bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Actively-Controlled Trailing Edge Flap Upon Airfoil Energy Harvester
Authors: Strahl Jordan , Liburdy James 
Published: September 2022

Abstract
An experimental study was undertaken to evaluate the power extraction of an airfoil undergoing large amplitude pitching and heaving using a trailing edge flapping motion for the application of energy harvesting for steady flow over the airfoil. The airfoil was a NACA0015 design, pitching at the 1/3 chord position, with an actively controlled trailing edge flap hinged at the 2/3 chord location (chord length of c = 150mm and aspect ratio AR = 2, however end plates were used to simulate a two-dimensional airfoil). Data were obtained over a range of wind speeds corresponding to Reynolds numbers in the 30,000–60,000 range in a low-speed wind tunnel with turbulence intensities below 2%. The results are characterized using the reduced frequency, k = fc/U∞ over the range of 0.04–0.08, where f is the oscillating frequency in Hz, and U∞ is the freestream velocity. The pitching and heaving amplitudes are θ0 = 70° and h0 = 0.6c respectively, with a phase delay of 90°. Two trailing edge motion profiles are presented, examining the relative phase of trailing edge flap to the pitching phase. For each motion, a positive and negative case are considered. This is a total of 4 trailing edge motion profiles. Trailing edge motion amplitudes of 20° and 40° are compared and results contrasted. Direct transient force measurements were used to obtain the cycle variation of induced aerodynamic loads (lift coefficient) as well as the power output and efficiency. Results are used to identify the influence of trailing edge flap oscillations on the overall performance for energy harvesting, with a maximum efficiency increase of 21.3% and corresponding cycle averaged heaving power coefficient increase of 29.9% observed as a result of trailing edge motion.
Data-Driven Dynamical System Models of Roughness-Induced Secondary Flows in Thermally Stratified Boundary Layers
Authors: Hansen Christoffer , Yang Xiang I. A. , Abkar Mahdi 
Published: September 2022

Abstract
The goal of this work is to investigate the feasibility of constructing data-driven dynamical system models of roughness-induced secondary flows in thermally stratified turbulent boundary layers. Considering the case of a surface roughness distribution which is homogeneous and heterogeneous in the streamwise and spanwise directions, respectively, we describe the streamwise averaged in-plane motions via a stream function formulation, thereby reducing the number of variables to the streamwise velocity component, an appropriately introduced stream function, and the temperature. Then, from the results of large-eddy simulations, we perform a modal decomposition of each variable with the proper orthogonal decomposition and further utilize the temporal dynamics of the modal coefficients to construct a data-driven dynamical system model by applying the sparse identification of nonlinear dynamics (SINDy). We also present a novel approach for enforcing spanwise reflection symmetry within the SINDy framework to incorporate a physical bias.
Simulation-Driven Blade Work Distribution Based Design Strategy and Optimization of a Low-Pressure Axial Fan
Authors: Fritsche Manuel , Epple Philipp , Delgado Antonio 
Published: September 2022

