bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Charge Density on Electrokinetic Ions and Fluid Flow Through Polyelectrolyte Coated Nanopore
Authors: Bera Subrata , Bhattacharyya S.
Published: October 2017

We have studied the electroosmotic flow (EOF) and its effect through a polyelectrolyte coated conical nanopore. The nanopore wall bears a uniform negative surface charge while charged density of the polyelectrolyte layer (PEL) bears positive charge. The degree of softness in the PEL is mainly affects the hydrodynamic field inside the nanopore while ionic current is not affected significantly by flow field. The characteristic of electrokinetic flow is based on the nonlinear Nernst-Planck equations for the ion transport coupled with the Brinkman extended Navier-Stokes equations for fluid flow and the Poisson equation for induced electric potential. The coupled set of governing non-linear equations for fluid flow and ionic species concentration are solved through a finite volume method on a staggered grid system. A numerical method based on the pressure correction iterative algorithm is adopted to compute the flow field. This study investigated the importance of the bulk concentration of the electrolyte, the geometries of the nanopore and both the thickness and the charged density of PEL on the electrokinetic ion and fluid transport. The ratio of the cross-sectional average flow of the present model with plane cylindrical channel, decreases with the increase of the scaled charge density of PEL for both low and high ionic concentration cases when softness parameter and thickness of PEL are fixed. The average flow rate decreases with the increase of the PEL sealed charge density in both low and high ionic concentration cases for fixed PEL thickness. The increase of nanopore radius increases the cross sectional averaged flow for fixed scaled charged density and PEL thickness. The average flow rate decreases with the increase of the PEL thickness for fixed charged density of PEL. The critical value of scaled charge density of PEL is defined for which there is no flow through the nanopore. The average current density increases with the increase of applied electric field for different charged density of PEL. But there is no different of average current density for different charge density of PEL in high ionic concentration cases.
Stochastic Sensitivity Analysis of Numerical Simulations of High-Pressure Injectors to Cavitation Modeling Parameters
Authors: Anderlini A. , Salvetti M. V. , Agresta A. , Matteucci L.
Published: October 2017

The work focuses on numerical simulation of the cavitating flow inside high-pressure injectors. Cavitation is modeled through a transport equation for the void fraction closed by the Schnerr-Sauer relation, containing four free parameters. As for turbulence, the URANS equations are considered, together with two different closure models. The sensitivity of URANS predictions to the parameters contained in the cavitation model is investigated for a throttle geometry, for which experimental and LES data are available. In order to obtain continuous response surfaces of the quantities of interest in the parameter space starting from a limited number of simulations, a stochastic approach is adopted. First, two out of the four parameters are identified as the most important through a preliminary analysis based on 2D simulations. Then, the sensitivity of 3D simulation results to the previously identified most important parameters is investigated. The stochastic range of variability of the results contains the reference data. Finally, a parameter optimization is carried out in order to obtain the values giving the best agreement with the LES data.
A Numerical Study on the Performance Improvement for a Vertical-Axis Wind Turbine at Low Tip-Speed-Ratios
Authors: Wang Zhenyu , Zhuang Mei
Published: October 2017

Vertical-axis wind turbines (VAWTs) are a promising solution for the use of renewable energy in residential areas. Compared to traditional horizontal-axis wind turbines (HAWTs), VAWTs are usually smaller, quieter, and insensitive to the wind direction and can be installed in a wide range of urban, suburban and rural places such as top of buildings, backyard, etc. In addition, VAWTs require a lower wind speed to self-start which increases the capability of wind energy extraction in the areas with low wind speed. However, VAWTs are less efficient and the power output of VAWTs is substantially affected by the phenomenon of dynamic stall induced by the variations of angle of attack of rotating blades, especially at low tip speed ratios (λTSR<4). When the dynamic stall vortices, formed near the leading-edge, are transported downstream, it creates large and sudden fluctuations in torques. At low values of the tip speed ratio and relatively low Reynolds number (Re<105), dynamic stall occurs periodically throughout the rotation of the blades. This results a sharp drop in lift coefficient and therefore rotor torque and power output are substantially reduced. The purpose of the present study is to investigate the prospects for improving the flow performances of small VAWTs using serrated leading-edge configurations on straight blades in a conventional H-type VAWT design to control dynamic flow separation. A numerical study is carried out to obtain the detailed flow fields for analysis and visualization. The results show that the turbine blade with the serration profiles of h = 0.025c (amplitude) and λs = 0.33c (wavelength) not only increased the power generation at low TSRs, but also enhanced the capability of wind energy extraction at the optimum TSR in comparison to the baseline model. The dynamic stall was suppressed significantly in the range of the azimuth angle from 80° to 160°. The flow separation induced by large angles of attack was essentially alleviated in the modified turbine model due to the serrated configuration implemented on the blade leading-edge.
How Computational Grid Refinement in Three Dimensions Affects CFD-DEM Results for Psuedo-2D Fluidized Gas-Solid Beds
Authors: Volk Annette , Ghia Urmila
Published: October 2017

