bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of Dynamic Characteristics of Pneumatic Control Valve With Smart Valve Positioner
Authors: Youn Chongho , Saito Kenji , Furuya Motohiro
Published: November 2019

In this research, in order to predict the dynamic characteristics of a regulating valve, a mathematical model is proposed for a pneumatic control valve using a smart valve positioner (AVP300), and the dynamic characteristics of the control valve were simulated. We modeled the components of the control valve (i.e., nozzle flapper, pilot valve, Auto/Manual (A/M) screw, bleed orifice, pneumatic actuator, gland packing, and pressure reducing valve), and simulated the dynamic characteristics using SimulationX, a one-dimensional analysis software.

For the nozzle flapper, we proposed a model that considers the influence of fluid force due to pressure change as well as the influence of the change in effective area by measuring the displacement, pressure, and flow rate of the nozzle flapper. The diaphragm chamber, which operates the pilot valve of the positioner, was made of transparent acrylic. The displacement of the pilot valve was measured by a laser displacement sensor, and its movement against pressure change was clarified. The sonic speed conductance and critical pressure ratio of the A/M screw and bleed orifice were determined experimentally and reflected in the model. In the pneumatic actuator, the effective cross-section of the diaphragm was obtained from the change in pressure and displacement. The change in volume was calculated from the experiment using a fixed chamber. The friction force of gland packing was modeled using static and dynamic friction forces.

The experiment on the dynamic characteristics of valve displacement was performed with the input signal of the valve displacement set from 20% to 80%. A comparison of the experimental results of the valve displacement and simulation results showed good agreement. The simulation in this study is considered effective in predicting the dynamic characteristics of the control valve.
Analysis on Heat Transfer and Phase Change for Two-Phase Boiling Flow in Quenching Process
Authors: Wang Lu , Oshima Nobuyuki , Kim Sangwon
Published: November 2019

A series of numerical simulations using “interThermalPhaseChangeFOAM” solver with improved VOF multiphase flow model in OpenFOAM were conducted to investigate the heat transfer and phase change characteristics for liquid-vapor boiling flow in quenching process. The computational domain is a cuboid with the heating wall at the bottom for both the variable and fixed wall temperature cases. The results for the variable wall temperature case with the heating wall temperature Twall = 150K show that the boiling phenomenon can be divided into the vapor film stage, the boiling stage and the convection stage. Then the fixed wall temperature cases with Twall = 110K, 120K and 140K are analyzed. It is found that 140K case is the most stable one, in which bubble formation is regular such as the bubble at the corner, resulting in the steady variation of heat flux. 120K case is the most unstable one, since the liquid phase and gas phase form the cross-interface shape and maintain this for a long time, leading to the fluctuations in heat flux. Finally, the influence of computational sizes on predicting the properties of boiling phenomenon is investigated. Although the variations of heat flux are not exactly same, the whole tendency is similar.
An Experimental Study of Influence of Slits in Throat Position on Suppression of Cavitation Instabilities in Liquid Propellant Rocket Inducer
Authors: Kanamaru Moena , Kamikura Yoshito , Kawasaki Satoshi , Shimura Takashi , Yuka Iga
Published: November 2019

Experiments of an inducer with symmetric slits were conducted. The purpose of the study is to explore the suppression effect on cavitation instabilities by slits. The slits are located in a throat position in each blade and it means symmetric slits. The experiments are done through measuring pressure fluctuation in the flow field and shaft displacement and visualization using high speed camera. In this study, the head performance, the suction performance, the cavity length and the occurrence range and the strength of the cavitation instabilities are compared with the results of inducer without slit. As a result, the slit in throat position does not give bad effect on head performance, improves suction performance, and has a relation to suppression of oscillation of cavitation instabilities because of the suppression effect of cavity length, although the occurrence range of super-synchronous rotating cavitation unfortunately increases because the cavity develops slowly.
Uncertainty Quantification of a Fluidized Bed Reactor
Authors: Kotteda V. M. Krushnarao , Kommu Anitha , Kumar Vinod , Spotz William
Published: November 2019