Abstract
Low pressure axial fans have a very wide range of applications in the field of heating, ventilation and air conditioning as well as refrigeration (HVAC&R). Due to stricter legal requirements, increasingly higher minimum fan efficiencies are required. That is why the optimized design of the fan is a crucial point in the development process. Therefore, the simulation-driven preliminary design strategy and optimization is very important in the product development of low-pressure axial fans.
For a specified design point, the blade work distribution along a finite partial section of the impeller flow channel was predetermined. From that, the distribution of the meridian velocities was computed applying the simplified radial equilibrium and the Euler equation for turbomachinery. Then, the blade angles, i.e. the shape of the blade of the axial impeller, were determined. Using the continuity equation and the simplified radial equilibrium, the method has also been extended for non-constant hub shapes, for example a conical hub shape. The blade shape was parameterized by 9 angles, i.e. three angles at the impeller inlet (leading-edge section), three angles at the mid-streamwise section and three angles at the impeller outlet (trailing-edge section).
The angles for the hub plane, the mid-span plane and the shroud plane were determined accordingly. The geometry of the impeller was generated, modeled and solved for the performance characteristics with the numerical flow simulation software ANSYS CFX.
In a subsequent optimization process, based on these pre-designs the parameter space of the leading edge was populated by a DOE analysis using the Latin Hypercube sampling method. Then a multi-objective optimization procedure (MOGA-II) has been performed with the optimization constraints of maximum efficiency and maximum pressure and, at the same time, minimum flow blocked area in the blade channel. From this optimization approach the optimal design was determined, i.e. the optimal angles at the impeller inlet (leading-edge). The same optimization procedure was then also conducted for the mid-streamwise angles and finally for the angles at the impeller outlet at the blade trailing-edge.
Then, for the optimized axial fan, the complete performance characteristics, i.e. at the design and off-design points, have been calculated with CFD showing very good improvements over the full performance characteristics. The method and the results are discussed in detail.
The Effects of Aspect Ratio on Turbulence Wake Flow Over Right Trapezoidal Prism
Authors: Kang Jinhao , Kumahor Sedem , Sagharichi Amir , Tachie Mark F. 
Published: September 2022

Abstract
The shear layer and the near wake region of right trapezoidal prisms with varying streamwise aspect ratios in a uniform flow were investigated using particle image velocimetry. The tested streamwise aspect ratios (AR) based on the height and upper surface were 1 and 4. The Reynolds number based on the prism height and the freestream velocity was 14700. The effects of aspect ratio on the mean flow, Reynolds stresses and third-order moments were investigated, and the results were compared with a square prism. The results show that mean flow separation at the leading edge is not affected by the different geometries and the streamwise aspect ratios. However, the mean recirculation bubbles over the prism and in the wake region show significant differences. Mean flow reattaches over the prism in the AR4 case, but there is no reattachment in the AR1. One-dimensional profiles are used to quantitatively assess the differences in the flow characteristics. It is observed that the magnitudes of Reynolds stresses in the near wake region are an order higher in the AR1 case than in the AR4 case.
Body Shape Effects on the Hydrodynamic Performance of Bio-Inspired Undulating Swimmers
Authors: Kelly John , Pan Yu , Dong Haibo 
Published: September 2022

Abstract
In this study, numerical simulations are performed to study the effects of body shape on propulsive performance in a carangiform-like swimming motion. A focus is given to the variation in performance due to changes in the maximum thickness, maximum thickness location, leading-edge radius, and boattail angle of an undulating foil. An immersed boundary method-based incompressible flow solver is implemented to solve for the propulsive performance of two-dimensional undulating foils. The resulting flow simulations yield the thrust, drag, efficiency, and flow for each body shape. From this study, we have found that better propulsive performance comes from a thinner maximum thickness, a maximum thickness location closer to the head of the fish, a narrower boattail angle, and a larger leading-edge radius. Particular care is given to the analysis of the boattail angle, because of the surprising and significant results. In changing only the boattail angle the efficiency is shown to vary by 10.3%. Changes in the leading-edge radius varies the efficiency by 4.4%, the maximum thickness by 4.0%, and the maximum thickness location along the body by 5.0%. The large improvement observed in the thinner boattail angle cases are caused by the increased curvature around the middle of the fish body leading to a high-pressure region at the tail that improves the thrust performance. The results can be used to improve understanding of fish body shapes observed in nature as well as better informing the design of bio-inspired underwater robots.
A Numerical Study on the Effect of Carrier Fluid Subgrid Scales Fluctuations on Deposition and Dispersion of Lagrangian Particles
Authors: Rousta Farid , Lessani Bamdad , Ahmadi Goodarz 
Published: September 2022

