

Then, CFD calculations were carried out in the whole skimmer tank, using the original manifold and the improved one. Results show an increase in the separation process, due to the new internal velocity field.

Supported by the simulations results, these geometrical improvements in the internal manifolds were applied/constructed in one of the skimmer tanks in Quifa Field. Field results show an improvement on separation efficiency, going from 38% average efficiency in the original tanks (Skim-10 and Skim-30), up to 87% in the modified one (Skim-30). The quality of exit-water was reduced from 300 ppm average up to 77 ppm. The flow capacity of the skimmer 30 has been improved and can handle up to 600 KBFPD. This represents 62% more capacity than Skimmer 10, and 42% more than Skimmer 20.

Commentary by Dr. Valentin Fuster
2018;():V002T09A028. doi:10.1115/FEDSM2018-83445.

This paper examines safety concerns related to flame speeds when warm relief gas snuffs out the pilot at the flare stack and pulls in ambient air and a spark ignites the vapor in the header. The flame speed essentially determines if the propagating flame speed is a deflagration or a detonation based on whether its subsonic or supersonic. While pipes are sized for deflagrations, they need to be analyzed and tested for detonation pressures and temperatures. Transient CFD calculations help determine the flame speeds, deflagration to detonation transition, pressures and temperatures are compared to pipe specifications and help determine if a detonation leads to a Loss of Containment and suggests mitigations.

Topics: Explosions , Flames
Commentary by Dr. Valentin Fuster
2018;():V002T09A029. doi:10.1115/FEDSM2018-83457.

This work performs computational fluid dynamics (CFD) simulations using a transient URANS (unsteady Reynolds averaged Navier–Stokes) turbulence model to investigate the influence of lateral skirts — located in the lower part of a semitrailer truck — in terms of reducing the total drag force and fuel consumption savings. The total drag force values are calculated for three semi-trailer trucks speeds (i.e. 60, 70 and 100 km/h), compared, and then validated against experimental results carried out in a wind tunnel reduced model scale (1:28). The relative errors of the aerodynamic drag force parameter are assessed in order to quantify the accuracy and the reliability of the numerical modeling results with regard to the experimental results. In addition, the flow pattern around the semi-trailer truck is then investigated to determine how the induced flow field is channeled, and where the recirculating zones are modified and developed when using the additional skirt device.

Commentary by Dr. Valentin Fuster
2018;():V002T09A030. doi:10.1115/FEDSM2018-83477.

The development of fluoride salt-cooled high-temperature reactors (FHRs) for nuclear power generation relies on the development of new technologies. Of the potential options being explored, twisted elliptical tube geometries for heat exchanger design are promising based on usage in other industries. They are expected to offer significant enhancement in heat transfer with only a marginal increase in frictional losses. This allows them to be deployed in relatively compact designs that are well suited for FHRs. The presented work focuses on the computational fluid dynamics (CFD) simulations of heated molten salt flows through various twisted elliptical tube geometries at low modified Froude numbers. The objectives of this work are to evaluate the available correlations at lower Froude numbers and to determine the impact of using non-zero tube to tube spacing to resolve contact points or numerical singularities for future CFD simulations efforts The spectral element CFD code Nek5000 was used for all simulations, which were performed in periodic domains of triangular (hexagonal) and square unit cells surrounding a single tube through a complete twist using an explicit filtering large eddy simulation (LES) method. Simulations were used to para-metrically test the effects of tube-to-tube spacing for laminar and turbulent flow regimes on frictional pressure drop and heat transfer. The tested Reynolds numbers covered both laminar flow and fully developed turbulent flow (90 < Re < 12200). The tested SL/dmax ratios cover the range of 1.02 to 1.08 for both unit cell types.

At moderate Reynolds number and comparitively high modified Froude number, excellent agreement for the Nusselt number was observed between simulations and the applicable correlation. As Froude number was decreased towards the bounds of the correlation, the agreement worsened. Cases were then simulated at low Froude number, testing the effects of tube spacing. It was determined that the laminar case for the square unit cell is the most affected by increasing SL/dmax and the gap size should be minimized to mitigate this. Whereas in the triangular unit cell the laminar flow regime is more significantly impacted by increasing SL/dmax compared to the turbulent flow regime which was only marginally impacted.

Commentary by Dr. Valentin Fuster
2018;():V002T09A031. doi:10.1115/FEDSM2018-83517.

The ExasSMR project focuses on the exascale application of single and coupled Monte Carlo (MC) and computational fluid dynamics (CFD) physics. Work is based on the Shift MC depletion, OpenMC temperature-dependent MC, and Nek5000 CFD codes. The application development objective is to optimize these applications for exascale execution of full-core simulations and to modularize and integrate them into a common framework for coupled and individual execution. Given the sheer scale of nuclear systems, the main algorithmic driver on the CFD side is weak scaling. The focus for the first four years of the project is on demonstrating scaling up to a full reactor core for high-fidelity simulations of turbulence. Full-core fluid calculations aimed at better predicting the steady-state performance will be conducted with a hybrid approach in which large eddy simulation is used to simulate a portion of a core and unsteady Reynolds-averaged Navier-Stokes handles the rest. This zonal hybrid approach provides an additional scaling dimension besides the number of assemblies. The present manuscript focuses on performance assessment using assembly-level simulations with Nek5000. We discuss the development of two benchmark problems: a subchannel (single-rod) problem to assess internode performance and a larger full-assembly problem representative of a small modular reactor (SMR). We note that current SMR assemblies are considerably simpler than pressurized water reactor assemblies since they contain no mixing vanes. This feature allows for considerable reduction in the degrees of freedom required to simulate the full core. We discuss profiling and scaling results with Nek5000, describe current bottlenecks and potential limitations of the approach, and suggest optimizations for future investigation.

Topics: Manufacturing
Commentary by Dr. Valentin Fuster

25th Symposium on Industrial and Environmental Applications of Fluid Mechanics

2018;():V002T11A001. doi:10.1115/FEDSM2018-83067.

Swirling flows in pipes are encountered in several industrial applications for separation or mixing purposes. In this work turbulent swirling flow is generated using a new swirl generator in the form of thick-walled pipe with multi-radial holes which is lodged inside a larger cylindrical housing, called the Swirl Cage. The swirling flow exiting from the Swirl Cage feeds into a long pipe where the Reynolds number based on the pipe diameter and average velocity is equal to 40836.67. Large Eddy Simulation (LES) is used to calculate the swirling flow and explore its characteristics in conjunction with the Dynamic Kinetic Energy Subgrid-Scale model. Experiments were conducted using LDV and the results are used for validation purposes and for the discussion of the flow features.

The results are discussed in relation with the mean fluid velocity and its RMS component. Profiles of the mean tangential velocity reveal a Rankine vortex swirling flow type along the whole axial distance. The core flow was slightly oscillating exhibiting a processing vortex behavior reflected by the radial velocities at the centerline. The profiles of the turbulent kinetic energy were characterized by a peak at the centerline increasing in magnitude with the axial distance. The swirl number decayed from 1.5 right at the outlet of the swirl cage to unity close to the outlet of the pipe.

Commentary by Dr. Valentin Fuster
2018;():V002T11A002. doi:10.1115/FEDSM2018-83105.