Computational Fluid Dynamics (CFD)-Discrete Element Method (DEM) simulations are designed to model a pseudo-two-dimensional fluidized bed. Bed behavior and accuracy of results are shown to change as the simulations are conducted on increasingly refined computational grids. Trends of the results with grid refinement are reported for both three-dimensional, uniform refinement, and for grid refinement in only the direction of bed thickness. Pseudo-2D simulation results are examined against previously published experimental data to assess relative accuracy compared to fully 3D simulation results. Two drag laws are employed in the simulations, resulting in different trends of results with computational grid refinement. From these results, we present suggestions for accurate model design.
Predicting Critical Heat Flux With Multiphase CFD: 4 Years in the Making
Authors: Baglietto Emilio , Demarly Etienne , Kommajosyula Ravikishore
Published: October 2017

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

Starting from this improved representation at the wall, the work concentrates on the bubble dynamics and dry spot quantification on the heated surface, which governs the Critical Heat Flux (CHF) limit. A new proposition is brought forward, where Critical Heat Flux is a natural limiting condition for the heat flux partitioning on the boiling surface. The first principle based CHF is qualitatively demonstrated, and has the potential to deliver a radically new simulation technique to support the design of advanced heat transfer systems.
Research on Heat-Transfer and Cooling Performance of Gas Turbine Endwall
Authors: Kakio Kazuto , Kawata Y.
Published: October 2017

Recently, the number of gas turbine combined cycle plants is rapidly increasing in substitution of nuclear power plants. The turbine inlet temperature (TIT) is being constantly increased in order to achieve higher efficiency. Therefore, the improvement of the cooling technology for high temperature gas turbine blades is one of the most important issue to be solved.

In a gas turbine, the main flow impinging at the leading edge of the turbine blade generates a so called horseshoe vortex by the interaction of its boundary layer and generated pressure gradient at the leading edge. The pressure surface leg of this horseshoe vortex crosses the passage and reaches the blade suction surface, driven by the pressure gradient existing between two consecutive blades. In addition, this pressure gradient generates a crossflow along the endwall. This all results into a very complex flow field in proximity of the endwall. For this reason, burnouts tend to occur at a specific position in the vicinity of the leading edge. In this research, a methodology to cool the endwall of the turbine blade by means of film cooling jets from the blade surface is proposed. The cooling performance and heat transfer coefficient distribution is investigated using the transient thermography method. CFD analysis is also conducted to know the phenomena occurring at the end wall and calculate the heat transfer distribution.
Experimental Analysis of Closed-Loop Flow Control Around Airfoil Using DBD Plasma Actuator
Authors: Shimomura Satoshi , Ogawa Takuto , Sekimoto Satoshi , Nonomura Taku , Oyama Akira , Fujii Kozo , Nishida Hiroyuki
Published: October 2017

This paper experimentally investigates the effectiveness of a closed-loop flow control method using a DBD plasma actuator for a NACA0015 airfoil, in which the surface pressure fluctuation is fed back to the system; the actuator was driven when the pressure fluctuation exceeds the setup threshold. The Reynolds number based on the chord length is set to 63,000 and the angle of attack is in the range from 12 to 15 degrees. The actuator was installed on the surface at 5% of the chord length from the leading edge. The results show that the closed-loop control worked better than the continuous operation. In the angle of attack of 12 and 14 degrees, the complete attached flow was attained by setting the appropriate threshold value of the pressure fluctuation. On the other hand, in 15 degrees, although the complete attached flow was not attained, the flow separation was partially suppressed.
Characteristics of Pneumatic Non-Contact Holder With Two Swirling Flows
Authors: Morisawa Takuya , Tsukiji Tetsuhiro , Suzuki Ryoichi
Published: October 2017