Fluidized beds are used in a wide range of applications in gasification, combustion, and process engineering. Multiphase flow in such applications involves numerous uncertain parameters. Uncertainty quantification provides uncertainty in syngas yield and efficiency of coal/biomass gasification in a power plant. Techniques such as sensitivity analysis are useful in identifying parameters that have the most influence on the quantities of interest. Also, it helps to decrease the computational cost of the uncertainty quantification and optimize the reactor. We carried out a nondeterministic analysis of flow in a biomass reactor. The flow in the reactor is simulated with National Energy Technology Laboratory’s open source multiphase fluid dynamics suite MFiX. It does not possess tools for uncertainty quantification. Therefore, we developed a C++ wrapper to integrate an uncertainty quantification toolkit developed at Sandia National Laboratory with MFiX. The wrapper exchanges uncertain input parameters and critical output parameters among Dakota and MFiX. We quantify uncertainty in key output parameters via a sampling method. In addition, sensitivity analysis is carried out for all eight uncertain input parameters namely particle-particle restitution coefficient, angle of internal friction, coefficient of friction between two-phases, velocity of the fluidizing agent at the inlet, velocity of the biomass particles at the inlet, diameter of the biomass particles, viscosity of the fluidizing agent, and the percentage of nitrogen/oxygen in the fluidizing agent.
Electrokinetic Transport of Power Law Fluid Through a Micro-Channel With Hydrodynamic Slippage
Authors: Haque Ainul , Nayak Ameeya Kumar , Weigand Bernhard
Published: November 2019

A pressure driven electroosmotic flow (EOF) is numerically studied in a slit micro-channel with alternating hydrodynamic slip patches. The coupled Poisson-Boltzman-Navier Stokes equations dealt with external electric potential are solved for the flow enhancement of non-Newtonian fluids in microfluidic domain, which is a big challenge in the transportation and mixing of fluids in BioMEMS devices as the drag effect is very strong along the walls. This effect can be minimized with the use of slip boundary conditions by the coupling effects of liquid-liquid or gas-liquid interface positioning. In the present article, the fluid is considered to be a power-law fluids which is driven due to the coupling effects of two superimposed electric fields: the externally imposed electric field and the induced potential. An additional pressure gradient is created by the electrokinetic pumping to generate a higher velocity gradient in the presence of viscous dissipation and Joule heating effects. The analytical quantification of the electroosmotic flow velocity and temperature distribution is made and compared with the numerical results due to the staggered grid based finite volume method. The results are presented in terms of flow enhancement factor (Ef) (provides maximum species transport) and the average entropy generation due to fluid friction, viscous dissipation and Joule heating effect. The advantages and disadvantages of utilizing slip conditions are discussed which has large scale applications on drug delivery, DNA analysis and sequencing and especially biomedical applications, since cell damage due to pumping will be minimized compared to the micro pumps with moving valves, blades and pistons.
Experimental Study on Drag Reduction Effect With Traveling Wave Control Using PIV Measurement
Authors: Suzuki Ichiro , Shimura Takaaki , Mitsuishi Akihiko , Iwamoto Kaoru , Murata Akira
Published: November 2019

The influence of the traveling wave control on flow fields is evaluated by experiments using a traveling wavy wall in a fully developed turbulent dual channel flow. We develop a traveling wave generator using a rubber sheet and piezoelectric actuator as a vibration source. A single piezoelectric actuator is installed in the upstream position of the channel. Experiments are performed using traveling waves attenuating in the downstream direction. With traveling wave control, effective drag reduction is confirmed when bulk Reynolds number is within the range of 2000 < Reb < 6000. For Reb = 3000, the maximum drag reduction rate of 10% is obtained. In order to evaluate a relationship between the amplitude attenuation of traveling wave and drag reduction effect, particle image velocimetry (PIV) at multiple positions is performed. Increase of drag is observed near the vibration source whereas drag decreased at other positions. Reduction of random component of Reynolds shear stress can be ascribed to the drag reduction.
Three-Dimensional Measurement of Smoke Density Distribution by Switching Volumetric Color Illumination Patterns
Authors: Park Hyun Jin , Sugano Yuhei , Tasaka Yuji , Murai Yuichi
Published: November 2019