Hydraulic machinery is widely used in delivering solid-liquid mixing medium. The abrasion and destruction caused by sediment particles occurs on the contact interface between the contacting seal elements, which has a considerable influence on the operational stability and safety.

Helical groove seal is a type of non-contacting dynamic seal. Relied on the reversed pressure produced by the rotary sealing element, the helical groove seal could reduce or prevent the leakage. Such seal has a good performance even if there is a big clearance between the sealing elements, so helical groove seal has its unique advantage on solid-liquid mixing medium. However, the study of helical groove seal on solid-liquid mixing flow is very poor.

In this paper, the certain conception and theoretical study of helical groove seal was introduced. With the commercial software FLUENT, the 3D internal flow of the seal was presented by using multiphase flow model. Based on the method of single variable model, the seals with different helical parameters were calculated to compare the characteristics of solid-liquid two phases flow in helical groove seals with different parameters, for example, the clearance and spiral groove depth. By this way, the relationship between structure and performance of particles-mixed helical groove seals is showed clearly, then the results can be used for design of helical groove seal structure.

Commentary by Dr. Valentin Fuster
2018;():V002T11A003. doi:10.1115/FEDSM2018-83122.

Sand particle erosion is the main cause of the failure of bends in the natural gas pipelines. The rapid progress of computational power and modern numerical methods has provided the opportunity for developing realistic simulation of the erosion process. The goal of this paper is to predict the sand erosion rates with the use of computational fluid dynamics in the gas/solid flows in the plugged tees and standard elbows. For this purpose, the Eulerian-Lagrangian approach was used. To simulate the flow, the SIMPLE algorithm and the k-ω SST turbulence model were used. Particles were injected into the inlet pipe with different sizes. To predict more realistic results the Grant and Tabakoff stochastic rebound model was applied and the Oka model was used to calculate erosion. The results showed that, the use of plugged tee instead of a standard elbow would reduce the erosion rate only for fine particles. Also, for them, by increasing the plugged length the pipe will experience less erosion. For coarser particles, however, the vortex created in the plugged section did not affect the particles velocity; therefore, the erosion rate was not reduced.

Commentary by Dr. Valentin Fuster
2018;():V002T11A004. doi:10.1115/FEDSM2018-83140.

Fillets at the junction of blade and endwall are employed to passively control the endwall secondary flows and total pressure losses in the cascade flow-field investigations. Film-cooling of the endwall using the slots at the entrance of blade passage is also investigated in the cascade setup to actively control the flow-field. The present paper reports the experimental measurements of the flow-field in a linear vane cascade that employs the endwall fillet and film cooling flow. The objectives are to investigate the additional effects of the film-flow on the secondary flows and total pressure losses in the cascade when the fillet is present. The fillet is employed at the vane-endwall junction from the leading edge to the throat region of the cascade passage. The film-cooling flow is provided from two slots located at the entrance of vane-passage simulating the platform gaps between the rotor/stator or combustor/NGV (nozzle guide vane) discs in the gas turbine. The vane-profile and cascade geometry are obtained from the first-stage of the GE-E3 gas turbine engine. The inlet Reynolds number based on the actual-chord of the vane is 2.0E+05. The inlet blowing ratio of the film cooling flow is varied between 1.1 and 2.3 as the density ratio of the film-flow to mainstream remains constant at 1.0. As the cascade is housed in an atmospheric wind tunnel, the measurements are obtained in the incompressible flow regime. The measurements include the distributions of endwall pressure, flow angles, axial vorticity, and total pressure losses along the vane passage. The results indicate the flow yaw angle and axial vorticity in the filleted passage without the film-cooling are reduced in the endwall region compared to the baseline case (no fillet and film cooling). Consequently, the passage vortex, which is the primary secondary flow, is weakened reducing the total pressure losses in the filleted passage. As the film-cooling flow is introduced in the filleted passage, the yaw angle in the endwall region is reduced further weakening the pitchwise-flow responsible for the development and strengthening of the passage vortex. The total pressure losses are also reduced further with the film-cooling flows and with the increasing blowing ratios. The film coverage of the endwall will be better as the passage vortex is weakened in the filleted passage. The present investigation is important for reducing the aerodynamic losses and improving of the film-cooling effectiveness in the gas turbine cascade.

Commentary by Dr. Valentin Fuster
2018;():V002T11A005. doi:10.1115/FEDSM2018-83159.

Hydropower stations play an important role in discharging the flood. Especially in wet seasons, the river water always contains several percentages of sediment, and the velocity of the water flowing through the flood discharging tunnel is very high. Arranging some energy dissipation orifice plates in the flood discharging tunnel, cannot only reduce the pressure and flow velocity, but also deposit sediment and reduce the sediment content. However, fouling on energy dissipation orifice plates can initiate material corrosion of perforated plates, even weaken the energy dissipation performance. In this paper, the fouling performance on energy dissipation orifice plates with sediment contained water flow is investigated. To begin with, the pressure along the path is used to compare with a reported experiment to verify the reliability of the numerical method. Then, effects of the solid particle diameter, the sediment volume concentration and the inlet flow velocity on the particle distribution are observed. The results show that with the increase of the Reynolds number, the sediment volume fraction and the sediment particle diameter, more sediments accumulate at both surfaces of the orifice plate. The Reynolds number and the sediment volume fraction affect the upstream surface more significantly, while the effect of sediment particle diameter is more notable on the downstream surface. Additionally, the energy dissipation coefficient of the orifice plate is mainly dominated by the Reynolds number. This work is of significance for further analysis of fouling problems in energy dissipation orifice plates or similar fluid machinery.

Commentary by Dr. Valentin Fuster
2018;():V002T11A006. doi:10.1115/FEDSM2018-83203.

The vacuum systems play crucial role in various industries including, but not limited to, power generation, refrigeration, desalination, and aerospace engineering. There are different types of vacuum systems. Among them, the ejector or vacuum pump is highly utilized due to its low capital cost and easy maintenance. Generally, the better operation of a vacuum system can dramatically affect the performance of its upper-hand systems, e.g., the general efficiency of a thermal power plant cycle. This can be achieved if such vacuum systems are correctly designed, implemented, and operated. The focus of this work is on an existing steam jet-ejector, whose primary flow is a high pressure superheated steam and the suction flow is a mixture of steam and air. The main goal of this work is to optimize the geometry of the ejector including the nozzle exit position (NXP), the primary nozzle diverging angle, and the secondary throat length, etc. From the computational fluid dynamics perspective, there are some major challenges to simulate this ejector. It requires predicting the correct turbulent fluid flow and heat transfer phenomena with great complexities in treating the mixed subsonic and supersonic flow regimes, very high and very low pressure regions adjacent to each other, and complex mixing two phase flow jets. Indeed, the latter one has been almost neglected in literature. The main concern of this study is to reduce the consumption of motive steam, i.e., to increase the entrainment ratio via modifying the ejector geometry and investigating its performance under different operating conditions that helps to save the water consumption.

Commentary by Dr. Valentin Fuster
2018;():V002T11A007. doi:10.1115/FEDSM2018-83210.