When products requiring careful handling such as semiconductor wafers and food (hereinafter called “workpieces”) are transported in manufacturing processes, problems can occur due to malfunctions that degrade sanitary conditions during the transport of workpieces through contact. An excellent device for transporting workpieces is a pneumatic non-contact holder (hereinafter called “cup”). This device holds a workpiece without contact by using pneumatic pressure, and so a workpiece doesn’t suffer damage or contamination. The purpose of this paper is to propose a method for overcoming the weaknesses in vortex-type non-contact holders, which is a cup that can hold a workpiece by using the negative pressure generated by the centrifugal force of a swirling flow, and propose a shape of cup which will generates a larger holding force from the point of view of energy saving. Specifically, we changed the shape of the chamfer in the swirling chamber exits and the number of the nozzles, and measured the holding force characteristics and the pressure distribution of the cup, thereby examining the performance of the cups. The experimental results indicate that the holding force is strongly related to both the shape of the chamfer in the swirling chamber exits and the number of the nozzles.
Exit Loss Model for Plain Axial Seals in Multi-Stage Centrifugal Pumps
Authors: Bruurs K. A. J. , van Esch B. P. M. , van der Schoot M. S.
Published: October 2017

Plain axial seals are often used in centrifugal pumps as a means to achieve acceptable sealing against leakage flow without the much higher friction losses that are associated with mechanical seals. Examples of their application are the front seals in shrouded radial and mixed-flow pumps and the inter-stage seals in multi-stage pumps. Knowledge about the relation between leakage flow rate and pressure drop over the seal is vital, not only for estimating the volumetric losses, but also for calculating the axial thrust and shaft power of a pump.

Investigations up till now have mainly concentrated on the frictional pressure drop in the seal (e.g. Yamada [1], Weber [2]), and hardly on the expansion losses at the exit of the seal. These exit losses are commonly modelled by a kinetic loss coefficient equal to or close to 1, but recent measurements by Storteig [3] have shown that exit loss coefficients can have values well above 1.

This paper presents an analytical method to compute the exit loss coefficient of a plain axial seal. It is derived from energy and momentum balances and assumes power-law profiles for the velocity distribution in the seal. The power-law coefficients are computed using CFD and are found to only depend on the Reynolds numbers based on axial flow, Reax, and Couette flow in circumferential direction, ReΩ. The resulting exit loss coefficients are shown to range between 1 and 2, depending on the ratio of Reax and ReΩ. Results of the analytical model are compared with measurements and CFD calculations.

This new analytical model can help improve the prediction of rotor dynamic stability, efficiency and axial thrust of turbomachinery without the need for dedicated CFD calculations in these tight clearances.
Unstable Flow Characteristics in S-Shaped Region of Pump-Turbine Runners With Large Blade Lean
Authors: Ma Zhe , Zhu Baoshan , Rao Cong , Tan Lei
Published: October 2017

As the reversible pump-turbines operate in the S-shaped region, instability problems including backflow, vortex formation and rotating stall may appear. Previous researches studied instabilities at different guide vane opening (GVO) on their inception and evolution but few studies explored the effect of the blade lean at the leading edge. In present work, two runners tested by experiments, the runner A with a negative and the runner B with a positive blade lean at leading edge, were studied in CFD mode with a reduced scale model. Six operating points, namely, best efficiency point (OP#1), two points in the normal operating region (OP#2, OP#3), two points near runaway line (OP#4, OP#5) and a low discharge point in turbine brake (OP#6) were calculated for both runners. As the discharge reduces, the flow in the runners loses its symmetry and the efficiency becomes lower and lower. The flow of OP#1, OP#2 and OP#3 is healthy but slight separations locate near the inlet of the passages. At OP#4, obvious vortexes occupy the passages and the visible vortexes prevent the flow from entering the channels. The blockage generates strong backflow near the inlet of the runner. Moreover, the main backflow area locates near the hub for runner A while for runner B it is near the shroud. Unsteady vortex formation and rotating stall respectively exist at the near runaway points (OP#4 and OP#5) and low discharge point (OP#6). At these three points, the pressure fluctuations in the vaneless gap between the runner and guide vanes are very high and the amplitude shows a small difference between the two runners. Dramatic distinction appears on the frequency of the fluctuation. For both of the two runners, a peak corresponding to 70% fn, where fn is the runner rotating frequency, rises in the spectra of OP#4 and OP#5. This peak appears at all the monitors in the vaneless space at the same time standing for the unsteady vortex formation, which does not rotate with the blades. In addition, at OP#6, 40% and 50% fn are detected as the dominant frequencies for runner A and runner B respectively. In addition, the propagation of such two low frequency signal along the annulus in the vaneless space proves the existence of the rotating stalls.
Numerical and Experimental Analysis of Vertical Ascendant Liquid-Gas Flow Under Action of Centrifugal and Gravitational Fields
Authors: Eidt Henrique K. , Rodrigues Carolina C. , Dunaiski Rafael , Ofuchi César Y. , Neves Flávio , Santos Paulo H. D. , Morales Rigoberto E. M.
Published: October 2017