Abstract
Large-eddy simulation (LES) coupled with a Lagrangian particle tracking was performed, and the particle deposition and dispersion in turbulent channel flows were investigated. Different test cases with particle Stokes numbers varying from St = 2 to St = 100 were considered in a fully developed turbulent channel flow at a friction Reynolds number of Reτ = 180. The Dynamic Smagorinsky model was used to model the sub-grid scale fluctuations of carrier flow. In the first set of simulations, the effects of sub-grid scale fluctuations in LES were not considered on the Lagrangian particles. Instead, the velocity of carrier flow seen by particles was simply taken as the fluid filtered velocity. Next, direct numerical simulations (DNS) for the same test cases were performed to clarify the importance of sub-grid scale fluctuations seen by the Lagrangian particles. To clarify the differences, the predicted deposition velocities predicted by both LES and DNS methods were compared with the available data in the literature. Deposition velocities predicted by LES were significantly less than those predicted by DNS, especially for the cases with lower particle Stokes numbers. In addition to the deposition velocity, the particle dispersion was also significantly affected by the sub-grid scale fluctuations in the channel. To shed light on differences between particle dispersion for different cases, time and space averaged particle concentrations were evaluated and compared. Finally, the particle mean and fluctuating velocity profiles for different cases were reported.
Effects of Tire Attributes on the Aerodynamic Performance of a Generic Car-Tire Assembly
Authors: Rath Shubham , Untaroiu Alexandrina , Fu Gen 
Published: September 2022

Abstract
The effect of tires on the overall aerodynamic drag in a car-tire assembly has been studied and deemed considerable from past studies. It has been shown that it is important to understand how the vehicle body and the tires influence the flow structures generated. Previous studies focused on the tire attributes that have an impact on the aerodynamic performance of the vehicle. These tire attributes, however, have not been studied to the extent where one can get a better understanding of the impact of each of these attributes. This paper studies the impact that specific tire attributes have on the overall aerodynamic drag on the vehicle. A thorough and systematic sensitivity study of the effect of tire attributes of a standalone tire was performed to better understand the flow structures around the car body and the improvement in the aerodynamic performance of the vehicle.
In this study, the DrivAer model is used due to the extensive research that has been done on the model. A baseline CFD model of the tire-vehicle assembly of the DrivAer model is simulated using Ansys FLUENT in the open road domain to understand the flow structures around the body of the vehicle. Simulations are done on the fastback configuration of the DrivAer model. A smooth underbody is chosen for this simulation in order to avoid complexities in the meshing. A cuboid shaped open road domain is created, keeping in mind the blocking ratio that is adequate to emulate the flow around the vehicle under open road conditions. Ground simulation and rotating wheel boundary conditions are used to simulate the vehicle moving on the road. The contribution of the tire towards the aerodynamic drag on the vehicle is studied. Coefficient of Drag and coefficient of pressure results from the simulation are validated from experimental data. This is used to create a simulation procedure with appropriate meshing techniques and solution methods in order to simulate for the baseline tire-vehicle assembly and the optimized tire-vehicle assembly. Data from these simulations are used to quantitatively compare the drag contribution of different parameters of the tires.
The sensitivity analysis of the tire-vehicle assembly model performed gives a better insight into the modelling techniques that can be used on a car-tire assembly, as well as the impact of the parameters that could be selected for future tire model optimization.
Impact of Aspect Ratio on Drag and Flow Structure for Cylinders With Two Free Ends
Authors: Shepard Thomas , Law Deify , Dahl Jacob , Reichstadt Rhett , Selvamani Arun Sriniwas 
Published: September 2022

Abstract
When examining the literature for flow effects on circular cylinders one can find many studies on infinite cylinders and cantilevered cylinders but minimal data related to cylinders with two free ends. The limited data available shows that the cylinder aspect ratio affects the drag and frequency content of flow within the wake however these studies were done at discreet Reynolds numbers. In order to better understand the combined impact of aspect ratio and Reynolds number a series of wind tunnel tests and numerical simulations has been conducted for cylinders with two free ends having aspect ratios of 2–15. Test were conducted in the subcritical regime with Reynolds numbers ranging 9300–105,000. Tip vortex effects, which vary with aspect ratio, are shown to impact the cylinder surface pressure, drag coefficient and wake Strouhal numbers though Reynolds number effects are minor for the conditions studied. The results are compared against existing historical data and show the trend of drag coefficient increasing with cylinder aspect ratio.
A Wall-Modeled Large Eddy Simulation Method for High-Order Spectral Element Solvers
Authors: Walters D. Keith , Bhushan Shanti , Strasser Wayne 
Published: September 2022

