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ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V007T00A001. doi:10.1115/IMECE2017-NS7.
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This online compilation of papers from the ASME 2017 International Mechanical Engineering Congress and Exposition (IMECE2017) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Fluids Engineering: 13th Forum on Recent Developments in Multiphase Flow

2017;():V007T09A001. doi:10.1115/IMECE2017-70085.

During drilling, the precipitation velocity of cuttings within an annulus depends on the density, configuration, and size of the cuttings, and on the density, viscosity, and rheological characteristics of the drilling fluid. In this study, in order to identify transfer features of cuttings, an experiment was performed under wide-ranging conditions by constructing a slim hole annulus (44 mm × 30 mm) device. In this experiment, the pressure loss and the particle transport ratio were measured in upward flow of Newtonian and non-Newtonian fluids. These quantities were influenced by particle concentration within the flow, pipe rotation, flow rate, and inclination of the annulus. For both water and CMC (carboxymethylcellulose) solutions, the higher the concentration of the solid particles is, the larger the pressure gradients become. The experimental uncertainty of this study varies from a minimum of 3% to a maximum of 9% depending on the experimental conditions.

Commentary by Dr. Valentin Fuster
2017;():V007T09A002. doi:10.1115/IMECE2017-70337.

The Eulerian-Eulerian two-fluid model [1] (EE) is the most general model in multiphase flow computations. One limitation of the EE model is that it has no ability to estimate the local bubble sizes by itself. Thus, it must be complemented either by measurements of bubble size distribution or by additional models such as population balance theory or interfacial area concentration to get the local bubble size information. In this work, we have combined the Discrete Phase model (DPM) [2,8] to estimate the evolution of bubble sizes with the Eulerian-Eulerian model. The bubbles are tracked individually as point masses, and the change of bubble size distribution is estimated by additional coalescence and breakup modeling of the bubbles. The time varying bubble distribution is used to compute the local interface area between gas and liquid phase, which is used to estimate the momentum interactions such as drag, lift, wall lubrication and turbulent dispersion forces. This model is applied to compute an upward flowing bubbly flow in a vertical pipe and the results are compared with previous experimental work of Hibiki et al. [3]. The newly developed hybrid model (EEDPM) is able to reasonably predict the locally different bubble sizes and the velocity and void fraction fields. On the other hand, the standard EE model without the DPM shows good comparison with measurements only when the prescribed constant initial bubble size is accurate and does not change much.

Commentary by Dr. Valentin Fuster
2017;():V007T09A003. doi:10.1115/IMECE2017-70965.

Large eddy simulations of pre-designed micro-hydrokinetic turbine were conducted to investigate the oxygen transfer from air to water. Simulations were performed in extreme conditions having a tip-speed ratio of 3.8 that is higher than the tip-speed ratio at turbine’s design point. Air was injected from the turbine hub downstream in axial direction. Both single phase and multiphase simulations were performed to reveal the influence of air admission on the flow structures and the turbine performance. The mixture multiphase model was employed in multiphase simulation. The results indicated that turbine power generation was reduced roughly 10.5% by air admission, however the torque applied on turbine surface in axial direction did not vary significantly by aeration. The aeration assisted in the suppression of vortices within the flow field. The deviation of the power coefficient and the thrust coefficient was reduced roughly 32% through the inclusion of aeration process.

Commentary by Dr. Valentin Fuster
2017;():V007T09A004. doi:10.1115/IMECE2017-71085.

The current study shows computational and experimental analysis of multiphase flows (gas-liquid two-phase flow) in channels with sudden area change. Four test sections used for sudden contraction and expansion of area in experiments and computational analysis. These are 0.5–0.375, 0.5–0.315, 0.5–0.19, 0.5–0.14, inversely true for expansion channels. Liquid Flow rates ranging from 0.005 kg/s to 0.03 kg/s employed, while gas flow rates ranging from 0.00049 kg/s to 0.029 kg/s implemented. First, single-phase flow consists of only water, and second two-phase Nitrogen-Water mixture flow analyzed experimentally and computationally. For Single-phase flow, two mathematical models used for comparison: the two transport equations k-epsilon turbulence model (K-Epsilon), and the five transport equations Reynolds stress turbulence interaction model (RSM). A Eulerian-Eulerian multiphase approach and the RSM mathematical model developed for two-phase gas-liquid flows based on current experimental data. As area changes, the pressure drop observed, which is directly proportional to the Reynolds number. The computational analysis can show precise prediction and a good agreement with experimental data when area ratio and pressure differences are smaller for laminar and turbulent flows in circular geometries. During two-phase flows, the pressure drop generated shows reasonable dependence on void fraction parameter, regardless of numerical analysis and experimental analysis.

Topics: Two-phase flow
Commentary by Dr. Valentin Fuster
2017;():V007T09A005. doi:10.1115/IMECE2017-71133.

Here we observe the spatial and temporal patterns that erosion fronts driven by pulsed radial wall jets develop in double ring arrays of pulse tubes within slurry mixing vessels with curved bottoms. Although erosion of unbounded particle beds driven by individual steady jets has been studied for decades, the patterns developed within mixing vessels as neighboring transient erosion fronts collide and the subsequent relaxation of the particle bed towards the vessel center when the jets stop (i.e., as the pulse tubes refill within mixing vessels) remain incompletely understood. Relaxation here refers to motion of fluidized particle beds that were driven toward the vessel seam by radial wall jets that subsequently return or relax from the seam toward the center of the vessel when the jets turn off. Relaxation does not refer to downward individual or hindered particle settling. Spatial variations in the particle bed due to these relaxing particle beds comprise an important “initial” condition to the mathematical description of the evolution of the jet driven erosion front, and erosion fronts other than the one that expands radially from the pulse tube axis have only recently been described. For example, Bamberger, et al. (2017) [9], recently evaluated five selected cases of erosion patterns found in vessels 15 and 70 inches in diameter with 2:1 semi-elliptical bottoms. A highlight of that study was the discovery of a second type of erosion front that forms at the plane of symmetry between two adjacent pulse tubes. As neighboring radial wall jets collide they form an upwelling sheet of fluid; this second type of erosion front forms immediately beneath this upwelling flow. However, variations in this type of planar erosion front have not been cataloged previously.

In this study, we systematically probe the erosion fronts driven by these upwelling sheets in greater detail and evaluate the relaxation of the particle bed to its “initial” condition after the pulse ceases. Variations in the erosion patterns and particle bed relaxation are evaluated as a function of particle concentration, density, and size. This study specifically focusses on video images collected from the 15 inch vessel because it provides distinctive visualization of erosion pattern behavior. We find the upwelling sheets to be more influential on the erosion patterns at lower particle concentrations, making these findings particularly important to low solids concentration vessels. At lower particle concentrations, flow at the base of the plane of symmetry readily erodes particle beds. At higher particle concentrations, piles of unmobilized solids accumulate beneath colliding jets either because the erosion mechanism vanishes or because erosion at the plane of symmetry is slow compared to radial erosion. We also find that the upwelling sheets introduce a flow that drives erosion patterns from outer ring jets toward the vessel center along the curved vessel floor along the plane of symmetry between nozzles.

We further find that the rate of particle bed relaxation back toward the vessel center after the pulse ceases may correlate with concentration, particle density, and size. Higher concentrations and particle densities relax faster. The rate at which the entire bed relaxes toward the vessel center is faster near the vessel seam but slows as the relaxing front approaches the vessel center. This paper discusses competing mechanisms to explain these observations, including particle rolling, bed avalanches, gravity driven fluidized bed motion, and suspended particle sedimentation.

Topics: Erosion , Vessels , Pulsejets
Commentary by Dr. Valentin Fuster
2017;():V007T09A006. doi:10.1115/IMECE2017-71512.

In the oil industry the localization of a leak that occurs in a pipeline is an important piece of information that needs to be obtained before mitigating actions can be taken to remedy the leak effects. In this paper we are particularly interested in testing a leak localization model for two-phase flows based upon the intersection of the hydraulic grade lines emanating from the pipeline ends. This methodology is commonly applied to single-phase-flows. In two-phase flows, the flow-pattern that develops along the entire pipeline upstream and downstream of the leak strongly affects the pressure gradient and has significant influence on the location of the leak. We consider this two-phase flow to be steady and to occur in a nearly horizontal pipeline characterized by the stratified-flow pattern. We also assume that the flow is isothermal with a compressible gas phase and an incompressible liquid phase. The results of the numerical simulations allow the model sensitivity to be studied by changing the leak location, for a given leak magnitude. From this analysis, we may observe how these parameters affect the pressure gradients along the pipeline that develop upstream and downstream of the leak and the model’s ability to predict the leak location.

Commentary by Dr. Valentin Fuster
2017;():V007T09A007. doi:10.1115/IMECE2017-71591.

The investigation of the dynamics of a droplet traversing through constricted channels is an interesting field of research. In the present work, the motion and deformation of a neutrally buoyant droplet in planar constricted micro channels containing another immiscible fluid is studied computationally using an open-source finite-volume fluid flow solver, Gerris. The important non-dimensional parameters pertaining to such type of flow are — the Capillary number, which gives the relative importance of the viscous force over the surface tension force, the viscosity ratio between the dispersed and suspending medium and the ratio of the drop diameter to the channel height. Both symmetrical and asymmetrical constrictions are considered and results obtained are compared with a straight channel without any constriction. The parametric studies are conducted to study the effect of droplet size, viscosity ratio, Capillary number and presence of constriction in the channel. Depending on the parameters chosen, the drop extends to a maximum length as its front passes through the constriction and the deformation increases with the increase in number of constrictions. In the case of large drops, it is observed that the droplet disintegration rate increases in the presence of constrictions.

Commentary by Dr. Valentin Fuster
2017;():V007T09A008. doi:10.1115/IMECE2017-71810.

Clarifying two-phase flow characteristics in a nuclear reactor core is important in particular to enhance the thermo-fluid safety of nuclear reactors. Moreover, bubbly flow data in subchannels with spacers are needed as validation data for current CFD codes like a direct two-phase flow analysis code. In order to investigate the spacer effect on the bubbly flow behavior in a subchannel of the nuclear reactor, bubble dynamics around the simply simulated spacer was visually observed by a high speed camera. Furthermore, the void fraction and interfacial velocity distributions just behind the simulated spacer were measured quantitatively by using a wire-mesh sensor system with three wire-layers in the flow direction. From the present study, bubble separation behavior dependence upon the spacer shape was clarified.

Commentary by Dr. Valentin Fuster
2017;():V007T09A009. doi:10.1115/IMECE2017-71854.

This paper develops an artificial neural network (ANN) model for steady-state two-phase flow pressure drop estimation in pipelines. Mechanistic models are traditionally considered in pipeline flow modeling. However, their reliance on fundamental laws of physics can negatively impact their accuracy when dealing with large experimental data sets and various pipeline inclinations. Hence, ANN models prove to be highly accurate compared to mechanistic models. Dimensional analysis is used to derive a broad reservoir of dimensionless groups and form candidate inputs to the ANN model. Identifying the groups leading to the best correlation of the output variable requires a laborious and nonsystematic trial-and-error procedure. To circumvent this problem, genetic algorithms (GA) were considered to identify the best ANN input combination, thereby allowing a good prediction of steady-state two-phase flow pressure drop in pipelines with all inclinations. The sensitivity of the model accuracy to some GA parameters such as the population size and the parent selection scheme was investigated. The proof of concept of the proposed approach was illustrated using the Stanford multiphase flow database. Based on the obtained results, the proposed model was shown to outperform existing mechanistic models when cross-examined using the same database. In addition, the proposed model allowed good prediction accuracy for all pipe inclinations and all flow patterns.

Commentary by Dr. Valentin Fuster
2017;():V007T09A010. doi:10.1115/IMECE2017-71909.

Cavitation process in microchannels has been widely studied from variety of perspectives. In diesel engines, smaller droplets provide a larger surface area and this leads to more efficient combustion. It has been observed that the atomization process is influenced by turbulence and cavitation in the nozzle. These factors therefore contribute to the size of the droplets, the spray angle, penetration of the fuel and other characteristics. In the present study, a numerical simulation of cavitation process in microchannels similar to nozzles is conducted using ANSYS Fluent. Cavitation phenomenon has been analyzed numerically for a variety of downstream pressures and L/D ratios. The effect of the geometry of the nozzle (length to diameter ratio) and downstream flow pressure conditions on the cavitation are also studied. The results can be used for optimal design of diesel injectors.

Commentary by Dr. Valentin Fuster
2017;():V007T09A011. doi:10.1115/IMECE2017-72113.

