bluuebunny/crossref_metadata_2025 huggingface dataset:
Wake Characteristics Comparison Between Isolated and Pair Configurations of Marine Hydrokinetic Crossflow Turbines at Low Reynolds Numbers
Authors: Alayeto Iván Hernández , Doan Minh Nhat , Kumazawa Kana , Obi Shinnosuke
Published: November 2019

Wake characteristics and power coefficient of laboratory scaled marine hydrokinetic cross flow turbines were studied both experimentally and numerically. Single and turbine pair configurations were experimentally tested in a 3.5 m long, 0.3 m wide and 0.15 m deep water channel facility. Each turbine was built with three straight NACA0012 blades with chord 2.54 cm and 6.828 cm diameter, corresponding to a solidity of 1.2. The Reynolds number associated with the velocity given by the water pump and blade chord oscillated near 7000. Empirical power measurement was obtained multiplying the average torque by average rotational velocity. These measurements were obtained with a magnetic hysteresis brake utilized as control system and a Hall effect sensor used as speed transducer, respectively. Wake velocity profile was obtained by image processing of Particle Image Velocimetry (PIV) measurements at different positions. The empirical results were contrasted with numerical computational fluid dynamics (CFD) simulations carried out with Salome and OpenFoam. The computational model solved the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations in 2 dimensions using the turbulence models k-ω Shear Stress Transport (SST) and Spallart-Allmaras (SA). The experimental and numerical results show a clear difference of power coefficient and wake shape for both turbine configurations. This influence of two nearby blades on the flow can be exploited to obtain higher ratios of power per land area, leading to an increase of the overall generation of a power plant by a careful arrangement.
Multi-Objective Hydraulic Optimization on Intake Duct of Water-Jet Propulsion Using NSGA-II
Authors: Zhu Rui , Cao Puyu , Wang Yang , Ning Chao
Published: November 2019

Flow distortions occur at the outlet section of the intake duct owing to its shape properties, which is a component of water-jet propulsion. Since the noticeable influence of intake’s flow characteristics upon propulsive efficiency, it’s necessary to focus on intake duct redesign. In this paper, a systematic methodology for reducing flow distortions and power losses within the intake duct through a shape optimization process was obtained. In addition, the mechanism of flow distortions was also developed.

The flush type inlet applied in the marine vessel with the speed of 30 knots was chosen as research project. Four characteristic parameters were set as optimization variables depending on the geometrical relationship of thirteen characteristic parameters referred to the duct longitudinal midsection, which were the ramp angle α, the radius of the upper lip R3, the radius of the lower lip R4 and the lip height h respectively.

Subsequently, a sample space was built by Latin Hypercube Sampling (LHS) and the parameters were normalized in the range of 0 to 1. With the commercial software CFX, the numerical simulation was accomplished driven by SST k-ω turbulence model. Multi-objective optimization based on the Non-Dominated Sorting Genetic Algorithm II (NSGA-II) was utilized to minimize the non-uniformity at outlet section and maximize the minimal pressure at lip simultaneously. Moreover, the Radial Basis Function (RBF) neural network was employed to approximate the functional relationship between variables and objectives, which could be applied in the NSGA-II to get the Pareto Front.

The minimum non-uniformity point and the trade-off point (The point both satisfies the minimum non-uniformity and the maximum minimal pressure at lip strategically) were selected from the Pareto Front. With regard to the characteristic parameters of the trade-off point, the ramp angle, the radius of the upper lip, the radius of the lower lip and the lip height are 31.91°, 11.42 mm, 400.97 mm and 55.43 mm respectively.

Meanwhile, the characteristic parameters of the minimum non-uniformity point are 30.22°, 25.59 mm, 166.65 mm and 89.90 mm respectively. Ultimately, the duct outflow characteristics of prototype and optimization are compared. In terms of the trade-off point, the minimal pressure at lip increases 66.40% to −24488.93 Pa and the non-uniformity has a drop of 4.56% to 0.1571. The non-uniformity of the minimum point is 0.1481 which is reduced by 10.02%. Through the optimization of duct shape, the secondary flow (Dean vortices) is suppressed effectively. This paper is expected to provide a better comprehension of the flow field within the intake duct of water-jet propulsion.
Numerical Simulation of a Gas Bubble Rising in Power-Law Fluids Using a Sharp Surface Force Implementation
Authors: Kumar Purushotam , Jin Kai , Vanka Surya Pratap
Published: November 2019

In this paper, we have applied a recently-developed numerical technique to study the three-dimensional dynamics of a confined air bubble rising in shear thinning and shear-thickening power-law fluids. The method is a blend of Volume of Fluid and Level Set methods and incorporates a Sharp Surface Force Method (SSF) for surface tension forces by solving a second Pressure Poisson Equation (PPE). The gas-liquid interface is captured by an equation for the liquid volume fraction and advected using the geometry reconstruction method. The interface normal and curvature are computed using level-set and height function methods. The accurate representation of the interface and interfacial forces significantly suppressed the spurious velocities commonly observed with conventional volume of fluid method and the Continuum Surface Force (CSF). The algorithm is implemented in a in-house code called CUFLOW and runs on multiple GPUs platform.