Abstract
A new method for implementation of wall-modeled large eddy simulation (WMLES) for use with high-order spectral element methods is introduced. Spectral element methods present unique challenges for wall modeling, specifically related to the application of appropriate wall boundary conditions and the specification of modeled fluxes in the near-wall region. The new method addresses these difficulties through the use of an assumed wall function velocity profile in the first layer of near-wall elements, which is used to determine the wall shear stress as well as appropriate pseudo-fluxes to be summed and implemented as source terms at each grid point located in the near-wall elements. Furthermore, the method ensures that the mean velocity field is C1 continuous at the interface between the wall-modeled region and the outer region. Simulations are performed using the spectral element solver Nek5000, and results are compared to high-fidelity DNS data. The test cases considered are fully developed channel flow and flow over a backward-facing step with separation and reattachment. Variations are investigated including different values of the subgrid stress model coefficients for the baseline LES method used. The results show that the new wall function methodology produces results in close agreement with more fully resolved LES for attached channel flow and produces good agreement with field quantities for the backward facing step. The magnitude of wall shear stress in the separated/reattaching flow is underpredicted, and potential reasons for this are discussed. Because WMLES provides a savings in computational cost that scales with Reynolds number, further improvements to the new wall-modeling strategy can potentially lead to significant savings in computational effort for scale-resolving simulations using spectral element numerical methods.
Development of a Finite Element Solver Including a Level-Set Method for Modeling Hydrokinetic Turbines
Authors: Hamada Ahmed A. , Fürth Mirjam 
Published: September 2022

Abstract
Hydrokinetic flapping-foil turbines in swing-arm mode have gained considerable interest in recent years because of their enhanced capability to extract power, and improved efficiency compared to foils in simple mode. The performance of foil turbines is closely linked to the development and separation of the Leading-Edge Vortex (LEV). To accurately model the formation and the separation of the LEV on flapping foils, a purpose-built 2D numerical model was developed. The model is based on weighted residual Finite Element Method (FEM); this is combined with an interface capturing technique, Level-Set Method (LSM), which was used to create a reliable and high-quality numerical solver suitable for hydrodynamic investigations. The solver was validated against well-known static and dynamic benchmark problems. The effect of the mesh density was analyzed and discussed. This paper further covers an initial investigation of the hydrodynamics of flapping-foil in swing-arm mode, by studying the structure of the vortex around a NACA0012 foil. The presented method helps to provide a better understanding of the relation between the Leading-Edge Vortex creation, growth, and separation over the flapping-foil in swing-arm mode and the extracted power from a hydrokinetic turbine.
Development of Three-Dimensional Velocity Vector Profiler Using Ultrasonic Pulsed Doppler Method
Authors: Shoji Naruki , Takahashi Hideharu , Kikura Hiroshige 
Published: September 2022

