bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow Behavior and Heat Transfer Characteristics Between Outer and Slotted Inner Cylinders
Authors: Yuasa Tomohisa , Kaneko Akiko , Abe Yutaka
Published: October 2021

The performance of air-cooled generators can be improved only if they have efficient system designs for heat removal. An air-cooled generator is composed of a pair of coaxial cylinders, namely, a fixed outer cylinder (stator) and a rotating inner cylinder (rotor); the rotor has axial slits. In this study, we experimentally and numerically clarified the flow behavior and the heat transfer characteristics of rotating coaxial cylinders by simulating a salient-pole rotor in an air-cooled generator. The flow behavior in the slit between the salient poles was observed by using a high-speed video camera. We measured the temperature on the slit walls to investigate the heat transfer. The velocity fields and the heat transfer coefficient between the rotor and the stator were obtained via a numerical simulation. From the results, we experimentally and numerically observed the vortex structure in the slit. The local Nusselt numbers on the front-side wall of the slits near the impinging flow were higher than those on the back-side wall near the separated flow. The local Nusselt numbers on the front-side wall were high because the gap flow between the cylinders impinged on the front-side wall and promoted heat transfer. By contrast, the local Nusselt numbers on the back-side wall were low because a separated flow appeared near the back-side wall, where the hot fluid was retained, thereby causing the separated flow to disturb the heat transfer on the back-side wall.
Remaining Useful Life Estimation and Prognostication of SAC305 Printed Circuit Boards for Dynamic Conditions of Temperature and Vibration Loads
Authors: Lall Pradeep , Thomas Tony , Blecker Ken
Published: October 2021

This study focuses on the feature vector identification and remaining useful life (RUL) estimation of SAC305 solder alloy printed circuit boards (PCBs) of two different configurations during varying conditions of temperature and vibration. The feature vectors are identified using the strain signals acquired from four symmetrical locations of the PCB at regular intervals during vibration. Two different types of experiments are employed to characterize the PCB's dynamic changes with varying temperature and acceleration levels. The first type of analysis emphasizes the vibration characteristic for varying acceleration conditions while holding the temperature levels constant, and the second studies the shift in characteristics for various ambient temperatures by maintaining constant acceleration levels. The above analyses attempt to imitate an electronic board's actual working conditions in an automobile subjected to varying temperature and vibration environments. The strain signals acquired during each of these experiments are compared based on both time and frequency domain characteristics. Different statistical and frequency-based techniques were used to identify the strain signal variations with changes in the environment and loading conditions. The feature vectors in predicting failure at a constant working temperature and load were identified, and as an extension to this work, the effectiveness of the feature vectors during varying conditions of temperature and acceleration levels is investigated. The principal component analysis (PCA) is used as the data reduction and pattern recognition technique to the different operating conditions of vibration environments. The residual of the autocorrelation function (ACF) of frequency and instantaneous frequency (IF) matrices shows behavior that can predict the packages' failure on the PCB irrespective of varying conditions of temperature and acceleration levels. This feature vector's effectiveness is verified on two different configurations of PCB and for the two separate analyses discussed prior in the study. The RUL of the packages was estimated using a deep learning approach based on long short-term memory (LSTM) network. This technique can identify the underlying patterns in multivariate time series data that can predict the packages' life. The ACF's residuals were used as the multivariate time series data in conjunction with the LSTM deep learning technique to forecast the packages' life at different varying temperatures and acceleration levels during vibration.
Effect of Synthesis Procedure on Particle Dispersion and Hardness of Al- Sic Functionally Graded Metal Matrix Composite
Authors: Hassan Noha M. , Antar May , Saleem Natalie , Aboukhelil Sara , Ghonim Lina
Published: October 2021

Fabrication of Functionally Graded Metal Matrix Composites (FGMMC) especially with high ceramic reinforcement's volume fraction is highly challenging. Depending on the processing technique and process parameters various defects may arise. This research aims to find the best procedure to make FGMMCs with the highest quality and minimum cost. A new method is proposed that incorporates lost-foam and melt infiltration with semicentrifugal casting to produce FGMMC. Experiments were performed to in-situ fabricate 6061-Aluminum alloy reinforced with gradient distributed Silicon carbide particles (Al/SiC FGMMC). Effect of SiC %, Al pouring temperature and rotational speed on the fabricated specimens hardness and reinforcement gradient were investigated using design of experiments and regression analysis. Results reveal the optimum procedure and process settings based on desired properties/gradient required. Mathematical model formulated captures the effect of these process parameters on process cost, and cost of poor quality. Improper selection of those parameters may lead to extensive losses due cost of poor quality which is 12 times higher than the material cost. The proposed manufacturing process proved satisfactory in ensuring proper dispersion. A desirability function can by used to determine the process parameters and volume fraction that minimizes the defects and gives superior properties for a specific application.
Comparative Analysis of the Wear Performance of Spindle Hook Teeth During Fieldwork
Authors: Gu Yanqing , Zhang Hongwen , Fu Xiuqing , Wang Lei , Wang Jun , Cai Yunxiao , Li Haiyang
Published: October 2021

