bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of Turbulence Model Performance in Computational Fluid Dynamics Simulations of Horizontal Axis Wind Turbines
Authors: Mullenix Keaton , Walters D. Keith , Villegas Arturo , Diez F. Javier 
Published: October 2020

Abstract
Wind turbines are critically important in the quest to decrease global dependence on non-renewable energy sources. With the space to add 5M wind turbines, the United States is at the forefront of this transition. Horizontal axis wind turbines (HAWTs) have been studied numerically and experimentally at length. The vast majority of computational fluid dynamics (CFD) studies of HAWTs documented in the open literature have been carried out using two-dimensional simulations. Currently, the available three-dimensional simulations do not provide a comprehensive investigation of the accuracy of different options for modeling of fluid turbulence. In this paper four sets of CFD simulations are carried out using four different turbulence models that are commonly used for engineering level CFD analysis: SST-k-ω, Transition k-kL-ω, Standard k-ε, and Monotonically Integrated Large Eddy Simulation (MILES). These models were compared with experimental performance and coefficient of power results for a small-scale industrial wind turbine with inverse tip speed ratios (λ−1) in the range 0.072–0.144. They were further investigated to highlight the similarities and differences for the prediction of coefficient of pressure and skin friction coefficient. The results showed that no singular model, of the four investigated, was able to consistently predict the power performance with a high degree of accuracy when compared to the experimental results. The models also exhibited both similarities and key differences for the other aspects of flow physics. The results presented in this study highlight the critical role that turbulence modeling plays in the overall accuracy of a CFD simulation, and indicate that end users should be well aware of the uncertainties that arise in CFD results for wind turbine analysis, even when other sources of numerical error have been carefully minimized.
The Fluids Rap: It’s All About Flow
Authors: Nedyalkov Ivaylo 
Published: October 2020

Abstract
Most of the currently-enrolled undergraduate engineering students grew up with exposure to social media websites like Facebook and Youtube. Making sure that students are not distracted by their mobile devices in class has become more challenging, and one way to address the issue is to present engineering in a more entertaining and engaging way. A rap song about fluid mechanics was created by the author for entrainment, outreach, and education purposes. The song covers the fundamentals of fluid mechanics and mentions some theoretical basics, as well as some of the most widely used computational fluid dynamics and experimental fluid dynamics techniques. The song was written with the intention to be entertaining and educational — the goal was that someone with no prior fluid mechanics background will be able to understand it after spending 10–20 minutes reading through the lyrics explanations. A music video was produced for the song. The video production was sponsored by the American Society of Mechanical Engineers and includes visuals of experimental facilities and equipment.
The paper provides the background of the project, marketing plans, some of the lessons learned, the lyrics, and the explanations of the lyrics.
Effect of Formation Pattern on Schooling Energetics in Fish-Like Swimming
Authors: Pan Yu , Han Pan , Huang Jing , Dong Haibo 
Published: October 2020

Abstract
In the present study, an immerse-boundary-method-based in-house numerical solver is employed to investigate the effects of school pattern on energetics in fish-like swimming. Following Weihsys theory, two-dimensional diamond schools are formed for numerical simulations. The effects of the lateral distance and the longitudinal distance have been investigated to reveal the energetic saving mechanism in a fish school. It is found that the energetic performance in a narrow diamond school (2dy = 0.4) is very different from that in a wide school. In the wide school, the beneficial effect will decay gradually with the increase of longitudinal distance; however, in the narrow school, the variation of the effect is needed to divide into three phases. When the longitudinal spacing is small (2dx = 0.4 ∼ 2), the variation of power efficiency is complex. It increases sharply when 2dx changes from 0.4 to 1.2, then decrease. When the longitudinal distance is larger than two, the variation of energetics in a narrow diamond school has the same trend as that in a wide school. It is because, in the narrow school, the channeling effect is harmful to the energetics of individuals and plays an important role when the longitudinal distance is small. However, the detrimental effect will decay quickly with the increase of the longitudinal distance. Besides, when the longitudinal distance is large (2dx &gt; 3.4), the narrow school shows a better power efficiency than the wide school. It is because, at this time, the fishes at the rear of school are still located at the instructive vortex wake produced by fishes in the front. These findings will give insight on how to form a power-efficient robotic school under water.
Experimental Investigations of the Surface Groove Effect in Taylor-Couette-Poiseuille Flow
Authors: Gaied Lamia , Aloui Fethi , Lippert Marc , Berrich Emna 
Published: October 2020