Hypoplastic Right Heart Syndrome is a type of congenital heart defect where the right ventricle is underdeveloped in an infant to pump blood from the body to the lungs. The three-staged surgical Fontan procedure provides a temporary treatment; however, in most of the cases, a heart transplantation is required due to postoperative complications. Currently, there are no devices commercially available in the market to provide a therapeutic assistance to these patients until a donor heart is available. Thus, a novel dual propeller pump concept is developed to provide cavopulmonary assistance to these patients.

The designed blood pump would be percutaneously inserted via the Femoral vein and deployed at the center of the Total Cavopulmonary Connection (TCPC). The two propellers, each placed in the Superior Vena Cava (SVC) and the Inferior Vena Cava (IVC) are connected by a single shaft and rotating at same speed. The device is supported with the help of a self-expanding stent whose outer walls are anchored to the inner walls of the IVC and the SVC. Each of the IVC and the SVC propeller without the stent provides a modest pressure augmentation of 5–6 mm Hg. To expand on this, the current study focusses on studying the effect of the introduction of stent around the propeller on the hemodynamic performance of the pump.

Five different stent design parameters, viz. the strut thickness, width, number, the stent length and number of strut columns were selected for a range of values. Each of the design parameters was varied by keeping all others constant and equal to the base stent design. All the stent models were analysed to see their effect on pressure rise, flow pattern and blood damage using 3D CFD analysis. The blood damage potential for different studied designs was predicted using a non-linear mathematical power law model along with Lagrangian particle tracking to predict the blood flow path. The introduction of stent resulted in pressure reduction of around 0.4 and 0.2 mm Hg around the IVC and SVC propeller with an increase in blood damage index (BDI) by almost 2 times for the final dual propeller pump assembly. It was observed that the blood damage potential was directly related to the amount of pressure rise where the stent length, stent column number, strut width, and strut thickness had a converse effect showing a reduction in pressure rise and blood damage with their increment. While the number of struts gave a desirable effect of increasing pressure rise and reducing blood damage with its increment. The study also demonstrated that the introduction of stent around a circulatory pump increases the Wall Shear Stress (WSS) value at the stent-artery wall interface thereby preventing the occurrence of restenosis and thrombosis initiating due to very low WSS (< 0.5 Pa). Thus, this study acts as an initial step to design a protective stent support around a percutaneous assist device by analysing the sensitivity of stent design parameters on the hemodynamic performance of the pump.

Commentary by Dr. Valentin Fuster
2018;():V002T11A008. doi:10.1115/FEDSM2018-83260.

The use of air-cooled steam condenser (ACSC) in thermal power plants has become so normal since a few decades ago. It is because there are so many valuable advantages with the ACSC implementation, e.g., little dependency on water consumption and benefiting from the forced convection heat transfer instead of the natural one to condense the steam. However, the thermal performance of an ACSC can be readily defected by the ambient wind; specifically, when the ambient temperature is high. This research work benefits from the computational fluid dynamics tool to study the details of ACSC’s thermal performance in such undesirable ambient windy conditions. Furthermore, this work suggests an effective remedy to increase the heat rate from the proposed ACSC. Evidently, the flow rate of cold air through the heat exchangers of proposed ACSC has direct influence in heat transfer rate from the heat exchangers of ACSC. One remedy to achieve higher cold air flow rates through these heat exchangers is to improve the design of its fans or blowers. However, for an ACSC already in service, one should look for other cost-effective remedies. So, if one wishes to improve the performance of those fans without changing their design one should pay attention to some other simple ways with little costs to implement them. This work suggests to tune up the pitch angles of blades of ACSC’s fans properly. The details of implementing this remedy are presented in this paper.

Commentary by Dr. Valentin Fuster
2018;():V002T11A009. doi:10.1115/FEDSM2018-83277.

The flow under sluice gates is well known in open channel hydraulics. There are theoretical, semi-empirical and empirical equations to determine the flow rate under a sluice gate Most of these formulas are based on the Bernoulli equation applied at the inflow cross section and in the vena contracta behind the gate. In 2017 Malcherek [1] showed that it is also possible to apply the integral momentum balance to the sluice gate. When assuming hydrostatic pressure distributions in the inflow cross section and on the weir’s plate then the simple formula Display FormulaVA=(3/4)gh0=0.6122gh0 is obtained, which is in perfect agreement with the classical vena contracta theory for small opening ratios h0/a. In the outflow cross section under the gate the bottom pressure was assumed to be the mean of the hydrostatic bottom pressure before and behind the sluice gate. In this paper Malcherek’s momentum balance theory will be investigated in further detail with numerical CFD RANS computations of the free surface flow below sluice gate. The exact pressure distributions on the bottom as well as on the gate were obtained for different openings ratios and flow conditions at the sluice gate in a systematic parameter study. These pressure distributions have been introduced into the integral momentum equation and the discharge velocity as well as the flow rate at the sluice gate were investigated and compared with the pure numerical results. These results were also compared with the theoretical and empirical approaches of the literature and a detailed analysis is given.

Commentary by Dr. Valentin Fuster
2018;():V002T11A010. doi:10.1115/FEDSM2018-83300.

Due to geographical and environmental constraints, highspeed railways use a variety of subgrade structures such as ground, embankments with different height, viaducts, etc. When trains run on embankments and viaducts, the flow around the car body is more complex than the ground. Under the action of crosswind, there are obvious differences in the cross-wind aerodynamic characteristics of high-speed trains on different subgrade structures. The unreasonable subgrade structure will affect the cross-wind safety of the train. At the same time, the structure of the train is complex, the bogie and pantograph have an important role on the flow field characteristics of the train, and the over simplified profile of the short train cannot accurately reflect the true aerodynamic characteristics of the train. In the present paper, in order to study the influence of typical subgrade structure on the aerodynamic characteristics of high speed trains, a real high-speed train with 9 carriages at the speed of 200 km/h was taken for case study, and the details of windshields, bogies and pantographs were taken into consideration. The cross wind velocities were chosen as 20, 30, 35 and 40 m/s. The aerodynamics performance of the highspeed train under the four conditions of plane ground, 3m-embankment, 6m-embankment and viaduct were simulated and compared, and the differences and regularities in the aerodynamic characteristics under cross wind conditions on different subgrade were analyzed. The results provide a reference for train safety control on complex subgrade structures under cross wind condition.

Topics: Trains , Wind
Commentary by Dr. Valentin Fuster
2018;():V002T11A011. doi:10.1115/FEDSM2018-83347.

A combined sewer system is a facility that collects both municipal sewage and surface runoffs. These facilities may overflow (combined sewer overflow or CSO) during large storms which results in serious pollution, i.e. the flows exceed the capacity of the treatment plant. An approach to reduce the number of combined sewer overflows is to store rainfall runoffs temporarily [1]. The Treatment Shaft system is a relatively new but proven patented technology (U.S. Patent [2] and other patents) that includes the necessary CSO control and treatment, with less footprints than existing systems, and at a reduced cost. In this system, wastewater is collected in a large shaft equipped with baffles and partitions designed to ensure a very slow velocity within the system. In this study, the efficiency of the Treatment Shaft system for separation of solid contents without the use of flocculation agents is investigated. Moreover, the effect of geometry modifications on the separation efficiency is evaluated. For this purpose, a Computational Fluid Dynamics (CFD) approach for multiphase flow of particulate wastewater is used to evaluate the performance of various Treatment Shaft designs for a 10-year, 1-hour rainstorm event. It is shown that the Treatment Shaft is an effective technology to separate particles larger than 175μm, and more than 50% of the particles of size 175μm or more are settled. Additionally, several design variations are assessed and a design with a less footprint is specified.