The wear performance of the spindle hook teeth during fieldwork was compared, and the causes of the wear failure of the spindle hook teeth were analyzed. Samples of three kinds of spindle were obtained from the fixed installation position under continuous field operation conditions. The hardness, phase structure, elemental composition, and micromorphology of the spindle hook teeth were characterized using microhardness, X-ray diffractometer (XRD), energy spectrum analyzer (EDS), and scanning electron microscope (SEM) after cutting of the spindles. Results show that the coating hardness and element penetration zone of No.3 spindle hook tooth are the largest, and the surface coating phase structure of the three kinds of the spindle is mainly a body-centered cubic structure of Cr (211). Micro-crack and hole defects exist in the coating of all three kinds of the spindle. The thicknesses of the coating of No.1, No.2, and No.3 spindles are 74, 100, and 130 µm, respectively. During the field operation, the wear of the spindle hook tooth coating is caused by abrasive wear and fatigue wear, while the wear of the substrate is the result of the combined effect of abrasive wear and oxidation wear. Extracting the wear area and width of spindle hook teeth shows that the wear area of all three kinds of spindle hook teeth increases exponentially and the wear width changes linearly with the increase in the field operation area.
Online Signal Denoising Using Adaptive Stochastic Resonance in Parallel Array and Its Application to Acoustic Emission Signals
Authors: Kim Jinki , Harne Ryan L. , Wang K. W.
Published: October 2021

Signal denoising has been significantly explored in various engineering disciplines. In particular, structural health monitoring applications generally aim to detect weak anomaly responses (including acoustic emission (AE)) generated by incipient damage, which are easily buried in noise. Among various approaches, stochastic resonance (SR) has been widely adopted for weak signal detection. While many advancements have been focused on identifying useful information from the frequency domain by optimizing parameters in a post-processing environment to activate SR, it often requires detailed information about the original signal a priori, which is hardly assessed from signals overwhelmed by noise. This research presents a novel online signal denoising strategy by utilizing SR in a parallel array of bistable systems. The original noisy input with additionally applied noise is adaptively scaled, so that the total noise level matches the optimal level that is analytically predicted from a generalized model to robustly enhance signal denoising performance for a wide range of input amplitudes that are often not known in advance. Thus, without sophisticated post-processing procedures, the scaling factor is straightforwardly determined by the analytically estimated optimal noise level and the ambient noise level, which is one of the few quantities that can be reliably assessed from noisy signals in practice. Along with numerical investigations that demonstrate the operational principle and the effectiveness of the proposed strategy, experimental validation of denoising AE signals by employing a bistable Duffing circuit system exemplifies the promising potential of implementing the new approach for enhancing online signal denoising in practice.
Estimation of Turbulent Length Scales at a Turbocharger Inlet Using Particle Image Velocimetry
Authors: Banerjee Deb , Selamet Ahmet , Dehner Rick
Published: October 2021

Stereoscopic Particle Image Velocimetry measurements are carried out at the inlet of a turbocharger compressor at four different shaft speeds from 80,000 rpm to 140,000 rpm and over the entire range of flow rates from choke to mild surge. This paper describes the procedure used in processing the PIV data leading to the estimates of turbulent length scales – integral, Taylor, and Kolmogorov, to enhance the fundamental understanding and characterization of the compressor inlet flow field. The analysis reveals that at most operating conditions the three different length scales have markedly different magnitudes, as expected, while they have somewhat similar qualitative distributions with respect to the duct radius. For example, at 80,000 rpm and at a flow rate of 15.7 g/s (mild surge), the longitudinal integral length scale is of the order of 15 mm, the Taylor scale is around 0.5 mm, and the Kolmogorov scale is about 10 microns. With the onset of flow reversal, the turbulent kinetic energy and turbulent intensity at the compressor inlet are observed to increase rapidly, while the magnitudes of the Kolmogorov scale and to a certain extent, the Taylor scale are found to decrease suggesting that the increased turbulence gives rise to even smaller flow structures. The variation of length scales with compressor shaft speed has also been studied.
CFD Modelling for Gas-Liquid and Liquid-Liquid Taylor Flows in the Entrance Region of Microchannels
Authors: Etminan Amin , Muzychka Yuri S. , Pope Kevin
Published: October 2021

