bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Microscopic Vortices Caused by Flow Interaction With Solid Obstacles on Heat Transfer in Turbulent Porous Media Flows
Authors: Huang Ching-Wei , Srikanth Vishal , Li Haodong , Kuznetsov Andrey V. 
Published: November 2019

Abstract
Turbulent flow in a homogeneous porous medium was investigated through the use of numerical methods by employing the Reynolds Averaged Navier-Stokes (RANS) modeling technique. The focus of our research was to study how microscopic vortices in porous media flow influence the heat transfer from the solid obstacles comprising the porous medium to the fluid. A Representative Elementary Volume (REV) with 4 × 4 cylindrical obstacles and periodic boundary conditions was used to represent the infinite porous medium structure.
Our hypothesis is that the rate of heat transfer between the obstacle surface and the fluid (qavg) is strongly influenced by the size of the contact area between the vortices and the solid obstacles in the porous medium (Avc). This is because vortices are regions with low velocity that form an insulating layer on the surface of the obstacles. Factors such as the porosity (φ), Pore Scale Reynolds number (Rep), and obstacle shape of the porous medium were investigated. All three of these factors have different influences on the contact area Avc, and, by extension, the overall heat transfer rate qavg. Under the same Pore Scale Reynolds number (Rep), our results suggest that a higher overall heat transfer rate is exhibited for smaller contact areas between the vortices and the obstacle surface. Although the size of the contact area, Avc, is affected by Rep, the direct influence of Rep on the overall heat transfer rate qavg is much stronger, and exceeds the effect of Avc on qavg. The Pore Scale Reynolds number, Rep, and the mean Nusselt number, Num, have a seemingly logarithmic relationship.
Influence of Turbulence Models in Transient Simulations of Inducers Under Steady Operation
Authors: Gwiasda Björn , Mohr Matthias , Herrmann-Verspagen Dennis , Böhle Martin 
Published: November 2019

Abstract
A significant uncertainty in full transient 3D-CFD simulations of inducers is the used turbulence model. To investigate the influence of different turbulence models (Spalart-Allmaras, SST, SSG) on the transient effects experiments and simulations are performed for two inducers. In this paper the results of simulations are represented that are performed under noncavitating conditions to exclude the additional influence of the cavitation model in order to gain an isolated understanding for the influence of turbulence models. Comparison of transient data from simulations as well as experiments determines the influence of the turbulence model. For the investigations two different inducers are designed with different leading edges. One inducer with a straight leading edge and one with a back swept leading edge. All other geometrical parameters are kept constant, such as the hub contour which is purely axial.
CFD Simulations of the Rheological Behavior of Aqueous Foam Flow Through a Half-Sudden Expansion
Authors: Dallagi Heni , Al Saabi Ahmad , Faille Christine , Benezech Thierry , Augustin Wolfgang , Aloui Fethi 
Published: November 2019

Abstract
Aqueous foam is a non-Newtonian complex fluid. Its flow through the singularities presents many fundamental aspects. The rheological character of the foams flowing in this kind of geometries can create important disturbance on its behavior, according to the flow rate set and therefore a modification in its texture and in the nature of its established regime. During this study, numerical simulation for the case of a half-sudden expansion was developed using the Herschel-Bulkley rheological model. The model is used to describe the response of foams during under flowing conditions through this type of singularity. Obtained CFD results are focused on the pressure losses, velocity fields of the foam flow in various positions of the channel using different qualities (variation of void fraction) for lower velocities’ case (one-dimensional regime) and for the three-dimensional regime. Firstly, we validated the use of this type of non-Newtonian foam flow fluid to describe the flow reorganization through a half-sudden. In a second step, we used an experimental database to validate our CFD pressure losses and velocity fields. The comparison of these results with those obtained experimentally by Chovet shows a good agreement for lower speed foam flow, but with some uncertainty for higher foam flow velocities.
A Study of Multiphase Flow and Heat Transfer in Proton Exchange Membrane Fuel Cells With Perforated Metal Gas Diffusion Layers
Authors: Berning Torsten , Tanaka Shiro 
Published: November 2019

