bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Comparison of the Flow Structure in a Normal Triangular Tube Array Obtained Based on the SFV Technique and on a CFD Analysis
Authors: Martins Rocha Douglas , Toshio Kanizawa Fabio , Hayashi Kosuke , Hosokawa Shigeo , Tomiyama Akio , Ribatski Gherhardt 
Published: October 2020

Abstract
This paper presents an analysis of the performance of the Spatial Filter Velocimetry (SFV) technique applied to external flows across tube bundles to evaluate the benefits of using low particle concentration in a complex geometry. The experimental vector velocity fields were obtained in a tube bundle test section made of acrylic with 20 rows of 4 tubes of 20mm O.D. mounted in a normal triangular configuration and transversal pitch per diameter ratio of 1.25. The SFV results reliability was evaluated by comparing the volumetric flow rates estimated by the experimental vector velocity fields with the volumetric flow rates measured by the flowmeter, showing good agreement. Additionally, the experimental results are used to check the validity of numerical results obtained through CFD simulation. The experiments were conducted for Reynolds numbers of 909, 1842 and 3902. The velocity profiles obtained through the SFV technique agree with the CFD simulations results, which indicate consistent results for both analyzes. Therefore, the numerical and experimental results indicate that the SFV technique provides accurate velocity data and is suitable to be applied to complex geometries, especially in regions away of the test section wall due to the good visibility provided by low particle concentration.
A Quantitative Analysis of Machine Learning Based Regressors for Pressure Reconstruction in Particle Image Velocimetry Applications
Authors: Basu Manan , Kumar Sushrut , Gupta Priyam , Kumar Singh Raj 
Published: October 2020

Abstract
With the recent advances in Artificial Intelligence, avenues for the application of Machine Learning (ML) are increasing in many engineering problems pertaining to Fluid Mechanics. Particle Image Velocimetry is an advanced fluid measurement technique but the pressure evaluation requires the data to be further processed. In the proposed work, we focus on developing a novel computational framework using Machine Learning techniques, primarily Artificial Neural Networks (ANN) to infer the pressure fields from velocity obtained from PIV data. The framework was tested for a case of flow over a periodic hill. The data for training was generated by performing LES simulations for different hill curves and Reynolds number. Various Regression models were developed in conjunction with the Adam and Limited Memory - BFGS (L-BFGS) optimizers and suitable activation functions. A detailed study of the performance of each model was done to determine the optimum values of the hyperparameters. Further, a comparative analysis of various models and the respective optimization algorithms used was performed. It was concluded that the multi-layered perceptron model with L - BFGS optimizer showed the best performance. Overall, it is observed that the models can predict the pressure values with a high degree of accuracy as confirmed by validation with the previous literature data.
Effects of Streamwise Aspect Ratio on Turbulent Flows Over Forward-Backward Facing Steps
Authors: Chalmers Heath , Fang Xingjun , Tachie Mark F. 
Published: October 2020

Abstract
Separated and reattached turbulent flows induced by two-dimensional forward-backward-facing steps with different streamwise lengths submerged in a thick turbulent boundary layer are investigated using a time-resolved particle image velocimetry. The examined aspect ratios of the step range from 1 to 8, and the Reynolds number based on the free-stream velocity and step height is 13 200. The thickness of the oncoming turbulent boundary layer is 6.5 times the step height. The effects of varying aspect ratio of the steps on the mean flow, Reynolds stresses, triple correlations and unsteadiness of turbulent separation bubbles are studied. It was found that the mean flow reattaches over the step for forward-backward facing steps with aspect ratios of 2 and higher. The temporal variation of the first proper orthogonal decomposition (POD) mode and reverse flow area, which is used to examine the flapping motion of separation bubble, shows remarkable synchronization.
Dielectric Barrier Discharge Plasma Actuators for Active Flow Control, Ice Formation Detection and Ice Accumulation Prevention
Authors: Rodrigues F. F. , Abdollahzadeh M. , Pascoa J. 
Published: October 2020