Two-phase flows are commonly found in the extraction and production of petroleum and the separation process involving the liquid gaseous phases has great importance. The separators used for this purpose have usually high separation efficiency, however their large dimensions make difficult the construction, installation and maintenance of these equipment in offshore applications. An alternative to reduce the dimensions of these systems is to use a distribution method that can divide the flow, making it possible to use more than one separator. This distributor ideally will produce flow rates equitably distributed across all outlets. The distribution system proposed in this work has a cyclonic chamber, where a vertical ascendant liquid film flow occurs under the action of centrifugal and gravitational fields. This study aims to analyze the development and behavior of the liquid film flow and the efficiency of the distribution system as a function of the liquid and gas flow rates, using an experimental setup and CFD simulations performed with the software ANSYS-CFX 15.0. For the experimental setup a Wire-mesh sensor with 12×12 wires and two others with 8×8 wires were used in order to analyze the variation of the thickness of the liquid film formed in the cyclonic chamber and evaluate the flow pattern at the inlet of the system. In the numerical study, a three-dimensional hybrid mesh was constructed, using the Eulerian-Eulerian two fluid model coupled with the compressive discretization scheme to capture the liquid-gas interface, the Shear Stress Transport (SST) turbulence model and the finite volume based on finite elements. It was possible to carry out a numerical model validation through a comparison with the experimental data. The development of this numerical model might help the advance of new technologies applied in the petroleum industry and this study is focused on area that lacks more studies related to vertical ascendant liquid film flows under centrifugal and gravitational field effects.
Characteristics of Dynamic Forces Generated by a Flapping Butterfly and its Wake Structure
Authors: Fuchiwaki Masaki , Tanaka Kazuhiro
Published: October 2017

A typical example of the flow field around a moving elastic body is that around butterfly wings. Butterflies fly by skillfully controlling this flow field, and vortices are generated around their bodies. The motion of their elastic wings produces dynamic fluid forces by manipulating the flow field. For this reason, there has been increased academic interest in the flow field and dynamic fluid forces produced by butterfly wings. A number of recent studies have qualitatively and quantitatively examined the flow field around insect wings. In some such previous studies, the vortex ring or vortex loop formed on the wing was visualized. However, the characteristics of dynamic forces generated by the flapping insect wing are not yet sufficiently understood. The purpose of the present study is to investigate the characteristics of dynamic lift and thrust produced by the flapping butterfly wing and the relationship between the dynamic lift and thrust and the flow field around the butterfly. We conducted the dynamic lift and thrust measurements of a fixed flapping butterfly, Idea leuconoe, using a six-axes sensor. Moreover, two-dimensional PIV measurement was conducted in the wake of the butterfly. The butterfly produced dynamic lift in downward flapping which became maximum at a flapping angle of approximately 0.0 deg. At the same time, the butterfly produced negative dynamic thrust during downward flapping. The negative dynamic thrust was not produced hydrodynamically by a flapping butterfly wing because a jet was not formed in front of the butterfly. The negative dynamic thrust was the kicking force for jumping and the maximum of this kicking force was about 6.0 times as large as the weight. On the other hand, the butterfly produced dynamic thrust in upward flapping which was approximately 6.0 times as large as the weight of the butterfly. However, the attacking force by the abdomen of the butterfly was included in the dynamic thrust and we have not yet clarified quantitatively the dynamic thrust produced by the butterfly wing.
Experimental and Numerical Analysis of Failure for 4-Fan Wall With Different Number of Fans Units
Authors: Dou Hua-Shu , Chi Shaoqing
Published: October 2017

Fan wall is a new approach to air handler design making up of regular parallel arrangement of fans units without volute casing to replace a traditional single large fan. It is important to investigate the operation performance of fan wall for the optimal designing of fan wall central-station air handling units. In this paper, it is found with experiment that the static pressure drop for one fan unit’s failure is twice higher than that when it is off. The optimum working point in the static pressure efficiency curve is shifted to the left and the optimum efficiency is reduced by 30%. The numerical and experimental results show that when the fan fails, a lot of air will flow back to the entrance. Back flow at the entrance in the fan wall will form vortex blockage which reduces the inlet flow rate. The backflow also deteriorates the flow which will dissipate energy in the fan outlet. The research result shows that if the flow rate decreases the backflow will also decay and this finding can be employed as reference of high performance fan wall designing.
Numerical and Experimental Investigations of Rotating Wheel Aerodynamics on the DrivAer Model With Engine Bay Flow
Authors: Haag Lukas , Kiewat Marco , Indinger Thomas , Blacha Thomas
Published: October 2017