This paper presents the results of both visualization experiment and numerical simulation for two-phase (water-air mixture) flows in a horizontal tube. A visualization experimental setup was used to observe various two-phase flow patterns for different flow rates of water/air mixture flow in a glass tube of 12 mm in diameter. Total of 303 experimental data points were compared with Mandhane’s flow map. Most of the data for stratified, plug and slug flows were found to be in good agreement. However, annular flow was observed for relatively lower gas flow rates and also wavy flow occurred at relatively higher liquid flow rates in this experiment. A three-dimensional Computational Fluid Dynamics (CFD) simulation was performed using OpenFOAM employing “interFoam” as the solver to simulate the two-phase flows in horizontal pipe based on Volume-Of-Fluid (VOF) method. The simulated and experimentally observed flow patterns for the same set of superficial velocities shows acceptable similarities for stratified, wavy, plug, slug and annular flows. Also, the computed values of the void fraction and pressure drop for the numerical simulations shows reasonable agreement with well-known correlations in literature.

Commentary by Dr. Valentin Fuster
2017;():V007T09A012. doi:10.1115/IMECE2017-72315.

The spontaneously jumping motion of condensed droplets by coalescence on superhydrophobic surfaces has been an active area of research due to its great potential for enhancing the condensation efficiency. Despite a considerable amount of microscopic observations, the interfacial wetting characterization during jumping-droplet condensation is still notably lacking. This work focuses on applying a novel acoustic sensor - quartz crystal microbalance (QCM), to characterize the interfacial wetting on nanostructured surfaces during jumping-droplet condensation. Copper oxide nanostructures were generated on the surface of QCM with a chemical etching method. Based on the geometry of the nanostructures, we modified a theoretical model to reveal the relationship between the frequency shift of the QCM and the wetting states of the surfaces. It was found that the QCM is extremely sensitive to the penetrated liquid in the structured surfaces. Then, the QCM with nanostructured surface was tested on a customed flow condensation setup. The dynamic interfacial wetting characteristics were quantified by the normalized frequency shift of the QCM. Combined with microscopic observation of the corresponding drop motion, we demonstrated that partial wetting (PW) droplets with an about 25% penetrated area underwent spontaneously jumping by coalescence. However, the PW droplets no longer jumped when the penetrated area exceeds 50% due to the stronger adhesion between liquid and the surface. It shows that the characterization of the penetrated liquid in micro/nanostructures, which is very challenging for microscopic observation, can be easily carried out by this acoustic technique.

Commentary by Dr. Valentin Fuster

Fluids Engineering: 15th Symposium on Electric, Magnetic and Thermal Phenomena in Micro and Nano-Scale Systems

2017;():V007T09A013. doi:10.1115/IMECE2017-71334.

Microwave and radio frequency heating has great promise in many engineering and biomedical applications because of its non-contact, volumetric selective heating. However, the heating patterns and temperature distributions are non-uniform due to non-uniform electromagnetic power absorptions. In this study, we present a closed-form analytic expression of electromagnetic field distribution and power absorption in a spherical shaped object. A simplified Maxwell’s equation that represents plane wave is solved in spherical coordinates using vector potentials and separation of variables. The electromagnetic power absorption is obtained from the electromagnetic field distribution within the object using Poynting theorem. The analytical expressions of the electric field and power generation are evaluated for meat balls of 1.0, 2.0, 3.0 and 5.0 cm radii and two different electromagnetic frequencies. Results show that the strength of the absorbed electromagnetic wave and power absorption is highly dependent on the radius of the dielectric sphere. The presence of local maxima of electric and magnetic field strength due to the constructive interference of the reflection and transmission of electromagnetic wave in the target object are found in all sizes. However numbers of peaks or valleys are more in larger meat balls. The spatial distribution of microwave power absorption follows the trend of electromagnetic field distribution. The positions of local maxima and minima of power absorption and electromagnetic field distributions vary with the radius of the sphere and applied frequencies. It indicates that the uniform and effective electromagnetic power absorption can be facilitated by the proper design of the object of interest and selection of an appropriate frequency.

Commentary by Dr. Valentin Fuster
2017;():V007T09A014. doi:10.1115/IMECE2017-72206.

In this study deformation and breakup of a falling drop which is surrounded by another liquid are modeled numerically. The drop is influenced by an external electric field which is applied uniformly on the side walls of the domain. An open-source volume-of-fluid solver, Gerris with dynamic adaptive grid refinement has been used for numerically modeling the three-dimensional deformation of a falling droplet. The numerical results are presented for various values of density ratios and electrical conductivity and permittivity. The current numerical results are compared with previous experimental and analytical works which shows a great agreement between them.

Commentary by Dr. Valentin Fuster

Fluids Engineering: 17th International Symposium on Measurement and Modeling of Environmental Flows

2017;():V007T09A015. doi:10.1115/IMECE2017-70145.

An experimental and numerical study was conducted to study unsteady lid-driven cavity flows. More specifically, the development of the circulation patterns inside a square cavity due to the movement of a rigid impermeable lid at constant velocity was observed experimentally and predicted numerically by CFD codes.

Particle Image Velocimeter (PIV) technique was used to determine the flow field as it develops from stagnation to steady state inside a one inch (25.4 mm) square cavity driven by an impermeable lid. To avoid the three dimensional effects on the primary vortex, the depth of the cavity is taken to be 5 inches (127 mm). Working fluid is water and it is seeded with hallow glass spheres with 10 microns diameter. Experimental study was conducted for different lid velocities corresponding to Reynolds numbers for laminar to intermittent turbulence. The numerical study was carried out using commercial and in-house CFD codes for the steady state case, and using a commercial CFD code for the unsteady case. The predictions of unsteady flow field inside the two-dimensional square cavity were made using these codes which employ second order accurate (temporally and spatially) implicit numerical schemes. A time and mesh independence study was carried out to determine the optimum mesh size and time increment for the unsteady case study. Comparisons of the numerically predicted and experimentally measured velocity fields are made for steady and unsteady cases. The results indicate that the numerical predictions capture the characteristics of the circulation inside the cavity reasonably well however the magnitude of the velocities are underestimated.

Topics: Cavity flows
Commentary by Dr. Valentin Fuster
2017;():V007T09A016. doi:10.1115/IMECE2017-70212.

Natural ventilation is the process of supplying and removing air through an indoor space by natural means. There are two types of natural ventilation occurring in buildings: winddriven ventilation and buoyancy driven ventilation, or stack ventilation. The most efficient design for natural ventilation in buildings should implement both types of natural ventilation. Stack ventilation which is temperature induced is driven by buoyancy making it less dependent on wind and its direction. Heat emitted causes a temperature difference between two adjoining volumes of air, the warmer air will have lower density and be more buoyant thus will rise above the cold air creating an upward air stream. Combining the winddriven and the buoyancy driven ventilation will be investigated in this study through the use of a windcatcher natural ventilation system. Stack driven air rises as it leaves the windcatcher and it is replaced with fresh air from outside as it enters through the positively pressured windward side. 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 the winddriven ventilation alone and on the combined buoyancy and winddriven ventilation.

Topics: Buoyancy , Ventilation
Commentary by Dr. Valentin Fuster
2017;():V007T09A017. doi:10.1115/IMECE2017-71458.

The method of Elementary Effects (EE) is a parameter screening type sensitivity analysis technique that combines advantages of inexpensive one-at-a time methods and expensive variance decomposition based global Sensitivity Analysis (SA) techniques. Most of the sampling strategies for EE either use random sampling or maximize sample spread through oversampling. The Sampling for Uniformity (SU) is the only available strategy that combines the principle of sample spread with the principle of uniformity.

In this work, we proposed modifications to SU (eSU) to further improve sample uniformity. Performance of eSU was compared to that of SU based on uniformity, sample spread, sample generation time, and screening efficiency. Importance of the concept of uniformity was strengthened as eSU outperformed SU across all evaluation criteria. Further, it was found that eSU does not need oversampling and can result in better screening with relatively few trajectories indicating significantly reduced requirement on computational resources.

Commentary by Dr. Valentin Fuster
2017;():V007T09A018. doi:10.1115/IMECE2017-71507.

Methods for reducing surface reflections during PIV measurements are commonly discussed, but the effects of those surface reflections on PIV measurements are generally neglected. In this study, a comparison of light gathering characteristics of an experimental tomographic PIV system is made using a bluff body model that is coated: i) first, with a commercially available flat white aerosol paint and ii) second, with an airbrushed Rhodamine (R6G) fluorescent paint. For each coating, PIV measurements are compared from flow regions that are affected by either direct or indirect reflections. Measurements show that very little incident light is absorbed at white boundaries, producing strong light reflection; this effect, in turn: i) saturates the light signal from far-removed suspended particles and ii) greatly reduces the signal-to-noise ratio for particles situated even close to the receiving optics. By contrast, Rhodamine (R6G) fluorescent paint provides excellent surface reflection mitigation when paired with the 532 nm filters, producing a signal-to-noise ratio sufficient to allow uniform imaging of particles across the entire calibrated volume.

Commentary by Dr. Valentin Fuster
2017;():V007T09A019. doi:10.1115/IMECE2017-71818.

Heat pump water heaters (HPWH) are an energy efficient method for water heating compared to conventional electric water heaters. A wrapped coil around the water tank is often used as the condenser for the heat pump for such applications. Thermal stratification, caused by varying heat transfer rate from the condenser to the water depending on the phase of the refrigerant and the wrap configuration, is often observed inside the tank, especially for HPWHs using CO2 as the refrigerant. The current study investigates the impact of the charging/discharging process on thermal stratification. A series of simulations were conducted based on the draw patterns recommended by the DOE method of test for rating water heater performance. We also analyzed the water circulation patterns during charging/discharging process. The thermal stratification was adversely affected because of the circulation even when the Heat Pump (HP) was operational. It was observed that a relatively higher charge/discharge flow rate disrupts the thermal stratification quickly and thus lowers the supply water temperature. Furthermore, the duration of charging/discharging also plays an important role. It was noticed that the back flow has insignificant effect on the supply water temperature if charging/discharging time is relatively small. However, the effect was obvious for larger water draw flow rates that last for longer time.

Topics: Water
Commentary by Dr. Valentin Fuster

Fluids Engineering: 22nd Symposium on Fundamental Issues and Perspectives in Fluid Mechanics

2017;():V007T09A020. doi:10.1115/IMECE2017-70291.

Recently, the use of flapping plates or ‘flags’ as vortex generators has gained attention for its potential application in heat transfer enhancement in channels. The motion of the flag generates additional turbulence which leads to enhanced heat transfer. However, very few reports deal with the turbulence characteristics inside a channel with flag vortex generators. This paper presents some flow turbulence properties experimentally measured behind a flapping flag. Using multi-hole pressure (cobra) probes, the flow properties behind a flag (M* = 0.42) were measured in a rectangular channel (aspect ratio, α = 1/3) at four levels of flow Reynolds number (Redh = 11.5k–19.7k). Results show that the spectral properties of the flow parameters are closely dependent on the flag oscillation properties. Depending on streamwise location and Redh, measurements reveal that the flag can generate as high as 20% turbulence intensity in the channel centerline, almost six times that of a bare channel at the same Redh. In addition, a streamwise location has been identified where the flag’s oscillation no longer influences the spectral characteristics of the flow. The insights gained from this study may serve as a basis for the design and analysis of systems using flags as turbulence enhancers.

Topics: Flow (Dynamics)
Commentary by Dr. Valentin Fuster
2017;():V007T09A021. doi:10.1115/IMECE2017-70633.

The aerodynamic loads and the flow around an Aspect Ratio 1 circular cylinder in the range of 300K to 400K Reynolds number, pose a surprisingly rich fundamental problem. This aspect ratio demonstrates features from the ‘coin’ limit as well as the high aspect ratio limit. Well-resolved measurements of all 6 components of aerodynamic loads became possible with the Continuous Rotation method. The genesis of the side loads, drag and yawing moment on a yawed aspect ratio 1 cylinder, is examined using 3 different methods. The first is direct pressure sensing on the flat side surface using pressure taps and individual sensors, done on similar setups at two different facilities. This is of course sparse but gives direct quantitative measures for validation. The second is pressure-sensitive paint (PSP), which provides a full distribution of pressure across the surface, with high spatial resolution that is limited only by the optics of the setup. The third is to extract the surface pressure using an algorithm that uses measured three-dimensional velocity data, along with the continuity and Navier-Stokes equations with a streamline-curvature model used to obtain the initial estimate. As possible, the measurements are compared with those computed from first principles using a Navier-Stokes solver. The streamline curvature method is validated against a numerical test case for an infinite cylinder, operated in the Foppl regime. It is then applied to the AR1 cylinder test case, and found to yield satisfactory comparison with interpolated surface plots from point measurements. The single-shot/transient PIV technique is applied to obtain the pressure map on the leeside and windward side of the yawed cylinder. The results are compared to point sensor data and PSP data. Comparisons of all these are shown, and linked to prior aerodynamic load measurements and computations. Agreement is good, with reasons for disagreement and uncertainty identified.

Commentary by Dr. Valentin Fuster
2017;():V007T09A022. doi:10.1115/IMECE2017-70882.