Abstract
An experimental investigation was conducted in order to understand the ability of plasma actuators to operate in three different modes: flow control, ice formation detection and ice accumulation prevention. When plasma actuators are operated with voltage levels, above the breakdown voltage, a plasma discharge surface is generated and with that, an ionic wind is produced. By using this phenomena, plasma actuators may be used to manipulate flow fields and control adjacent flows to the surface in which they are applied. However, a big part of the power applied to the device is dissipated as heat. Due to heat dissipation, the actuator surface temperature rises and the adjacent air is heated. Considering this, actuators may operate as ice prevention devices by heating the surface where they are applied and preventing the ice formation and accumulation. On the other hand, plasma actuators present a behavior similar to a capacitor and they may operate as a capacitive sensor. In the presence of water or ice on the top of the surface, the electric field changes and with that, several plasma actuator electrical features change as well. By monitoring that changes, the presence of water or ice on the top of the surface can be detected and the plasma actuator may be used as an ice sensor device. Therefore, in the present study a plasma actuator was experimentally tested operating in these three different operation modes and its feasibility to perform these different tasks is shown.
Performance Evaluation of a Non-Linear Explicit Algebraic Reynolds Stress Model for Surface Mounted Obstacles
Authors: Taylor Benjamin H. , Jamal Tausif , Walters D. Keith 
Published: October 2020

Abstract
The presence of complex vortical structures, unsteady wakes, separated shear layers, and streamline curvature pose considerable challenges for traditional linear Eddy-Viscosity (LEV) models. Since Non-Linear Eddy Viscosity Models (NEV) models contain additional strain-rate and vorticity relationships, they can provide a better description for flows with Reynolds stress anisotropy and can be considered to be suitable alternatives to traditional EVMs in some cases. In this study, performance of a Non-Linear Explicit Algebraic Reynolds Stress Model (NEARSM) to accurately resolve flow over a surface mounted cube and a 3D axisymmetric hill is evaluated against existing experimental and numerical studies. Numerical simulations were performed using the SST k-ω RANS model, SST k-ω-NEARSM, SST-Multiscale LES model, and two variants of the Dynamic Hybrid RANS-LES (DHRL) model that include the SST k-ω and the SST k-ω-NEARSM as the RANS models. Results indicate that the SST k-ω RANS model fails to accurately predict the flowfield in the separated wake region and although the SST-NEARSM and SST-Multiscale LES models provide an improved description of the flow, they suffer from incorrect RANS-LES transition caused by Modeled Stress Depletion (MSD) and sensitivity to changes in grid resolution. The SST-DHRL and the SST-NEARSM-DHRL variants provide the best agreement to experimental and numerical data.
Micro Flow Direction Analysis Using Gold Sputtered Planar V-Shaped Electrode Pattern
Authors: Parvez Mohammad Salman , Rubby Md Fazlay , Ucchyash Sajid Mahfuz , Biswas Prosanto , Huq Hasina , Islam Nazmul 
Published: October 2020

Abstract
Sensing and detecting micro particles require a bulk fluid motion towards the sensing element in order to get a desirable response from the sensing element. Specially for low-concentrated fluid suspension response time is very long. So both for detection and sensing mechanism if the fluid flow is guided at a reasonable speed and at a low voltage and relatively low frequency which is suitable for bio-particles; the sensing mechanism can be enhanced largely. But sometimes it is required to re-accumulate or recombine the fluid. Previously parallel plate configuration was used to concentrate particle, but this is for the first time a V-shaped electrode pattern used to guide the bulk flow for concentration purpose. The V-shaped electrode set-up was made by following an unconventional way using sputtering machine which was cheaper than the conventional Photolithography method. AC-Electroosmosis from planar electrodes is a strong mechanism for creating micro-flows from several hundred microns away from the electrode surface. The mechanism for the AC Electroosmotic fluid flow is based on Capacitive charging which causes due to the generation of counter-ions at the electrode-electrolyte interface and Faradaic charging which is generated by the accumulation of co-ions. These two different methods are responsible for a converging and diverging surface flow of the fluid particles. At lower voltage capacitive charging method plays a significant role and most of the applied voltage drops occur at the electrical double layer but up to a certain voltage level Faradaic charging method takes over and starts dominating. The induced flow velocity by both methods has different relationship with the applied voltage. In this experiment Electrical Impedance Spectroscopy (EIS) was used to determine the suitable frequency range for the application & 2.12Vrms was used initially which is a very low voltage. An equivalent circuit for the setup was analyzed. Finally, an analysis was made on this setup using conductive fluid to observe the AC Electrothermal (ACET) effect. In our experiment the goal was to get an optimum velocity for concentration at low voltage and low frequency also to observe the guiding direction of the fluid flow in order to find a way to focus the fluid flow towards the desired direction.
Effect of Localized Blockages on the Friction Factor of a 61-Pin Wire-Wrapped Bundle
Authors: Childs Mason , Muyshondt Robert , Busco Giacomo , Yildiz Mustafa Alper , Vaghetto Rodolfo , Hassan Yassin 
Published: October 2020