Wheel design and wheel rotation have been identified to be key factors influencing the overall aerodynamic performance of passenger cars. Hence, wheel aerodynamics has been the topic of various studies over the past few years. Recently, vehicle manufacturers have moved towards time-resolving CFD simulation methods. Therefore, a trend towards resembling the physical effect of wheel rotation by utilizing the Sliding Mesh Method can be observed in academia and the industry. The first part of the presented paper shows the results of CFD simulations using the Sliding Mesh Method on two generic test cases employing the Delayed Detached Eddy Simulation turbulence model. A rotating cylinder is investigated as well as a rotating wheel geometry, both in ground contact and lifted from the ground. The results show dependencies on the solution algorithm and the background turbulence model applied within the RANS region of the Delayed Detached Eddy Simulation model. The prediction accuracy of the CFD setup is assessed by comparing the results to experimental results on the rotating wheel geometry with ground contact obtained in a model scale wind tunnel. The second part of the paper focuses on the influence of the rim design on the aerodynamics of a full vehicle. Four rim geometries are investigated regarding their aerodynamic influence on the DrivAer reference body by CFD simulations using the Sliding Mesh Method. The DrivAer has recently been updated to include an engine bay geometry. This new version of the DrivAer is used for the presented study because the engine bay flow is expected to have a considerable influence especially on the flow around the front wheels. The simulation results are compared to experimental results obtained on a 1:2.5 scale model of the DrivAer with engine bay flow and are in good agreement.
Modeling the Viscoelastic Effects in the Hydrodynamic Lubrication of Journal Bearing in a High-Torque Low Speed Diesel Engine
Authors: Zia Talha , Qasim Syed Adnan , Azim Raja Amer
Published: October 2017

Multi-grade diesel lubricants exhibit viscoelastic characteristics, which affect journal bearing lubrication of a high torque engine at a low speed. During engine operation the main end of the crankshaft journal is most vulnerable to the cyclic combustion loads and must be protected against adhesive wear. This research models the Newtonian behavior of a lubricant by solving the 2-D Reynolds equation and determining the film thickness between the bearing and the crankshaft. It is followed by solving the continuity and Navier-Stokes equations to ensure conservation of mass and momentum of the lubricant flows. The constitutive equations exhibiting viscoelastic characteristics are coupled with the momentum conservation equations to generate simulation results for non-Newtonian lubricant response. The steady state wedging and transient squeeze effects are studied for a viscoelastic engine lubricant at low speed. The simulation results for Newtonian and viscoelastic engine lubricants are analyzed separately and then compared for definite conclusions. The results show that at a low initial speed the Newtonian lubricant is not affective against the cyclic loads to prevent physical contact and wear of interacting surfaces. The viscoelastic characteristics of the lubricant visibly contribute towards improving the pressure and film thickness profiles of a high-torque low-speed engine. It reduces the chances of breakdown of lubricant film and enhances the life of crankshaft by preventing adhesive wear.
Experimental and Numerical Investigations of a Low-Cost Axial Pump Design for the Drainage of Flooded Areas
Authors: Wulff Sebastian , Palamarchuk Evgenii , Abou Ackl Raja , Haeusler Stephan , Thamsen Paul Uwe
Published: October 2017

This paper presents the optimization of an existing low-cost axial pump for drainage of flooded areas with respect to the efficiency, by means of a CFD analysis and experimental investigation. The numerical simulations helped to analyze the flow conditions inside the pump, to understand the stator implementation effect and to verify the blade design. Based on the results, constructive suggestions were derived for the design of the impeller and the diffuser.
The Destruction-of-Dissipation Tensor εεij in Wall Turbulence
Authors: Gerolymos G. A. , Vallet I.
Published: October 2017

The paper investigates the destruction-of-dissipation tensor εεij in low-Reynolds number turbulent plane channel flow. This tensor, which represents the destruction of the dissipation tensor εij (appearing in the budgets of the covariances of fluctuating velocities rij) by molecular viscosity, exhibits specific near-wall anisotropy and is not 2-C at the wall. The budgets of εεij (turbulent and viscous diffusion, pressure-term, various production mechanisms, and destruction by molecular viscosity εεεij) are studied and various scaling relations are examined.
Particle-Cluster Formation and Vorticity in Gas-Solid Flows
Authors: Guda Sai Satish , Celik Ismail B.
Published: October 2017