Erosion problems due to droplet impacts are widely encountered in many fields. This may result in deterioration or even failure of the elements, and should be taken into consideration in the design of machines. The impact force is thought of as an essential factor in material erosion. In this paper, a highly sensitive piezoelectric force transducer was employed to record the impact force of the low-speed droplet colliding on an aluminum plate at different impact angles, in combination with a high-speed camera used to capture the impact process of the droplet. The results showed that the experimental setup can measure the impact force evolution precisely and reliably. The peak of the normal impact force increases with the normal velocity quadratically, while the impulse increases with the normal velocity linearly. In addition, a smaller impact angle would lead to longer time duration of the impact force. The high-speed images show that the initial impact patterns of the droplet have similar behavior in the initial impact process, with regardless of vertical or oblique impacts.

Topics: Drops
Commentary by Dr. Valentin Fuster
2017;():V007T09A023. doi:10.1115/IMECE2017-71005.

Unmanned multi-rotor VTOL vehicles have recently gained importance in various applications such as videography, surveillance, search and rescue etc. suited to their small size and relatively cheap construction. Small scale UAVs struggle in providing satisfactory performance in terms of payload, range, and endurance because of higher viscosity-dominated losses, and due to yet to be understood rotor-rotor and rotor-airframe aerodynamic interactions. Viscosity dominated rotational flow field makes most potential flow methods, such as free wake model, invalid. A full N-S based approach for this problem is too expensive. Thus, a multi-rotor aerodynamic interaction study is necessary for understanding crucial phenomena, which will help in developing physics-based models which will be instrumental in multi-rotor UAV performance prediction and design optimization. In present work, a flow visualization and a high-speed stereo Particle Image Velocimetry (SPIV) study is done on two low Reynolds number multi-rotor arrangements with the aim of capturing vortex-vortex, blade-vortex and vortex-duct interactions. The first arrangement is a coaxial rotor in forward flight and another is an in-plane quad-rotor with and without duct. Instantaneous and average PIV data is being presented here with some observations and corresponding interpretations.

Topics: Rotors
Commentary by Dr. Valentin Fuster
2017;():V007T09A024. doi:10.1115/IMECE2017-71640.

To maintain efficiency and high productivity in pipeline operations, it is necessary to keep an updated maintenance program. To accomplish this goal, the use of pigs is a very common task, but not a simple one, since there are uncertainties and risks associated to their passage, especially inside long pipelines. For these reasons, it is important to understand how the motion of the pig impacts the line operation and vice-versa. Therefore, it becomes crucial to accurately predict the pig motion and the fluid flow within the pipeline. To do so, numerical simulations are the easiest and cost-effective way to address such a problem. This paper presents a mechanical model, along with a numerical scheme, to obtain approximate solutions to the resulting initial-boundary-value problem that describes the pig movement in a transient two-phase flow inside a pipeline. The model is discretized using the Flux-Corrected Transport (FCT) method along with the Petzold-Gear method. A numerical simulation was carried out for a foam pig travelling in a typical stratified-pattern two-phase flow in a gas pipeline and the obtained results were compared with the well-known commercial software OLGA.

Commentary by Dr. Valentin Fuster
2017;():V007T09A025. doi:10.1115/IMECE2017-72221.

In this paper, dynamics of the falling droplet under gravity near the wall has been studied numerically. Electrohydrodynamics (EHD) force has been applied to the falling drop to investigate the effect of electric field on its behavior. In order to study the effects of wall boundaries on falling drop dynamics the initial drop is placed close to side walls. The open-source volume-of-fluid solver, Gerris has been used due to its dynamic adaptive grid refinement feature. Three-dimensional study of drops falling under gravity and nonsymmetrical electric field for different ratios of density and viscosity have been studied on the drop dynamics. The numerical results of EHD field and falling drop have been validated with previous analytical, experimental and numerical data. The parameters that govern the dynamics are the Galilee (Ga) and the Bond (Bo) numbers.

Commentary by Dr. Valentin Fuster
2017;():V007T09A026. doi:10.1115/IMECE2017-72479.

Two-phase gas-liquid slug flow is present in several industrial enterprises, especially in the oil industry where the flow of oil, gas and solid particles are frequent. Slug flow is characterized by the intermittent succession of a liquid slug followed by an elongated gas bubble. Some numerical models for the simulation of this flow pattern can be found in the literature. In this work, a slug tracking model is utilized. Simulations for horizontal flows of air and water in pipes with an internal diameter of 26 mm and lengths of up to 1500 m were performed, varying the inflow frequency of the bubbles in the pipe in all simulations so as to verify the influence of the frequency variation on the flow development,. The role of each correlation for the wake effect on the simulator was evaluated along the tube, and three comparisons between the obtained results were made, disregarding the wake effect and using the correlations proposed by Grenier (1997) and Rodrigues (2008). It was shown that the wake effect influences the time required for the flow to develop. In the analyses performed without the application of the wake effect, the flow developed and stabilized faster than when those correlations were applied.

Commentary by Dr. Valentin Fuster
2017;():V007T09A027. doi:10.1115/IMECE2017-72653.

An appendage is a boat tail which is installed at the rear section of the passenger car. An inflatable appendage has been developed to reduce the aerodynamic drag experienced by passenger cars. It can be inflated when driving under high-speed conditions and deflated while parking. In this study, an appendage is designed to maintain the streamlined rear body configuration and reduce flow separation. The profile of this aerodynamic device is based on several mathematical curves such as kappa curve, lame curve, catenary curve and aerofoil curve. Four types of boat tailing devices with different lengths and profiles were installed, and computational fluid dynamics (CFD) analysis was performed under moving ground conditions. The primary objective of this study is to find an optimum shape for the appendage and explain the aerodynamic drag reduction mechanism. Comparisons between the base model and modified models were made on the basis of the coefficient of drag, pressure contours, velocity contours, velocity streamlines and pressure distribution plot. It is shown that significant drag reduction can be obtained with the proposed aerodynamic device. Improvement in fuel efficiency varies based on the profile of add-on device. It is shown numerically that the aerodynamic performance is improved by 18.8% compared to the base model. As a result, the fuel consumption of the modified sedan reduces by 4.5%.

Commentary by Dr. Valentin Fuster

Fluids Engineering: 24th Symposium on Fluid Mechanics and Rheology of Nonlinear Materials and Complex Fluids

2017;():V007T09A028. doi:10.1115/IMECE2017-70236.

To improve the capacity of the two-phase fluid movement through the horizontal pipes, in the turbulent regime, it is necessary to determine as correctly as possible the turbulent drag coefficient and to be estimated the associated energetic balance. For a hydrodynamic flow, the gas-liquid interfacial distribution may have different possible forms, with effect in various flow patterns, due to the different flow rates of the fluid and gas. Usually, we may express the dimensionless pressure gradients as drag coefficients. During the time, some analytical available methods, described the two-phase flows in the horizontal tubes. In previous researches, the author has tested four models: the homogeneous model, the separated-flow model, the mechanistic models, and the drift-flux model. In the present paper, there were selected to accomplish the research, the results obtained from the first three mentioned models. The theoretical and experimental results proved that there are more accurate and more suitable for the actual dedicated applications. The two-phase flow is important in a large variety of applications from engineering, such as natural gas production, oil transportation, the drilling, the food processing, polymer processing industry, pharmaceutical domains, etc. In the case of flow for a single phase, the shear forces on the wall create friction, losses, followed by a pressure decreasing, known as linear hydraulic losses. In the case of the two-phase flows, an additional interaction appears between the two phases, having as consequence a supplementary difficulty in the evaluation of the pressure drop. For the mentioned models, there were considered different flow rates for oil and gas. We vary in laboratory the gas flow rate. For each model the variables were made dimensionless, to enable generalization at different types of horizontal tubes, pipelines, with different diameters. The accuracy of the developed correlations from this paper is evaluated by comparing the predictions of previous calculations and correlations with the measured and obtained results, and with the data from technique literature. The relation between the pressure gradient and mass flow is expressed also in dimensionless form, as a relation between the drag factor and the Reynolds number, considered for the two-phase flow. This one was correlated with the generalized Reynolds number, with values from 6000 to 140000. For this Reynolds range were tested in the laboratory more than 200 measurements points, for each of the three selected models. The analyzed cases allowed the estimation in a proper manner of the accuracy of the drag turbulent factor, by calculating all 10 statistical parameters, for pipes up to 80 cm.

Commentary by Dr. Valentin Fuster
2017;():V007T09A029. doi:10.1115/IMECE2017-70540.

Tests are conducted in a low-pressure combustion chamber of 3 × 2 × 4.65m3 in volume to investigate the effect of low pressure on the drainage and expansion characteristics of AFFF (Aqueous Film-Forming Foam). A manipulator equipment with the frequency of 4 Hz and the amplitude of 32cm is designed for the foaming of AFFF in the chamber. The parameters of expansion and drainage ratio are obtained under two different ambient pressure of 101kPa and 30kPa. Two fluorocarbon surfactants contained commercial AFFF (AFFF1 is type of 3% and AFFF2 is the type of 6%) that were used in precious studies are both diluted into different quality percentage resolutions, and then achieve foaming in a 130ml measuring cylinder with a cone bottom. The foaming expansion ratio and drainage time are obtained based on the recorded videos. Experimental results show that the expansion ratio of both AFFF1 and AFFF2 resolutions (the expansion ratio <6) is lower under the pressure of 30kPa than that under 101kPa. The drainage time (25% and 50%) of AFFF1 is increasing in the lower pressure environment. On the contrary, 50% drainage time of AFFF2 is shorter under 30kPa than that under 101kPa, but 25% drainage time of AFFF2 is almost the same under two ambient pressures. The variations under low pressure environment are obvious and various from each other, but the further tests should be conducted to reveal and explore the mechanism.

Topics: Pressure , Drainage
Commentary by Dr. Valentin Fuster
2017;():V007T09A030. doi:10.1115/IMECE2017-70722.

Formation of the boundary layer in the laminar flow of Herschel–Bulkley fluid between parallel plates is taken into consideration. In particular, the study is focused on the flow of the shear thinning and shear thickening fluids past a partial vertical wall in between the plates. Upon numerically solving the continuity and momentum equations the flow is analyzed throughout the domain using a finite volume scheme. The shear stress at the wall together with velocity distribution are evaluated and compared with experimental results for several values of Herschel-Bulkley coefficients for fluidity and flow behavior index.

Commentary by Dr. Valentin Fuster
2017;():V007T09A031. doi:10.1115/IMECE2017-70832.

As a common phenomenon in liquid motions, sloshing usually happens in a partially filled liquid tank of moving vehicle or structure. The objectives of this paper are to study sloshing behavior in rigid tank and deformable tank, and to develop a better performance baffle design in the tank under seismic excitations. The tank is surged with a sinusoidal oscillation about horizontal x-direction. The hydro-elasticity effect of sloshing pressure on the tank wall was taken into consideration due to the fluid-structure interaction between impact pressures and tank structures. ABAQUS finite element program using Coupled Eulerian-Lagrangian (CEL) technique was employed to simulate fluid sloshing. The sloshing phenomenon was studied in rigid tank and deformable tank models with three different water levels, and the effect of wall thickness of the deformable tank on sloshing behavior was discussed. One way to minimize the effect of sloshing in a tank, baffles are used and installed in the middle of the tank, and then various heights and material types of baffle were evaluated. The simulation results show that higher water level case creates greater pressure impact on the tank wall than lower water level case, and the elasticity of the tank structure would reduce the impact pressure of the wall. For the simulation tank model with size of 1m (H) × 1m (W) × 0.2m (D), better performance baffle was found to be the one with the height of 0.35m and was made of acrylic material. Moreover, the conclusion of this study can be extrapolated to other dimensions of the model based on similarity theory. This paper also can serve as an aid in further studying sloshing phenomenon. The findings of this study can be applied to restrain or minimize sloshing motions inside a tank.

Commentary by Dr. Valentin Fuster
2017;():V007T09A032. doi:10.1115/IMECE2017-70994.

This paper presents the preliminary findings of an optimization study of transversal flow strength in tube cross-sections with arbitrary external contours and an internal inclusion. The eccentric tube contours are generated through a one-to-one mapping of a base circular cross-section. The working fluid obeys the non-linear modified Phan-Thien-Tanner (MPTT) constitutive model. The computation of the total transversal flow rate leads to the determination of effective cross-sections for heat transfer enhancement.

Commentary by Dr. Valentin Fuster
2017;():V007T09A033. doi:10.1115/IMECE2017-71001.

The interplay of yield stress and elasticity on the temperature field and heat transfer rates in tube flow of elastoviscoplastic (EVP) fluids is investigated in this paper. The constitutive structure of the EVP fluid obeys a linear combination of the Phan-Thien-Tanner model for viscoelastic fluids and the Bingham model for viscoplastic fluids. The momentum and energy equations are solved asymptotically under constant wall heat flux. The fluid behavior is governed by the Weissenberg Wi and the Bingham N numbers.

Commentary by Dr. Valentin Fuster
2017;():V007T09A034. doi:10.1115/IMECE2017-71184.