Abstract
A numerical analysis of a proton exchange membrane fuel cell (PEMFC) that contains a perforated metal plate at the cathode side has been conducted. The model utilizes the Eulerian multi-phase approach to predict the occurrence and transport of liquid water inside the cell. The PEMFC that was modelled contained micro-channels at both anode and cathode side. Results suggest that despite the fact that the inlet gases are fully saturated (RH = 100%), the holes in the metal sheet remain in the single phase, and the predicted maximum current densities are accordingly high. The high thermal conductivity of the metal sheets result in only a moderate temperature increase in the cell, and the fuel cell membrane is predicted to be hydrated under all conditions investigated. The fact that the cathode channel and the holes in the metal sheet remain dry is attributed to the high pressure drop inside the flow channel.
Global Sensitivity Analysis for Stay Vane and Casing Design of Reaction Hydraulic Turbine
Authors: Cho Hyunkyoo , Shrestha Ujjwal , Choi Young-Do , Park Jungwan 
Published: November 2019

Abstract
Global sensitivity analysis (GSA) estimates influence of design variables in the entire design domain on performance measures. Hence, using GSA, important design variables could be found for an engineering application with high dimension which require computationally expensive analyses. Then, similar engineering applications could use selected variables to carry out design process with smaller dimension and affordable computational cost. In this study, GSA has been carried out for the performance measures in design of stay vane and casing of reaction hydraulic turbines. Global sensitivity index method is used for GSA because it can fully capture the effect of interaction between the design variables. For efficiency, genetic aggregation surrogate models are constructed using the responses of computational fluid dynamic (CFD) analysis. Global sensitivity indices for the performance measures of stay vane and casing have been evaluated using the surrogate models. It is found that less than three design variables among 12 are effective in the design process of stay vane and casing in reaction hydraulic turbines.
Predicting Cooling Fan Noise of Electric Motor Using Compressible Large Eddy Simulation
Authors: Kaneko Kimihisa , Yamamoto Tsutomu 
Published: November 2019

Abstract
This paper describes prediction of aeroacoustics from a rotating machinery fan using compressible Large Eddy Simulation (LES). The fan is installed semi-opened space located between the fan cover and the body of rotating machinery such as a electric motor. The fan distributes air from the fan cover intake onto the cooling fins. The Reynolds number of the rotating fan is 9 × 105; its Mach number is approximately 0.1. Under the low Mach number regime, hybrid computational aeroacoustics (hybrid CAA) method, which is solved turbulent flow and acoustics separately, is generally used. However, we used a direct CAA method because interaction between pressure fluctuation from the turbulence and sound propagation should be considered.
For the direct CAA method approach, compressible Navier–Stokes equations are solved. Density is calculated from the ideal gas law. To compute turbulence phenomena, LES is used as the turbulence model. The Dynamic Smagorinsky Model is used for the subgrid scale. The sound propagation speed is approximately 10 times faster than the flow speed.
Therefore, the numerical schemes, time step, and computational grids size were evaluated with line sound source in the two-dimensional domain as a fundamental study to determine the numerical schemes. Subsequently we evaluated the sound pressure level with the electric motor fan, which is an experimental structure.
Through verification of the direct CAA model, we obtained the following results. (1) The predicted pressure fluctuation spectra show good agreement with the experimentally obtained spectra. Specifically, the blade passing frequency (BPF) and trend of the pressure fluctuation decay in the inertial turbulence subrange were predicted. (2) The predicted sound pressure spectra also show good agreement with BPF. Specifically, the acoustic mode and broadband turbulence noise level were predicted.
Numerical Calibration of 3D Printed Five-Hole Probes for the Transonic Flow Regime
Authors: Passmann Maximilian , aus der Wiesche Stefan , Joos Franz 
Published: November 2019