In this paper, we introduce an imaging technique for capturing 3-imensional smoke density distribution by adopting a three-layer color illumination and a six-layer color illumination for air flow measurements. A camera capable to capture three primary color components (red, green, blue) and a liquid crystal display projector are used as optical equipment. Each color layer is aligned parallel to a photographed plane of the video camera. The present technique assumes two things; three primary color signals are received proportionally to smoke density in each color layer and there is a linear relation between the smoke density and the color signals. These assumptions allow that the smoke density can be obtained from the color signals by solving inverse problem. In the three-layer case, solving inverse problem is possible by these assumptions. In the six-layer color illumination, a color layer illumination consisting of three primary colors and their intermediate colors (yellow, cyan, magenta) are projected toward measurement space. This forms an inverse problem with lack of information to reconstruct the smoke density because the number of independent color signals is lower than the number of color layers. To fix this issue, we apply a method to increase the number of color signals in time direction by switching two different illumination patters. The number of color signals becomes six to be equal to the number of variables to solve algebraically.
Hybrid RANS-LES Simulation of Turbulent Heat Transfer in a Channel Flow With Imposed Spanwise and Streamwise Mean Temperature Gradient
Authors: Shobayo Olalekan O. , Walters D. Keith
Published: November 2019

Computational fluid dynamics (CFD) results for turbulent flow and heat transfer in a plane channel are presented. This study presents an idealized fully-developed planar channel flow case for which the mean velocity gradient is non-zero only in the wall-normal direction, and the mean temperature gradient is imposed to be uniform and non-zero in the streamwise or spanwise direction. Previous studies have documented direct numerical simulation results for periodic channel flow with mean temperature gradient in both the streamwise and wall-normal directions, but limited investigations exist documenting the effect of imposed spanwise gradient. The objective of this study is to evaluate turbulent heat flux predictions for three different classes of modeling approach: Reynolds-averaged Navier-Stokes (RANS), large-eddy simulation (LES), and hybrid RANS-LES. Results are compared to available DNS data at Prandtl number of 0.71 and Reynolds number of 180 based on friction velocity and channel half-width. Specific models evaluated include the k-ω SST RANS model, monotonically integrated LES (MILES), improved delayed detached eddy simulation (IDDES), and dynamic hybrid RANS-LES (DHRL). The DHRL model includes both the standard formulation that has been previously documented in the literature as well as a modified version developed specifically to improve predictive capability for flows in which the primary mean velocity and mean temperature gradients are not closely aligned. The modification consists of using separate RANS-to-LES blending parameters in the momentum and energy equations. Results are interrogated to evaluate the performance of the three different model types and specifically to evaluate the performance of the new modified DHRL variant compared with the baseline version.
Deformation of a Moving Micro-Droplet
Authors: Zhong Yonghong , Nie Qichun , Liu Zhongyi , Fang Haisheng
Published: November 2019

Inkjet technology being an essential tool features high resolution and wide applicability. The generation of stable droplets is of great significance in many applications including 3D printing, solar cells and drug delivery. A stable ejected droplet can be a single droplet without satellite droplets (Situation 1), or a single primary droplet with a satellite that merges into the primary later (Situation 2). The deformation process of a stable droplet is directly related to accuracy and efficiency of the droplet delivery. In this paper, we adopt computational fluid dynamics to investigate deformation of a moving stable micro-droplet. It is found that as the driving force rises, the ejected droplets change from Situation 1 to Situation 2, and then to the unstable state after the driving force exceeds a critical value. In the meantime, the maximum deformation of the droplet firstly increases, and then decreases followed by a further increase. The minimum deformation undergoes a converse transition. It further reveals that two essential points of the maximum deformation curves, the peak point (within Situation 1) and the transition point (from Situation 1 to Situation 2), are correlated with ratio of the droplet velocity to the Capillary velocity. The peak point has a ratio between 2.7 and 3.1, and the transition point locates where the ratio plus a constant equals 3.4. New control methods have proposed based on the locations of the maximum deformation extent.
Using Jet Engine Simulator in Propulsion Education
Authors: Taghavi Ray , Farokhi Saeed
Published: November 2019

Undergraduate education in jet propulsion can benefit from a modern real-engine simulator. The traditional lecture/laboratory course in propulsion continues to emphasize fundamental aerothermodynamics and often includes a propulsion laboratory that tests small engines (e.g., micro-turbojet engines) mounted on a thrust stand. Modern engine simulators, as virtual test bench, offer new tools and capabilities that help students learn the fundamentals as well as jet engine response to dynamic throttle setting. Geared, high-bypass ratio, two-spool turbofan engines can be simulated in a virtual test bench from takeoff to cruise at different altitudes and Mach numbers. The simulator employs an electric start, a real FADEC (Full Authority Digital Electronic Control) system and system communication that is coupled to a real power lever. The tools that are embedded in the virtual test bench allows for various studies, including control systems, comparing open-loop and closed-loop control. The integration of a state-of-the-art engine simulator in the jet propulsion course at the University of Kansas, Aerospace Engineering shows enhanced student engagement and learning.
Discrete Vortex Modeling of a Flapping Foil With Activated Leading Edge Motion
Authors: Prier Michael W. , Liburdy James A.
Published: November 2019