Abstract
A test campaign has been conducted to study the effects of localized blockages on the friction factor of a 61-pin wire-wrapped bundle replica. Blockages of selected sizes and locations within the bundle have been installed, and fluid pressure drop was measured across one wire pitch. The friction factor was compared with the unblocked bundle friction factor, and with the predictions of a well-established friction factor correlation.
A computational fluid dynamics model of the experimental bundle was prepared, and simulations were compared with experimental results with the ultimate goal to complement the experimental activity with validated simulation data. The unique sets of experimental data, complemented with simulation results, provide a quantification of the increase of the bundle friction factor produced by the blockages, and the different expected effects based on blockage size and location for various flow regimes.
Effects of Pipe Diameter and Stokes Number on Erosion in Elbows
Authors: Karimi Soroor , Asgharpour Alireza , Fallah Elham , Shirazi Siamack A. 
Published: October 2020

Abstract
Large diameter pipes and elbows are vastly used in industry especially in mining and oil and gas production. Solid particle erosion is a common issue in these pipelines, and it is important to predict it to avoid failures. Currently, laboratory experiments reported in the literature are limited to diameters less than 4 inches. Therefore, there is not much experimental data available for large diameter elbows. However, the erosion can be predicted by CFD simulations and applying erosion equations in such elbows. The goal of this project is to examine the effects of elbow diameter and Stokes number on erosion patterns and magnitude for various flow conditions for elbow diameters of 2, 4, 8, and 12 inches.
The approach of this work is to first perform CFD simulations of liquid-solid and gas-solid flows in 2-inch and 4-inch elbows, respectively, and evaluate the results by available experimental data. Then CFD simulations are carried for 2, 4, 8, and 12-inch standard elbows for various Stokes numbers corresponding to gas dominant flows with the velocity of 30 m/s, and liquid dominant flows with the velocities of 6 m/s. For gas dominant flows erosion in air and for liquid dominant flows erosion in water is investigated. All these simulations are carried for four particle sizes of 25, 75, 150, and 300 microns. The results indicate that Stokes number and diameter of elbows have significant effects on erosion patterns as well as magnitudes in this geometry.
This work will have various applications, including validating mechanistic models of erosion predictions in elbows and developing an Artificial Intelligence (machine learning) algorithm to predict erosion for various flow conditions. Such algorithms are limited to the range of conditions they are trained for. Therefore, it is important to expand the database these codes are accessing. Overall, the CFD database of large diameter elbows will reduce the computational costs in the future.
Experimental and Numerical Investigations of Unsteady Flows Downstream Confined Rectangular Obstacles
Authors: Aloui Fethi , Elawady Amal 
Published: October 2020

Abstract
In this work, we present an experimental and numerical study in a horizontal duct with a rectangular cross-section (300 × 30mm2). In the middle of this cross-section, a rectangular obstacle (20 × 10mm2) then a squared obstacle (10 × 10mm2) were placed in order to study experimentally and numerically the vortex shedding and their interactions in the flow. Upstream obstacles, the studied flows are laminar. In our experimental study, the PIV technique was used in order to obtain instantaneous velocity fields downstream the used obstacles. From these measurement results, a post-processing was used (especially the Γ2 criterion) in order to well extract instantaneous vortices contained in the flow downstream obstacles. In parallel with this experimental study, a 2D numerical simulation was achieved in order to be validated by the experimental results. Other complementary PIV measurements were carried out in the duct top by visualizing the flow downstream obstacles in order to study the 3D effects of the flow.
RANS VOF Simulations of Density-Stratified Air-Water Flow in a 2D Channel
Authors: Maiti Chandrima Jana , Ghia Urmila , Turkevich Leonid A. 
Published: October 2020