Abstract
This paper presents a method for a cost- and time-effective calibration procedure for five-hole probes for the transonic flow regime based on additive manufacturing and a numerical calibration routine. The computational setup and calibration routine are described in detail. The calibration procedure is tested on a custom-built L-shaped conical probe of 30° half-angle with a flat tip and an outer diameter of 2.4mm. The probe tip is manufactured in stainless steel using DMLS. Numerical calibration is carried out over a Mach number range of 0.2 to 1.4 and pitch and yaw angles of ±45°. The numerical calibration charts are validated with wind tunnel tests and the expected accuracy of the numerical calibration method is quantified. Exemplary results of area traverses up- and downstream of a linear transonic turbine cascade with tip clearance are presented and discussed briefly.
Investigation on the Effects of Torque Converter Blade Thickness Based on FSI Simulation
Authors: Liu Cheng , Guo Meng , Wei Wei , Yan Qingdong , Li Pengyu 
Published: November 2019

Abstract
A lot of efforts were put into the design of torque converter blade angles and the analysis of transient flow behaviors; yet little is known about the influence of the blade thickness distribution on the performance or structural response of a torque converter. This study proposed a parameterized blade thickness design model and analyzed the effects of the blade thickness on hydrodynamic performance and structural response using fluid-structure interaction (FSI) models. Both one-way FSI model and two-way FSI model were built and evaluated against test data, and it was found that the transient two-way FSI model outperformed the steady-state FSI model in terms of both flow and structure simulations. It was found that the stall torque ratio and peak efficiency exhibited positive correlations with blade thicknesses, whereas the stall capacity constant was inversely related to blade thicknesses. Both numerical and experimental results suggested that the pump-turbine interaction induced serious flow fluctuations, and FSI simulations were required in the design process to avoid potential resonance.
Transient Simulation on Unbalanced Torque of Piston Type Valve Cores During Dynamic Motion
Authors: Hou Cong-wei , Mu Juan , Li Wen-qing , Jin Zhi-jiang , Qian Jin-yuan 
Published: November 2019

Abstract
Piston type valve cores are widely adopted in check valves, globe valves, pressure reducing valves and so forth. With the irregular inlet flow channel, the bottom of piston type valve core exits unbalanced torques usually. The unbalanced torque causes the valve core to squeeze sealing elements and increases the energy consumption. To analyze the unbalanced torque on the bottom of the piston type valve core, a transient numerical model of the piston type valve core is established and the simulation results are compared with the theoretical formula for the purpose of validation. The dynamic flow characteristics are studied to investigate pressure characteristics on the bottom of the piston type valve core with the dynamic motion of the valve core. Meanwhile, pressure characteristics under different valve core displacements are obtained, and the sensitive range of the unbalanced torque is found. This work can be helpful for the further structural optimization on the valves with piston type valve cores.
CFD Investigation of a PEMFC Stack Assembly
Authors: Anderson Kevin R. , Murphy Andrew 
Published: November 2019

Abstract
In this study 3-D CFD modeling of a cylindrical stack Proton-exchange membrane fuel cell (PEMFC) is provided. The H2O-O2 PEMFC uses a 10.8 mm2 area membrane and Platinum (Pt) catalyst. The paper presents the methodology for the PEMFC commercial software module, the set-up of the Computational Fluid Dynamics (CFD) geometry, mesh and boundary conditions. Results for the current-voltage performance curves and 3-D contour plots of the fluid, heat and species concentrations within the PEMFC are given. Results are presented for a low-temperature fuel cell using NAFION membrane and a high-temperature fuel cell using BZY membrane.
Performance Improvement of Electro-Hydraulic Servo Valve Using a Feed-Forward Control and an Input Shaping Filter
Authors: Lee Illyeong , Iwan Istanto , Choi Saeryung , Huh Junyoung 
Published: November 2019