In order to apply the multi-particle collision dynamics (MPCD) method to a magnetic particle suspension, we have elucidated the dependence of the translational and rotational Brownian motion of magnetic particles on the MPCD parameters that characterize the MPCD simulation method. We here consider a two-dimensional system composed of magnetic spherical particles in thermodynamic equilibrium. The diffuse reflection model has been employed for treating the interactions between fluid and magnetic particles. In the diffuse reflection model, the interactions between fluid and magnetic particles are transferred into the translational motion more strongly than into the rotational motion of magnetic particles. The employment of relatively small simulation time steps gives rise to a satisfactory level of the translational Brownian motion. The activation level of the Brownian motion is almost independent of both the size of the unit collision cell and the number of fluid particles per cell. Larger values of the maximum rotation angle induce stronger translational and rotational Brownian motion, but in the present magnetic particle suspension the range between around π/4 and π/2 seems to be reasonable. We may conclude that the MPCD method with the simple diffuse reflection model is a feasible simulation technique as the first approximation for analyzing the behavior of magnetic particles in a suspension. If more accurate solutions regarding the aggregate structures of magnetic particles are required, the introduction of the scaling coefficient regarding the interactions between fluid and magnetic particles can yield more accurate and physically reasonable aggregate structures in both a qualitative and quantitative meanings.

Commentary by Dr. Valentin Fuster
2017;():V007T09A035. doi:10.1115/IMECE2017-71413.

Reflow soldering process is widely implemented in the electronics industry. This method allows the attachment of electronic components to a printed circuit board (PCB) through the melting of solder paste, which makes the interconnection between them. The reflow soldering process must ensures the correctly melting of the solder paste and heating of the adjoining surfaces, without the electronic components suffer overheating or any other type of damage.

Solder paste is the most widespread material in the SMT (Surface Mount Technology) process using reflow soldering. An ideal solder paste will increase production efficiency, decreasing the amount of defects associated with the reflow soldering process. However, several factors affects the performance of the solder paste, from rheology, printability, and reliability to the adhesion strength of components and the ability to avoid defects related to reflow. Therefore, all these factors need to be considered during the selection of a solder paste for a specific application.

The rheological properties were determined using both a double cylinder (PHYSICA-RHEOLAB MC1) and a double plate (Malvern) rheometers. The later enable the determination of viscoelastic properties.

The present paper analyses the rheological behavior of a SAC405 solder paste, a mixture containing a metal alloy powder (25–45 μm) and a flux which at its base is a resin. The tests were carried out at conditions (temperature and shear rate) of relevance to the printing process. The results obtained show that the paste viscosity closely follows the Herschel-Bulkley model and shows a thixotropic behavior without fully recovery between applications. In addition, the viscosity decreases with the increase of shear rate confirming that the solder paste is a non-Newtonian fluid, shear thinning in behavior. The oscillatory tests have shown that the transition from elastic to viscous behavior occurs at a shear stress above 35 Pa. On the other hand, the creep/recovery test confirms that the level of solicitation influences the capacity of recovery of the solder paste.

Topics: Solders , Rheology
Commentary by Dr. Valentin Fuster
2017;():V007T09A036. doi:10.1115/IMECE2017-72545.

The traditional lubricating materials used in space, such as mineral oils, polyol ester, PFPE, Pennzane, etc. have limited lifetimes in vacuum due to the catalytic degradation on metal surfaces, high vaporization at high temperatures, dewetting, and other disadvantages. The lubricants for the space applications must have vacuum stability (i.e. low vapor pressure), high viscosity index (wide liquid range), low creep tendency, good elastohydrodynamic and boundary lubrication properties, radiation atomic oxygen resistance, optical or infrared transparency. Thermophysical and chemical analyses are another important required set of tests for the newly developed space lubricants. Some of these properties for liquid lubricants are base oil and additive volatility, creep, surface tension, viscosity, chemical composition, weight loss, density, vapor pressure, etc. Unfortunately, the properties such as non-linearity in the rheological behavior of the lubricants were not studied well for newly developed systems. The rheological properties are crucial to analyzing thermodynamic and energy dissipative aspects of the lubrication process. The rheological measurements for the newly developed ionic liquid nanolubricant were conducted using rotational rheometer AES G-2 of “parallel-plates” mode.

Commentary by Dr. Valentin Fuster
2017;():V007T09A037. doi:10.1115/IMECE2017-72547.

A rheometric characterization of the functional Polyurethane (PU) foam composite with and without solid additives (aluminum flakes) were experimentally measured using a computer controlled mechanical spectrometer (rheometer) ARES-G2. It is determined that PU composite exhibits a strong time thickening and shear thinning behavior. The rheological behavior of this composite can be described with the power-law generalized non-Newtonian fluid model. The rheometric tests showed that the PU/Al mixture exhibits thermal thickening and shear thinning behavior with the yield stress. The system can be described with the power-law generalized non-Newtonian fluid (Ostwald-de-Waele) model. The effective viscosity of PU composite increases with both the testing time (exponentially) and the solid content (polynomial) in the mixture.

Commentary by Dr. Valentin Fuster

Fluids Engineering: 26th Symposium on Industrial Flows

2017;():V007T09A038. doi:10.1115/IMECE2017-70165.

An experimental study on ESP boosting pressure under air-water flow with/without surfactant injection is presented. The experimental facility comprises of a 3-inch-diameter stainless steel liquid loop and ½-inch-diameter gas loop. A radial-type ESP with 14 stages assembled in series was installed in the testing bench. Pressure ports were drilled at inter-stage to measure the stage-by-stage boosting pressure. Surfactants, isopropanol (IPA) were injected to change interfacial properties of working fluids. Experiments were carried out with mapping and surging test schemes to evaluate pump behaviors at different operational conditions. ESP pressure increment under single-phase water flow agrees well with manufacture curves. For mapping tests without surfactant injection, ESP performance suffers from a severe degradation as gas flow rate increases. High gas entrainment rate causes oscillations of liquid flow rate and pump boosting pressure. A sudden drop of ESP pressure increment, termed as pressure surging, occurs at the critical inlet gas volumetric fraction (GVF). At higher rotational speeds, the critical GVF is higher. With surfactant injection, ESP boosting pressure improves significantly. With different GVFs, only mild degradation was observed. Pressure surging phenomenon disappeared. Further, liquid flow rate and pump boosting pressure are more stable at high GVFs compared to experimental data without surfactant injection.

Commentary by Dr. Valentin Fuster
2017;():V007T09A039. doi:10.1115/IMECE2017-70327.

Growing demands for higher specific output power in turbomachinery applications have drawn attention to aerodynamic design philosophy for a single-stage transonic centrifugal compressor with higher pressure ratios. As Part 1 of numerical efforts, some fundamental approaches in aerodynamic design were carried out in a classical 6:1 pressure-ratio compressor design of 1970’s which was selected as a baseline. The effects of the impeller blade angle distribution, the addition of the splitter blade, the changes of the tangential divergence angle of the channel-wedge diffuser and some tweaks in diffuser vane shapes near the trailing-edge were investigated in steady-state RANS CFD solutions with the conventional mixing plane interface. New blade angle distributions together with the introduction of splitter blades in the impeller brought significant improvements in the compressor pressure ratio, efficiency and operability, thanks to reduced shock strengths and enhanced blade loadings in the spanwise direction. Helicity contours on the cross sectional planes in the impeller support the benefits observing a power balance among the shroud passage vortex, the blade vortices and the tip leakage vortex. With a reduced tangential divergence in the channel-wedge diffuser passage from the original design, an impressively extended surge margin was obtained. It was confirmed from the helicity contours that a streamwise vortex structure at the entrance region of the diffuser vane plays a key role in the range of operation. A diffuser vane shape with the curved pressure surface near the trailing-edge provided a slightly higher pressure ratio and efficiency around design flow than that with the original cut-off trailing-edge. An elliptical trailing-edge diffuser vane showed rather performance drops because of the counter-clockwise hub vortex breakdown near the suction surface, resulting in less flow diffusion. Through investigations of a set of design cases, two final compressor designs, differing in the diffuser vane shape near the trailing-edge, were obtained within the work scope of the present study. However, selecting one of the two will depend on design duties for the following component because of the level of exit swirls and their rate of changes over the flow rates.

Topics: Compressors , Design
Commentary by Dr. Valentin Fuster
2017;():V007T09A040. doi:10.1115/IMECE2017-70672.

Radioactive waste resulting from production of weapons is stored at five U.S. Department of Energy (DOE) locations. The waste characteristics range from fluid to sludge to granular salts with radiation levels exceeding 10,000 rad/h.

Innovative tools are used to remotely remove the solidified radioactive waste from underground storage tanks. When available, commercial systems are evaluated for waste dislodging and retrieval applications. A waste dislodging and sluicing system developed to dislodge and fracture deposits of ore in underground mining, called a borehole miner, was evaluated by Pacific Northwest National Laboratory (PNNL) and Waterjet Technology, Inc., for removing solidified nuclear waste stored in underground tanks. This compact system may be installed in tanks via small diameter risers and has the capability to both dislodge and retrieve in a single unit. The borehole miner arm includes an extendible nozzle that operates at high pressure using either water or slurry as the dislodging fluid, while providing a focused high-pressure jet to dislodge solidified material. The sluicer nozzle is attached to a retractable arm that can extend and angle to enhance dislodging in specific areas of the tank by changing the standoff distance.

This paper describes the borehole miner system and presents results of experiments to evaluate its ability to dislodge solidified saltcake and sludge materials. Tests were conducted with a stationary jet to evaluate the potential to develop an extendible-nozzle borehole miner system for deployment to dislodge radioactive saltcake and sludge wastes stored in underground storage tanks. The tests were successful and identified ranges of parameters for jet diameter and standoff distance applicable for waste remediation. For saltcake simulants, erosion models were developed that represent the data.

Commentary by Dr. Valentin Fuster
2017;():V007T09A041. doi:10.1115/IMECE2017-70884.

Reverse Osmosis (RO) is a process whereby solutes are removed from a solution by means of a semipermeable membrane. Providing access to clean water is one of our generation’s grand engineering challenges, and RO processes are taking center stage in the global implementation of water purification technologies. In this work, computational fluid dynamics simulations are performed to elucidate the steady state phenomena associated with the mass transport of solution through cylindrical hollow fiber membranes in hopes of optimizing RO technologies. The Navier-Stokes and mass transport equations are solved numerically to determine the flow field and solute concentration distribution in the hollow fiber membrane bank, which is a portion of the three-dimensional feed channel containing a small collection of fibers. The k-ω Shear Stress Transport turbulence model is employed to characterize the flow field. Special attention is given to the prediction of water passage through hollow fiber membranes by the use of the solution-diffusion model, which couples the salt gradient, water flux, and local pressure at the membrane surface. This work probes hollow fiber membrane arrangement in the feed channel by considering inline and staggered alignments. Feed flow rates for Reynolds number values ranging between 400 and 1000 are considered. Increased momentum mixing within the feed channel solution can substantially enhance the system efficiency, and hollow fiber membrane arrangements and feed flow rates dictate the momentum mixing intensity. Velocity and vorticity iso-surfaces of the flow domain are presented in order to assess the momentum mixing achieved with various hollow fiber membrane arrangements and flow rates. The total water permeation rate per hour is calculated to compare system efficiencies, and the coefficient of performance is calculated to compare membrane performance relative to the necessary power input, both for the various hollow fiber membrane arrangements and feed flow rates.

Commentary by Dr. Valentin Fuster
2017;():V007T09A042. doi:10.1115/IMECE2017-71142.

The transport processes in the mixing of either two gases or two miscible liquids in a T-junction are investigated numerically. Both laminar and turbulent flow fields are considered. The 3-D time-dependent flow fields are calculated for the T-junction (of two circular cross-section pipes that meet orthogonally at the junction). For turbulent flow regimes, the large eddy simulation (LES) technique is employed. In the 3-D mathematical model, the transport of species is described by the species conservation equations. The results obtained by the numerical simulations are verified with available experimental data in the literature for methane-air mixing in a T-junction. The effect of variation of the value of turbulent Schmidt number is investigated. Temporal concentration fluctuations are calculated and are compared to the spatial fluctuations. The mixing of two miscible liquids (water and peracetic acid-water mixture) are also investigated for the laminar and turbulent flow fields (using the LES technique). The mixing behavior of two gases and two miscible liquids in a T-junction are compared and contrasted for both laminar and turbulent flows.

Topics: Gases , Junctions
Commentary by Dr. Valentin Fuster
2017;():V007T09A043. doi:10.1115/IMECE2017-72255.

Black powder (BP) is a typical contaminant usually found in sales gas pipelines. Its presence may cause major operational and maintenance issues including blockage of sensors and filters, erosion of pipeline bends and compromise the sales gas quality. There has been little known about its composition and sources of formation in the gas pipelines. Understanding its characteristics is considered crucial for appropriate mitigation planning and execution of smooth pipelines operations. Black powder samples collected from sales gas pipelines network of a Middle Eastern gas company are analyzed using scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDX) and x-ray diffraction (XRD) methods for surface analysis and phase identification of the crystalline material. These analyses revealed variation in size distribution and shape of the BP samples. Likewise, most of the BP particles were found agglomerated. EDX analysis of the sample has shown presence of iron as the most abundant element after sulfur. XRD patterns can be indexed with both iron oxides and sulfides suggesting presence of moisture and hydrogen sulfide in the gas.