Abstract
We perform RANS-VOF simulation of density-stratified, fully developed air-water flow in a 2D channel. The flow is completely specified by the (common) driving pressure gradient down the channel and by the fill factor (relative height of the heavier phase to the total height of the channel). Varying the pressure gradient and fill factor results in different flow combinations: namely, laminar air/laminar water, turbulent air/laminar water, turbulent air/turbulent water, laminar air/turbulent water. The focus of the study is the near-interface interaction when either or both phases are turbulent. The RANS-VOF equations are solved on a 2D channel with periodic inlet/outlet boundary conditions. For a fixed fill factor, the Reynolds numbers of each phase varies monotonically with driving pressure gradient. However, at fixed pressure gradient, the fluid Reynolds numbers are non-monotonic at high fill factor. This Reynolds number phase diagram is important in understanding the laminar and turbulent regimes of each phase. The mean velocity is axial (down the channel) and exhibits a dip below the free surface whenever one of the phases is turbulent. As expected, the diagonal Reynolds stresses &lt;u’u’&gt;, &lt;v’v’&gt;, are strongly coupled between the phases, however coupling in &lt;u’v’&gt; is less pronounced.
Aerodynamic Subsonic Model at Transitional/Turbulent Reynolds Number for Bluff-Ellipsoidal Hulls
Authors: Ricardo Jorge A. , dos Santos Davi Antônio , dos Santos Magalhães Elisan 
Published: October 2020

Abstract
The present work addresses the subsonic aerodynamic coefficients model for bluff ellipsoidal hulls at transitional and turbulent Reynolds number. The drag, lift, and moment aerodynamic coefficients model are based on computational fluid dynamics (CFD) simulations for four bluff ellipsoids with aspect ratio of 1, 2, 3, and 4, in the Reynolds number range of 1 × 103 to 2 × 106 and angle of attack range from 0 to 20 degrees. The Large Eddy Simulation (LES) turbulence model is used with the sub-grid turbulence model Wall-Adapting Local-Eddy Viscosity (WALE) to solve the fluid field. To reduce computational simulation time, at a first instant, the mesh is gradually refined until the point that it does not influence anymore in the final result (mesh independence). For each aerodynamic coefficient a nonlinear equation structure, valid for all the ellipsoids, is proposed as a parametric model with parameters estimated using the least mean square algorithm applied to the results of the computational fluid dynamics simulations. The proposed equations have a superior performance, in terms of precision and number of terms, when compared to polynomial equations fitted to the same data.
Experimental and Numerical Analysis on the Performance of Spiral Two-Fluid Atomizer Using DPM Method
Authors: Lee Jin-Woo , Jung Kuk Jin , Sherman Morely , Kim Hyun Sin , Kim Youn-Jea 
Published: October 2020

Abstract
A two-fluid atomizer has been frequently used in a wide range of industries for various purposes such as painting, cleaning particles and snow making. In particular, the manufacturing of advance semiconductors using sensitive devices such as organic light emitting diodes (OLED) and dynamic random access memory (DRAM), require high performance nozzle. The droplets sprayed with a high relative gas velocity are widely used for cleaning particles. In this paper, two-fluid atomizer is numerically studied according to four variables to confirm the effect on the atomizer performance. The numerical results using the discrete phase model (DPM) with several break-up models are compared with the experimental data measured by the phase doppler particle analyzer (PDPA). Design of experiment (DOE) and genetic algorithm (GA) were used to obtain design points, and conduct sensitivity analysis, respectively. The results showed that the WAVE model has a good agreement compared to the other models, and the orifice diameter is a crucial factor for this model to determine the performance of Weber number and pressure.
Pressure Drop Study in Cylindrical Microchannels: Using Graphene Oxide and Magnesia Nanofluids
Authors: Ali Abdallah Y. M. , Fuseini Mohammed , Abo-Zahhad Essam M. , El-Kady M. F. , El-Shazly A. H. 
Published: October 2020