Abstract
The control performance of hydraulic systems is basically influenced by the performance of electro-hydraulic servo valve used in a hydraulic control system. In this study, the authors propose a control design to improve the control performance of servo valves with a non-contact eddy current type displacement sensor. Mathematical model for the valve is obtained through an experimental identification process. A PI-D controller together with a feedforward (FF) controller is applied to the valve. To further improve the response of the servo valve, an input shaping filter (ISF) is incorporated into the valve control system. Finally, the effectiveness of the proposed control system is verified experimentally.
CFD-Simulation of Centrifugal Fan Performance Characteristics Using Ideal and Real Gas Models for Air and Organic Fluids
Authors: Fritsche Manuel , Epple Philipp , Hasselmann Karsten , Reinker Felix , Wagner Robert , aus der Wiesche Stefan , Russwurm Hans 
Published: November 2019

Abstract
Efficient processes with organic fluids are becoming increasingly important. The high tech fluid Novec™ is such an organic fluid and is used, for example, as a coolant for highperformance electronics, low-temperature heat transfer applications, cooling of automotive batteries, just to mention a few. Thus, efficient designed fans for the transport of organic fluids are becoming more and more important in the process engineering. CFD-simulations are nowadays integral part of the design and optimization process of fans. For air at the most usual application conditions, i.e. no extreme temperatures or pressures, the ideal gas model is in good agreement with the real gas approach.
In the present study, this real gas approach for organic fluids have been investigated with CFD methods and, the deviation from the ideal gas model has been analyzed. For this purpose, a simulation model of a centrifugal fan with volute has been designed as a test case. First, the ideal gas model approach has been compared with the real gas approach model of Peng-Robinson for air using the commercial solver ANSYS CFX. Thereafter, the same comparison has been performed using the organic fluid Novec™.
After a detailed grid study, the entire fan characteristics, i.e. the design point and the off-design points, have been simulated and evaluated for each fluid (air and Novec™) and gas model (ideal gas and Peng-Robinson real gas). The steady state simulations of the centrifugal fan have been performed using the Frozen Rotor model. The simulation results have been compared, discussed and presented in detail.
Investigation of Unsteady Performance Characteristics of a Submersible Axial-Flow Pump for Different IGV and Blade Pitch Angles
Authors: Kim Youn-Sung , Shim Hyeon-Seok , Kim Kwang-Yong 
Published: November 2019

Abstract
This paper presents a study of the effects of blade pitch angle and inlet guide vane (IGV) angle on the performance of a submersible axial-flow pump. To analyze the interaction effects between the IGVs and the rotor blades, both steady and unsteady three-dimensional Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model were solved. Hexahedral meshes were used in the computational domain and a grid-dependency test was performed to obtain an optimal number of grid nodes. The performance curves obtained by numerical simulation showed good agreement with experimental data. The results show that the fluctuation of hydraulic efficiency and head coefficient increased significantly under overload conditions as the IGV setting angle increased. Additionally, both the steady and unsteady performance characteristics were shown to be quite dependent on the combination of IGV angle and blade pitch angle, because the relative velocity at leading edge played an important role in the performance under overload conditions.
Operational Performance and Locally Resolved Outflow of Brush Seals
Authors: Schur Fabian , Friedrichs Jens 
Published: November 2019

Abstract
As a result of the superior leakage efficiency of brush seals compared to conventional labyrinth seals, compliant contacting filament seals are used to increase the efficiency of jet engines as well as stationary gas and steam turbines. The widespread application of brush seals at different and varying pressure differences combined with variable contacting velocities at the rotor surface requires a profound understanding of the influences of different design parameters on the operational leakage performance. In order to systematically investigate the impact of different design parameters on sealing performance, a new cold air test rig was developed. The new test rig with rotating shaft enables hot-wire anemometry measurements downstream of the seals. These measurements provide insight into the locally resolved flow structure in addition to the integral leakage measurements. For the investigations, one welded and five different clamped brush seals at rotational speeds up to 3000rpm and pressure differences across the seals up to 500kPa are considered. Therefore, the influence of two different designs on the flow through the bristles is presented. For the clamped brush seals, variations of the front and backing plate are investigated. Additionally, the effects of bristle diameter and three different axial inclinations of the bristle pack on the sealing efficiency are shown. Furthermore, initial wear development during the first 30 to 60 hours of brush seal operation at varying experimental conditions is presented and linked to the design parameters. Consequently, the effects of major design aspects on the operational performance of brush seals are examined and presented.
Mixing of Dry Air With Water-Liquid Flowing Through an Inverted U-Tube for Power Plant Condenser Applications
Authors: Yousef Khaled , Hegazy Ahmed , Engeda Abraham 
Published: November 2019