This paper presents a CFD-based simulation method for air/water and water/dodecane Taylor flows through an axisymmetric microchannel with a circular cross-sectional area. A systematic analysis is conducted by exploring the effects of different superficial velocities and apparent viscosities on the hydrodynamics of a slug flow regime. A concentric junction is employed to make bubbles of air in a continuous flow of water and slugs of water in a continuous flow of dodecane oil. A time-history study is conducted to predict the air-bubble and water-slug evolution processes, in particular at the moment of slug breakup. The results show that the larger apparent viscosity ratio of phases involved in the liquid-liquid flow generates a more stable interface. However, the liquid slug length is less and film thickness is slightly larger in liquid-liquid compared to gas-liquid flow. Furthermore, variations in gas and liquid holdups are correlated by the superficial velocity ratio. The numerical analysis developed in this paper is in good agreement with the correlations and data in the literature.
Experimental Study on Heat Transfer of Dielectric Barrier Discharge Plasma Actuator Considering Heat Conduction of Dielectric Material
Authors: Hatamoto Asami , Emori Kenta , Nishida Hiroyuki
Published: October 2021

The plasma actuator is an active flow control device utilizing the atmospheric dielectric barrier discharge. It has many advantages, and it is expected to be applied to a number of fluidic machines including enhancement of convection cooling. However, there is a significant problem when we apply the plasma actuator in the field of cooling, that is the actuator itself is a heat generation source due to the discharge. Although some research efforts have been devoted to understanding the heating characteristics of the plasma actuators, they made discussions only on the surface temperature, and any quantitative discussions on the amount of heating to the dielectric were not performed. The purpose of this study is to quantitatively discuss the heat transfer to the dielectric surface of the plasma actuator. For this purpose, the heat transfer coefficient and temperature of the wall-surface jet are estimated by applying it to a theoretical solution of the one-dimensional heat conduction inside the actuator. The time variation of temperature of the dielectric surface is measured using the IR camera. As a result, the estimation was reasonable near the electrode edge, but unphysical values were obtained downstream because of the small temperature rise and two-dimensional heat conduction in the dielectric. In the future, we need to analyze considering two-dimensional heat conduction utilizing numerical calculation.
Movement of Myoblast Flowing Through Electric Field Perpendicular to Flow Channel
Authors: Hashimoto Shigehiro , Yoshinaka Kiyoshi
Published: October 2021

The sorting technology with little invasion to cells would be applied to regenerative medicine and diagnosis. In this study, dielectrophoresis is focused on. The dielectrophoretic effect on the flowing myoblasts was maximized by adjusting several parameters: the shape of the electrodes, the amplitude and frequency of the alternating current. The suspension of C2C12 (mouse myoblast cell line) was injected into the channel, and the movement of each flowing cell was analyzed at the microscopic movie image. A pair of titanium-coated (200 nm thick) asymmetric surface electrodes (a triangular electrode with a tip angle of 0.35 rad and a rectangular reference electrode with a flat edge) was manufactured by photolithography technique. With the alternating square cyclic wave at the frequency of 3 MHz and the amplitude of current of ± 7.5 mA, 70 μm movement along the electric field (perpendicular to the main flow direction) of the cell was obtained. The movement along the electric field is governed by several parameters of the cell: the diameter, the deformation ratio, and the direction of the major axis. The method can be applied to cell sorting.
Impacts of Circular Liquid Jet Injection Angle Into Low Subsonic Crossflow
Authors: Kasmaiee Si. , Tadjfar M. , Kasmaiee Sa.
Published: October 2021

One of the most common ways to obtain mixing between liquid and air, is by injecting the liquid jet into an incoming gaseous crossflow. The physics of this mixing flow is very complicated due to the presence of many flow interfacial instabilities. Usually, a perpendicular liquid jet into the cross flow airstream is used as the standard method of mixing. In the present work, the effect of the injection angle of the liquid flow emanated from a circular nozzle into airstream was experimentally investigated. The flow characteristics of the liquid jet were visualized by diffused backlight shadowgraph technique and high-speed photography. Water was used as the working liquid and tests were conducted into an incoming airstream at room temperature and pressure. A circular nozzle with 1.5 mm in diameter was used. The injection angles of the 30, 45, 60 and 90 degrees of the liquid jet into the airstream were considered. Different parameters of liquid jet flow such as breakup length and trajectory were measured. It was found that at low angles the path was independent from the momentum ratio.
Volume of Fluid Simulations of Copper Droplet Splat and Sensitivity to Modeling Methods
Authors: Florio Laurie A.
Published: October 2021

Liquid droplet interactions with solid surfaces are fundamental to a wide range of phenomena from novel manufacturing processes, ice accretion on surfaces, to ablation and fouling build-up when droplets are carried with fluid flow along a flow path. Computational fluid-dynamics based simulations offer a controlled environment in which to explore the details of the droplet motion, deformation, or break-up and solidification and melting as droplet impingement on a surface occurs. The operating, material, or geometric conditions can be altered and the resulting changes in the droplet related phenomena can be used to gain the information needed to control the droplet related processes for an intended purpose. The present work investigates the sensitivity of the predicted splat development as a single copper droplet impact upon a cool copper substrate to variations in a volume of fluid based computational modeling method.