We explored the effects of fluid rheology, Bond number, and wall confinement on bubble’s transient shape, rise velocity, rise path, and generated vortex structures. The power-law index is varied from 0.25 to 1.50 covering shear-thinning and shear-thickening regimes. Three Bond numbers (Bo = 2, 10 and 50) and three confinement ratios (Cr = 4, 6 and 8) are considered, and their impacts on bubble’s dynamics are analyzed. For the range of parameters examined here, bubble motion in a shear-thinning fluid is seen to be unsteady with significant shape oscillations. The bubble rises with a secondary motion in the cross-sectional plane along with its primary vertical rise. However, in the Newtonian and shear-thickening fluids, the bubble’s shape is seen to reach a steady-state in a relatively short time and rise with only minor deviations from the vertical path.
Experimental Investigation of Turbulent Cavitating Flows in a Small Venturi Nozzle
Authors: Zhang Guangjian , Khlifa Ilyass , Coutier-Delgosha Olivier
Published: November 2019

The cavitating flows created in a small Venturi tube with throat cross section 4 × 15.34 mm2 are investigated based on ultra-fast x-ray imaging. The instantaneous velocities of the liquid and vapor are measured simultaneously by tracking seeding particles and vapor structures respectively while the vapor volume fraction is derived from the different x-ray attenuation. Wavelet decomposition with appropriate thresholds is used to separate seeding particles from vapor structures, so that image cross-correlations could be applied on the two phases separately. This study presents data on mean velocity and void ratio field, statistical turbulent quantities in three different cavitation levels with the same reference velocity. A type of cavitation associated with a weak but persistent re-entrant jet is described. The comparison between the cavitation and the noncavitating flow shows that the averaged flow field is significantly altered by the presence of cavitation and the vapor formation near the throat area is observed to suppress velocity fluctuations.
Effect of Interface Condition on the Hydraulic Performance of a Pump-Turbine at Various Guide Vane Opening Conditions in Pumping Mode
Authors: Suh Jun-Won , Kim Seung-Jun , Choi Young-Seok , Kim Jin-Hyuk , Joo Won-Gu , Park Jungwan
Published: November 2019

Nowadays, pumped-storage power stations require high flexibility and reliability in operation under off-design conditions, especially in the pump mode. When a pump-turbine operates under various part load conditions in pump mode, highly dynamic phenomenon such as stationary vortex and rotating stall occur. Therefore, the performance characteristics in pump mode are vital for the safe and effective operation. A number of studies have been conducted to investigate the flow characteristics in turbine or pump mode under different GVOs through numerical simulations. However, the studies about influence of the position of interface and interface condition on the pump characteristics of pump-turbines are not completely clear.

In this paper, the three-dimensional steady and unsteady Reynolds-averaged Navier–Stokes equations were solved for a detailed analysis of the influence of interface conditions with various guide vane opening conditions in pump mode. To ensure the reliability of the numerical analysis, the numerical results were validated in comparison with the experimental data.
Multiphase Flow Simulation of In-Line Gas-Liquid Separator for Multiphase Metering
Authors: Seo Nakyeong , Kharoua Nabil , Khezzar Lyes , Alshehhi Mohamed , Meribout Mahmoud
Published: November 2019

The present study addresses itself to the performance assessment of a novel in-line gas-liquid separator. The separator is developed by FRAMES company under the name of SwirlSep based on the interaction of a swirling flow, generated by an innovative devise called swirl cage, and a hollow conical bluff body designed to deviate the gaseous phase internally.. The separator is intended to be implemented within a multiphase flow metering system in oil field gathering stations in the Gulf region. The study represents a preliminary step among a design process including elaborate lab-scale and filed tests.

The flow in the gas-liquid separator is studied using Computational Fluid Dynamics CFD. The Shear Stress Transport (SST) k-ω turbulence and Eulerian-Eulerian multiphase models, under different flow conditions, were used to simulate real flow scenarios. The scenarios were chosen to replicate flow conditions that could exist during the operation of oil wells over their lifetime with the aim to provide guidance for proper control of the separator valves. The fraction of the total flow is prescribed at each outlet, using an outflow boundary condition, to mimic the action of the control valves. At the inlet, the phase velocity and volume fraction were prescribed.

The outlet streams and their phase’s content were, then, analyzed together with the distribution of the velocity and concentration fields inside the separator. Velocity and pressure drop were found to increase with the increase of the outflow in one outlet when changing the flow split. Flow control, at the outlets, caused an increase of the oil-in-gas entrainment when trying to minimize gas-in-oil entrainment which is a non-trivial task. The effects of the flow split specified appeared downstream of the conical bluff body only when the inflow conditions were kept constant whereas the flow field remained identical upstream of the cone. A recirculation zone was generated in the annular space downstream of the cone and affected the separator performance considerably. The recirculation zone was due to the effect of the higher flow rate towards the gas outlet and disappeared when the flow rate towards the oil outlet tended to be equal or higher. The phase distribution was identical upstream of the cone and depended on the flow split downstream of the cone.