Abstract
This paper presents a Computational Fluid Dynamic (CFD) simulation for dry air/water-liquid and two-phase flow mixing in a vertical inverted U-tube using the mixture multiphase and turbulence models. This study is to investigate the flow behaviors and underlying some physical mechanisms encountered in dry air/water-liquid flow in the inverted U-tube. Water flows through the inverted U-tube while the dry air is entrained using the side-tube installed after the water flow downward. The inverted U-tube is tested at water mass flow rates of 2,4,6 and 8 kg/s, air mass flow rates, 0.000614–0.02292 kg/s, with dry air volume fractions 0.2–0.9. The obtained results are compared with the experimental data for model validation and the present CFD model is able to give an acceptable agreement. Also, the results show that, at water mass flow rate of 2 kg/s, there are vortices and turbulent intensity disturbances are noticed at the inverted U-tube higher part, which refers to an air entrainment occurrence from the side-tube. Theses disturbances starts to be stabilized at air mass flow rate around 0.00736 kg/s and air volume fraction, αa = 0.75. This means, if the air mass flow rate increases above this limit, the air entrainment may be blocked. On the other side, at water mass flow rate of 4 kg/s, there are little noticed disturbances until air mass flow rate of 0.00368 kg/s and αa = 0.43 and thereafter stabilized. After this point for water mass flow rate of 4 kg/s, increasing air mass flow rate may block the water flow and the whole inverted U-tube system possible stop flowing. Therefore, this study is able to estimate the required operational conditions and mass ratios for stable air entrainment process. Beyond these operational conditions, air entrainment may be blocked and the whole system discontinues its normal induced gravitational flow. In addition, this study proves that the inverted U-tube is able to generate a vacuum pressure up to 53.382 kPa based on the present geometrical configuration. This generated low-pressure by the inverted U-tube can be used for engineering applications which are working under vacuum and need continuous evacuating form the dry air and non-condensable gases. Furthermore, these findings motivate the utilizing of inverted U-tube for the air evacuation purposes for less power consuming in power plants.
Numerical Design of a Partial-Support Axial Blood Pump
Authors: Liu Guangmao , Jin Donghai , Wang Mengyu , Gui Xingmin 
Published: November 2019

Abstract
Partial-support is the main support mode for “less sick” patients with severe heart failure. But there were fewer partial-support blood pumps for clinical use. An implantable partial-support axial blood pump was developed for heart failure patients. To gain better hemolytic performance and lower pump thrombus risk, the rotor blades were extended to the contractive section of the rotor hub while cone-bearing was adopted. The hydraulic and hemolytic performance of the blood pump was simulated and analyzed by computational fluid dynamics (CFD) method. The flow velocity, hydraulic efficiency, exposure time, scalar shear stress (SSS) and hemolytic performance of the axial blood pump was analyzed. The numerical results showed that the axial blood pump could produce a 1–8 Lpm flow rate with a 54.7–186.7 mmHg pressure head when the pump rotating from 9000 to 13000 rpm. The hydraulic efficiency and SSS distribution corresponded with the typical performance of a blood pump. The mean hemolysis index of the blood pump calculated by the Giersiepen’s model was 5.0 × 10−5%. After extending the rotor blades to the contractive section of the rotor hub, the spiral flow at the inlet of the rotor impeller was reduced. Hemolysis in the blood pump was improved because the exposure time was reduced and the blood damage caused by SSS was reduced.. The designed blood pump satisfies the clinical requirements of partial-assist for less-sick heart failure patients.