One liquid copper droplet is assigned an initial velocity and temperature and is set to impact a cold solid copper surface. The splat profile, as time progresses, is compared to the results in the literature. Among the computational modeling method changes investigated are the surface tension treatment, the solution method for the volume fraction equation, the volume fraction time sub-step calculation method, the volume fraction cut-off value and Courant number, the frequency of the volume fraction updates, the volume fraction discretization method, the mushy zone parameter, and mesh refinement. The study results can be used to provide information to aid in the generation of the models that can more accurately interrogate droplet-surface interactions.
Control Optimization Through Prediction-Based Wastewater Management
Authors: Tilcher David Konstantin , Popescu Florin , Sommer Harald , Thamsen Lauritz , Thamsen Paul Uwe
Published: October 2021

As part of a collaborative research project (OPTIMA) by Fraunhofer FOKUS, Engineering Company Prof. Dr. Sieker mbH, Department of Distributed and Operating Systems and Department of Fluid System Dynamics, TU Berlin, an „Intelligent Pumping Station” is being developed. In this research project, the operation of wastewater pumping stations is to be optimized by integrating precipitation forecasts and recording operating conditions on one hand, and by integrating historical data on use and operation on the other. The individual strategies for optimizing the operation of pumping stations and the possibilities of data integration will be systematically investigated.

The focus of this paper is on the method for developing an optimized pump control. It examines how knowledge of predicted inflow can be used to achieve energy savings and a reduction in wastewater overflows. This method is based on the development of an algorithm in which detailed consideration of pump specifics and future pumping station inflow can be used to predict all possible suction head level curves for the considered period of time. Depending on the target criterion — minimum energy consumption per transported cubic meter or minimum overflow volume — the algorithm calculates the optimum path from all possible suction chamber level curves.
A Three-Dimensional Phase Field Based Nonorthogonal Multiple-Relaxation-Time Lattice Boltzmann Method for Interface Tracking
Authors: Zhang Shengyuan , Tang Jun , Wu Huiying
Published: October 2021

Based on a conservative Allen-Cahn phase field method, a three-dimensional nonorthogonal multiple-relaxation-time (MRT) lattice Boltzmann (LB) model for interface tracking in multiphase flow is proposed in this paper. Different from the traditional MRT LB model, the transformation matrix in the present model is constructed based on a set of nonorthogonal basis vectors to simplify the transformation process between the discrete velocity space and the moment space. Therefore, a higher computational efficiency is achieved by the present model. The present model is developed on two different three-dimensional lattice sets (D3Q19 and D3Q27) to obtain a thorough perspective about the performance of the nonorthogonal matrix. Coupled with the nonorthogonal transformation matrix, simplified discrete source terms are also developed for both two lattice sets to further improve the efficiency of the present model. Numerical tests demonstrate that compared with the traditional MRT LB model, the present model shows a significantly higher computational efficiency and better stability while maintaining a comparable accuracy. It is also found that the D3Q19 nonorthogonal model does not obviously weaken the accuracy of D3Q27 nonorthogonal model while D3Q27 nonorthogonal model dose not decrease the stability of the D3Q19 nonorthogonal model, which is different from the orthogonal model.
The Four Stage Development of Starting Turbulent Buoyant Plumes
Authors: Tran Thanh , Bhaganagar Kiran
Published: October 2021

Turbulent heated and buoyant plumes have important applications in the atmosphere such as wildland fire plumes, volcanic plumes, and chemical plumes. The purpose of the study is to analyze the turbulence structures, and to understand the stages of the development of the starting turbulent plumes. For this purpose, data generated from an in-house Weather Research Forecast model coupled with Large-eddy simulation (WRF-bLES) with two-way feedback between the buoyant plume and the atmosphere developed has been used. The release of both dense gases (Co2, So2) and, buoyant gases (He, NH3, heated air) from a circular source at the bottom of the domain have been investigated. The simulations of the axisymmetric plume were performed at a high Reynolds number of 108. Vortex Identification methods were used to extract the Coherent structures and the large-scale features of the flow. The results have demonstrated that both the dense and the buoyant heated plumes with different initial characters exhibited universal characteristics and the development of the starting plumes occurred in four characteristic stages: Stage 1 is the plume acceleration stage, followed by stage 2 which corresponds to the formation of the head of the plume which grows spatially. Stage 3 is when the plume head is fully formed and the flow transitions to quasi-steady-state behavior. The final stage is the fully developed plume.