Energy harvesting performance for a flapping foil device is evaluated to determine how activated leading edge motion affects the aerodynamic forces and the cycle power generated. Results are obtained for a thin flat foil that pitches about the mid-chord and operates in the reduced frequency range of k = fc/U of 0.06–0.10 and Reynolds numbers of 20,000 and 30,000 with a pitching amplitude of 70° and heaving amplitude of h0 = 0.5c. Time resolved data are presented based on direct force measurements and are used to determine overall cycle efficiency and coefficient of power. These results are compared against a panel-based discrete vortex model to predict power production. The model incorporates a leading edge suction parameter predictor for vortex shedding and empirical adjustments to circulatory forces. It is found that the leading edge motions that reduce the effective angle of attack early in a flapping stroke generate larger forces later in the stroke. Consequently, the energy harvesting efficiencies and power coefficients are increased since the generated aerodynamic loads are better synchronized with the foil motion. The efficiency gains are reduced with increasing reduced frequencies.
Pulsatile Flow Characteristics in a Stenotic Aortic Valve Model: An In Vitro Experimental Study
Authors: Zhang Ruihang , Zhang Yan
Published: November 2019

Aortic stenosis (AS) is one of the most common valvular heart diseases around the globe. The accurate assessment of AS severity is important and strongly associated with accurate interpretation of the hemodynamic parameters across the stenotic valve. In this study, we conducted in vitro fluid dynamic experiments to investigate the pulsatile flow characteristics of a stenotic aortic valve as a function of heart rate. An in vitro cardiovascular flow simulator was used to generate pulsatile flow with a prescribed waveform (40% systolic period and 4L/min cardiac output) under varied heart rates (50 bpm, 75 bpm and 100 bpm). The stenotic valve was constructed by molding silicone into three-leaflet aortic valve geometries wrapping around thin fabrics which increases its stiffness and tensile strength. Two-dimensional phase-locked particle image velocimetry (PIV) was employed to quantify the flow field characteristics of the stenotic valve. Pressure waveforms were recorded to evaluate the severity of the stenosis via the Gorlin and Hakki equations. Results suggest that as the heart rate increases, the peak pressure gradient across the stenotic aortic valve increases significantly under the same cardiac output. Analysis also shows the estimated aortic valve area (AVA) decreases as the heart rate increases under the same cardiac output using Gorlin equation estimation, while the trend is reversed using Hakki equation estimation. Under phase-locked conditions, quantitative flow characteristics, such as phase-averaged flow velocity, turbulence kinetic energy (TKE) for the stenotic aortic valve were analyzed based on the PIV data. Results suggest that the peak systolic jet velocity downstream of the valve increases as the heart rate increases, implying a longer pressure recovery distance as heart rate increases. While the turbulence at peak systole is higher under the slower heart rate, the faster heart rate contributes to a higher turbulence during the late systole and early diastole phases. Based on the comparison with no-valve cases, the differences in TKE was mainly related to the dynamics of leaflets under different heart rates. Overall, the results obtained in this study demonstrate that the hemodynamics of a stenotic aortic valve is complex and the assessment of AS could be significantly affected by the pulsating rate of the flow.
Thermo-Fluid Dynamic Design Exploration of a Double Pipe Heat Exchanger
Authors: Hirano Tomohiro , Yoshimura Mitsuo , Shimoyama Koji , Komiya Atsuki
Published: November 2019