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

The goal of this study is to find the cause and effect relation between the gas vorticity and the high particle concentration regions; in particular whether the gas vorticity causes particle agglomeration into clusters or vice-versa. Numerical study has been performed on a vertical pipe by creating a vortex field. In this regard, very large eddy simulations with Lagrangian Discrete Phase model have been performed using Ansys FLUENT and MFIX software packages. The influence of particles on the vorticity has been studied. Influence of several factors such as particle size, injection velocity etc. have also been studied. Correlations among turbulent kinetic energy, vorticity, and particle clustering and/or roping are illustrated.
Investigation of the Effect of Inlet Turbulence on Transitional Wall-Bounded Flows
Authors: Tuna Burak Ahmet , Li Xianguo , Yarusevych Serhiy
Published: October 2017

The present work investigates experimentally the effects of grid-generated turbulence on the transition and the hydrodynamic entrance length in a developing duct flow. Particle Image Velocimetry (PIV) and hot-wire anemometry are used to characterize the flow in a rectangular duct with a length of 1m (∼40Dh) and an aspect ratio of 2 (20mm × 40mm). The inlet turbulence intensity is controlled using different grids, and experiments are performed for a Reynolds number based on hydraulic diameter ReDh = 17,750. Hot-wire and PIV results show that the inlet turbulence intensity has a substantial effect on the flow evolution in the duct, as it substantially changes the boundary layer characteristics in the hydrodynamic entrance region. Analysis shows that, as expected, transition to turbulence advances upstream as the inlet turbulence intensity increases, leading to the decrease in the entrance length. The primary effect is confined to boundary layer development, as the turbulence intensity decays rapidly in the core flow, becoming independent of the initial conditions after about 10 hydraulic diameter (Dh) downstream from the grid. Thus, the analysis is focused on characterizing the boundary layer development and quantifying the associated changes in the flow development along the duct.
Experimental Analysis of a Cyclic Pitch Turbine
Authors: Prasad Rao Jubilee , Diez F. Javier
Published: October 2017

Cyclic pitch turbine is a drag based vertical axis fluid turbine which aims to optimize the drag forces that act on its blades. During operation, the turbine blades remain perpendicular to the flow in the drive stroke for maximum positive drag force and remain parallel to the flow in the recovery stroke for minimal negative drag. The blades pitch by 90 degrees between the two strokes using a dual cam mechanism. The blade pitching principle is inspired by bird’s wing motion and oar blade motion in rowing. Multiple turbine prototypes have been built and have been tested in air and water for functionality as well as for quantifying the performance. Water tunnel tests are conducted to measure power output at different turbine loads and flow velocities. Experimental setup included turbine speed, position senor and also a torque sensor. Experiments were aimed at understanding the performance of the turbine at different conditions and also finding the best blade configuration for maximum efficiency. The results show the cyclic variation of speed, torque and power output and coefficient of performance (CP) at different tip speed ratios (TSR). They show that the coefficient of performance is maximum which is 0.17 at around 0.55 tip speed ratio which is typical of drag based turbines and the value reduces with both increase and decrease in the value of TSR similar to conventional turbines.
Experimental Investigation on the Influence of Particle Size in a Submerged Slurry Jet on Erosion Rates and Patterns
Authors: Karimi Soroor , Mansouri Amir , Shirazi Siamack A. , McLaury Brenton S.
Published: October 2017

Sand particles entrained in fluids can cause erosive wear and damage to piping materials by impacting their surfaces which could result in failure of the piping system. Several parameters have been determined to affect the erosion behavior and mechanism of solid particle erosion. Some of these parameters include surface material, particle impact speed and angle, and particle size, shape and hardness. However, the effect of particle size on the total erosion rate and local erosion pattern has not been thoroughly investigated. It has been observed that sand particles with various sizes cause different slurry erosion patterns. Changing the particle size alters the Stokes number and consequently produces different erosion patterns and magnitudes. Thus, the effects of particle size on total erosion rate and erosion pattern in a submerged slurry jet are investigated for different impingement angles. Experiments are performed on 316 stainless steel specimens for average particles sizes of 25, 75, 150, and 300 μm. The jet angle is varied to 45, 75 and 90 degrees, and the slurry jet velocity is set to 14 m/s. The erosion pattern of the specimen is examined by obtaining the 3D microscopic profile of the eroded specimen by means of an optical profiler. It is found that the erosion profile changes as the jet angle varies. It is also observed that erosion profile is significantly different for smaller particles as compared to the larger particles. Moreover, these differences become more pronounced as the jet angle decreases. The present work discusses the differences of erosion patterns produced by both large and small particles. Computational Fluid Dynamics (CFD) is also used to study the effect of particle size on particle trajectories, impact speed, and impact angle. Also, CFD results help in explaining the differences observed in the erosion profiles caused by different particle sizes.
LES and PANS of Turbulent Flow Through a Staggered Tube Bundle
Authors: Minelli G. , Krajnović S. , Basara B.
Published: October 2017