Commentary by Dr. Valentin Fuster
2018;():V002T11A012. doi:10.1115/FEDSM2018-83348.

A Marcellus shale rock fracture was subjected to four shearing steps and at the end of each shearing step CT (computed tomography) scans with resolution of 26.8 μm were obtained. The CT images were used to generate full aperture maps of the fracture configuration at the end of each shearing phase. The pressure drops along the fracture were also measured for different water flow rates through the fracture. The aperture map of the fracture was used to generate the geometry of the fracture for use in numerical simulations. The water flows and pressure drops in the fracture were simulated with different computational methods that included the full Navier-Stokes simulation, Modified Local Cubic Law (MLCL), and Improved Cubic Law (ICL) methods. Full 3-D Navier-Stokes simulation is the most accurate computational approach which was done with use of the ANSYS-Fluent software for each shear step and different flow rates. The MLCL is a 2-D relatively fast method which is commonly used for prediction of transmissivity of fractures. ICL is a 1-D method proposed in this study in which the effects of surface roughness and tortuosity were included in calculation of the effective aperture height of fractures. To provide an understanding of the accuracy of each of these models their predictions were compared with each other and with the experimental data. Also, to examine the effects of resolution of CT scans and the surface roughness on prediction of fractures transmissivity, similar simulations were performed on average aperture maps. Here the fracture of the full resolution data was averaged over 10 × 10 pixels. Comparing the results of the average aperture maps with those of the full maps showed that the lower resolution of CT scans led to underestimation of the fracture pressure drop due to missing the small features of the fracture surfaces and smoothing out their roughness.

Commentary by Dr. Valentin Fuster
2018;():V002T11A013. doi:10.1115/FEDSM2018-83354.

A turbo-compression system design and its performance analysis procedure for a high altitude long endurance UAV (HALE UAV), of which cruising altitude is within the stratosphere, is presented. To fly at a relatively low speed for a long time and to make engine performance less sensitive to flight altitude, a hydrogen fueled internal combustion engine was chosen for a propulsion system. To utilize an internal combustion engine as a propulsion system at a high altitude, a proper inlet pressure boost system such as a series of turbochargers is required. Hydrogen is highly reactive gas and sometimes backfiring or preignition may occur due to its low ignition energy at stoichiometric ratio. Therefore, fuel to air ratio should be reduced as low as 0.6 to avoid such phenomena. Then rarefied ambient intake air pressure should be boosted up to 1.7 bar to produce required power from the lean burn engine. To gain high pressure ratio from the turbo compression system, at least three stage serial turbocharger with proper intercooler system at each compressor exhaust is required. To analyze multi-stage turbocharger performance at the cruising altitude, an explicit one-dimensional analysis method has been established mainly by matching required power between compressors and turbines. Each compressor performances were corrected according to Reynolds number at a given flight altitude. Compressor efficiency and surge margin deteriorate as the operating altitude increases. Then compressor efficiencies were reflected as functions of flight altitude and corresponding Reynolds number. Once operating points of each turbocharger was determined, then adequate turbochargers were searched for from commercially available models based on performance analysis results. Also, adequate water to air intercoolers were chosen for the turbo-compression system to secure flexibility of placing main components inside the engine bay as well as to obtain high heat exchange efficiency of the heat exchangers. Based on the designed turbo-compression system, technical demonstration test of the turbo-compression system inside altitude environment test chamber in Korea Aerospace Research Institute is planned. Altitude condition in stratosphere is simulated mainly with two stage centrifugal compressor and additional fan will be used to fine control the flight altitude. The turbo compression system will be controlled with a single waste gate located just downstream of the engine to secure simple controllability of the turbo compression system. The test results will validate main components as well as system layout design methods and give more reliable control schedule of the turbo compressions system according to the flight altitude.

Commentary by Dr. Valentin Fuster
2018;():V002T11A014. doi:10.1115/FEDSM2018-83374.

Rough surfaces of flying and swimming animals help to reduce the aerodynamic or hydrodynamic drag when they move in the environment. In this research, biomimetic rough surface is introduced for high-speed train to reduce the aerodynamic drag. CFD tool is used to numerically study how the aerodynamic drag is altered by applying the biomimetic structures to the high-speed train surface. Rough surface is distributed in three areas: pantograph, bogie and windshield areas to reduce the drag at train speed of V = 400km/h. Concave is employed on these areas and orthogonally distributed with diameter of 40mm and center-to-center distance from 60mm to 80mm. The drag force is slightly increased/decreased in the pantograph area, while in the bogie and windshield areas rough structures lead to drag reduction with same distribution configuration. For all cases, the amount of shear drag change is much less than the pressure drag change. The total drag reduction mainly comes from pressure change. Rough surface positively contributes to changing the surface flow and thus reducing the aerodynamic drag.

Commentary by Dr. Valentin Fuster
2018;():V002T11A015. doi:10.1115/FEDSM2018-83379.

The historical HW2 rocket was a liquid propulsion rocket, designed by the German rocket pioneer Johannes Winkler in 1932. With this rocket, Winkler tried to reach a much higher altitude than with his first model, the HW1, which was the first liquid propulsion rocket in Europe and reached an altitude of 60 meters. Because of technical problems, the HW2 exploded immediately after the launch on October 6th in 1932 [1] [2].

To estimate the performance of this historical liquid propulsion rocket its maximum flight altitude was computed with the use of CFD. The equation of the vertical flight trajectory was solved numerically, with the classical Runge-Kutta method. For the computation of the vertical trajectory standard atmospheric conditions were considered. To determine the thrust and the drag of the rocket, the Navier-Stokes equations were solved with the commercial CFD solver Star-CCM+ from Siemens PLM Software. The rocket hull and the rocket engine were first simulated independently for different Mach-numbers and atmospheric flight conditions. Finally the complete rocket with running rocket engine was also computed in atmospheric flight conditions. These results were compared with the standalone simulations of the rocket drag without the running rocket engine and with the simulation of the rocket engine alone. The results are shown and analyzed in detail in this work.

Commentary by Dr. Valentin Fuster
2018;():V002T11A016. doi:10.1115/FEDSM2018-83426.

Designing structures resistant to failure due to fluid induced vibration is a challenge. This paper shows a methodology of evaluating the cycles to failure of thermowells placed in a fluid flow through a large pipe in supercritical operation. The ASME PTC guide describes using Finite Element Analysis (FEA) to evaluate these conditions on a case by case basis. One case from several validated cases is presented using measurements available from the field.

Commentary by Dr. Valentin Fuster
2018;():V002T11A017. doi:10.1115/FEDSM2018-83444.

The research on the external aerodynamics of ground vehicles can nowadays be related to sustainable development strategies, confirmed by the worldwide CO2 regulation target. Automotive manufacturers estimate that a drag reduction of 30% contributes to 10g/km of CO2 reduction.