Abstract
In this paper, we investigate the effects of an imposed axial flow on hydrodynamic instabilities’ Couette-Taylor flow in the case where the wall of the inner cylinder of the system is grouved.
Without imposed axial flow, the basic flow of a fluid between two coaxial cylinders known by Couette flow, which is characterized by several temporal and spatial symmetries. The increase in the rotation causes the breaking of these symmetries.
In both cases where the surface of the inner cylinder is smooth and grooved, five different flow regimes can be determined: Taylor vortex flow (TVF), wavy vortex flow (WVF), and Modulated Wavy vortex flow (MWVF). Each time the flow passes from one hydrodynamic regime to another until it enters a state of turbulence, which is characterized by the destruction of all the symmetries that existed at the beginning.
In addition, when an axial flow is imposed on a Taylor-Couette flow, new helical vortex structures are observed in both cases (with and without surface groove).
The influence of surface structures (grooves) on the shear stress of the wall is discussed with and without axial base flow. A spatio-temporal description of several flow models was obtained using firstly, a visualization’s qualitative study using kalliroscope particles. Secondly, a quantitative study by polarography using simple probes have been used to characterize the impact of vortex structures on the Couette-Taylor flows without and with an axial flow on the transfer.
A Hybrid Method for Fan Simulations in Full Vehicle Thermal Analyses
Authors: Wu Zhilei , Blatnik Michael , Kress Eamonn , Deleon Lester 
Published: October 2020

Abstract
In full vehicle thermal flow analyses, the most often used procedure to simulate fluid motions driven by the cooling fan is the Moving Reference Frame (MRF) method. In the MRF approach, the fan is fixed in space and the fan rotation is modeled using grid fluxes. This method is widely used because it provides a fast and effective means of simulating fans. However, the MRF method does not always accurately predict the thermal wake and the mass flow rate through the fan, which causes errors in predicted temperatures on the parts downstream of the fan. Another method for fan simulation is the Rigid Body Motion (RBM) method in which the fan rotates in time. The RBM method models the fan motions directly, thus it can accurately predict the mass flow rate and thermal wake. However, an RBM simulation is transient and needs a time-average to obtain statistically steady-state results. The RBM method requires a significant amount of CPU resources and simulation time, which prevents it from being widely used in industry.
In the current work, a Hybrid Rigid Body Motion (HRBM) method is developed and validated. The HRBM method splits the full vehicle thermal simulation into two simulations, and then couples them at the interface. The first simulation is transient, utilizes the RBM method for the fan, and only models the fan regions. The second simulation is steady, which models the full vehicle except the fan regions. The solution from the transient simulation is time-averaged on the exchange interface and used as boundary conditions for the steady simulation. Conversely, the solution for the steady simulation is used as boundary conditions for the transient simulation at the exchange interface. Due to the slight differences resulting from time-averaging, there is a mismatch in the physical quantities at the exchange interface. This causes stability issues which prevent the coupled simulations from converging. Special techniques have been used in this work to stabilize the solution at the interface, which ensured the convergence of the coupled simulations.
The HRBM method greatly improves the accuracy of the full vehicle thermal flow simulation compared to using the MRF method. The thermal wake that results from using HRBM to model the fan is very similar to that produced by RBM, but HRBM utilizes ∼20–30% of the simulation resources required by RBM to achieve convergence.
Investigation of Numerical Scheme and Model Combinations for CFD Simulation of a Thermosyphon
Authors: Wang Huiyu , Walters D. Keith , Walters Keisha B. 
Published: October 2020