Toward a practical application of the additive manufacturing (AM), this study proposes a shape optimization approach for the cross-sectional shape of the inner pipe of a counter-flow double pipe heat exchanger. The cross-sectional shape of the inner pipe is expressed by an algebraic expression with a small number of parameters, and their heat transfer performance is evaluated by a commercial Computational Fluid Dynamics (CFD) solver. The optimization is conducted by the Non-Dominated Sorting Genetic Algorithm II (NSGA-II) assisted by the Kriging surrogate model, and the NSGA-II finds the optimal cross-sectional shape with many protrusions around the perimeter of the inner channel to improve the heat transfer performance. In this study, heat transfer performance is evaluated from the temperature drop at the outlet of the high-temperature fluid. Through the comparison of two cross-sectional shapes with the same heat transfer surface area — average temperature at the outlet of the optimal high-temperature channel is 324.58 K while average temperature at the outlet of a circular high-temperature channel with the same area as the optimal channel is 331.93 K, it is revealed that the number of protrusions plays important roles which contribute not only to increase heat transfer area but also to improve heat transfer performance.
Experimental Study on Small Hydraulic Pump Using Visualization Technique
Authors: Woo Jangmi , Gim Yeonghyeon , Sohn Dong Kee , Ko Han Seo
Published: November 2019

Recent developments of smart materials such as piezo devices have been applied to small hydraulic pumps, enabling to meet various demands. For the compact pump, the valves are critical components in the aspect of fluid dynamics. In this study, the flow inside the reed valve port driven by the piezo actuator was experimentally observed. When a sine wave with a driving frequency of 90 Hz was applied, the maximum flow rate could be obtained. It was found that the developed flow opposite to the outlet direction at the root portion of the valve prevented further increase of the flow rate according to the operating frequency.
Direct Numerical Simulation of Radial Convection in a Cylindrical Annulus With and Without Rotation
Authors: Pitz Diogo B. , Wolf William R.
Published: November 2019

In rotating systems with temperature gradients, convection may occur due to gravitational or centrifugal effects. In cases where rotation is strong enough so that the centrifugal acceleration is higher than gravity, the flow is induced by centrifugal buoyancy and gravitational effects can be neglected. The problem of flow induced by centrifugal buoyancy in a cylindrical annulus has been used as a canonical setup to investigate industrial configurations, such as buoyancy-driven flows occurring in gas turbine secondary air systems, as well as geophysical flows, such as convection in the core of planets and the global circulation of the atmosphere. Due to the constraints imposed by the Taylor-Proudman theorem, such flows are quasi-homogeneous along the axial direction, and heat transfer as well as turbulent fluctuations tend to be suppressed by the action of the Coriolis force. Previous work has demonstrated that when the annulus is bounded by parallel disks, boundary layers scaling consistently with laminar Ekman layers are formed near each of the disks, even though the flow is purely buoyancy-induced. Also, the Nusselt number measured on the outer cylindrical surface has been shown to scale with the Rayleigh number as in natural convection between horizontal plates. In the present work we use direct numerical simulation (DNS) to investigate buoyancy-induced flow in an air-filled cylindrical annulus bounded by two adiabatic parallel disks, with and without rotation around the axis. In both cases the outer cylindrical surface is at a higher temperature than the inner one, so that a radial acceleration directed outwards induces an unstable stratification. In the case with rotation, the flow is induced by the centrifugal acceleration in the radial direction, and Coriolis forces are considered. For the case without rotation, the Coriolis terms are suppressed in the calculations, whereas the radial acceleration is the same as in the rotating case. Statistics are obtained and compared in the two cases, including the time-averaged Nusselt number, mean temperature profiles, velocity and temperature fluctuations, as well as terms of the turbulent kinetic energy equation. By analysing such statistics, the extent to which rotation suppresses heat transfer and turbulent fluctuations, as well as the contribution of each term to the turbulent kinetic energy budget, can be assessed.
Numerical Investigation on Multiphase Reacting/Combusting Turbulent Flows: Aerodynamics, Kinetics, Heat and Mass Transfer Inside a Cement Kiln Precalciner
Authors: Cristea Eugen-Dan , Conti Pierangelo
Published: November 2019

This paper reports the modeling work to develop a computational fluid dynamics (CFD) engineering application, based on an appropriate 3D mathematical model able to perform the thermo-fluid dynamic numerical simulation of multiphase reacting/ combusting turbulent flows within a precalciner of an industrial four-stage cyclone preheater/precalciner cement kiln. In the precalciner furnace the hot micron-sized limestone (calcite/dolomite) meal, held in suspension, is quiet completely converted to quicklime (CaO(s)), and the CO2(g) by-product is driven-off during calcination process. Since, the thermal decomposition mechanism is a very endothermic reaction, the necessary heat is balanced by pulverized petcoke combustion.