However, this drag reduction should be obtained without constraints on the design, the safety, comfort and habitability of the passengers.

Thus, it is interesting to find flow control solutions, which will remove or remote recirculation zones due to separation edges with appropriate control techniques. In automotive sales, the SUV, 4x4 and compact cars represent a large part of the market share and the study of control approaches for this geometry is practically useful.

In this work, appropriate control techniques are designed to decrease the drag forces around a reduced scale SUV car benchmark called POSUV. The control techniques are based on the DMD (Dynamic Mode Decomposition) algorithms generating an optimized drag reduction procedure. It involves independent transient inflow boundary conditions for flow control actuation in the vicinity of the separation zones and time resolved pressure sensor output signals on the rear end surface of the mockup. This study, that exploits dominant flow features behind the tailgate and the rear bumper, is performed using Large Eddy Simulations on a sufficient run time scale, in order to minimize a cost function dealing with the time and space average pressure coefficient. The resulting dynamic modal decomposition obtained by these LES simulations and by wind tunnel measurements has been compared for the reference case, in order to select the most appropriate run time scale. Analysis of the numerical results shows a significant pressure increase on the tailgate, for independent flow control frequencies. Similar decomposition performed in the wake with and without numerical flow control help understanding the flow modifications in the detachment zones.

Commentary by Dr. Valentin Fuster
2018;():V002T11A018. doi:10.1115/FEDSM2018-83471.

Nearly 45% of the residential site energy in the US is consumed by the gas furnace for space heating. The design practice of next-generation product often refers to CFD-based design tool, in order to reduce the development cost and cycle. In the present study, Particle Image Velocimetry (PIV) is applied to measure the detailed flow field inside a general gas furnace model for establishing a benchmark database and validating CFD predictions. The furnace model is equipped with multiple observation windows and is connected to an air circulation system with seeding particles introduced, simulating different well-controlled operation conditions. The flow field around the four primary heat exchangers and at the outlet of the furnace is measured and analyzed statistically. The mean velocity displays symmetric patterns as the differential pressure between inlet and outlet of the furnace is low. The symmetry is transiently lost as the differential pressure increases. Statistical analysis also shows turbulence in regions with flow separation and vortex shedding. The results provide a clear understanding of the change of flow characteristics under different operation conditions.

Commentary by Dr. Valentin Fuster
2018;():V002T11A019. doi:10.1115/FEDSM2018-83515.

The main control valve is a key part of mobile hydraulic control systems. The main control valve consists of several types of spool valves. A notch is usually introduced to the end of the spool valve to reduce the influence of the flow force generated by the movement of fluid. In this study the flowrate from a spool valve combined with a servo-valve system is controlled based on an accurate prediction of transient pressure-flow relations by CFD. The transient analyses inside the spool valves with three typical types of notch are performed using a commercial CFD code of Fluent™. The flow characteristics such as flow pattern, discharge coefficient, and flow force, which depend on the notch shapes and their openings, are analyzed via vorticity distributions. Hysteresis of flow coefficients is observed for opening and closing motions of the spool valve, which should be compensated by the servo-valve in order to control the designed rate change of flowrate.

Commentary by Dr. Valentin Fuster

2nd Symposium on Fluid Measurement and Instrumentation

2018;():V002T14A001. doi:10.1115/FEDSM2018-83021.

Shock tunnels create very high temperature and pressure in the nozzle plenum and flight velocities up to Mach 20 can be simulated for aerodynamic testing of chemically reacting flows. However, this application is limited due to milliseconds of its test duration (generally 500 μs–20 ms). For the force test in the conventional hypersonic shock tunnel, because of the instantaneous flowfield and the short test time [1–4], the mechanical vibration of the model-balance-support (MBS) system occurs and cannot be damped during a shock tunnel run. The inertial forces lead to low frequency vibrations of the model and its motion cannot be addressed through digital filtering. This implies restriction on the model’s size and mass as its natural frequencies are inversely proportional the length scale of the model. As to the MBS system, sometimes, the lowest natural frequency of 1 kHz is required for the test time of typically 5 ms in order to get better measurement results [2]. The higher the natural frequencies, the better the justification for the neglected acceleration compensation. However, that is very harsh conditions to design a high-stiffness MBS structure, particularly a drag balance. Therefore, it is very hard to carried out the aerodynamic force test using traditional wind tunnel balances in the shock tunnel, though its test flow state with the high-enthalpy is closer to the real flight condition.

Commentary by Dr. Valentin Fuster
2018;():V002T14A002. doi:10.1115/FEDSM2018-83027.

The turbulent structure of flow field with microbubbles which is generated by electrolysis in a horizontal water channel is investigated at Reynolds number Rem = 24000 (based on the channel height). Firstly, Shadow Image Technique (SIT) is applied to investigate the relation between the shape and the velocity of microbubbles. The experiments have been carried out at the current value 100mA, 200mA, 300mA. The amount of gas generated by electrolysis per unit time is estimated 1.89–5.67 mm3/s. The void fraction is 0.95 × 10−5 – 2.93 × 10−4 %. The mode of the equivalent diameter is 5–10 μm regardless of the condition of the current value. In contrast the mean of the equivalent diameter increases with the increasing of the current value. The mean streamwise velocity of microbubbles increases with the current value. Secondly, Particle Image Velocimetry (PIV) is applied to investigate the turbulent structure in a microbubble channel flow. The experiments have been carried out at the current value 250mA, 300mA. The streamwise mean velocity decreases with the increasing of the current value. The velocity normal from the wall increases by microbubbles. The turbulent intensity with microbubble is bigger than that without microbubble. The Reynolds shear stress with microbubble, however, is smaller than that without microbubble. The decreasing of contribution to the friction coefficient of the turbulent component is calculated about 6.4 % using FIK identify at a low void fraction 2.93 × 10−4 %. The increasing of the frequency of inner interaction and outer interaction causes the decreasing of Reynolds shear stress is clarified by quadrant analysis.

Commentary by Dr. Valentin Fuster
2018;():V002T14A003. doi:10.1115/FEDSM2018-83030.

Power generation of laboratory-scaled marine hydrokinetic (MHK) cross-flow (vertical axis) turbines in counter-rotating configurations was scrutinized both experimentally and numerically. A tabletop experiment, designed around a magnetic hysteresis brake as the speed controller and a Hall-effect sensor as the speed transducer was built to measure the rotor rotational speed and the hydrodynamic torque generated by the turbine blades. A couple of counter-rotating straight-three-bladed vertical-axis turbines were linked through a transmission of spur gears and timing pulleys/belt and coupled to the electronic instrumentation via flexible shaft couplers. A total of 6 experiments in 3 configurations, with various relative distances and phase angles, were conducted in the water channel facility (3.5 m long, 0.30 m wide, and 0.15 m deep) at rotor diameter base Reynolds number of 20,000. The power curve of the counter-rotating turbines (0.068-m rotor diameter) was measured and compared with that of a single turbine of the same size. Experimental results show the tendency of power production enhancement of different counter-rotating configurations. Additionally, the two-dimensional (2D) turbine wakes and blade hydrodynamic interactions were simulated by the shear stress transport k-omega (SST k-omega) model using OpenFOAM. The computational domain included a stationary region and two rotating regions (for the case of counter-rotating turbines) set at constant angular velocities. The interface between the rotating and stationary region was modeled as separated surface boundaries sliding on each other. Velocity, pressure, turbulent kinetic energy, eddy viscosity, and specific dissipation rate field were interpolated between these boundaries.