Topics: Pipelines , Sales
Commentary by Dr. Valentin Fuster

Fluids Engineering: 3rd Forum on Multiphase Flow With Bio-Applications

2017;():V007T09A044. doi:10.1115/IMECE2017-71608.

The formation and breakup of a liquid jet in air with gravity acting perpendicular to the direction of the jet is studied computationally. The liquid jet follows a parabolic path due to the influence of gravity which curves the jet trajectory. Both symmetric and asymmetric perturbations develop on the liquid surface which lead to jet breakup with varying droplet size distribution. The limiting length of the jet at breakup increases with increase in the Weber number and Ohnesorge number. At higher value of Weber number, the liquid jet traverses a longer horizontal distance when released from the same vertical height. Increasing the Bond number leads to a significant increase in the curvature of the jet trajectory. The volume of drops produced varies temporally for a given Weber number and decreases with the increasing value of Weber number. The detached drops undergo rolling motion as well as shape oscillations as they continue to fall on their trajectories.

Topics: Gravity (Force) , Jets
Commentary by Dr. Valentin Fuster

Fluids Engineering: Microfluidics 2017 - Fluid Engineering in Micro- and Nanosystems

2017;():V007T09A045. doi:10.1115/IMECE2017-70342.

Circulating Tumor Cells (CTCs) have been considered as important biomarkers for cancer prognosis and treatment. However, there are only tens of CTCs in one billion of healthy blood cells. This CTC rarity challenge has been addressed by microfluidics technology that sheds light on efficient CTC detection and isolation. Using antibodies or aptamers to capture CTCs is one of the strategies for CTC isolation. A lot of work has been carried out to improve CTC capture efficiency and purity (i.e., specificity). The main consideration to optimize microfluidic device performance includes increasing surface-area-to-volume ratio and reducing shear stress, both of which are closely related to the interaction between CTCs and the microfluidic device. Here we report a detailed study on the interactions between CTCs and aptamer-functionalized microposts in a microfluidic device. We have evaluated the distribution of captured CTCs around a micropost. In addition, simulation was conducted to model CTC capture patterns around microposts. We found the simulated CTC capture pattern largely agree with the experimental results. The simulation methodology could be applicable for other affinity-based CTC isolation devices and approaches. The goal of the study is to improve the microfluidic device performance and provide a rapid and economical way to optimize the geometry design of the microfluidic devices for CTC isolation.

Commentary by Dr. Valentin Fuster
2017;():V007T09A046. doi:10.1115/IMECE2017-70544.

This study compares the hydraulic performance of rectangular micro heat sinks (MHS) with different in-line and staggered arrangements of micro pin fins (MPF). With fixed MHS dimensions of 50 × 1.5 × 0.1 mm3 (1 × w × h), the height (H) and diameter (D) of MPFs are both set to be 0.1 mm which corresponds to a fixed H/D ratio of 1 in all cases. Four in-line and four staggered arrangements of MPFs with alternative horizontal and vertical pitch ratios (SL/D and ST/D) of 1.5 and 3 are considered. Streamline profiles are used to illustrate the flow patterns and wake regions. Using ANSYS FLUENT v.14.5 for this single phase study, the simulations are done at five Reynolds numbers of 20, 40, 80, 120 and 150, ensuring the flow remains in the laminar flow regime. Considering water as the coolant, a constant heat flux of 30 W/cm2 is applied through the bottom surface of the MHS and the MPFs liquid interacting surfaces. The results show a great dependency of the evaluating parameters on the arrangement type, geometrical specification and Reynolds numbers. For pressure drop, clear comparison could be made regarding each of the geometrical specifications. However, the trends with friction factor depend on geometrical specification and Reynolds number at the same time.

Topics: Fins , Heat sinks
Commentary by Dr. Valentin Fuster
2017;():V007T09A047. doi:10.1115/IMECE2017-71484.

Arrays of carbon nanotubes (CNTs) have shown significant promise for delivering biomolecules into cells with high efficiency and low toxicity. In these applications, biomolecules are flowed from a large fluid reservoir, through the lumens of vertically-aligned, open-ended CNTs, and into cells cultured over top of the CNTs on the other side. Over the course of several transfection experiments, it was discovered that biomolecule delivery varied considerably depending on the type of biomolecule being delivered. It was also inferred that the number of CNTs the cells covered would affect the transfection rate. In this work, an experiment was designed and conducted to visually characterize fluid flow through these CNT arrays and other nanoporous membranes. The experiment utilizes a 3D printed flow device consisting of anodized alumina oxide (AAO) membranes and restricts flow to a predefined circular area. Flow data was taken by measuring the intensity of fluorescent dye as it diffused through the AAO membrane. The intensity measurements were then plotted as a function of time from which diffusion times constants were calculated. This work establishes a platform technique for visualizing fluid transport through AAO membranes, which can be applied to CNT arrays, and allow for the testing of the effects of other parameters on flow.

Commentary by Dr. Valentin Fuster
2017;():V007T09A048. doi:10.1115/IMECE2017-71542.

Recent advent of Aqueous-Two-Phase-System (ATPS), more biologically friendly compared to conventional oil-water systems, has shown great potential to rapidly generate aqueous droplets without tedious post-processing. However, understanding of underlying physics of droplet formation in ATPS is still in its infancy. In this paper, we investigate hydrodynamic behaviors and mechanisms of all-aqueous droplet formation in two flow-focusing droplet generators. Two incompatible polymers namely polyethylene glycol (PEG) and dextran (DEX) are mixed in water to make ATPS. The influence of inlet pressures and flow-focusing configurations on droplet sizes, and thread breakup length is studied. Flow regime mapping for two different configurations of droplet generators possessing junction angles of 30° and 90° is also obtained. The results show that droplet size is very susceptible to the junction angle while inlet pressures of the PEG and DEX flows readily control four main flow regimes including back flow, dripping, jetting and stratified.

Topics: Physics , Drops
Commentary by Dr. Valentin Fuster
2017;():V007T09A049. doi:10.1115/IMECE2017-71611.

Important industrial processes including oil extraction, mineral processing and wastewater treatment, rely on the separation of buoyant particles from a liquid phase. The capillary attraction between floating particles and fixed collectors can be leveraged to improve the efficiency of the separation process. The capture of an advected floating particle by a fixed cylindrical obstacle is due to direct interception and capillary attraction for sub-millimeter particles. The capillary attraction stems from the local deformation of the air/liquid interface. Previous work has established that floating particles placed on the surface of a still liquid bath, spontaneously move toward or away from one another depending on their surface properties. More recently, a numerical study has considered the competition between hydrodynamic and capillary interactions as floating particles are advected past a fixed cylinder. This seminal work revealed that capillary interactions can enhance the capture of particles at low flow velocity. Building on these results, we develop a numerical approach to study the interactions between advected particles and an array of obstacles. The results are obtained with the finite element modeling of the fluid flow in the channel, in presence of obstacles. Assuming that the particles do not alter the fluid flow, we solve the momentum conservation equation for each advected particle using the Basset Boussineq Oseen equation. If contact occurs, we assume that the particle is captured by the obstacle, thus neglecting inertial effects. We demonstrate that an array of obstacles can capture most of the particles traveling down the channel. First, we show that the efficiency of an array of obstacles, i.e. the fraction of particles captured depends on interfacial and hydrodynamic effects. For example, parameters such as the Reynolds number, capillary length, contact angle and collector size influence the trapping efficiency. Second we vary the geometry of the array and seek to minimize the amount of static material needed to get the maximum efficiency. These results provide guidelines for the design of efficient filters.

Commentary by Dr. Valentin Fuster
2017;():V007T09A050. doi:10.1115/IMECE2017-71652.

With the development of modern industry, the separation of suspended droplets from the gaseous flow has become increasingly important. In many industrial applications it is required to control the fine liquid droplets concentration in moving gaseous media. Refrigeration and Heating Ventilation Air Conditioning (HVAC) system is one major application. Electrostatic Precipitator (ESP) can be adopted for separation of fine droplets in gases, since corona discharge could charge these droplets, then use of electrostatic force to implement separation and collection. However, separation of droplets in gaseous flow is a complex process which is combination of electrostatic and flow field. The current study investigates effects of key parameters like applied voltage, flow temperature, flow velocity and particle’s size on particles separation efficiency using a wire-cylinder assembly. Monodisperse particles are used in this study where above mentioned parameters have shown significant effect on the separation efficiency.

Commentary by Dr. Valentin Fuster
2017;():V007T09A051. doi:10.1115/IMECE2017-71681.

This work computationally investigates local flow behavior in tree-like flow networks of varying scale, bifurcation angle, and inlet Reynolds number. The performance of the tree-like flow networks were evaluated based on pressure drop and wall temperature distributions. Microscale, mesoscale, and macroscale tree-like flow networks, composed of a range of symmetric bifurcation angles (15, 30, 45, 60, 75, and 90°) and subject to a range of inlet Reynolds numbers (1000, 2000, 4000, 10000, and 20000) were evaluated. Local pressure recoveries were evident at bifurcations, regardless of scale and bifurcation angle which may result in a lower total pressure drop when compared with traditional parallel channel networks. Similarly, wall temperature spikes were also present immediately following bifurcations due to flow separation and recirculation. The magnitude of the wall temperature increases at bifurcations was dependent upon both bifurcation angle and scale. When compared with mesoscale and macroscale flow networks, microscale flow networks resulted in the largest local pressure recoveries and the smallest temperature jumps at bifurcations. Thus, while biologically-inspired flow networks offer the same advantages at all scales, the greatest performance increases are achieved at microscale.

Commentary by Dr. Valentin Fuster
2017;():V007T09A052. doi:10.1115/IMECE2017-71698.

Most flow visualizations and flow measurements to understand particle mobility in porous media are typically performed in transparent microfluidic devices (micro-models) with 2D pore-throat networks. Nano-particle mobility studies to date have been limited to micro-models made of transparent thermoplastic or silicone-based materials. In an effort to fabricate materials close to reservoir rock, ceramic micro-model has been designed and micro fabricated by our group to study nano-particle transport in rock-based ceramic micro-model. A Confocal Micro-Particle Image Velocimetry (C-μPIV) technique augmented with associated post processing algorithms [1] is used in obtaining 3D distributions of nano-particle velocity and concentration at selected locations of the ceramic micro-model. Furthermore, a novel in-situ, nondestructive method of measuring 3D geometry of non-transparent ceramic micro-model is described and validated. The particle experiment uses 860 nm fluorescence labeled polystyrene neutrally buoyant, and electrically neutral nano-particles. The data was acquired using confocal laser-scanning microscope to quantify 3D particle transport at selected observation locations. In addition, fluorescence microscope was used to measure in-situ geometry of porous media. Results of detailed 3D measurements of nano-particle velocity and particle concentration from experiment conducted at a constant flow rate of 30 nL/min in the rock-based micro-model are presented and discussed. Particle velocities range from 0 to 20.93 μm/sec in magnitude, and average concentration range from 6.02 × 103 to 6.79 × 103 particles at inlet channel while velocities range from 0 to 73.63 μm/sec and concentration range from 4.9 × 101 to 1.45 × 103 particles at selected observation locations of the ceramic micro-model. 3D velocity fields at selected locations also indicate that mean velocity closer to the top wall is comparatively higher than bottom wall, because of higher planar porosity and smooth pathway for the nano-particles closer to the top wall. The three dimensional micro-model geometry reconstructed from the fluorescence data can be used to conduct numerical simulations of the flow in the as-tested micro-model for future comparisons to experimental results after incorporating particle transport and particle-wall interaction models.

Commentary by Dr. Valentin Fuster
2017;():V007T09A053. doi:10.1115/IMECE2017-72288.

The potential applications of micromixers continues to expand in the bio-sciences area. In particular, passive micromixers that may be used as part of point-of-care (POC) diagnostic testing devices are becoming commonplace and have application in developed, developing, and relatively undeveloped locales. Characterizing and improving mixing efficiency in these devices is an ongoing research effort. Micromixers are used in some lab-on-chip (LOC) devices where it is often necessary to combine two or more fluids into a mixed solution for testing or delivery. The simplest micromixer incorporates a tee junction to combine two fluid species in anti-parallel branches, with the mixed fluid leaving in a branch perpendicular to the incoming branches. Micromixers rely on two modes of mixing: chaotic advection and molecular diffusion. In micro-mixers flow is typically laminar, making chaotic advection occur only via induced secondary flows. Hence, micromixers, unless carefully designed, rely almost exclusively on molecular diffusion of fluid species. A well designed micromixer should exhibit significant chaotic advection; which is also a sign of large strain rates and large entropy generation rates.