The identification of the four-stage development of the plume in the neutral environment is the first step in studying the turbulent heated and buoyant plumes development in order to characterize realistic plumes and to quantify the extent of mixing at each of these stages. This work has important contributions to fundamental fluid dynamics of buoyant plumes with implications on forecasting the plume trajectory of smoke, wildland fire, and volcanic plumes.
Performance of Kaplan Turbine Operating at Design Condition
Authors: Altimemy Muhannad , Watheq Saif , Caspar Justin , Oztekin Alparslan
Published: October 2021

Design and optimization using computational fluid dynamics to enhance the hydro turbine’s performance are becoming gradually more common because of its flexibility, minor detailed flow description, and cost-effectiveness. These features are not easily achievable in model testing. k–ω simulations conducted in OpenFOAM 7 characterize the flow structure inside an industrial-sized Kaplan turbine module operating at the peak design flowrate. The power signal, velocity, vorticity, and pressure field are presented over the blades and throughout the draft tube. Additionally, pressure fluctuations were probed along the draft tube wall. The simulation shows a tip vortex rope in the narrow gap between the blade tip and turbine casing. The strong influence of the swirl leaving the runner had a negative impact on the flow pressure fluctuation. Also, high vortical activity was presented near the draft tube wall, leading to turbine instability. It was demonstrated that the turbine generates 14.923 MW of average power. The power signal showed minor fluctuations induced by the vortical activity close to the runner region and the corresponding pressure fluctuations. The Fast Fourier Transform showed the system is dominated by low frequency, high amplitude fluctuations.
Pressure Drop Mechanisms Generated in a Cooling System Enclosure of Construction Machinery
Authors: Kawano Takashi , Fuchiwaki Masaki
Published: October 2021

A potential way to reduce cooling system noises generated by heavy construction machines is to generate the required cooling airflow with a low fan speed, and one way to accomplish this is to optimize the ventilation path through which the airflow generated by the cooling fan must travel. However, while the computational fluid dynamics (CFD) approach would be effective for modeling the three-dimensional (3D) pressure drop characteristic of such systems, there have been few reports aimed at clarifying the loss generation mechanisms or suggesting minimization methods based on flow field viewpoints. Accordingly, in this study, we visualize the 3D flow field characteristics of an electric cooling fan system installed within the cooling enclosure of a heavy construction machine and investigate the details of the system’s pressure drop mechanisms.

Our results confirm that airflow pressure declines in areas other than the radiator account for more than half of the reduced pressure experienced by the whole system. Additionally, we found that, in the exhaust side enclosure, pressure drops increased because the exhaust port outlet shapes were not optimized to the annular airflow of the cooling fan. Most notably, we found that in the region before reaching the exhaust port outlets, the airflow from the fan repeatedly collides with obstacles within the enclosure, thus producing stagnation and turbulence that exacerbates pressure drops before being expelled into the outside environment.
Multiphase Flow Simulation of Subsea Pipeline Leakage Detected by Acoustic Emission Method
Authors: Shama Ahmed M. , Swidan Ahmed , Young John
Published: October 2021

Subsea pipelines are the heart of the oil transportation system. Oil leakages from subsea pipelines is one of the principal risks associated with oil transportation. An experimental test rig was designed to identify a range of scenarios that could cause leakage, and consequently marine pollution. The Acoustic Emission (AE) technique was employed to sense the flow behaviour inside the pipeline through quantifying and analysing key parameters, such as; energy, amplitude, and the counts number. Although, the size and location of the oil leakage were acquired experimentally utilising highly sensitive acoustic sensors. Two series of numerical simulations utilising Computational Fluid Dynamics (CFD) – Reynolds-Averaged Navier-Stokes (RANS) model, were performed to accurately predict the rate of the oil spill and the corresponding trajectory to the free-surface at Reynolds number Re range from 0.3702 × 103 to Re 9.775 × 103 for flow inside pipeline. The computed results showed good agreement with the experimental data. The results demonstrated that the current experimental measurements analysis could determine the leakage location and the leakage hole capacity, then the numerical calculations could predict the leaked oil volume and the leaked oil route to prevent oil diffusion and mitigate its harmful impact. The findings of this work is a step forward for preventing and controlling oil pollution to protect the marine environment.
Experimental Characterization of Two-Phase Swirl Flow Interacting With a Circular Bluff Body
Authors: Gonzalez Hernandez Rafael , Goharzadeh Afshin , Meribout Mahmoud , Khezzar Lyes
Published: October 2021

This study presents an experimental investigation of two-phase swirl flow interacting with a circular bluff body. A horizontal and transparent multiphase flow loop is employed to investigate the dynamic of swirl flow close to the circular bluff body. Using high-speed photography, air-core development during the transition period is characterized. Analysis of both instantaneous and averaged images provides key information on air-core length and diameter for steady state conditions. The distance from air-core tip to the disk depends on a critical gas-liquid ratio (GLRc). The presence of air pocket behind the circular bluff body depends on a critical distance to the disk.
Influence of the Blade Design Parameters on Hydraulic Noise Generation by a Low Specific Speed Radial Pump With Narrow Channel Flow
Authors: Gangipamula Rajavamsi , Ranjan Pritanshu , Patil Ranjit S.
Published: October 2021