Commentary by Dr. Valentin Fuster
2018;():V002T14A004. doi:10.1115/FEDSM2018-83076.

Organic vapor flows are met in a wide range of technical applications (e.g., energy conversion, chemical processes, and refrigeration). Typically, organic fluids contain complex molecules, and their thermodynamic behavior deviates significantly from the ideal or perfect gas laws. The applicability of scaling laws to organic vapor flows is very limited, and there is a need for detailed experimental investigations under relevant process conditions. Furthermore, such investigations can provide a validation basis for the simulations performed with Computational Fluid Dynamics (CFD) tools. On the other hand, there exists a serious lack in experimental organic vapor flow test facilities. In this contribution, a novel Closed Loop Organic vapor Wind Tunnel (CLOWT) is presented. The concept of CLOWT is based on a closed-loop continuously running wind tunnel cycle. Its main components are a blower, a diffuser, a settling chamber, a contraction zone, a test section module, and a return, including a throttle valve and a mass flow meter. The test facility CLOWT applies the modular design approach which enables analysis of various flow configurations and components like blowers, small axial test turbines, nozzle flows or transonic flows past test objects. Thanks to an auxiliary heating system, organic vapor flows can be investigated at elevated pressure and temperature levels. The operation of CLOWT is based on closed gas turbine cycle control methods (e.g., inventory control). In addition to the general test facility concept, the paper gives a detailed discussion of the CLOWT special design features.

Commentary by Dr. Valentin Fuster
2018;():V002T14A005. doi:10.1115/FEDSM2018-83134.

The tip leakage vortex (TLV) cavitation mechanism of axial flow pump was investigated with the results of high speed photography and pressure pulsation measurement. The tip leakage vortex cavitation morphology and the transient characteristics of the TLV-induced suction-side-perpendicular cavitating vortices (SSPCV) were analyzed under different flow rates and different cavitation numbers which were combined with the time domain spectrum of pressure fluctuation to elucidate the relationship between the tip cavitation and pressure pulsation. The results showed that cavitation inception occurs earlier with more unstable tip leakage vortex cavitation shape under part-load flow rate condition, and the cavitation is more intense with the decrease of the cavitation number. The inception of SSPCV is attributed to the tail of the shedding cavitation cloud originally attached on the suction side (SS) surface of blade, moving toward the adjacent blade perpendicular to the suction surface, resulting in a flow blockage. With further decrease of pressure, the SSPCVs grow in size and strength, accompanied with a rapid degradation in performance of the pump. The cavitation images and the corresponding circumferential pressure distribution with the same phase showed that the lowest pressure coincides with the suction surface (SS) corner, The pressure was found to decrease along with the occurrence of the cavitation structure.

Commentary by Dr. Valentin Fuster
2018;():V002T14A006. doi:10.1115/FEDSM2018-83139.

Green or living walls are active bio-filters developed to enhance air quality. Often, these walls form the base from which plants are grown; and the plant-wall system helps to remove both gaseous and particulate air pollutants. They can be classified as passive or active systems. The active systems are designed with ventilators which force air through the substrate and plant rooting system, therefore the air is purified and filtered through a bio-filtration process which also acts as a natural cooling system. Their benefits include temperature reduction, improvement of air quality and reduction of air pollution, oxygen production as well as the social and psychological wellbeing. They can produce changes in the ambient conditions (temperature and humidity) of the air layers around them which create an interesting insulation effect. The effect of green wall modules on the air temperature and on humidity is investigated in this work. A closed chamber made of acrylic sheets is used to monitor the temperature and humidity variation caused by a green wall module placed at its center. A fan positioned at the back center of the module drives air at ambient conditions and direct it into the module. Temperature and humidity are measured at different locations inside the chamber during operation for different modules with different plant species. The effect of changing the surrounding ambient conditions is also investigated.

Topics: Temperature
Commentary by Dr. Valentin Fuster
2018;():V002T14A007. doi:10.1115/FEDSM2018-83163.

Cavitation has negative influence on pump operation. In order to detect incipient cavitation effectively, experimental investigation was conducted to through acquisition of current and vibration signals during cavitation process. In this research, a centrifugal pump was modeled for research. The data was analyzed by HHT method. The results show that Torque oscillation resulted from unsteady flow during cavitation process could result in energy variation. Variation regulation of RMS of IMF in current signal is similar to that in axial vibration signal. But RMS of IMF in current signal is more sensitive to cavitation generation. It could be regarded as the indicator of incipient cavitation. RMS variation of IMF in base, radial, longitudinal vibration signals experiences an obvious increasing when cavitation gets severe. Such single variation regulation could be selected as the indicator of cavitation stage recognition. Hilbert-Huang transform is suitable for transient and non-stationary signal process. Time-frequency characteristics could be extracted from results of HHT process to reveal pump operation condition. The contents of current work could provide valuable references for further research on centrifugal pump operation detection.

Topics: Cavitation , Pumps
Commentary by Dr. Valentin Fuster
2018;():V002T14A008. doi:10.1115/FEDSM2018-83178.

To ensure the proper operation of hydroelectric generators, their cooling must be well understood. However, the airflow within such machines is difficult to characterize, and although Computational Fluid Dynamics (CFD) can be a reliable engineering tool, its application to the field of hydroelectric generators is quite recent and has certain limitations which are, in part, due to geometrical and flow complexities, including the coexistence of moving (rotor) and stationary (stator) components. For this reason, experimental measurements are required to validate CFD simulations of such complex flows. Of particular interest is the quantification of the flow within the rotor rim ducts, since it is directly responsible for cooling the poles (one of the most critical components of a hydroelectric generator). Thus, to measure the flow therein, an anemometer was designed. The anemometer had to be accurate, durable, cost-effective, easy to install, and able to withstand the extreme conditions found in hydroelectric generators (temperatures of 45°C, centrifugal forces of 300 g, etc.). In this paper, a thermal mass flow meter and a method for validating its performance, using hot-wire anemometry and a static model of a rotor rim, are described. Preliminary tests demonstrate that the thermal mass flow meter is capable of i) measuring the mass flow rate in the rotor rim ducts with an accuracy of approximately 10%, ii) fitting inside small rectangular ducts (12.2 mm by 51 mm), and iii) resisting forces up to 300 g.

Commentary by Dr. Valentin Fuster
2018;():V002T14A009. doi:10.1115/FEDSM2018-83199.

Green or living walls are active bio-filters developed to enhance air quality. Often, these walls form the base from which plants are grown; and the plant-wall system helps to remove both gaseous and particulate air pollutants. They can be classified as passive or active systems. The active systems are designed with ventilators which force air through the substrate and plant rooting system, therefore the air is purified and filtered through a bio-filtration process which also acts as a natural cooling system. A fan positioned at a central opening on the module’s back face drives air through the medium-plant-roots mix and then onward through the plants’ canopy; and these would help to remove both gaseous and particulate pollutants from the air. Pressure drop across the module, air flow distribution through it as well as the total flow rate have been obtained. The effect of different fan speeds on the total air flow and on its distribution through the module is investigated in this study in order to optimize the energy consumption of the fans whilst maintaining the modules biofiltration efficiency.