This paper describes the development of an analytical relationship for the entropy generation rate and the mixing efficiency as function of the outgoing branch Reynolds number. Though there has been extensive research on tee junctions, entropy generation, and the mixing efficiencies of a wide variety of micromixers, a functional relationship for the mixing efficiency and the entropy generation rate has not been established. We hypothesize a positive correlation between the mixing index and the entropy generation rate. The worked described here establishes a method and provides the results for such a relationship.

A basic tee junction with square cross sections has been analyzed using computational fluid dynamics to determine the entropy generation rate and outgoing mixing efficiencies for Reynolds numbers ranging from 25–75. The mixing efficiency is determined at a location in the outgoing branch where the effects of molecular diffusive mixing is minimized and chaotic advective mixing is the focus. The entropy generation rate has been determined for the indicated range of Reynolds number and decomposed into its viscous and diffusive entropy terms. The functional relationships that have been developed are applicable for micromixer design and serve as a reference for more complex passive micromixer designs.

Topics: Entropy , Junctions
Commentary by Dr. Valentin Fuster
2017;():V007T09A054. doi:10.1115/IMECE2017-72297.

In recent years, particle hydrodynamic focusing and ordering in a confined microchannel has been developed as a promising technique in lab-on-a-chip systems such as microparticle/cell separation, on-chip flow cytometry and detection. During the focusing, the uniformly distributed finite-sized particles from the channel inlet migrate across streamlines to several equilibrium positions according to the balance between series of hydrodynamic lift forces. While most studies in literature focus on single particle’s motion in the hydrodynamic focusing process by considering particle-liquid interactions, very few of them investigate particle-particle interactions, which is important in particle ordering and manipulation at high throughput. In this study, we use an immersed boundary (IB) - lattice Boltzmann (LB) coupled model to investigate the dynamic behaviors of a particle pair traveling through a square microchannel. The utilized numerical model retains the advantages of both LBM and IBM, which can accurately model the momentum exchange between liquid and particles, and conveniently treat complex geometry and movement of liquid-particle surfaces. By conducting numerical simulations, the time-dependent dynamic behaviors of particle pairs, including trajectories and interactions from initial rest condition to final quasi-equilibrium condition are obtained. Influences of important factors, such as Reynolds number and particle sizes on particles’ motions are discussed and the underlying physical mechanisms of particle-particle interactions are revealed in-depth.

Commentary by Dr. Valentin Fuster
2017;():V007T09A055. doi:10.1115/IMECE2017-72314.

A durable superhydrophobic coating formulation with epoxy binder thermoset was used to coat on surfaces, which provide high quality for corrosion protection, reduced biofouling and improved hydrodynamic behavior. The single and double layers coating of these nanostructured epoxy were fabricated and coated on a novel quartz crystal microbalance (QCM) technique to investigate their hydrophobic properties. Different static and dynamic wettability were obtained and characterized by evaluating the electrical impedance of QCM coated with nanostructured epoxy in air and DI water. It was found that QCM is able to quantitatively characterize the hydrophobicity of these nanostructured polymer surfaces. For double layer coating, the frequency shift in DI water was smaller in comparison to the single layer one. The reduction in mechanical impedance of QCM clearly demonstrates the effect of enhanced hydrophobicity for both single and double layers. The experimental results show that the hydrophobic surface resulted in smaller mechanical impedance loading, while the hydrophilic surface exerted much larger mechanical impedance. The outcome of this research will build a solid foundation for the further improvement of vehicles coated with superhydrophobic surfaces operating in water and increased equipment life.

Commentary by Dr. Valentin Fuster
2017;():V007T09A056. doi:10.1115/IMECE2017-72328.

Passive micromixers have application in the biosciences area. In particular, passive micromixers that may be used as part of point-of-care (POC) diagnostic testing devices are becoming common-place and have application in developed, developing, and relatively undeveloped locales. Characterizing and improving mixing efficiency in these devices is an ongoing research effort. Different channel geometries and flow obstacles lead to varying degrees of mixing effectiveness and serve to increase chaotic advective mixing in contrast to the molecular diffusive mixing that occurs even in the absence of these obstacles. Entropy is generated due to these, and other, irreversible processes. Efficient micromixer design is of interest to biomedical and mechanical engineers working in the biosciences area. The entropy generation rate, we contend, can provide an aid in determining how thoroughly mixed fluids in the channel have become, as well as provide insight into improving channel design to maximize desired outcomes, such as mixing, and minimizing losses due to heat transfer and power consumption.

In this paper, we focus our analysis on numerical simulations conducted using computational fluid dynamics (CFD) on a supercomputer-cluster to do simulations with extended mesh refinement and very small residuals. This enabled us to test a wide range of flows with varying Reynolds numbers. The configuration of flow and species parameters within the simulations were compared to experimental results to confirm their validity.

We show that varying the geometry of the channel can lead to a measurable increase in entropy generation via the Second Law of Thermodynamics. Further, we show that this increase in entropy is linked to mixing from obstacle-induced chaotic advection and diffusion. We provide evidence of a positive correlation between the efficiency of the mixing process and entropy generation. These findings will aid in the design of more efficient portable health care-related devices, particular in remote or underdeveloped regions where power utilization is a critical concern.

Commentary by Dr. Valentin Fuster

Fluids Engineering: Symposium on CFD Applications for Optimization and Controls

2017;():V007T09A057. doi:10.1115/IMECE2017-70012.

The detailed investigation of flow behavior inside the combustion chamber and performance of engine is most challenging problem due to constraints in Experimental Data collection during testing; However, Experimental testing is essential for establishment of correlation with CFD Predictions. Hence, the baseline engine was tested at different load conditions and validated with CFD results, before it was optimized for performance improvement. The objective of the CFD Prediction was not only to optimize performance (Fuel Efficiency, Power, Torque, etc.) & Emissions Reduction, but also to assess feasibility of Performance Upgrade Potential.

In the present CFD study, surface mesh and domain was prepared for the flame face, intake valve, intake valve seat, exhaust valve, exhaust valve seat and liner for closed volume cycle, between IVC and EVO using CFD code VECTIS. Finally simulations for three different load conditions were conducted using VECTIS solver. Initially, in-cylinder pressure vis a vis crank angle prediction was carried out for 100%, 75% and 50% load conditions. Then the fine tuning of (P-ϴ) diagram for different load conditions was conducted by varying different combustion parameters. Further, the engine performance validation was carried out for rated and part load conditions in terms of, IMEP, BMEP, break specific fuel consumption and power output, while NOx mass fractions were used to convert the NOx to g/kWh for comparison of emission levels with the test data. Finally optimized re-entrant combustion chamber and modified valve timing with optimum fuel injection system simulation was carried out to achieve target performance with reduced fuel consumption. A 3D CFD result showed reduction in BSFC and was in close agreement with the test data.

Commentary by Dr. Valentin Fuster
2017;():V007T09A058. doi:10.1115/IMECE2017-70089.

The flow over two different shaped bluff bodies in tandem arrangement was numerically investigated by using the finite volume method with Computational Fluid Dynamics (CFD) techniques. The shape of the downstream main bluff body is a right circular cylinder, with shape unchanged, while the shape of the upstream bluff body varies between: circle, triangle, square, ellipse and cylindrical half-shell. The hydraulic diameters of both front and rear bluff bodies are equal. The analysis is carried out for Reynolds numbers of 100, 300 and 500, and center-to-center distance ratios, L/D, of 1.5, 2, 3, 4.5 and 6. Flow characteristics in terms of the lift and drag coefficients and Strouhal number are analyzed and the vortex shedding patterns around the bluff bodies are described. The influence of the shape of the fore cylinder on the flow characteristics is the innovation point of this paper. It is concluded that the center-to-center distance ratio, L/D, and the shape of the upstream bluff body have important effects on the drag and lift coefficients, vortex shedding frequencies from the two bluff bodies, and flowfield characteristics.

Commentary by Dr. Valentin Fuster
2017;():V007T09A059. doi:10.1115/IMECE2017-70255.

A number of cars are found to have an unconventional radiator. The radiator is placed at the back of the car instead of front, for which the radiator does not get the incoming airflow to cool the engine down and the engine gets overheated very easily. In order to deal with this problem, a channel has mounted at the top of the vehicle to navigate incoming air flow and direct it through the radiator to cool down the engine. The channel that is provided has three cases, which will indicate the different way of studying this problem. Both steady and transient state analysis has been performed. Each case has its own characteristics. For example, a longer channel creates little circulation but more axial flow towards the radiator, while shorter channel creates smooth but less axial flow towards the radiator. All these cases in the steady state have the same domain and will have similar inlet variables like velocity, shape, size, and position. However, the domain geometry was slightly changed for transient state scenario.

At steady state simulation, most of the circulation were shown in the left-mid plane especially in longer channels. On the other hand, the transient state gives more uniform flow distribution. For longer channels in transient case, the flow is symmetric and smooth. The results were all made and developed in ANSYS for the final design where the data were simulated.

Commentary by Dr. Valentin Fuster
2017;():V007T09A060. doi:10.1115/IMECE2017-70457.

The linear and non-linear growth of instabilities in a two dimensional parallel three jet flow configuration is carried out using DNS. A method is presented that enables the study of growth of instability modes using a combination of LSA and DNS. The linear growth of spatial and temporal LSA modes for a single shear layer is verified using DNS. Then DNS is used to study the transition from linear growth to non-linear instabilities. In test, the growth rate of temporal modes found using DNS matches with growth rate predicted by LSA for viscous and inviscid flows. DNS of a non-parallel flow with a spatially growing viscous LSA mode is found to create absolute instability and match between DNS and LSA is not possible. In a temporal analysis, it is found for a multiple shear layer case it is found that the growth of the temporal mode increases with increasing the strength of the additional shear layer for both inviscid and viscous flows. Longer DNS runs show that presence of a stronger shear layer enhances vortex shedding and vortex pairing mechanism of a shear layer. This enhanced mixing in the non-linear region is to be linked with the growth of perturbation in the linear region.

Topics: Jets
Commentary by Dr. Valentin Fuster
2017;():V007T09A061. doi:10.1115/IMECE2017-70599.

A vortex cell is a cylindrical aerodynamic cavity that traps separated vortices to prevent the formation of large-scale vortex shedding. Due to the presence of complex vortical structures, regions with varying turbulent intensities, and rotation-curvature effects on turbulent structure; the flow inside a vortex cell is a valuable test case for newly proposed turbulence models and numerical schemes. In the present study, numerical simulations were carried using a Reynolds-averaged Navier-Stokes (RANS) turbulence model and two hybrid RANS/large-eddy-simulation (LES) models. The computational domain consists of a cylindrical cavity with an incoming transitional boundary layer and a Reynolds number of 9.4 × 104 based on the diameter of the cavity. Results indicate that the RANS model provides general information about the flow characteristics, while the hybrid RANS-LES models predict the flow characteristics with more accuracy but suffer inaccuracies due to the details of the RANS to LES transition. Most significantly, the dynamic hybrid RANS-LES (DHRL) model in combination with a low-dissipation numerical scheme overpredicts the turbulent mixing in the vortex cell and fails to provide an accurate representation of the physics of the trapped vortex. It is concluded that the hybrid RANS-LES models used in this study need further work to be able to fully and accurately predict the flow in a vortex cell.

Commentary by Dr. Valentin Fuster
2017;():V007T09A062. doi:10.1115/IMECE2017-70778.

With advances in computing power and Computational Fluid Dynamics (CFD) algorithms, the complexity of CutCell based simulation models has significantly increased. In this study three dimensional numerical simulations were carried out for steady incompressible flow around an airfoil shape. The authors extended their previous work on more complex geometries; a NACA-23012 wing with 20 percent C Clark Y flap was used for this study. The boundary layer thickness, mesh expansion ratio, and mesh density variation parameters were examined. The skin friction coefficient vanishes where the flow separation starts. Although there is no experimental data available to compare the simulation work the results can be subjected to future work experimentally.

Commentary by Dr. Valentin Fuster
2017;():V007T09A063. doi:10.1115/IMECE2017-70848.

The complete understanding of the aerodynamics of wings and blades under transonic conditions represents a substantial challenge in the design of modern airplanes and turbomachinery. Transonic flow over airfoils may result in appearance of shock waves, which lead to increase in drag if not properly considered during the design stage. Therefore, it is a major challenge to design transonic airfoils such that potential appearance of shock waves is foreseen and negative drag effects are minimized. This paper presents the computational study of the SC(2)-0714 airfoil, focusing on its aerodynamics characteristics at Reynolds number of 35 × 106 and angle of attack of 2 and 10 degrees which are the most common operational conditions of transonic wings using this airfoil. The study was undertaken at free-stream Mach 0.72. The numerical simulation was conducted using the finite volume method on platform ANSYS CFX™ and solving the Reynolds-Averaged Navier-Stokes, mass conservation and energy equations. Mesh verification and model validation are presented. The latter is developed by using two different isotropic turbulence models: k-ω and Shear Stress Transport (SST) and the comparison of results with NASA experimental data to determine the best among the treated models. Thereafter, effects of local boundary-layer suction on shock wave strength and characteristics during transonic speed are analyzed for the two aforementioned angles of attack. Two suction slots were placed along the airfoil contour to determine their control effectiveness when compared to standard closed-contour airfoil. Suction slots were placed at the leading edge and in the middle of the upper camber of the airfoil with inflow in the normal direction to the surface. The slot length was 2.5 % of the chord with inflow velocity of 30%, 40% and 50% of free-stream velocity. Effects of suction slots were assessed on the wake region and by computing the resulting lift-to-drag ratio. Concluding remarks on the turbulence model and global aerodynamics performance of the airfoil are presented.