The cases considered served as an assessment of the separator performance under different multiphase flow conditions replicating realistic scenarios.
Flow Characteristics of Rectangular Liquid Jets Injected Into Low Subsonic Crossflow
Authors: Tadjfar M. , Jaberi A. , Shokri R.
Published: November 2019

Perpendicular injection of liquid jets into gaseous crossflow is well-known as an effective way to obtain good mixing between liquid fuel and air crossflow. Mostly, injectors with circular holes were used as the standard method of fuel spraying. However, recently a great attention to injectors with non-circular holes has emerged that aims to improve the quality of fuel mixing and consequently combustion efficiency. In the present work, rectangular injectors with different aspect ratios varying from 1 to 4 were experimentally studied. Using a wind tunnel with maximum air velocity of 42 m/s, tests were performed for a wide range of flow conditions including liquid-to-air momentum ratios of 10, 20, 30 and 40. Backlight shadowgraphy and high speed photography were employed to capture the instantaneous physics of the liquid jets discharged into gaseous crossflow. The flow physics of the rectangular liquid jets were investigated by means of flow visualizations. Different regimes of flow breakup including capillary, arcade, bag and multimode were observed for rectangular jets. Moreover, a new technique was used to calculate the trajectory of the liquid jets. It was shown the nozzle’s shape has no significant effect on jet trajectory. Also, the momentum ratio was found to has a profound effect on jet trajectory.
A New Vacuum System for Steam Plant Condenser
Authors: Hegazy Ahmed , Yousef Khaled , Engeda Abraham
Published: November 2019

In the current work, a simple and low energy consuming system is proposed for holding on the vacuum in the steam power plant system. In this system, vacuum is created at the tip of an inverted U-pipe through which water flows by siphon effect. The stream of water through this pipe is brought about from a reservoir to another one whose water surfaces are at certain height difference. This height difference along with the height of the inverted U-pipe tip defines the value of the vacuum that can be produced. At this tip, the U-pipe is linked to the discharge pipe of a compressor which draws a mixture of air, non-condensable gases and some water vapor from the steam condenser and raises their pressure a little higher than that of the inverted U-pipe tip so that the resistance of connecting pipe is overcome and the pressure at exit of this pipe is equal to that at the inverted U-pipe tip. The mixture flows along with the water down the inverted U-pipe till it leaves the pipe with the water. A thermodynamic and fluid flow analysis is developed for predicting the performance of the proposed system. The results of this analysis show that the right selection of the mass flow rates ratio of water flowing in the inverted U-pipe and air and water vapor mixture sucked by the compressor from the steam plant condenser, in the range of 25000, the height of the inverted U-pipe summit from the water level of the higher water tank greater than 9.2 m and the height difference of the water levels in the two water tanks small enough, in the range of 0.1m saves the power of vacuum system by 80% less than that consumed when using compressor alone for venting the steam plant condenser.
Experimental Investigation on Cavitation Performance of Torque Converter Using Transparent Model
Authors: Katayama Yusuke , Hosoi Yuki , Fukuda Yuta , Watanabe Satoshi , Tsuda Shin-ichi , Mori Yoshihide , Ito Kazuyoshi
Published: November 2019

In this study, we experimentally investigated the influence of the amount of dissolved air in working fluid and the rotation speed ratio of turbine to pump elements on cavitation phenomenon in automotive torque converter. In order to directly observe the cavitation phenomenon, transparent model was used. The applied charge pressure was varied to change the significance of cavitation. The pump and turbine torques were simultaneously measured to clarify the relation between torque performance and cavitation phenomenon. As a result, the cavitation region was found to depend on the speed ratio; cavitation occurred on the suction side of turbine blades at low speed ratios while in the pump region at high speed ratios. The effect of the amount of dissolved air was significant, which enhanced the growth of cavitation bubbles through the deposition of dissolved air. In such cases, with the further decrease of charge pressure, a large number of gaseous cavitation bubbles appeared in the whole flow passage. The torque performance was deteriorated at this stage.
Experimental Study of Temperature and Phase Transition of Liquid Oxygen at Ignition in Impinging Injector of Gas Generator
Authors: Yagihashi Hiromitsu , Nakata Daisuke , Minato Ryojiro , Yoshikawa Inaho , Arimatsu Koki , Uchiumi Masaharu
Published: November 2019

This paper describes the ignition transients of a LOX/ethanol gas generator that is used for a gas generator cycle air turbo ramjet engine. It is essential to know the temperature history of the LOX injector manifold in order to determine the appropriate ignition sequence. Following a chill-down process, an inert gas purge is performed prior to ignition. Once the main valve is opened, liquid oxygen is discharged after a short period of discharging gaseous oxygen. The period of the gas discharge is a critical parameter for the success of the ignition that is affected by the injector temperature at the time that the valve opens. As a result of the experiments, the gas discharge period was found to be in the range of 0.5–1.0 second, whereas the injector temperature when the valve was opened ranged from 120–170 K under various experimental conditions.
Sea Water, Oil and Surfactant Three Phases Mixing Simulation Using Population Balance Model (PBM) Coupling With CFD
Authors: Mao Shaolin , Cowan Chris , Ozen Metin
Published: November 2019