Present work aims to investigate the hydro acoustic behavior of a typical low specific speed radial type centrifugal pump with narrow channel impeller passage. The blade design parameters play an important role in hydraulic noise generation by a low specific speed radial pump with narrow impeller channels. Though, these pumps are hydraulically efficient for a given design point, the hydraulic noise production may be higher at duty point. The blade passage length along with the outlet width of the impeller are the two main design parameters of a radial impeller with narrow channels, which can impact the flow quality along the impeller blade passage. To understand the effect of the narrow channel, initially steady state simulation is conducted to predict and validate the hydraulic performance. Then transient simulations were conducted using Detached Eddy Simulation (DES) using STAR-CCM+ to predict the hydro acoustic behavior of the pump in terms of pressure fluctuations and far field noise spectra of the pump at specific points. The velocity profiles along the impeller channels, shows the formation of wake region, which strongly affects the jet wake flow phenomenon near impeller trailing edge. This results in high pressure fluctuations near impeller outlet.
An Improved Hybrid Alternative WENO Scheme for High Mach Number Flows
Authors: Rajput Uttam Singh , Singh Krishna Mohan
Published: October 2021

This study presents the development of a fifth-order hybrid alternative mapped weighted essentially non-oscillatory scheme (HAW-M) for high-speed compressible flows. A new, improved smoothness indicator has been developed to design the HAW-M scheme. The performance of the present scheme has been evaluated through different one and two-dimensional test cases. The developed scheme shows higher accuracy and low dissipation. Further, it captures the fine-scale structures smoothly than the existing high-resolution method.
Comparative Evaluation of Dielectric Materials for Plasma Actuators Active Flow Control and Heat Transfer Applications
Authors: Rodrigues F. F. , Nunes-Pereira J. , Abdollahzadeh M. , Pascoa J. , Lanceros-Mendez S.
Published: October 2021

Dielectric Barrier Discharge (DBD) plasma actuators are simple devices with great potential for active flow control applications. Further, it has been recently proven their ability for applications in the area of heat transfer, such as film cooling of turbine blades or ice removal. The dielectric material used in the fabrication of these devices is essential in determining the device performance. However, the variety of dielectric materials studied in the literature is very limited and the majority of the authors only use Kapton, Teflon, Macor ceramic or poly(methyl methacrylate) (PMMA). Furthermore, several authors reported difficulties in the durability of the dielectric layer when the actuators operate at high voltage and frequency. Also, it has been reported that, after long operation time, the dielectric layer suffers degradation due to its exposure to plasma discharge, degradation that may lead to the failure of the device. Considering the need of durable and robust actuators, as well as the need of higher flow control efficiencies, it is highly important to develop new dielectric materials which may be used for plasma actuator fabrication. In this context, the present study reports on the experimental testing of dielectric materials which can be used for DBD plasma actuators fabrication. Plasma actuators fabricated of poly(vinylidene fluoride) (PVDF) and polystyrene (PS) have been fabricated and evaluated. Although these dielectric materials are not commonly used as dielectric layer of plasma actuators, their interesting electrical and dielectric properties and the possibility of being used as sensors, indicate their suitability as potential alternatives to the standard used materials. The plasma actuators produced with these nonstandard dielectric materials were analyzed in terms of electrical characteristics, generated flow velocity and mechanical efficiency, and the obtained results were compared with a standard actuator made of Kapton. An innovative calorimetric method was implemented in order to estimate the thermal power transferred by these devices to an adjacent flow. These results allowed to discuss the ability of these new dielectric materials not only for flow control applications but also for heat transfer applications.
Investigating the Potential Drag Reduction and Thermal Transport Improvement in Textured Microchannels
Authors: Rabiei Nastaran , McDonough Grace , Hidrovo Carlos H.
Published: October 2021

Over the past few decades, microscale duct flow has been the key element for many applications, such as drug delivery and microelectronics cooling. To enhance the performance of such systems and to save more energy, looking for new ways to control the hydrodynamic and thermal characteristics of the microchannel flow has been of great interest lately. The aim of this research is to gain a better understanding of the flow physics within microchannels with microtextured walls. Therefore, a set of numerical study has been conducted on the combined effect of flow and heat transfer for spanwise rectangular trenches. The surface microstructures increase the wetting surface area, which is supposed to increase friction (skin drag). Recirculation produced inside the grooves, on the other hand, aids in increasing main flow slippage and lowering pressure drop along the microchannel. It is also worth noting that recirculation creates a negative pressure difference in the opposite direction of the flow (pressure drag). The geometrical parameters of the trenches have a significant impact on the trade-off between the drag reducing and drag increasing factors in textured microchannel flow, which is addressed in this research. Furthermore, the textures disrupt the thermal boundary layer, which can boost thermal transport through recirculation mixing. However, the stagnant fluid trapped within the grooves has weak convective heat transfer. So far, the results have been promising and a drag reduction of about 25% has been reported for wide trenches at low Reynolds numbers. Thermal transport enhancement is also possible for some tested geometries when the flow has not achieved the thermally fully development.
A CNN With Deep Learning for Non-Equilibrium Characterization of Al-Sm Melt Infusion Into a B4C Packed Bed
Authors: Aguilar Julio , Sandoval Laura , Rodriguez Arturo , Kumar Sanjay Shantha , Terrazas Jose , Adansi Richard , Kumar Vinod , Bronson Arturo
Published: October 2021