Commentary by Dr. Valentin Fuster
2017;():V007T09A064. doi:10.1115/IMECE2017-70900.

Computational fluid dynamics simulations have been conducted for flows past two finite tandem plates at Reynolds number of 50,000. Large Eddy Simulations (LES) were employed in two and three-dimensional geometries to study the interference between tandem plate pair. In order to study the effects of plate corner angle on the flow field and drag forces, two different plate end corners, 90° and a sharp 45° corner angle, were also investigated. The switching from 90° to 45° corners complicate the flow pattern, increase the mean value of drag force and the fluctuations of the drag on the plate. As vortices shed from the upstream plate and reached close proximity to the face of the downstream plate, the vortex cores deformed highly. This behavior reduces the drag coefficient in the downstream plate. Drag coefficient was higher in the 45° case, for both the up and downstream plates by 5% and 10% respectively. Drag coefficient of downstream is recovered almost fully in the 45° case with just 3% difference from the upstream compared to 7% difference in 90° case. Lagrangian Coherent structures were identified and presented in a two-dimensional geometry. This gave a better understanding of the wake flow structure and their influence on the hydrodynamic loading on plates. Contours of vorticity fields and iso-surfaces of Q-criterion, and pressure distribution around the plates were also presented and discussed.

Commentary by Dr. Valentin Fuster
2017;():V007T09A065. doi:10.1115/IMECE2017-71037.

Gravity dust-catchers are widely utilized in steelmaking plants to separate particles from the gas flow produced by the blast furnace (BF). The BF recycle system often experiences high total suspended solid (TSS) levels with a significant increase in sludge generation. This increased sludge generation results in higher costs in operation, chemical treatment and sludge removal. Due to the environmental limitations inside an operating dust-catcher, direct measurement of operating conditions can be extremely difficult. Computational fluid dynamics (CFD) models provide a method of gaining an understanding of the operating conditions and phenomena that occur inside a blast furnace dust-catcher on both full process and detailed levels. In this paper, a numerical geometry of the dust-catcher is designed and simulated under typical operating conditions. The Discrete Phase Model (DPM) is employed to track the flow patterns and paths of dust particles. The collection efficiency performance is evaluated at different conditions (quarter full, half full, and three quarter full). From these results, an alternative design to enhance process efficiency is proposed and investigated.

Commentary by Dr. Valentin Fuster
2017;():V007T09A066. doi:10.1115/IMECE2017-71185.

The diffusion of radioactive material in the atmosphere is vital for environmental assessment. Many researches have focused on the diffusion and deposition outside the construction, whereas less attention was paid on the law of the diffusion from the outside into the room. In this paper, three-dimensional numerical simulation was carried out by using OpenFOAM, an open source software for CFD. The incompressible steady flow around the construction with opening windows was investigated. The influence of inflow wind velocity and windows distribution was considered. The results show that as the inflow wind velocity increases, the diffusion is more significant. The vortexes is related to the windows distribution. When windows are perpendicular to the direction of the inflow wind, the concentration inside the construction is higher than that outside. Besides, the radioactive material gathers in the vicinity of the indoor downstream wall. When windows are parallel to the direction of the inflow wind, the concentration of indoors and outdoors is opposite, and the indoor radioactive material is distributed evenly. This study can provide theoretical support for the emergency evacuation around the construction.

Commentary by Dr. Valentin Fuster
2017;():V007T09A067. doi:10.1115/IMECE2017-71230.

Oil and gas producing rates have increased rapidly with the development of shale oil and fracturing technology. Besides, advances in horizontal wells have increased the slugging issue, especially in complex geometry wells. Therefore, Artificial lift systems, especially rod-pumps and electrical submersible pumps, always suffer from associated gas and require an economical way to avoid problems like gas lock, gas pound, gas interference and slugging. Among all kinds of the downhole separator, and the gravitational separator are the most economical devices, which can handle severe slugging problems.

The rule of thumb liquid maximum downward velocity for the gravitational separator is 0.6 in/s [13, 14]. However, the criterion needs to be improved by considering pressure, temperature and fluid properties. This article first uses CFD simulations to validate the critical liquid velocity and then obtains pressure field, velocity profile, gas distribution and sensitivity factors under complicated field situations. The results could be used to develop an empirical or even a mechanistic efficiency prediction model in the future.

In this paper, 2-D simulation is first utilized to study the critical separation velocity and effective parameters. Comparing with Stokes’ law, the simulation shows density, and surface tension have a strong effect of critical separation velocity, while viscosity has lower influence. Then extended 2-D simulations are conducted on different inner tube to annulus connection geometry, which shows a strong effect on separation efficiency. Later on, 3-D CFD simulations are generated based on a newly designed separator by TUALP and an existing design from the Don-Nan separator. Simulations are used to validate 2-D conclusion and illustrate the improvement of the new design.

Commentary by Dr. Valentin Fuster
2017;():V007T09A068. doi:10.1115/IMECE2017-71322.

Butterfly valves are typically used as emergency closure devices in dam penstocks; these valves must be capable of closing if a penstock bursts. This paper summarizes a 3D CFD (Computational Fluid Dynamics) study that was conducted on the water flow across a sizable butterfly valve (1.6m in diameter) in a dam penstock with 57m of water head. The main aim is to determine the maximum torque required to close the valve. Thus semi steady flow conditions across the valve at various degrees of closure were investigated and the corresponding torque calculated. A maximum torque of about 87 700 N-m has been obtained, occurring at valve angle 40° (with valve totally closed at 0°, and fully open at 90°). Visual results were analyzed at each valve angle to understand the nature of the flow through the butterfly valve using various 2D contours and streamline images. The CFD software ANSYS Fluent has been used employing a Finite Volume Method. The RANS (Reynolds-Averaged Navier-Stokes) approach with Realizable K-epsilon turbulence model was employed. A grid independence study with up to 10 million cells has also been carried out, resulting in the adoption of 7.5 million cells in all models. Comparison with other available data was also completed, adding to the reliability of the computational results. Distribution of pressure, flow velocity, and turbulence parameters are also presented.

Commentary by Dr. Valentin Fuster
2017;():V007T09A069. doi:10.1115/IMECE2017-71749.

Oil-lubricated bearings are widely used in high speed rotating machines such as those used in the aerospace and automotive industries that often require this type of lubrication. However, environmental issues and risk-adverse operations have made water lubricated bearings increasingly popular. Due to different viscosity properties between oil and water, the low viscosity of water increases Reynolds numbers drastically and therefore makes water-lubricated bearings prone to turbulence effects. The turbulence model is affected by eddy-viscosity, while eddy-viscosity depends on wall shear stress. Therefore, effective wall shear stress modeling is necessary in producing an accurate turbulence model. Improving the accuracy and efficiency of methodologies of modeling eddy-viscosity in the turbulence model is important, especially considering the increasingly popular application of water-lubricated bearings and also the traditional oil-lubricated bearings in high speed machinery. This purpose of this paper is to study the sensitivity of using different methodologies of solving eddy-viscosity for turbulence modeling.

Eddy-viscosity together with flow viscosity form the effective viscosity, which is the coefficient of the shear stress in the film. The turbulence model and Reynolds equation are bound together to solve when hydrodynamic analysis is performed, therefore improving the accuracy of the turbulence model is also vital to improving a bearing model’s ability to predict film pressure values, which will determine the velocity and velocity gradients in the film. The velocity gradients in the film are the other term determining the shear stress. In this paper, three approaches applying Reichardt’s formula were used to model eddy-viscosity in the fluid film. These methods are for determining where one wall’s effects begin and the other wall’s effects end. Trying to find a suitable model to capture the wall’s effects of these bearings, with aim to improve the accuracy of the turbulence model, would be of high value to the bearing industry. The results of this study could aid in improving future designs and models of both oil and water lubricated bearings.

Commentary by Dr. Valentin Fuster
2017;():V007T09A070. doi:10.1115/IMECE2017-71807.

Aerodynamic design is getting continuously more important for formula student race cars. One very important aerodynamic device of these cars is the front wing. The front wings, as well as the rear wings generate a downforce to improve the stability of the vehicle especially when driving on curves. The front wings are mounted so close to the ground that they are already in ground effect. The rear wings are already too far from the ground and therefore are not in ground effect. Therefore it is very important to design the front wings in such a way as to maximise the ground effect. Therefore these wings have to be mounted at a proper distance from the ground in order to have the maximum ground effect. If the front wings are too close to the ground the ground effect disappears or even the downforce is less than far from the ground. Since the rear wings are out of the ground effect they have not been considered in this investigation.

In this work a series of wing designs, with different aspect ratios, at different angles of attack and at different distances from the ground where designed and investigated with computational fluid dynamics using the commercial Navier-Stokes solver STAR CCM+. The downforce lift coefficients of these wings in free flight as well as in ground effect and as the corresponding drag coefficients are presented. The best configurations of aspect ratio and angle of attack as well as the optimum distances from the ground to operate these front wings in ground effect are shown and the results discussed in detail.

Topics: Automobiles , Wings , Students
Commentary by Dr. Valentin Fuster
2017;():V007T09A071. doi:10.1115/IMECE2017-71825.

Fans in industrial plants can be exposed to a strong erosion load due to particle flows. In the present work, the erosion behavior for large radial fans with spiral casings is investigated using the Finnie erosion model, see [1] [2]. Theoretical approaches concerning particle velocity and particle impact angle are validated by numerical methods. For this purpose, a baseline impeller and a parameterized baseline spiral casing have been designed and simulated using computational fluid dynamics. Than different geometrical variations of the spiral casing shape and the blade shapes of the impellers have been designed and simulated in order to determine their respective influence on the erosion behavior as well as on the performance characteristics. Finally, recommendations for an optimal design are presented and explained in detail.

Commentary by Dr. Valentin Fuster
2017;():V007T09A072. doi:10.1115/IMECE2017-71830.

Incompressible jets transversely issuing into a spatially-developing turbulent boundary layer is one of the most challenging and crucial types of three dimensional flows due to its fluid-dynamic complexity and technological applications; for instance, film cooling of turbine blades, chimney plumes, fuel injection, etc. In this investigation, Direct Numerical Simulation (DNS) of a jet in a crossflow under different streamwise pressure gradients (zero and favorable pressure gradient, hereafter ZPG and FPG) is performed. The goal is to accurately model the interaction between the wall-normal laminar jet with the incoming spatially-developing turbulent boundary layer in order to elucidate the physics behind the thermal coherent structures in crossflow jets at different streamwise pressure gradients (ZPG vs. FPG) and low velocity ratios (∼ 0.5). The analysis is done by prescribing accurate turbulent information (instantaneous velocity and temperature) at the inlet of a computational domain for simulations of spatially-developing turbulent boundary layers. The methodology is based on the Dynamic Multiscale Approach (DMA) by Araya et al. (JFM, Vol. 670, pp. 581–605, 2011). The major effect of strong FPG on crossflow jets has been identified as a damping process of the counter-rotating vortex pair system (CVP).

Commentary by Dr. Valentin Fuster
2017;():V007T09A073. doi:10.1115/IMECE2017-71856.

In this work the influence of different radial work distributions on the performance of low pressure axial fans for automotive cooling purposes was investigated. The general standard solution in the design of axial fans is to assume constant work distribution (free vortex design). This also leads to a constant meridional flow velocity and thus makes the calculations for the design rather simple. To fulfill the constant work assumption, however, a high swirl component of the absolute outlet flow velocity results near the hub. Assuming the incoming airflow to be swirl-free, this means that the flow near the hub must be strongly deflected, leading to a very high blade load in this area and to very long chords. Thus, the assumption of constant radial work distribution leads to a high risk of flow separation near the hub, especially for low pressure cooling fans, where a small hub to shroud diameter ratio is needed in order to achieve higher flow rates.

Furthermore, in fan applications, often the total-to-static pressure and total-to-static efficiency are the relevant design parameters, and not the total-to-total pressure and the total-to-total efficiency. In order to address these issues, linear and parabolic non-constant work distributions were investigated. These distributions were parametrized and for each work distribution a series of designs was created with the airfoil theory method. These designs were computed with the commercial Navier-Stokes-Solver STAR CCM+ and the results were analyzed in detail. As an application example a series of fans for a Formula Student racing cars cooling applications was developed.

With this method, it was possible to achieve smaller hub to shroud diameter ratios, higher flow rates and better total-to-static efficiencies. The result was a new series of fans with improved cooling properties for automotive applications. These new fans, the design method and the results are presented in detail in this work.