Abstract
In March 2011, the severe accident of the Fukushima Daiichi (1F) nuclear power plant was happened by the earth quack and massive tsunami in Tohoku, Japan. And then, fuel debris was generated within the primary containment vessels (PCVs) of units 1, 2, and 3, respectively. Recently, the decommissioning of 1F is underway to remove the fuel debris, and the inside inspection with robots was conducted so far. Optical techniques have been applied for inspecting the PCVs, but information of the contaminated water leakage has been not unveiled due to non-clear water causing poor visibility of the camera. Therefore, non-optical techniques are required to unveil the leakage location, and we focused on the ultrasonic measurement technique. In this study, we have developed the ultrasonic velocity profiler (UVP) system for the investigation of leaking locations. The UVP is based on the pulsed Doppler method, and it can measure instantaneous velocity profile along an ultrasonic beam path. In the original UVP principle, it can measure only one-dimensional velocity measurement. Therefore, we extended the UVP to multi-dimensional measurement. To achieve this, a transducer array was used and an algorithm of three-dimensional (3-D) velocity vector reconstruction was developed. The 3-D vector measurement is realized by simultaneous receiving Doppler signal at each ultrasonic element. The measurement performance was evaluated by the rigid rotating flow measurement. In addition, we checked the validity of the system for leakage detection by measuring the simulated leakage flow.
Fabrication of a Multi-Well Plate Channel Device With Reversible Seals
Authors: Zhang Haipeng , Emeigh Carson , Brooks Stephen , Wei Timothy , Ryu Sangjin , Chatzizisis Yiannis S. , Liu Xiang-der 
Published: September 2022

Abstract
Mechanical forces acting on cells have been recognized as an important aspect of cells’ environment because cells adjust their cellular functions in response to such forces, including fluid shear force. For studying such mechanobiological responses of cells, multi-well plate microchannel devices have been used to apply flow shear stress on a cell culture for a long duration. The device includes microfluidic channels attached to the bottom of a conventional multiple-well plate. Such readily available multi-well plate channel devices are costly, and they allow neither direct access to cells cultured in the channel nor easy modification of the device.
In this paper, we propose an easy-to-adopt, cost effective fabrication method for a multi-well plate channel device with reversible seals. This device consisted of two modules. For the top module, a conventional 24-well plate was modified as the base. An inlet/outlet layer and a channel layer were fabricated using polydimethylsiloxane (PDMS) and soft lithography, and they were permanently bonded to the bottom of the plate. The bottom module was a detachable flow chamber layer made with Ecoflex, PDMS, and transparent film using soft lithography. Since Ecoflex can form weak bonding to PDMS, the flow chamber layer could be easily attached to, and then detached from, the PDMS layer of the top module.
As a proof-of-concept, we fabricated a prototype device and tested it by flowing dyed water through the device. No leaking was observed. Then, the device was disassembled and then reassembled for further testing. The weak bonding between Ecoflex and PDMS could create leak-free, reversible seals for the device.
The proposed method has the following advantages. First, fabrication of the device is cost-effective because it can be easily created using common lab instruments and inexpensive materials. Second, the proposed method allows easy modification of the channel design. Last, the reversible seal between the two modules allows direct access to a cell culture for further analysis of the sample after flow stimulation.
Comparative Analysis of Step Change and Reduced Slew Rate Input on the Boundary Layer Response to Forcing by an Array of Plasma Actuator Vortex Generators
Authors: Varacalli Michael , Khanjari Hossein , Hanson Ronald E. 
Published: September 2022

Abstract
In this study, simulations of the laminar boundary layer response to forcing by an array of streamwise oriented plasma actuators are performed. The objective of this study is to evaluate a method to mitigate the non-minimum phase behaviour of the flow that occurs during the step response to input by the actuators. It was recently shown that when the actuators are abruptly started the non-minimum phase response of the wall shear and near-wall disturbance velocity is detected downstream of the actuators. This was shown to be caused by a secondary flow generated between the wall and the front of the tilted vortex structure that is advected downstream [1]. In the present study the step input response is compared to gradually applied inputs. For the step response, the actuators are abruptly activated for 0.2 s followed by a rest period for the flow to return to the undisturbed Blasius condition. For the gradually applied input, the body force of the actuators increases linearly from zero for either 0.005 s, 0.01 s, 0.02 s and 0.04 s to the same maximum value of the step, which simulates a reduced slew rate applied to the physical actuator. The value is held constant and then linearly decreases over a total duration of 0.2 s. It is shown the that inverse response remains for the gradually applied input. However, the peak magnitude is less for the lower ramp rates and the overall response appears more damped.