Water is widely used in enhanced recovery operation in hydraulic fracking technology nowadays. Water or sea water, oil (e.g., resin) with surfactant mixing is a promising way to improve the efficacy to the recovering operation. In this study, we apply advanced multiphase flow models such as population balance model (PBM) coupling with CFD to analyze the three phases mixing process. The simulation will target more than 30 minutes of physical time, validate the evolution of mixing through experimental observations. The goal of this study is in two-fold: 1) assessment of population balance model with applications to high volume fraction of dispersed phases (e.g., resin), and 2) enhancement of the computational capability available in commercial software such as ANSYS FLUENT.
Numerical Study on Unsteady Wake Characteristics of an Urban Maglev Train
Authors: Sun Zhenxu , Yao Yongfang , Kong Fanbing , Yang Guowei
Published: November 2019

As the running speed increases, the aerodynamic loads become dominant for high-speed ground vehicles. Meanwhile, the aerodynamic lift of the trailing car becomes crucial at higher speed, which may lead to security and comfort problems. Flow field details are the root to the aerodynamic loads. Study on the wake characteristics of the train could shed light to learn the mechanism of their aerodynamic loads and know how to improve their aerodynamic performance. In the present paper, the urban maglev train with a design speed of 200 km/h is mainly focused on. Numerical investigation is adopted for current study. The Improved Delayed Detached Eddy Simulation (IDDES) numerical approach is utilized to count for unsteady flow details. To characterize the vortex structures, the iso-surface of Q for urban maglev train is obtained and compared. Due to the existence of guide way, the streamline of maglev trains is much more influenced by the guide way. The ground effect for maglev trains is more obvious. The streamlined shape is quite essential to the flow phenomena, and as a result, the vortex structures for urban maglev trains are also different. Guide way could lead to more vortices, which is common for maglev trains. However, lateral vortex could be observed for urban maglev trains, which is unique and is a result of the flat shape of the trailing nose. Meanwhile, the slipstream in the wake of the train is also compared. The streamlined shape of urban maglev trains is the bluntest, which induces the relatively biggest train wind. Based on the above analysis, the unsteady characteristics of flow field for urban maglev train are obtained and the main vortex structures are characterized. Based on the unsteady analysis of flow field, the relationships between aerodynamic loads of the trailing car and different kinds of trailing vortices are obtained. Current study could shed light on the understanding of mechanism of aerodynamic performance of a train and how to design the streamlined shape for trains with certain operational speed.
CFD Simulation of Slug Dissipation in an Enlarged Impacting Tee
Authors: Mohammadikharkeshi Mobina , Parsi Mazdak , Dabirian Ramin , Mohan Ram S. , Shoham Ovadia
Published: November 2019

Slug flow, which commonly occurs in the petroleum industry, is not always a desired flow pattern due to production operation problems it may cause in pipelines and processing facilities. To mitigate these problems, flow conditioning devices such as multiphase flow manifolds and slug catchers are used, where dissipation of slugs occurs in downward flow or in larger diameter pipe sections. Tee-junctions are important parts of these flow conditioning devices.

In this work, Computational Fluid Dynamics (CFD) simulations are conducted using ANSYS/FLUENT 17.2 to investigate slug dissipation in an Enlarged Impacting Tee-Junction (EIT). An Eulerian–Eulerian MultiFluid VOF transient model in conjunction with the standard k-ε turbulent model is used to simulate slug dissipation in an EIT geometry. The EIT consists of a 0.05 m ID 10 m long inlet, which is connected to the center of a 0.074 m ID 5.5 m long section that forms the EIT branches. Moreover, experimental data are acquired on slug dissipation lengths in a horizontal EIT with a similar geometry as in the CFD simulations.

The CFD results include the mean void fraction and cross-sectionally averaged void fraction time series in the EIT for different gas and liquid velocities. These results provide the inlet slug length and dissipation length in the EIT branches. The CFD results are evaluated against the experimental data demonstrating that the slug dissipation occurring in EIT branches can be predicted by simulation.
Wake Flow and Vortex Shedding Patterns Behind Rotating Finite Length Cylinders
Authors: Donaldson Amber , Vaccaro John C. , Rooney David M.
Published: November 2019

An experimental wind tunnel study was performed to assess the effect of aspect ratio and rotational speed of circular cylinders of varying diameter on the flow patterns behind the cylinders in the presence of a uniform upstream crossflow. Six circular cylinders of constant length but different diameters, producing aspect ratios 6 ≤ AR ≤ 32 were examined at a single upstream velocity such that the Reynolds number varied between 1920 ≤ Re ≤ 10240. Rotational speeds from stationary up to 3600 rpm were applied to the cylinders, so that the maximum relative velocity α = πfD/U∞ = 0.80. Mean velocity profiles were measured three diameters downstream of the cylinder axis at 6 equidistant locations, and PSD power spectral density were generated for 26 equidistant locations along the cylinder, to create a comprehensive record of spanwise variations under all rotational conditions. For the highest aspect ratio tested, the wake velocity profiles were independent of rotational speed at all spanwise locations, whereas at lower aspect ratios, the maximum velocity defect diminished with increasing rotational speed along most of the span and became asymmetric near the free end. Two distinct shedding cells were found only for a cylinder with an aspect ratio of twelve at three relative spin rates of 0.067, 0.27, and 0.4. In cases where only a single cell existed, increased rotational speed produced a higher vortex shedding frequency on a given aspect ratio cylinder.
Experimental and Numerical Investigation on Pressure Fluctuation of the Impeller in an Axial Flow Pump
Authors: Shen Xi , Zhang Desheng , Xu Bin , Jin Yongxin , Gao Xiongfa
Published: November 2019