Two unsteady numerical techniques, Partially-Averaged Navier Stokes (PANS) and Large Eddy Simulation (LES), are used to predict the flow in a tube bundle. The results were compared with the existing experimental data. Both methods predicted the flow in a relatively good agreement with the experimental data although the PANS simulation used only fifty percent of the computational nodes compared to the LES. The results of the simulations are used to study the unsteadiness in the flow and identify a dominant frequency of the flow.
A Simplified Model for the Normal Collision of Arbitrary Shape Particles in a Viscous Flow
Authors: Mohaghegh Fazlolah , Udaykumar H. S.
Published: October 2017

Modeling collision of finite size arbitrarily shaped particles is a tedious task because of difficulties in finding the collision parameter for the non-spherical particles. These parameters include the contact point, direction of the collision force and the collision forces and moments. In this paper a new collision algorithm is proposed to simulate collision of arbitrary shape particles to tackle flows containing a large number of particles. A pseudo-potential function is defined to quantify the collision parameters. This potential is defined based on the distance from the particle interface using either level set method or an analytical representation. With this definition, we can find the direction of collision forces and the amount of overlapping during the collision course. The collision forces are applied through a spring with a coefficient defined based on the collision course. In order to apply the damping, after the maximum collision course is achieved a spring with a lower stiffness in devised to achieve the desired bounce velocity. The results are validated for a spherical particle colliding with a wall. Then we show the capability of the model in simulation of collision of non-spherical particles with a wall. The new collision method not only is simple to implement but also it is applicable for any particle shape.
An Immersed Boundary Direct Numerical Simulation Study of the Wall Effect on the Dynamics of a Rigid Sphere
Authors: Gatewood Jason , Feng Zhi-Gang
Published: October 2017

The presence of a wall near a rigid sphere is known to disturb the particle fore and aft flow field and thereby affect particle drag and lift. This effect has wide ranging implications in particulate flows such as the dynamics of blood cells in microvessels or the transport of particulates in channel and pipe flows. In this study, an Immersed Boundary Direct Numerical Simulation (IB-DNS) is used to predict the dynamics of a rigid spherical body in the presence of a wall at laminar flows. The wall effect is shown to be significant when the dimensionless ratio (L/D) of the particle diameter (D) to the wall distance (L) is less than 3, and when particle Reynolds number is less than 10. Based on the IB-DNS results, a correlation for the wall effect on drag coefficient is derived that can be used to predict the actual drag coefficient for rigid spheres under the influence of a wall for L/D between 0.75 and 3 and Reynolds number between 0.18 and 10. The data underlying the correlation developed herein is validated by comparison to published experimental, numerical, and analytical correlations. The application of the IB-DNS method to study the wall effect is both novel and significant. It is novel in that such an application is not yet demonstrated. It is significant in that it; (1) utilizes a uniform Cartesian fluid mesh and (2) requires no sub domains of higher grid resolution in the wall gap.
Experimental Investigation of Sand Bed Height and Wave Height in Gas-Slurry Stratified Flow
Authors: Padsalgikar Ashwin , Dabirian Ramin , Mohan Ram S. , Shoham Ovadia
Published: October 2017

Unconsolidated reservoirs are notorious for production of sand with crude oil and natural gas. Bed formation in production pipelines poses several operational problems, such as partial or complete pipeline blockage, which decreases production rate and increases frictional pressure losses. Equipment failure may occur as well as erosion/corrosion and formation of corrosive cells under the sand beds. In this study, solid transport in horizontal stratified gas-liquid flow is investigated for a high concentration of 20,000 PPM, leading to sand bed formation. The experiments are conducted with air and water along with glass bead with particle sizes of 45–90 μm and 425–600 μm. The sand bed formation is studied by conducting experiments with gas-slurry flow. The experimental results confirm that the height of the bed decreases with increasing superficial gas velocity, and increases with increasing superficial liquid velocities. It is also observed that the height of the bed created with smaller diameter particles is larger than the one created by the bigger. The acquired experimental data shed more light on the formation of sand beds. It also serves as a basis for theoretical mechanistic models to enable prediction and design of stratified gas-liquid-solid flow.
Numerical Study of One Dimensional Pipe Flow Under Pump Cavitation Surge
Authors: Nohmi Motohiko , Yamazaki Satoshi , Kagawa Shusaku , An Byungjin , Kang Donghyuk , Yokota Kazuhiko
Published: October 2017