Abstract
This paper investigates the performance of a commercially available computational fluid dynamics (CFD) solver (Ansys FLUENT) to predict the flow and heat transfer characteristics of a two-phase closed thermosyphon (TPCT). Specifically, the study compares two different discretization schemes for the volume fraction equation with different time step sizes using three different sets of mass transfer time relaxation parameters for evaporation and condensation. The present study evaluates use of the Compressive scheme to increase the time step size compared to the Geo-Reconstruct scheme. In addition, a model is proposed to adjust the global saturation temperature of the system based on the volume of the vapor phase in order to balance the mass transfer inside TPCT and more accurately represent the realistic operating conditions of a TPCT. In this study a total of nineteen simulations are performed, and two types of boundary conditions for the condenser are investigated to determine the effect on the accuracy of the simulation results. The baseline simulation uses the Geo-Reconstruct method with a fixed saturation temperature. Other additional cases are performed using the Geo-Reconstruct method with variable saturation temperature, and the Compressive method with and without variable saturation temperature using different sets of mass transfer time relaxation parameters. Results show that the case using the Compressive method with the variable saturation temperature model has good agreement with the reference experimental data and is less computationally expensive than the Geo-Reconstruct method. The 3D CFD models implemented in this study successfully predict the phase change process and flow behavior inside the TPCTs, at least in a qualitative sense.
Characterization of Oil Droplets in the Lower Cavity of a Rotary Compressor
Authors: Wu Puyuan , Chen Jun , Sojka Paul E. , Li Yang , Cao Hongjun 
Published: October 2020

Abstract
The rotary compressor is widely used in small air conditioners, and is the most important element in the system. It relies on eccentric rolling pistons that rotate at high speed to compress refrigerant in the cylinder. The lubricant oil in the rotary compressor is used for lubricating the bearing and sealing the clearance of sliding parts. However, the oil can experience complex and highly-coupled atomization processes when discharged from the cylinder, and part of oil droplets can exhaust from the rotary compressor by the refrigerant flow and reduce the efficiency and reliability of the compressor as a result. Thus, characterizing the behavior of oil droplets in the lower cavity of a rotary compressor where the atomization occurs is a major challenge for manufacturers who rely on CFD tools to predict the multiphase flow. By modifying a rotary compressor, the oil behavior in the lower cavity of a rotary compressor is observed and recorded by shadowgraphy. In the current phase, the number, size, and morphology of oil droplets are analyzed statistically with image processing method, which provides better understanding to the atomization mode in the lower cavity, the velocity of the mist of oil droplets is calculated with Optical Flow Velocimetry. The results can assist designers in improving the CFD analysis of compressors and ultimately reducing the Oil Discharge Rate (ODR).
Several Modifications to Improve Numerical Stability of Leishmen-Beddoes Dynamic Stall Model
Authors: Guo Jia , Meng Haoran , Zeng Pan , Lei Liping 
Published: October 2020

Abstract
Dynamic stall is dominant to aerodynamic performance of vertical axis wind turbines where angles of attack (AoAs) of blades vary periodically during operation. Therefore, dynamic stall models are necessarily employed in the simulation of wind turbines. Among them the Leishmen-Beddoes (LB) dynamic stall model are widely accepted nowadays. In the LB model, aerodynamic forces of blades are determined by AoAs and their rates of change. However, in consideration of the inevitable existence of numerical errors of AoAs, calculations of the rates of change may cause unexpected numerical problems. This paper focused on presence of fluctuations of blade forces due to minor numerical errors of AoAs in the LB model. Then three modifications, namely the implementation of filters of AoAs, alternative calculation of change of variables and scaling of time constants, were employed and their effect on numerical stability of the LB model was evaluated. It is found that the implementation of filters of AoAs can eliminate fluctuations of outcome forces but the phase delay is the side effect. In addition, alternative calculation of change of variables and scaling of time constants can reduce the maximum nominal fluctuations of results from 16.4% to 5.8% and 5.1%, respectively.
Parametric Optimization of a Dry Powder Inhaler
Authors: Kotteda V. M. Krushnarao , Badhan Antara , Kumar Vinod 
Published: October 2020