Abstract
The pressure drop and friction factor for the flow in horizontal smooth microtubes were investigated experimentally over a wide variety of Reynolds numbers in the laminar region under hydrodynamically fully developed conditions. The plain pipes are fabricated from 316 stainless steel and provided by (Swagelok Co., USA) with inner diameters of 0.770 mm and 0.510 mm and the length is 500 mm for both microchannels. For this purpose, graphene oxide (GO) nanosheets and magnesium oxide (MgO) nanoparticles were synthesized then characterized using standard methods such as X-ray powder diffractometer (XRD) and Transmission Electron Microscope (TEM). The prepared GO and MgO nanomaterial were added to distilled water to prepare nanofluids with mass fractions of 0.25, 0.5, 0.75, and 1 wt.% as working fluids and passes through one end of the microchannel to the other by a magnetically coupled gear programmable pump with variable speed that drives it. This study predicts the behavior of fluid flow in the microchannel for the range of dimensions used. Comparisons of pressure drop characteristics are given in terms of nanoparticle mass fractions and tube diameters. As a result, MgO nanofluids recorded higher pressure drop with an increase in the concentration of the nanofluids due to its higher viscosity followed by GO nanofluids.
Investigation of an Algebraic Reynolds Stress Model for Simulation of Wall-Bounded Turbulent Flows With and Without Buoyancy Effects
Authors: Jamal Tausif , Walters D. Keith 
Published: October 2020

Abstract
Complex turbulent flows such as those encountered in nuclear reactor cooling systems pose considerable challenges for computational fluid dynamics (CFD) simulation using traditional Reynolds-averaged Navier-Stokes (RANS) models based on the linear eddy-viscosity modeling (LEVM) framework. One particular difficulty is the use of low Prandtl number (Pr) fluids such as liquid metal coolants, which considerably alters the fluctuating thermal field and violates the Reynolds analogy upon which turbulent heat flux modeling in LEVMs is based. Although previous studies have shown that Reynolds Stress Models (RSM) offer some improvements over traditional LEVMs for flows containing complex inter-component interaction and Reynolds stress anisotropy, the added complexity, increased computational requirements, and the lack of robustness introduced by traditional RSMs do not always result in an overall improvement. This study evaluates the performance of a newly proposed Algebraic Reynolds Stress Model (ARSM) including an Algebraic Heat Flux Model (AHFM) against two industry standard RANS models, standard k-ε and realizable k-ε model, for a set of canonical test cases relevant to nuclear reactor cooling applications. Numerical simulations using the spectral element code Nek5000 are performed for fully developed channel flows with varying values of Reynolds number (Re) and Pr, both with and without the effects of buoyancy. Results are compared to Direct Numerical Simulation (DNS) data in terms of the velocity and thermal statistics. For all cases investigated, the ARSM model consistently outperforms the other RANS models in this study and it is concluded that the new ARSM model can be a suitable alternative to traditional LEVMs for complex turbulent flows without significant penalty to efficiency and robustness that are commonly associated with traditional RSMs.
Airflow Characterization Combined With 3D Reconstruction of Rabbit Vocal Cord Based on In-Vivo Phonatory Experiments
Authors: Lou Zhipeng , Wang Junshi , Daniero James J. , Dong Haibo , Xi Jinxiang 
Published: October 2020

Abstract
In this paper, a numerical approach combined with experiments is employed to characterize the airflow through the vocal cord. Rabbits are used to perform in vivo magnetic resonance imaging (MRI) experiments and the MRI scan data are directly imposed for the three-dimensional (3D) reconstruction of a 3D high-fidelity model. The vibration modes are observed via the in vivo high-speed videoendoscopy (HSVM) technique, and the time-dependent glottal height is evaluated dynamically for the validation of the 3D reconstruction model. 72 sets of rabbit in vivo high-speed recordings are evaluated to achieve the most common vibration mode. The reconstruction is mainly based on MRI data and the HSVM records are supporting and validate the 3D model. A sharp-interface immersed-boundary-method (IBM)-based compressible flow solver is employed to compute the airflow. The primary purpose of the computational effort is to characterize the influence of the vocal folds that applied to the airflow and the airflow-induced phonation. The vocal fold kinematics and the vibration modes are quantified and the vortex structures are analyzed under the influence of vocal folds. The results have shown significant effects of the vocal fold height on the vortex structure, vorticity and velocity. The reconstructed 3D model from this work helps to bring insight into further understanding of the rabbit phonation mechanism. The results provide potential improvement for diagnosis of human vocal fold dysfunction and phonation disorder.