Pump cavitation surge is highly coupled phenomenon with unsteady cavitation inside a pump and system dynamics of the pipe flow surrounding the pump. The piping system flow dynamics can be calculated under two kinds of assumptions; lumped parameter system (LPS) and distributed parameter system (DPS). In the lumped parameter system, the equations of motion of water columns inside pipes are calculated upstream and downstream of the pump. In the distributed parameter system, wave propagations along the pipes are calculated. In this study a simple system that consists of an upstream tank, an upstream pipe, a pump with cavitation, a downstream pipe and a downstream tank is analyzed by using two methods. Cavitation inside the pump is featured in the lumped parameters of cavitation compliance and mass flow gain factor. In the lumped parameter system case, equations of motion are calculated numerically by Runge-Kutta methods. In the distributed parameter system case, wave propagations are calculated by Method of Characteristics. From the comparison of two method results, appropriate criterion for practical piping system calculation is discussed.
Three Dimensional Simulations of Convective Heat Transfer With Spectral Element Method
Authors: Liu Don , Zheng Yong-Lai , Moore Arden
Published: October 2017

This paper presents new equations for simulating three-dimensional convective heat transfer using the complete viscous dissipation function in the energy equation to account for the viscous heating and incorporating the Boussinesq approximation for the thermal buoyancy term in the Navier-Stokes equations. In addition, new implementation of fourth order Stiffly Stable schemes were achieved and tested for time integration. In order to provide dual-level mesh refinement, for flexible spatial resolutions, a modal spectral element method was implemented in solving these equations in three dimensions. Simulation results demonstrate that these new equations and implementations are accurate enough for investigating convective heat transfer with viscous heating subject to complex thermal and flow boundary conditions in three dimensional irregular domains using the high order finite element method.
On the Predictive Capability of DNS-DEM Applied to Suspended Sediment-Turbulence Interactions
Authors: Pakseresht Pedram , Apte Sourabh V. , Finn Justin R.
Published: October 2017

DNS coupled with a Point-Particle based model (PP) is used to study and predict particle-turbulence interactions in an open channel flow at Reynolds number of 811 (based on the friction velocity) corresponding to the experimental observations of [Righetti & Romano, JFM 2004]. Large particles of diameter 200 microns (8.1 in wall units) with average volume loading on the order of 0.001 are simulated using four-way coupling with closure models for drag, added mass, lift, pressure, and inter-particle/particle-wall collision forces. The point-particle model is able to accurately capture the effect of particles on the fluid flow in the outer layer where particles are under resolved. However, the dynamical interaction of particle-turbulence is under predicted in the near wall region where particles size are much larger than Kolmogorov scale and grid resolution in wall-normal direction, but smaller in both stream and span wise directions. It is conjectured that due to the large size particles compared to the Kolmogorov length scale near the bed, the effect of disturbances and deflections in the flow due to presence of such large particles is not captured using Lagrangian Point-Particle approach. For this configuration, the point-particle model is not appropriate in the near wall region and a hybrid resolved particle approach may be necessary.
Single-Phase Heat Transfer Enhancement in Partially Blocked Rod Bundles
Authors: Nguyen Ngoc Hung , Song Chul-Hwa , Kim Jongrok , Hong SeungHyun , Moon Sang-Ki
Published: October 2017

Wall-to-vapor convective heat transfer is the dominant heat transfer mechanism in the reactor core during the blowdown phase and the early stage of reflooding phase in a postulated large-break loss-of-coolant-accident (LB LOCA). Experiments on single-phase convective heat transfer to vapor were conducted in partially blocked rod bundles of 90% flow blockage ratio. The experimental results showed increase in local heat transfer just downstream of the blockage caused by flow separation phenomenon. The single-phase heat transfer enhancement models implemented in the COBRA-TF code underpredicted the local heat transfer in the downstream region of the flow blockage. Hence, a new correlation was proposed to improve the prediction capability of the COBRA-TF models by more accurately describing the flow separation effect. The new correlation predicted well various sets of experimental data within 20% discrepancy.
Hemodynamics Characteristics of a Four-Way Right-Atrium Bypass Connector
Authors: Mack Elizabeth , Untaroiu Alexandrina
Published: October 2017

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