Abstract
In the present study, particles in cell method, a Eulerian-Lagrangian approach is used to simulate the flow in an inhaler. The number of uncertain parameters, including properties of particles, fluidizing agents’ properties, initial/boundary conditions, and numerical parameters related to PIC simulations, is fourteen. The residence time of 280 PIC simulations for different values of the uncertain parameters is used to test/train a data-driven framework. The values of the uncertain parameters are generated via the Latin Hypercube Sampling method and a normal distribution. The trained algorithm is used to predict the residence time for various unknown parameters. This framework is used to carry out the sensitivity analysis to find the most influential settings on the residence time of the particles in the inhaler. The optimum parameters of the influential parameters for a given residence time is calculated via the data-driven framework.
Influence of a Yield-Shear-Thinning Rheology on the Flow Behavior of Submerged Annular Jets
Authors: Hammad Khaled J. 
Published: October 2020

Abstract
The flow structure and decay characteristics of submerged annular yield-pseudoplastic jets are investigated. Numerical solutions to the governing mass and momentum conservation equations, along with the Herschel-Bulkley rheological model, are obtained using a finite-difference scheme. A parametric study is implemented to investigate the effects of annular nozzle diameter ratio, κ, the power-law index, n, and yield number, Y, over the following range: κ = {0, 0.5}; n = {1, 0.6}; and Y = {0, 1, 5}. The Reynolds number was fixed at Re = 100, which ensured steady and laminar jet flow conditions throughout the whole flow field. The selected yield number and power-law index values allowed for the investigation of the presence of yield stress and shear-thinning effects on the resulting structure and evolution of the flow field. The results demonstrate the substantial impact of the inflow conditions and rheology on the annular jet evolution, and on the extent of the outer recirculation region and recirculation strength of both the outer and central regions.
On the Boundary Condition for the Level Set Function in the Numerical Simulation of Moving Contact Lines
Authors: Gómez Pablo , Esteban Adolfo , Zanzi Claudio , López Joaquín , Hernández Julio 
Published: October 2020

Abstract
We present a method based on a level set formulation to reproduce the behavior of the contact line on solid walls in the simulation of 3D unsteady interfacial flows characterized by large density ratios. The level set method poses a particular difficulty, related to the reinitialization procedure, when used in the simulation of interfacial flows in which the interface intersects a solid wall, due to the appearance of a blind zone where standard reinitialization procedures produce inconsistent results. The proposed method overcomes this difficulty by introducing a boundary condition for the level set function on the solid surface based on the normal extension of the contact angle from the interface along the solid wall. In order to reproduce the dynamics of the contact line we use a simplified model that imposes a boundary condition on the interface curvature based on the static contact angle, and define a thin slip zone at the solid wall around the contact line. To assess the accuracy and robustness of the proposed method, we conducted several preliminary numerical tests in three dimensions, whose results are compared with analytical solutions and other results available in the literature.
Droplet Dynamics in Constricted Return Bends of Microfluidic Channels
Authors: Melbye Julie A. , Wang Yechun 
Published: October 2020

Abstract
Microfluidic delivery systems have been employed to facilitate cell seeding procedures in drug development for personalized medicine for cancer patients. Despite of the high-throughput nature and potential impact on clinical outcomes of these systems, the efficiency in cell trapping remains a challenge in the operation. Droplet-based microfluidics became one of the solutions due to the large size of the cell-enclosing droplets and their interfacial properties. This study is focused on the motion of the cell-enclosing droplet in a constricted return bends that help to restrict the release of the cells while maintaining the high-throughput nature of the device. In this preliminary study, a three-dimensional boundary element method is used to predict droplet shape, deformation and migration velocity under the influence of various fluid properties and operational conditions. A variety of channel geometries have been explored as well. The resulting computational framework will be used to guide the design of a droplet-based microfluidic delivery system for cell seeding in 3D tumor spheroid arrays.
Simulations of Flow Separation Control Using Different Plasma Actuator Models
Authors: Abdelraouf Hatem , Kassab Sadek Z. , Elmekawy Ahmed M. Nagib 
Published: October 2020