The Detached Eddy Simulation (DES) has been used to simulate the pressure fluctuation of the impeller in an axial flow pump. The results were combined with experiments including high-speed photography and transient pressure measurements to investigate the unstable flow induced by tip leakage vortex (TLV). Numerical results show that maximum predictive error values of head is 2.9%, compared with experimental results. The pressure fluctuation at different monitoring points present a certain regularity, with 3 peaks and 3 troughs in a period, corresponding to the number of blades. The amplitude of pressure fluctuation at P1 (impeller inlet) is the highest among those monitoring points, where the amplitude decreases with the flow rates. The dominant frequency of pressure fluctuation at impeller under cavitation condition is the blade passing frequency (BPF). Besides, there are also N* = 6, 9, 12 and other more harmonic frequencies. The cavitation flow was analyzed with the pressure fluctuation of the blade tip. For the existence of the pressure difference between pressure side and suction side, the pressure at monitoring points change alternately. The amplitude of the fluctuation near tip is affected seriously by the cavitation bubbles, as the cavitation could is a low pressure region with unstable fluctuation.
Capillary Impregnation of Viscous Fluids in a Multi-Layered Porous Medium
Authors: Ashraf Shabina , Phirani Jyoti
Published: November 2019

Capillary impregnation of viscous fluids in porous media is useful in diagnostics, design of lab-on-chip devices and enhanced oil recovery. The impregnation of a wetting fluid in a homogeneous porous medium follows Washburn’s diffusive law. The diffusive dynamics predicts that, with the increase in permeability, the rate of spontaneous imbibition of a wetting fluid also increases. As most of the naturally occurring porous media are composed of hydrodynamically interacting layers having different properties, the impregnation in a heterogeneous porous medium is significantly different from a homogeneous porous medium. A Washburn like model has been developed in the past to predict the imbibition behavior in the layers for a hydrodynamically interacting three layered porous medium filled with a non-viscous resident phase. It was observed that the relative placement of the layers impacts the imbibition phenomena significantly. In this work, we develop a quasi one-dimensional lubrication approximation to predict the imbibition dynamics in a hydrodynamically interacting multi-layered porous medium. The generalized model shows that the arrangement of layers strongly affects the saturation of wetting phase in the porous medium, which is crucial for oil recovery and in microfluidic applications.
Numerical Investigation of Fluctuating Aerodynamic Lift Acting on the Road Vehicle Which Affects Drivability
Authors: Ikeda Jun , Rios Javier Sanchez , Kuratani Naoshi , Ogawa Kenta , Tsubokura Makoto
Published: November 2019

In this study, unsteady flow simulations using a large-eddy simulation are conducted to analyze vehicle aerodynamics. The objective is to investigate flow structures that cause unsteady lift fluctuations potentially affecting the drivability of a vehicle. In addition, the dependence on the yaw angle of the incoming flow yaw angle is studied. The target model is a sedan-type vehicle that includes a complex underbody geometry and engine compartment. The model is based on production CAD drawings. The yaw angle of the incoming flow is set to 0°, 3°, and 5°. The simulation results are analyzed by several post-processing methods, such as root-mean-square of the transient pressure field, power spectral density of the lift force, and dynamic mode decomposition method to extract the flow features associated with the unsteady lift fluctuation. It is concluded that the aerodynamic fluctuation that may affect a vehicle’s vertical stability is concentrated on the rear tire and bumper area. In addition, when the yaw angle of the incoming flow increases, the fluctuation of the lift and the disturbance of flow structures are enhanced.
Laser Velocity and Surface Measurements Toward the Prediction of Turbulent Frictional Resistance on Irregular Rough Surface in Higher Reynolds Number Range
Authors: Okubo Kyohei , Suzuki Shunpei , Kuwata Yusuke , Kawaguchi Yasuo
Published: November 2019

In this research, we consider the relationship between roughness of the wall and frictional resistance in the range of high-Reynolds number regime which is important for practical use, and its goal is to build a more accurate and highly versatile formula for predicting the frictional resistance acting on the complex surface with irregular roughness. In addition to the parameter corresponding to the distribution of the roughness used in a conventional and empirical formula, we aim to construct an empirical formula including the parameter representing the wavelength of the rough surface. In this study, we conduct laboratory experiments of Taylor-Couette flow, using the cylindrical test specimens roughly sprayed with an actual ship paint, and investigate the influence of irregular roughness on flow field and the surface frictional stress based PIV (Particle Image Velocimetry) measurements and torque measurements in high Reynolds numbers. The azimuthal mean velocity for rough surfaces increased in the entire flow field in comparing to the flow for a smooth surface, and this tendency is remarkable in a bulk region. Also, we measure the rough surfaces of the specimens using a laser type one-shot three-dimensional measurement device. Based on the results of above measurements, we propose the direct relationship between the parameter of a rough surface and frictional resistance.
Three Dimensional Simulation of the Effect of Windcatcher’s Inlet Shape
Authors: Abdo Peter , Taghipour Rahil , Huynh B. P.
Published: November 2019