In seeking predictability of characterizing materials for ultra-high temperature materials for hypersonic vehicles, the use of the convolutional neural network for characterizing the behavior of liquid Al-Sm-X (Hf, Zr, Ti) alloys within a B4C packed to determine the reaction products for which they are usually done with the scanning electron microscope (SEM) or X-ray diffraction (XRD) at ultra-high temperatures (> 1600°C). Our goal is to predict ultimately the products as liquid Al-Sm-X (Hf, Zr, Ti) alloys infiltrate into a B4C packed bed. Material characterization determines the processing path and final species from the reacting infusion consisting of fluid flow through porous channels, consumption of elemental components, and reaction forming boride and carbide precipitates. Since characterization is time-consuming, an expert in this field is required; our approach is to characterize and track these species using a Convolutional Neural Network (CNN) to facilitate and automate analysis of images. Although Deep Learning seems to provide an automated prediction approach, some of these challenges faced under this research are difficult to overcome. These challenges include data required, accuracy, training time, and computational cost requirements for a CNN. Our approach was to perform experiments on high-temperature metal infusion under B4C Packed Bed infiltration in a parametric matrix of cases. We characterized images using SEM and XRD images and run/optimize our CNN, which yields an innovative method for characterization via Deep Learning compared to traditional practices.
An Investigation of the Effects of Volume Fraction on Drag Coefficient of Non-Spherical Particles Using PR-DNS
Authors: Mahyawansi Pratik , Lin Cheng-Xian
Published: October 2021

Prediction of the drag coefficient is required in gas-particle multiphase flow modeling and simulation. Experimental data and correlations on the fixed-bed system of spherical particles with high volume fractions for various possible arrangements are available in the literature. However, the effect of volume fraction on the drag coefficient of non-spherical particles is not well studied. In solving the momentum equation, the volume fraction plays a vital role in determining the flow resistances. In this paper, we study the impact of volume fraction in the range of 0.069 to 0.65 on the drag coefficient using the computational fluid dynamics (CFD) simulation of air for Reynold number in the range of 10 to 10000 using particle resolved direct numerical solution (PR-DNS). Regular non-spherical particles such as a cube, tetrahedron, and spheroids are used in this study since their single particle’s drag coefficient data are available in the literature for comparison. For this work, the simulations are carried out in the Ansys Fluent using polyhedral mesh, which consumes significantly less computational time and power. The study showed the sphericity and volume fraction have significant impact on the bed pressure drop and average drag coefficient of the particles in the bed especially in high Reynolds number regime. The bed of the spheroid experiences the lowest drag being the most streamlined particle, and the particles with the edges result in a large drag coefficient due to flow separation at the discontinuity. The vector plots verify this behavior where large wake regions are observed behind the tetrahedron particle.
Design of Gust Wind Tunnel With Unsteady and Shear Main-Flows
Authors: Nishio Yu , Miyazaki Ryotaro , Ogawa Takanobu
Published: October 2021

Micro air vehicles (MAVs) have been developed for many fields. The MAVs usually receive strong impact from a velocity change in time or space, and facilities for aerodynamic experiments of MAVs under a gusty environment have been required. The present study has developed a gust wind tunnel to generate unsteady and non-uniform flows. We developed a small wind tunnel with eight multi-fans and a shutter mechanism at the upstream of the test section. We controlled the outputs of the fans independently and obtained a linear shear layer with an error of 5 percent. The velocity gradient of the shear layer was from 5 to 8 s−1. The shutter mechanisms provided a longitudinal gust with the velocity change from 2 m/s to 10 m/s within 0.3 seconds.
Uncertainty Estimation in CFD Simulations of Erosion for Elbows
Authors: Fallah Shojaie Elham , Sedrez Thiana A. , Darihaki Farzin , Shirazi Siamack A.
Published: October 2021