Abstract
This study investigates the active flow control on NACA0012 airfoil numerically by introducing dielectric barrier discharge (DBD) plasma actuators. The flow over the airfoil simulations were performed using ANSYS program for free-stream velocity 14.6 m/s with wide range of angle of attacks (from 0 to 20 degrees) on NACA0012 airfoil with applied voltage 16 kV across the electrodes. There are several plasma actuator models, which simulate the effect of the plasma actuator. This paper focuses on two numerical methods: Shyy model and Suzen model. They depend on calculating the induced body force of the plasma and import it in Navier Stokes equation as an external body force. Mesh independence study is performed on the airfoil and validate the results without plasma activation with the experimental results. Two actuators were added at positions 0.1 and 0.3 of the chord length to the airfoil and an investigation is performed on the lift CL and drag Cd coefficients of the airfoil without and with the activation of the plasma. Thereafter, a comparison between the numerical results of two different plasma simulation models that were applied.
Optimized Gun Barrel Based on Numerical Simulation to Produced Oil With Low BSW Content
Authors: Daza Silvia Araujo , Villamizar Urbano Montañez 
Published: October 2020

Abstract
This work presents the methodology and results of the optimization of the internals (Inlet distributor, oil and water collectors) of a 20,000 BPD (0.037 m3/s) gun-barrel tank starting from an existing design. Computational fluid dynamics (CFD) was applied to simulate and evaluate the performance of various internal configurations. These simulations were performed to determine the best configuration to ensure efficient separation of the oil-water mixture and oil with a low BSW content &lt; 2% at the outlet. The simulations were carried out using the commercial software ANSYS Fluent under the two-phase flow VOF model and k-ε realizable turbulence model. Further CFD simulations were performed to evaluate the behavior of the gun barrel tank under different operating conditions (Different inlet flow rate) and to determine the maximum operation flow which allows obtaining the crude-oil with a maximum BSW content of 0.5%. From the simulation results, an operating curve (operating flow vs retention time) was constructed. This information allows, in practice, to identify the inlet flow rate based on the desired content of BSW in the separated oil.
Experimental and Numerical Modeling of Viscous Fluid Flow in Bifurcated Long Pipes for Oil Transport
Authors: Radulescu Victorita 
Published: October 2020

Abstract
The present paper presents some experimental and numerical modeling of the Newtonian and viscoelastic flows in bifurcated configurations of pipes, for stationary and non-permanent regimes. The main purpose of this study is to select an optimal design of the pipes ramifications, for minimizing the local pressure losses and to improve the efficiency of fluid transportation. The method is based on the transformation of the flow field obtained with particle image visualization technique, for different Reynolds numbers. Based on experimental results will be established optimum geometry of the ramifications. The results will be used as the boundary conditions for numerical modeling. The experimental measurements were performed into a closed circuit of pipes, with different diameters, consisting of a centrifugal pump supplied by a tank, sensors for estimating the pressure losses and devices for measuring the flow rate. It is detailed presented in a dedicated paragraph. The main pipe is connected to a transparent bifurcation with branches at different angles from the main pipe axis. The measurements illustrate that the flow has different aspects, depending on the bifurcation’s angle. The numerical simulations are performed with Fluent CFD based on the volume numerical method, to obtain the Navier-Stokes solutions for the Newtonian model in the laminar or turbulent flow conditions. A pre-processor has been used to create the geometry of the bifurcation and to generate the mesh. The 3D-flow domain contains 944390 volumes, tetrahedral hybrid. It was obtained the numerical solutions of the fluid flow in branching pipes for the Reynolds numbers from 1000 up to 40000. The governing equations were assumed from the k-ε model for turbulence flow, the equation of continuity, equation of fluid motion, and the transport equation. Finally, some conclusions and references are presented.