Windcatcher has been used over centuries for providing natural ventilation using wind power, it is an effective passive method to provide healthy and comfortable indoor environment. The windcatcher’s function is based on the wind and on the stack effect resulting from temperature differences. Generally, it is difficult for wind to change its direction, and enter a room through usual openings, the windcatcher is designed to overcome such problems since they have vertical columns to help channel wind down to the inside of a building. The efficiency of a windcatcher is maximized by applying special forms of opening and exit. The openings depend on the windcatcher’s location and on its cross sectional area and shape such as square, rectangular, hexagonal or circular. In this study the effect of the inlet design is investigated to achieve better air flow and increase the efficiency of windcatchers. To achieve this, CFD (computational fluid dynamics) tool is used to simulate the air flow in a three dimensional room fitted with a windcatcher based on the different inlet designs. The divergent inlet has captured the highest air flow with a difference of approximately 3% compared to the uniform inlet and 5% difference compared to the bulging-convergent inlet.
A Numerical Investigation of Heat and Mass Transfer in Air-Cooled Proton Exchange Membrane Fuel Cells
Authors: Berning Torsten
Published: November 2019

A numerical analysis of an air-cooled proton exchange membrane fuel cell (PEMFC) has been conducted. The model utilizes the Eulerian multi-phase approach to predict the occurrence and transport of liquid water inside the cell. It is assumed that all the waste heat must be carried out of the fuel cell with the excess air which leads to a strong temperature increase of the air stream. The results suggest that the performance of these fuel cells is limited by membrane overheating which is ultimately caused by the limited heat transfer to the laminar air stream. A proposed remedy is the placement of a turbulence grid before such a fuel cell stack to enhance the heat transfer and increase the fuel cell performance.
Flutter Study on High Speed Train External Windshield by a Tight Coupling Method
Authors: Jiang Qian , Zheng Guannan , Zhao Guilin
Published: November 2019

Flutter is a complex problem caused by the interaction between the elastic structure and the flow field around that. In this paper a study of flutter on high speed train external windshield is presented.

Here, a coupling scheme of computational fluid dynamics (CFD) and computational structure dynamics (CSD) is applied to simulate the flutter problems. Specifically, some key technologies like tight coupling method, information transfer and mesh deformation strategy are involved. Repeatedly exchanging information in the sub-iteration of physical time step is basically typical of tight coupling method, which is a second-order accuracy method. This flutter methodology has been applied for standard model AGARD 445.6 wing and other engineering examples, with lots of excellent results obtained.

In this high speed train external windshield flutter research, eight train speed conditions are chosen to simulate the flutter issue, including 250km/h, 300km/h, 350km/h, 400 km/h, 450 km/h, 500 km/h, 550 km/h and 600 km/h. As for structural model, the first 30 order modes of elastic windshield are taken into consideration for CFD/CSD coupling simulation. In addition, it is defined to be the flutter boundary once the generalized displacement curve performing as persistent oscillation, which is the critical stable state for the vibration of external windshield. According to the research, under a specific train speed condition, adjustment of modal eigenfrequency can lead to the change of vibration stability. Furthermore, it is found that there is a positive correlation between train speed and modal eigenfrequency. So the optimal windshield scheme under different operating speeds is proposed that in order for the convergent vibration, a measure of changing eigenfrequency can be taken to ensure the vibration convergent and flutter cannot occur.
Hydrodynamic Evaluation of Microtiter Plate Assay Using Computational Fluid Dynamics for Biofilm Formation
Authors: Zahra R. , Khan A. A. , Sajid M.
Published: November 2019

Biofilms are complex surface associated communities where bacterial cells are enclosed by self-produced extra cellular polymeric substances (EPS), mainly consisting of exopolysaccharides, proteins and extracellular DNA. Treatment of biofilm associated persistent infections is an emerging issue for clinicians as bacterial cells adhere with human epithelial cells or indwelling medical devices such as implants and catheters, used in urinary tract and respiratory infections. Several methods are in practice to assess the biofilm formation of bacterial strains. Most of these are phenotypic methods which include Congo red assay (CRA), Air liquid interface (ALI), tissue culture plate method and Microtiter plate assay (MTPA). MTPA is considered as a standard screening method for comparing adherence pattern and is the most widely used quantitative method for detection of biofilm formation. Generally, the assay is performed under standard static conditions and little is known about the hydrodynamics in the microtiter plates. A few studies have applied computational fluid dynamics (CFD) simulations to describe flow pattern in microtiter plates during biofilm production and optimized the suitable conditions to detect the biofilm formation which have proven to be efficient. In this work the dependencies of biofilm formation on the hydrodynamics in microtiter plate assays were evaluated using OpenFOAM® an open-source toolbox for numerical simulation. It was found that higher flow rates increase the nutrient availability, promote cell growth, and attachment pattern with increased production of exopolymer, while the increase in flow velocity increases the shear rate causing erosion and disassembly of biofilm production because of detachment from the surface.
The Effects of Nozzle Orientation on Mixing Characteristics of Elliptic Twin Free Jets
Authors: Morris Ella M. , Biswas Neelakash , Aleyasin Seyed S. , Tachie Mark F.
Published: November 2019