Computational Fluid Dynamics (CFD) is used extensively in the industry and academia for analyzing the motion of solid particles and the associated solid particle erosion that may occur in various pipe components. However, CFD simulations always carry levels of inherent uncertainties due to the numerical approximations of governing equations, generated grid, and turbulence models. Also, because of the complex nature of solid particle erosion, additional uncertainties are added to erosion prediction simulations. Aspects such as particle size, number of impacts, particles’ initial condition, near-wall mesh effects, forces considered in particle tracking procedures, particle-particle interaction, and near-wall particle-fluid interactions are all possible sources of uncertainties associated with erosion prediction in CFD. Furthermore, unique problems that accompany discrete phase handling and erosion calculation needed for the industrial applications magnify the importance of uncertainty estimation in erosion calculations. Commercially available CFD codes are used with user-developed subroutines to investigate particle erosion prediction uncertainties, numerically in elbows, by considering gas and liquid flow for several pipe sizes. Moreover, different particle sizes, inlet flow velocities, turbulence models, wall functions, and erosion models are examined. According to the ASME’s Verification and Validation (V&V) standard, uncertainties are divided into 3 categories; input, numeric, and modeling. Thus, it is possible to utilize the ASME’s standard as guidance to predict uncertainty for erosion simulations. Furthermore, an extra parameter was considered for uncertainties to account for the uncertainties induced by different simulation procedures and erosion models. The current investigations resulted in developing a framework for estimating uncertainties of erosion simulation. For each simulation result, two bounds (upper and lower) were predicted for erosion. The results show that the Reynolds Stress turbulence model (RSM) and Arabnejad’s erosion model usually predict results corresponding to the lowest uncertainties.
Aerodynamic Performance Evaluation of a Skydio UAV via CFD As a Platform for Bridge Girder Inspection: Phase 1 Study
Authors: Hewlin Rodward L. , Smith Elizabeth , Cavalline Tara , Karimoddini Ali
Published: October 2021

The goal of the proposed work was to analyze the aerodynamic performance of a Skydio 6 unmanned aerial vehicle (UAV) as a supplementary tool for bridge girder inspections. The use of UAVs has become more attractive due to their ability to gather critical information in less time and at a lower cost when compared to traditional bridge girder inspection techniques. In pursuit of this goal, the present work presents aerodynamic performance evaluation results via computational fluid dynamics (CFD) of a Skydio 2 UAV for bridge girder inspection. The study is implemented using the commercially available CFD solver, ANSYS FLUENT (v. 19). The evaluation study utilized an unstructured tetrahedron meshing technique throughout the numerical analysis, with a standard k-epsilon turbulence model. The Multiple Reference Frame (MRF) model was also used to model the rotation of the propellers toward their local reference frame at 6000 revolutions per minute (RPM). This paper presents the numerical modeling methodology as well as a discussion of parametric results. The parametric results presented show reliable moment coefficient and thrust making the Skydio 2 UAV suitable for bridge inspection.
Numerical Analysis of Oil/water Dispersion Interface Prediction in Horizontal Pipe Separators
Authors: Kolla Srinivas Swaroop , Mohan Ram S. , Shoham Ovadia
Published: October 2021

This paper presents the comparative study of experimental, modeling, and simulation results that are performed using commercially available ANSYS Fluent software to analyze the separation kinetics of oil and water in a horizontal separator at various velocities and watercuts. The horizontal pipe separator used in this study has an internal diameter of 0.0762 m and a length of 10.3 m separating oil and water with specific gravities of 1.0 and 0.857 and watercuts ranging from 20 to 90%. The mixture velocities studied are 0.08, 0.13, and 0.20 m/s. Numerical simulations are done using the hybrid Eulerian-Eulerian multifluid VOF model to study the effect of watercut on the creaming of the oil layer and sedimentation of the water layer respectively. As the mixture velocities increased, the initial length of separation increased like experimental results. As the watercut increased, the separation of water enhanced, while the oil creaming improved with the lowering of the watercut as expected. Numerical results showed good agreement for water/dispersion interface predictions for all the conditions studied. The CFD results are compared against experimental results obtained by Othman in 2010 and agree with the trend of separation. The numerical simulations gave insights into the velocity profiles in each of the layers such as creamed oil, sedimented water, and the layer of emulsion that is not separated. Also, the numerical results are validated against the extended Gassies (2008) model incorporating correlation for turbulent time decay and oil volume fraction proposed by Dabirian et al in 2018.
Prediction of Combustion Performance of Biodiesel in Gas Turbine Combustor
Authors: Yadav Priyanka , Yadav Nagendra P.
Published: October 2021

This paper focuses the computational fluid dynamics analysis inside the gas turbine combustor for the combustion of biodiesel and air mixture. The biodiesel (methyl soyate) is made from the vegetable oil (soybean oil). ANSYS fluent is used for Numerical simulation and model adapted Eddy dissipation concept for turbulence, discrete model, k-epsilon (standard), and the species transport. The model was validated and the combustion performance of biodiesel is predicted with an air-assist injector. The fuel spray is created by commercially available airblast atomizer in this study. The strength of recirculation increases with increased in equivalence ratio. The strong corner recirculation was observed at 0.75 equivalence ratio. The higher turbulence kinetic energy is found at the middle of the combustor. The temperature increases with the increase in the equivalence ratio in the flame stable region while it decreases with increases in the equivalence ratio. It was observed that an increase in the equivalence ratio, flame length increases. The profiles of carbon monoxide (CO) and nitric oxides (NOx) emissions can be obtained at 15% atomizing airflow rates, while the total airflow rate kept constant. The NOx and CO emissions are effected mainly by the fuel-air mixing process that the fuel-air mixing process and atomization have the great impact on CO and NOx emissions.