Topics: Air flow
Commentary by Dr. Valentin Fuster
2018;():V002T14A010. doi:10.1115/FEDSM2018-83251.

Many researchers have utilized submerged jet impingement geometry to study solid particle erosion/corrosion. However, only a few studies have investigated changing impingement angle and fluid viscosity. In this study, Particle Image Velocimetry (PIV) experiments were conducted using 14 micron glass spheres for direct impingement geometry at viscosities of 1, 14, and 55 cP. These viscosities correspond to Reynolds numbers of approximately 57000, 4000, and 1000, respectively. It was observed that by increasing the viscosity the flow exiting the nozzle transitioned from extremely turbulent to laminar flow. The data indicated fully turbulent flow at the outlet for viscosities of 1 and 14 cP. In the case of 55 cP flow, the flow exiting the nozzle became laminar contributing to a higher maximum velocity in 55 cP flow. Experiments at these viscosities were also conducted at impingement angles of 90, 75, and 45 degrees to investigate the effects of the impinging jet angle on a flat plate. Additionally, a series of Computational Fluid Dynamics (CFD) simulations of the flowfield were performed to compare with the experimental data collected in this paper.

Topics: Fluids , Viscosity
Commentary by Dr. Valentin Fuster
2018;():V002T14A011. doi:10.1115/FEDSM2018-83296.

This study is concerned with understanding and improvement of mass flow rate measurement uncertainty and errors encountered at low flow rates and start-up in commercially available flow rate measurement devices, such as orifice flow meters. The flow through a typical cylindrical flange-tapped orifice flow meter is modeled computationally so the actual mass flow rate is known a-priori. Empirical predictions from the reading of “virtual” pressure sensors are compared with the actual flow rate and the measurement errors are quantified and analyzed. Commercial code ANSYS-Fluent is compared in this study to the in-house high-fidelity spectral-element solver Nek5000, so that conclusions about the applicability of a commercial code to the calculations of measurement uncertainty in the orifice flow meters can be made.

Commentary by Dr. Valentin Fuster
2018;():V002T14A012. doi:10.1115/FEDSM2018-83378.

The present study mainly treats the flow measurement for the intake duct of a water-jet propulsion equipment using stereoscopic particle image velocimetry (SPIV) technique. To obtain clear flow field information in the intake duct, the authors have developed a suitable SPIV calibration method and used a time filter to preprocess images. The velocity distributions in an intake duct is investigated at the flow rate ranging from 0–35 m3/h by an independently designed test rig, which is composed of an open circulating water tank, a pump, a control valve and other measuring sensors. The pressure transducers are also used to measure the pressure fluctuations at two typical positions near the lip of the intake duct. The velocity distributions at the midplane of the intake duct depict that there is a jet flow due to the presence of duct lip, and a strong separation flow is induced between the jet and the duct wall. The experimental results are useful to give a clear insight into the flow behaviors inside the intake, and show the reason of the flow distortion at the outlet of intake duct. Moreover, some guidance can be provided for the application of SPIV in the intake duct.

Commentary by Dr. Valentin Fuster
2018;():V002T14A013. doi:10.1115/FEDSM2018-83405.

In support of a header/feeder phenomena study, an adiabatic, near-atmospheric, air-water flow loop was commissioned simulating a single feeder of a Pressurized Heavy Water Reactor’s primary heat transport system under a postulated Loss of Coolant Accident scenario. An extensive database in representative two-phase flow conditions was collected, 750 tests in total, in order to create a two-phase flow map to be used in the more complex geometries such as header/feeder systems. The flow loop consists of two vertical test sections, for upwards and downwards flow, and one horizontal test section, each with an inner diameter of 32 mm and at least 120 diameters in length. Superficial velocities extended up to 6 m/s for the water and 10 m/s for the air. Void fraction was measured by means of quick-closing valves and a pair of wire-mesh sensors (WMS) in each test section.

Two-phase repeatability tests showed that the liquid and gas superficial velocities varied by 1.1% and 0.6% at reference conditions of 2.0 and 2.8 m/s, respectively. The corresponding void fraction measurements varied for the quick-closing valves by at most 6.8%, which indicates a low sensitivity to the closure time of the valves and an appropriate axial distance between them, and 2.3% for the WMS. For both measurement techniques, the largest variations occurred in the vertical downwards test section.

For the formal two-phase tests, over 600 distinct flow conditions were performed. The results showed that the two measurement techniques agreed within 5% at high void fractions and low liquid flow rates in vertical flow. For all other cases corresponding to the transitional or dispersed bubbly flow regime, the WMS over-estimated the void fraction by a consistent bias. An empirical correction is proposed, with a root-mean-square error of 6.6% across all tests. The void fraction map resulting from this database provides validation for the WMS measurements, a quantitative assessment of its uncertainty and range of applicability, and will be used as a reference in future tests under similar scale and flow conditions.

Commentary by Dr. Valentin Fuster
2018;():V002T14A014. doi:10.1115/FEDSM2018-83465.

In this work, the thicknesses of impinging liquid sheets formed by two alike impinging jets with different flow rates are investigated via a non-intrusive measurement technique, the Partial Coherent Interferometry. The Reynolds number and Weber number are 720 to 780 and 120 to 150, respectively. An interferometer with the calibrated partial coherence property is used to record the interference pattern by passing one branch of the two optical paths through the impinging sheet. By examining the phase and the degree of coherence of the pattern, the absolute thickness distribution of the impinging sheet is measured. The thicknesses with different experimental conditions are compared to the previous theoretical models and the influences of the flow rate and impinging angle are concluded.

Topics: Interferometry , Jets
Commentary by Dr. Valentin Fuster
2018;():V002T14A015. doi:10.1115/FEDSM2018-83467.

Quantifying the early stage of bag-type breakup of droplet is an important way to study the mechanism of drop breakup, but remains a challenge due to the lack of spatial-temporal resolved diagnostic technique. High-speed digital in-line holography at 20 kHz is employed to characterize secondary droplets formed in bag rupture of an ethanol drop exposed in the gas stream. Droplets as small as 10 μm are resolved at the beginning of bag rupture at Weber number of 11. The velocities of secondary droplets can almost reach that of the gas stream. Then the thin wall shrinks to form wrinkles that will generate relatively larger secondary droplets with smaller velocities. Droplet diameters are statistically displayed and the relationship between velocity and diameter as well as time is analyzed. This will help the further understanding of fuel spray generation in gas turbine engines.

Topics: Holography , Drops
Commentary by Dr. Valentin Fuster
2018;():V002T14A016. doi:10.1115/FEDSM2018-83480.