The effects of nozzle orientation on the mixing and turbulent characteristics of elliptical free twin jets were studied experimentally. The experiments were conducted using modified contoured nozzles with a sharp linear contraction. The centers of the nozzle pair had a separation ratio of 5.5. Four nozzle configurations were tested, one twin jet orientated along the minor plane (Twin_Minor), one twin jet orientated along the major plane (Twin_Major), one single jet orientated along the minor plane (Single_Minor) and one single jet orientated along the major plane (Single_Major). In each case, the Reynolds number based on the maximum jet velocity and the equivalent diameter was 10,000. A planar particle image velocimetry system was used to measure the velocity field in the jet symmetry plane. It was observed that the velocity decay rate is not sensitive to nozzle orientation. However, close to the jet exit the spread rate was highest in the minor plane. In addition, contour plots of Reynolds shear stress and turbulence intensities revealed significant differences between the minor and major plane. Velocity profiles showed little variation close to the jet exit, while further downstream the variations between the velocity profiles were more pronounced between the major and minor planes.
Turbulent Channel Flow With a Modified k-ω Turbulence Model for High-Order Finite Element Methods
Authors: Bagheri-Sadeghi Nojan , Helenbrook Brian T. , Visser Kenneth D.
Published: November 2019

One-dimensional fully developed channel flow was solved using a modified k–ω turbulence model that was recently proposed for use with high-order finite element schemes. In order to study this new turbulence model’s behavior, determine its dependence on boundary conditions and model constants, and find efficient methods for obtaining solutions, the model was first examined using a linear finite element discretization in 1D. The results showed that an accurate estimate of the parameter εk which is used to define k in terms of the working variable k~ is essential to get an accurate solution. Also, the turbulence model depended sensitively on an accurate estimate of the distance of the first grid point from the wall, which can be difficult to estimate in unstructured grids. This is used for the boundary condition of specific dissipation rate on the wall. This model was then implemented in a high-order finite element code that uses an unstructured mesh of triangles to verify that the 1D results were predictive of the behavior of the full 2D discretization. High-order 2D results were obtained on triangular meshes with element aspect ratios up to 250000.
The CFD Modeling of the Water Braking Phenomena for the Holloman High-Speed Test Track
Authors: Terrazas Jose , Kotteda V. M. Krushnarao , Kumar Vinod , Edmonds Robert , Zeisset Michelle
Published: November 2019

At the Holloman High-Speed Test Track (HHSTT), momentum exchange with water is used to decelerate sleds from very high speeds (> Mach 1). This process, at the HHSTT, is called ‘water braking’. Improving the prediction capabilities of water braking phenomena has the potential to result in radical changes in the designs of sleds, improve rocket sled velocity-time test profile predictions, provide greater confidence of braking mechanisms, and decrease risk in the recovery of critical infrastructures. Understanding the water?s behavior with the sled is critical to predicting how the water could damage the sled, which affects the recoverability of the sled and can determine the success of a mission. Traditionally, sled design for the test missions for water braking has been guided by empirical/hand calculations to estimate the forces on various components. The calculations involved various approximations in arriving at the force balance law and predicting the acceleration/deceleration profile. In partnership with the HHSTT, we performed preliminary simulations to develop a predictive model for the HHSTT sled tests at various velocity regimes. The (preliminary) CFD results from different geometry configurations for the sled and modeling parameters will be presented.
Exploring and Improving the Flow Characteristics of an Empty Water Channel Test Section: The Application of TomoPIV and Flowrate Sensors for Whole-Flow-Field Visualization
Authors: Mousavi sani Seyedmohammad , Goudarzi Navid , Sheikhshahrokhdehkordi Mohammadamin , Bisel Tucker , Dahlberg Jerry , Tkacik Peter
Published: November 2019

This paper presents the quantitative results of improving the uniformity of the flow field within the test section of a constant cross section, closed-loop water channel. Tomographic Particle Image Velocimetry (TomoPIV) and four flowrate sensors are used to determine the mean velocity and velocity fluctuations at two motor frequencies: 7.5 Hz and 10 Hz (an approximate free stream flow velocity of 0.11 m/s and 0.18 m/s, respectively). The flow field velocity determined by the flowrate sensors showed great agreements with the TomoPIV results. For instance, at the 10 Hz water channel motor frequency, the flowrate sensors and TomoPIV obtained velocity ranges of 0.191–0.202 m/s and 0.185–0.21 m/s, respectively. In order to reduce the flow speed variations within the studied TomoPIV measurement volume, improvements were implemented on the water channel to include an adjustable screen and deflector to the first set of turning vanes downstream from the water channel motor. The modification improved the 7.5 Hz motor frequency measured flow velocity from 0.16–0.172 m/s to 0.106–0.108 m/s resulting in a final variation of flow speed within the measurement volume reduced to 1%.
Branch and Bound Analysis to Characterize Phase Variations in Laser Propagation Through Deep Turbulence
Authors: Rodriguez Luis F. , Kumar Vinod , Espiritu Jose , Bronson Arturo , Kotteda Krushnarao , Lozano Diego , Rodriguez Arturo
Published: November 2019

An analytical estimation of the wave diffraction due to turbulence is made and then it is compared with an estimate based on the Branch and Bound technique as a platform of a machine learning model. At the final step, the results are compared to verify the capacity of the machine learning model.