Topics: Cooling , Fans
Commentary by Dr. Valentin Fuster
2017;():V007T09A074. doi:10.1115/IMECE2017-71872.

To compute the trajectory of a rocket the knowledge of the external aerodynamics and the resulting forces is essential. The drag coefficient is an important parameter in the computation of rocket trajectory in case of vertical ascent. For compressible flows, at subsonic and supersonic velocities, the drag coefficient is a function of the Reynolds number and of the Mach number. Both dimensionless numbers depend on the temperature, however, not in the same way. For that reason, the Mach number dependency and the Reynolds number dependency are different. Since in the atmosphere pressure and temperature are functions of the height, the drag of rockets is also dependent on the height of the rocket in the atmosphere.

In this work, the dependence of the drag on the shape of the rocket is investigated at different heights and velocities, i.e. Reynolds and Mach numbers. For this purpose, the historical rocket from Johannes Winkler, the first liquid propulsion rocket in Europe, and a modern rocket geometry were chosen and compared. These rockets were investigated numerically with the commercial Navier–Stokes solver STAR-CCM+.

A detailed analysis of the drag coefficient, split into friction, pressure and wave drag was performed at these heights, Mach numbers and Reynolds numbers for the different aerodynamic shapes and rockets. In particular on the transonic and supersonic range the shock wave system leading to the wave drag was analysed in detail. Graphs of the corresponding friction, pressure, wave and total drag coefficients as a function of the Reynolds and as a function of the Mach numbers at different heights and a detailed analysis of these results are shown for the two rockets, the historical and a modern one.

Commentary by Dr. Valentin Fuster
2017;():V007T09A075. doi:10.1115/IMECE2017-72130.

In this study, a two-dimensional cylinder or a three-dimensional sphere is used as an example for a porous structure in the flow field. Immersed-boundary (IB) methods have been used to simulate flow around a cylinder/sphere, which is a typical problem to verify the effectiveness and accuracy of the methods. The flow was previously simulated by modeling the solid obstacles as a porous medium with flow resistivity. The current study makes an extension of the previous IB method. The fifth order WENO-Z scheme and third order Runge-Kutta method are used for space and time discretization, respectively. The Navier–Stokes equation is used for the fluids region and a ZK type of source term is applied in place of the forcing term for the porous domain. These two equations are solved simultaneously. Thus, there is no need to specify the interface conditions directly. In addition, the errors are estimated in terms of the flow resistivity that is zero for fluid, finite for porous, and infinite for non-porous solid. The aim of this paper is to establish estimates of the error induced by such an IB method. Numerical tests are performed to confirm the improvement of this method.

Commentary by Dr. Valentin Fuster
2017;():V007T09A076. doi:10.1115/IMECE2017-72570.

Submerged breakwaters are favored for their design simplicity in projects intended to dissipate wave energy and reduce erosion on coastlines. Despite their popularity, the effects that submerged breakwaters exhibit on the surrounding hydrodynamics are not clearly understood, mainly due to the flow complexity generated from 3-dimensional turbulent structures in the vicinity of the breakwaters that affect the mean flow characteristics and the transport of sediment. The objective of this study was to evaluate the effects that various geometric designs of submerged permeable breakwaters have on the turbulent flow characteristics. To meet the objective of this study, laboratory experiments were performed in a water-recirculating flume, in which the 3-dimensional velocity field was recorded in the vicinity of scaled breakwater models. Breakwaters that were tested include non-permeable, three-hole, and ten-hole models. The experimental data obtained was compared to results obtained from numerical simulations. Results demonstrated that permeable breakwaters exhibit more vertical turbulent strength than their non-permeable counterparts. It was also discovered that three-hole breakwater models produce higher turbulent fluctuations than that of the ten-hole breakwaters. The results from this study will be used eventually to enhance the performance of restoration projects in coastal areas in Louisiana.

Commentary by Dr. Valentin Fuster

Fluids Engineering: Symposium on Wind Turbines Aerodynamics and Control

2017;():V007T09A077. doi:10.1115/IMECE2017-70096.

Wind turbines are subjected to variable wind speeds and flow patterns, this can result in variable power output from the wind turbine. A common practice to counter this problem is to create a twisted wind turbine blade, which can produce optimum output when subjected to different velocities and angle of attack. The research paper discusses the performance characteristics of the same.

The research paper presents CFD modeling of a twisted blade. The strategy used for the modeling was to divide the research in two parts. In the first part CFD simulations for 2-D Airfoils were carried-out and the aerodynamic characteristics were examined. In the second part, for more realistic results, a complete 3-D Wind turbine 3 blades rotor with nacelle was examined. For both parts GAMBIT was used for geometry and grid creation (pre-processing), whereas ANSYS FLUENT was used for performing simulations and obtaining the contour plots (Processing and Post Processing).

Commentary by Dr. Valentin Fuster
2017;():V007T09A078. doi:10.1115/IMECE2017-70220.

The work presented in this paper used rigorous 3D flow-field analysis combined with multi-objective constrained shape design optimization for the design of bladelet (winglet) configurations for a three-blade propeller type wind turbine. The fluid flow analysis in this work was performed using 3D, steady, incompressible, turbulent flow Reynolds-averaged Navier-Stokes equations in the rotating frame of reference for each combination of a given wind turbine blade and a varying bladelet geometry. The free stream uniform wind speed in all cases was assumed to be 9 m s−1 and rotational speed was 12 rpm. These were off-design conditions for this rotor. The three simultaneous design optimization objectives were: a) maximize the coefficient of power, b) minimize the coefficient of thrust, and c) minimize twisting moment around the blade axis. The bladelet geometry was fully defined by using a small number of parameters. The optimization was carried out by creating a multi-dimensional response surface for each of the simultaneous objectives. The response surfaces were based on radial basis functions, where the support points were designs analyzed using the high fidelity CFD analysis of the full blade + bladelet geometry. The response surfaces were then coupled to a multi-objective optimization algorithm. The predicted values of the objective functions for the optimum designs were then again validated using the high fidelity computational fluid dynamics analysis code.

Results for a Pareto optimized bladelet on a given blade indicate that more than 4% increase in the coefficient of power at minimal thrust force penalty is possible compared to the same wind turbine rotor blade without a bladelet.

Commentary by Dr. Valentin Fuster
2017;():V007T09A079. doi:10.1115/IMECE2017-70288.

The Blade Element Momentum (BEM) theory is nowadays the cornerstone of the horizontal axis wind turbine design, as its application allows for the accurate aerodynamic simulation and power output prediction of wind turbine rotors in a remarkably short period of time. Therefore, efforts have been made for the extension of the classic BEM theory to the performance analysis of Diffuser Augmented Wind Turbines (DAWTs) as well. In this study, the development and assessment of such an in-house BEM code are presented. The proposed computational model is based on the modification of the momentum part of the classical BEM theory; thus, it is capable to account for the diffuser’s effect on the calculation of the axial and tangential induction factors, through the utilization of the velocity speed-up distribution over the rotor plane of the unloaded diffuser. Furthermore, a detailed Glauert’s correction model, which employs Buhl’s modification, specially tailored for the DAWT case is included, to deal with the high values of the axial induction factor. The accuracy of the model is assessed against numerical and experimental results available in the literature, while the impact of the Prandtl’s tip loss correction model on the rotor’s predicted power output is also examined.

Commentary by Dr. Valentin Fuster

Fluids Engineering: Young Engineers Program

2017;():V007T09A080. doi:10.1115/IMECE2017-73498.

Flapping, gliding, running, crawling, and swimming in animals have all been studied extensively in the past and have served as sources of inspiration for engineering designs. In this paper, we describe the aeromechanics of a mode of locomotion that straddles ground and air: jumping. The subject of our study is the spider cricket of the family Rhaphidophoridae, an animal that is among the most proficient of long-jumpers in nature. The focus of the study is to understand the aeromechanics of the aerial portion of the jump of this animal. The research employs high-speed videogrammetry to track the crickets’ posture and appendage orientation throughout their jumps. Experiments demonstrate that these insects employ carefully controlled and coordinated positioning of their limbs during their jumps so as to increase jump distance and stabilize body posture. Simple phenomenological models based on drag laws indicate that the conformation of the limbs during the latter portion of the jump is stable to pitch and enables these animals to land in a controllable manner. Insights from this study could be useful in the design of micro-robots that exploit jumping as a means of locomotion.

Commentary by Dr. Valentin Fuster
2017;():V007T09A081. doi:10.1115/IMECE2017-73499.

The use of spark-ignited (SI) production-style vehicle engines in high-performance applications is a growing trend in the aftermarket performance industry. However, the use of economically designed components, specifically cylinder heads, presents challenges when used in this manner. The study of flow through a cylinder head is a topic of extensive research where complex flow patterns have made modelling and computer simulation challenging. A variety of approaches have been employed including simplifying model assumptions, different boundary conditions, different meshing strategies, and different turbulence models. The focus of this research is modification of the air intake port geometry of a VR38DETT engine in order to increase the volumetric flow rate past a current limit of 330.4 CFM at 0.700” valve lift, which has been achieved by porting methods alone. Using SolidWorks, a computational fluid dynamics model was developed, verified, validated, and analyzed. The modelling methodology was verified using a mesh convergence study of the pressure drop along a pipe with a bend. Also, the bend loss coefficient was compared to published values for different ratios of the centerline radius of the bend to the internal pipe diameter. The model was then validated using steady-state flow bench test data. Results of the analysis indicate that the cylinder head can achieve a flow rate 5.15% above the current limit when the port geometry is enlarged and the short-side radius is increased, only in support of a cooling passage geometry change.

Commentary by Dr. Valentin Fuster
2017;():V007T09A082. doi:10.1115/IMECE2017-73500.

With global energy demands continually growing and environmental impacts a major concern in power production, maximizing the efficiencies of power plants is of top priority. EthosEnergy2 has sponsored a project at the University of Massachusetts Dartmouth to study and analyze the brush seals in steam turbines in pursuit of increasing steam turbine thermodynamic efficiency. Brush seals are incorporated circumferentially around the turbine blades in their housing. The brush seals provide a very minimal clearance height that compensates for start-up rotor deviation and minimizes high-pressure steam blow-by around the edges of the blades. Brush seals minimize the clearance height between the blades and housing, which allows the turbine to produce more work. However, overtime brush seals can be damaged, greatly reducing efficiency. The seals that are repeatedly showing excessive wear and damage, occur in the high-pressure sections of steam turbines with high Reynolds numbers. The bristle breakdown is attributed to high Reynolds numbers and aerodynamic flutter.

The purpose of this research is to design a prototype and empirically model steam turbine conditions with air to map out the fluid-solid interaction, determine the modes of bristle failure, and ultimately reproduce and record bristle flutter. A pressure vessel and pressure system was designed to test linear strips of brush seals with air as the working fluid. The pressure vessel accommodates varying clearance heights to identify the correlation of clearance height and the effects on fluid flow. The system also incorporates a high-speed camera that can capture the phenomena of flutter, precisely identify the modes of failure, and record fluid-solid interaction and the interaction of the bristles with each other. Designing a prototype to empirically model this problem serves as a fundamental and critical step in understanding the fluid interaction with seals in high-pressure steam turbines and will identify brush seal modes of failure. The prototype’s ability to model steam turbine conditions and rapidly test various seal designs will facilitate better brush seal designs to be constructed and will ultimately increase the thermal efficiencies of steam turbines, aid in accommodating the increase in global energy demands, and reduce the detrimental environmental impacts of producing power. The system successfully produced and recorded brush-seal-bristle flutter while modeling high-pressure steam turbine conditions. Matching Reynolds and Euler numbers of the steam turbine stages provided the ability to scale the steam turbine to our prototype, with air as the working fluid. Brush seal breakdown was occurring in steam turbines at Reynolds numbers above 20,000. The prototype repeatedly produced brush seal flutter at Reynolds numbers above 25,000, validating the theory that brush seal breakdown is dependent predominantly on the Reynolds number.

Commentary by Dr. Valentin Fuster
2017;():V007T09A083. doi:10.1115/IMECE2017-73502.

Herringbone grooved journal bearings are well known for their reliability and high rotor dynamic stability thresholds. While there is a large body of research surrounding the optimized groove geometry parameters, analysis on the material the groves are placed on has been mainly limited to metals. The ability to use plastic while maintaining desired qualities of reliability and stability is of great interest due to its light weight and low cost possibilities. The goal of the current study is to see if current technology limits on plastic 3D printed parts layer thickness inhibit lubricant flow, or if 3D printed parts can be used as an alternative choice in manufacturing journal bearings. The optimum geometries for square, circular, and beveled step groove profiles were 3D printed with layer thicknesses of 16, 50, 100, and 250 micrometers. Additionally, the effect of herringbone groove parameters such as groove width ratio, groove depth ratio, and groove angle were explored. Finally, a 2-dimentional Computational Fluid Dynamics simulation of a square, circular, and beveled step herringbone groove geometry velocity magnitude profiles are presented.

Commentary by Dr. Valentin Fuster

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