The scope of the work is to develop a cooling system which uses wing-bay air to cool the Electro-Mechanical Actuators (EMA). The wing-bay is enclosed. The system will operate between 20% and 100% of atmospheric pressure. Using high speed fans as a means of cooling the EMAs it is important to understand the characteristics of the fan. The study also closely observed the results obtained experimentally with that of the fan scaling analysis. The fan laws can be derived from dimensionless analysis of volumetric flow rate, static pressure, and power equations. Considering the current experimental data, the fan scaling laws can be used to verify the proper nature of the fan curves when using a certain measurement at the baseline. In this study, the results have been verified for various rotational speeds and ambient pressure conditions. Consequently, there are two fans that have been tested within the loop. The first fan is a 2 bladed fan whereas the other fan has a 12 bladed propeller. The fan performance curves will determine the cooling capacities of each and provide a means to compare geometrically different fans.

Commentary by Dr. Valentin Fuster

53rd Forum on Cavitation and Phase Change

2018;():V002T16A001. doi:10.1115/FEDSM2018-83019.

In this study, pressure transients are triggered by a steel ball, which is released from an upstream reservoir to hit a valve seat and shut off water flow in a horizontal straight copper pipeline. The pressure pulsations, cavitation and gas bubbles growth and collapse in the low pressure water-hydraulic pipeline are recorded by two pressure transducers and a high speed video camera, respectively. In addition, the influences of initial volume of gas bubbles in water and instant leakage in valve are investigated. The experimental results indicate that increasing initial gas bubble volume in water and the instant leakage of the valve will help to reduce magnitudes and numbers of pressure peaks during pressure transients. Then methods to reduce pressure pulsations in pipelines are put forward.

Commentary by Dr. Valentin Fuster
2018;():V002T16A002. doi:10.1115/FEDSM2018-83200.

Shedding is one of the most important expressions of the instability of cavitating flow. Most previous research works were focused on the shedding mechanism induced by the re-entry jet. Shock induced shedding on a wedge is identified recently by using time resolved X-ray densitometry which attracted lots of attention. In the present paper, cavitation dynamics around an axisymmetric body are investigated. Both shock propagation and re-entry jet as inducing factors of shedding are observed in different cycles in a single experiment. Relevant numerical simulations are carried out based on a fully compressible approach under the framework of the open-source code OpenFOAM. Numerical and experimental results agree well with each other. Results indicate shedding is induced by the re-entry jet in the first cycle. Re-entry jet occurs and cut the cavity off on the should which induces the shedding of cloud cavity in the first cycle. However in the second and subsequent cycles, shocks are generated by the collapse of shedding cavities and propagate to the cavity closure and induces stronger re-entry jet. Its effect on cavity instability is indirect which still needs a strong re-entry jet as the medium media.

Commentary by Dr. Valentin Fuster
2018;():V002T16A003. doi:10.1115/FEDSM2018-83223.

Cavitation inside fuel injector nozzles has been linked not only to erosion of the solid surface, but also to improved spray atomization. To quantify the effects of the resulting occurrences, the prediction of cavitation through computational modeling is vital. Homogeneous mixture methods (HMM) make use of a variety of cavitation sub-models such as those developed by Kunz, Merkle, and Schnerr-Sauer, to describe the phase change from liquid to vapor and vice-versa in the fluid system. The aforementioned cavitation models all have several free-tuning parameters which have been shown to affect the resulting prediction for vapor volume fraction.

The goal of the current work is to provide an assessment of the Kunz and Schnerr-Sauer cavitation models. Validation data have been obtained via experiments which employ both acoustic techniques (passive cavitation detection, or PCD) and optical techniques (optical cavitation detection, or OCD). The experiments provide quantitative information on cavitation inception and qualitative information as to overall vapor fraction as a function of flow rate, and nozzle geometry. It is shown that inception is fairly well captured but the amount of vapor predicted is far too low. A sensitivity analysis on the tuning parameters in the cavitation models leads to some explainable trends, however, several parameter sweeps results in outlier predictions. Recommendations for their usability and suggestions for improvement are presented.

Commentary by Dr. Valentin Fuster
2018;():V002T16A004. doi:10.1115/FEDSM2018-83396.

In this study, a numerical study has been performed on the two-phase heat transfer of a new nanostructured heat transfer fluid: Water-in-Polyalphaolefin (PAO) Nanoemulsion Fluid inside a mini-channel heat exchanger using ANSYS FLUENT. Nanoemulsion fluids are liquid suspensions of nanosized droplets, which are part of a broad class of colloidal dispersions. The nanoemulsion fluid can be formed spontaneously by self-assembly, in which these nanodroplets are in fact swollen micelles. To simplify the complexity of the numerical model, the nanoemulsion fluid was then treated as a homogenous fluid during single-phase and only the water vaporizes during the phase change. The volume of fraction (VOF) model with Pressure-Velocity coupling based Semi Implicit Method for Pressure Linked Equations (SIMPLE) iterative algorithm is employed to solve the continuity, momentum, energy equations in two dimensional domains. The thermophysical properties of the nanoemulsion fluid were measured and used for the current simulation. The results were verified using the experimental results and has shown good agreement. This study has demonstrated the feasibility of simplyig the simulation of flow boiling heat transfer of this new heat transfer fluid through treating it as a homogenous fluid during single-phase convective heat transfer and separating the vapor phase of the nano-micelles during flow boiling. This study has also shown that this Water-in-PAO nanoemulsion could function as a good and alternative conventional working fluid in heat transfer applications.

Commentary by Dr. Valentin Fuster
2018;():V002T16A005. doi:10.1115/FEDSM2018-83473.

Groundwater flow has an undesirable effect on ice growth in artificial ground freezing (AGF) process: high water flow could hinder the hydraulic sealing between two freeze pipes. Therefore, a reliable prediction of the multiphysics ground behavior under seepage flow conditions is compulsory. This paper describes a mathematical model that considers conservation of mass, momentum, and energy. The model has been derived, validated, and implemented to simulate the multiphase heat transfer between freeze pipes and surrounded porous ground structure with and without the presence of groundwater seepage. The paper discusses, also, the influence of the coolant’s temperature, the spacing between two freeze pipes, and the seepage temperature on time needed to create a closed, frozen wall. The results indicate that spacing between two pipes and seepage velocity have the highest impact on the closure time and the frozen body width.

Commentary by Dr. Valentin Fuster
2018;():V002T16A006. doi:10.1115/FEDSM2018-83509.

The present study reports the characterization of the transient flow behavior in the liquid PCM domain during the melting process, initiated by a planer heat source. Experiments were conducted at three angles of inclination of the heat source (0, 8 and 18-degrees) from the vertical. Paraffin wax was used as the PCM and was enclosed in an insulated, optically clear, thin rectangular chamber. Particle image velocimetry (PIV) was used during the melting process to measure the instantaneous velocity of the PCM and obtain two-dimensional velocity fields within the liquid domain. Results clearly show the presence of a dominant recirculation zone occurring at all angles. This recirculation zone was enhanced by an increase in the inclination of the heat source, supporting a direct correlation between the tilt angle and the bulk fluid flow in the melted region. The melting rate decreased with the progression of time for all investigated cases. A growing region of stagnant fluid flow within the center of the recirculation zone contributed to the reduction in the melt rate. The size of this stagnant region decreased with increases in the tilt angle due to the enhancement of natural convection. The data demonstrates significant changes in transient flow behavior with orientation in the liquid PCM domain. These results further our understanding of the phase change and associated heat transfer processes in PCM and have wide applicability to PCM-based thermal energy storage.

Commentary by Dr. Valentin Fuster

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