The reason for this analysis is based on the fact that communication via laser beam in the open atmospheric environment experiences the effects of the turbulence generating a disturbance of wave phases that affects the fidelity of such communication.
Theoretical Optimization of Splitter Blade Geometry in High-Efficiency Centrifugal Turbopumps
Authors: Apollonio Alessandro , Maddaluni Francesco , Pasini Angelo , Valentini Dario , d’Agostino Luca
Published: November 2019

The introduction of splitter blades (splitters) in the impeller represents a possible way to improve the head and efficiency of centrifugal turbopumps. Splitters decrease flow slip, deviation, blockage and losses at the impeller discharge by reducing the displacement flow and the adverse pressure gradient it induces on the boundary layers (BLs) developing on the pressure sides of the full blades. These benefits are to be balanced against the introduction of additional flow blockage and losses. It is therefore of interest to investigate which splitter blade geometry (position and length), if any, is most effective to best exploit the potential advantages of adding splitter blades to a centrifugal impeller. To this purpose a quasi-3D, reduced-order method, previously developed for preliminary prediction of the geometry and performance of centrifugal turbopumps, is extended to account for the introduction of splitter blades for the purpose of investigating their influence on the hydraulic performance of these machines. Splitters with radial leading edges and the same shape as the full blades are introduced in the six-bladed backswept impeller of the VAMPIRE turbopump, a high-efficiency machine previously used for experimental validation of the original version of the flow model. The results highlight the most relevant action mechanisms of splitter blades in affecting the turbopump performance and provide general indications on their most effective design for performance improvement. As a consequence of the evolution of the BLs in the blade channels, relatively longer splitters located closer to the pressure sides of the full blades are more efficient at and above design flow, while the reverse is the case at high blade loadings. The results also indicate that the introduction of splitter blades only marginally improves the performance of the already optimized VAMPIRE pump in view of its small residual margins for performance gains.
Thermal Cavitation Instability Analysis in Axial Inducers by Means of Casing and Hub-Mounted Pressure Sensors
Authors: Hadavandi Ruzbeh , Pasini Angelo , Valentini Dario , Pace Giovanni , d’Agostino Luca
Published: November 2019

The effects of thermal cavitation on the flow instabilities developing in a three-bladed, tapered-hub, variable-pitch space turbopump inducer are described by illustrating the results of similarity experiments in water carried out at Sitael in the Cavitating Pump Rotordynamic Test Facility (CPRTF). The operating conditions have been varied as required for investigating the onset and response of the fluid dynamic instabilities occurring in the test inducer over a wide range of cavitation numbers from noncavitating to heavy cavitation conditions, both at design and off-design flow. The CPRTF water temperature has been varied from room conditions to 80 °C ca. in order to induce thermal cavitation effects of increasing intensity capable of reproducing in the experiments the occurrence of typical cavitation phenomena in cryogenic space propellants. A wide variety and number of axial and rotating fluid dynamic instabilities have been detected, identified and characterized by spectral analysis of the pressure measurements obtained from statoric and rotoric transducers flush-mounted on the casing and the hub of the test inducer. The results indicate that thermal cavitation significantly affects the types of flow instabilities developing in cavitating inducers and the range of flow and suction conditions for their occurrence.
2D Velocity Vector Profile Measurement and Phase Separation on Swirling Bubbly Flow Using Ultrasound Technique
Authors: Wongsaroj Wongsakorn , Takahashi Hideharu , Kikura Hiroshige , Thong-un Natee
Published: November 2019

Two-phase swirling bubbly flow is a complex phenomenon which occurs in several industries such as a nuclear reactor. Its characteristic is indispensably necessary to be investigated especially the multi-dimensional velocity distribution. This present paper describes the development of Ultrasonic Velocity Profiler (UVP) method which is a noninvasive measurement and needless of optical access, to obtain a two dimensional (2D) velocity distribution of the bubble and liquid phase in swirling bubbly flow simultaneously. The measurement result is represented in the form of the 2D velocity vector. To achieve the target, the multiple transducers and developed signal processing have been applied to the UVP system to measure a 2D velocity vector affected by bubble and liquid separately. For confirming the ability of Developed-UVP, the experiment was conducted on a vertical pipe co-current flow apparatus. The UVP measurement was demonstrated non-intrusively and without the optical requirement. The measurement applicability of Developed-UVP was evaluated by comparing with Particle Image Velocimetry (PIV) method on liquid flow and bubbly flow. Then, it was applied to obtain the 2D velocity vector in swirling bubbly flow. The velocity vector of the bubble and liquid could be separated clearly. Also, velocity distribution in swirling motion which was interacted of both phases was investigated understandably by using this measurement technique.