These major physical and chemical processes inside the precalciner are properly described by the 3-D Favre-averaged Navier-Stokes equations with the species transport equations, the energy equation and the state equation, to be solved by an Eulerian-Lagrange approach. The CFD solver employed in this study is the commercial CFD code ANSYS Fluent R18.2. The used built-in models/sub-models include turbulence models and near-wall treatment, model of traditional air-pulverized petcoke combustion, pulverized-limestone calcination model, as well as the sub-models for radiation heat transfer and turbulence-chemistry interaction. They are used to formulate the closures of the unclosed terms in the PDEs system.

In summary, the trends of predicted results of limestone calcination and petcoke/TDF combustion processes in an industrial precalciner furnace are reasonable fair in confront to operation data measurable in the harsh environment conditions, typical for the pyroprocessing systems. The developed CFD engineering application can be used as an effective design tool for preliminary examination of the global effect of thermal-flow aerodynamics and turbulence on the precalciner processes.
Characteristics of Swirl Angle in Pump Intake Flow Near the Minimum Inlet Submergence
Authors: Norizan Tajul Ariffin , Harun Zambri , Wan Mohtar Wan Hanna Melini , Abdullah Shahrir
Published: November 2019

Swirling flow in pump sump intake has been the subject of discussion for the past decades due to the detrimental effects brought about by its existence. Among the effects of swirling flow are reduced pump efficiency, cavitation, excessive vibration and load imbalance at the pump impeller which are caused by hydraulic problems associated to swirling flow such as swirls and vortices. One of the remedial measures for preventing such occasion is by keeping the pump inlet submerged above a defined value known as the minimum inlet submergence. It is the minimum submergence required to reduce the probability of the occurrence of free surface vortices. However, this requirement may not be fulfilled in some situations due to on site conditions or operational restrictions. In this paper, an experimental study was conducted to investigate the characteristics of swirl angle in the pump intake flow when the pump inlet is submerged near the value of minimum inlet submergence. The ratio of pump submergence to the minimum submergence was varied between 0.8 to 1.2 with constant inlet Froude Number which referred to as submergence ratio. The strength of the swirl in the intake flow was determined by measuring the swirl angle which was accomplished using a swirl meter attached in the suction pipe. Measurements using Acoustic Doppler Velocimeter (ADV) was performed to capture the velocity profile in the intake sump. The swirl angle distribution across the range of submergence ratios was dominated by a subsurface vortex formed at the sump floor. As soon as the submergence was reduced below the minimum submergence, a free surface vortex emerged near the pump inlet and brought a swirl retardation effect to the swirl meter rotation resulting in a bigger fluctuation of the swirl meter reading. An anti vortex device (AVD) called the floor splitter commonly used to reduce vorticity at pump inlet was installed and its effect on the reduction of swirls and vortices was evaluated.
Data-Driven Reduced Order Modeling of Flows Around Two-Dimensional Bluff Bodies of Various Shapes
Authors: Hasegawa Kazuto , Fukami Kai , Murata Takaaki , Fukagata Koji
Published: November 2019

We propose a reduced order model for predicting unsteady flows using a data-driven method. As preliminary tests, we use two-dimensional unsteady flow around bluff bodies with different shapes as the training datasets obtained by direct numerical simulation (DNS). Our machine-learned architecture consists of two parts: Convolutional Neural Network-based AutoEncoder (CNN-AE) and Long Short Term Memory (LSTM), respectively. First, CNN-AE is used to map into a low-dimensional space from the flow field data. Then, LSTM is employed to predict the temporal evolution of the low-dimensional data generated by CNN-AE. Proposed machine-learned reduced order model is applied to two-dimensional circular cylinder flows at various Reynolds numbers and flows around bluff bodies of various shapes. The flow fields reconstructed by the machine-learned architecture show reasonable agreement with the reference DNS data. Furthermore, it can be seen that our machine-learned reduced order model can successfully map the high-dimensional flow data into low-dimensional field and predict the flow fields against unknown Reynolds number fields and shapes of bluff body. As concluding remarks, we discuss the extension study of machine-learned reduced order modeling for various applications in experimental and computational fluid dynamics.
A Study on Improvement of Aerodynamic Performance for 100HP Axial Fan Blade and Guide Vane Using Response Surface Method
Authors: Choi Young-Seok , Kim Yong-In , Kim Sung , Lee Seul-Gi , Yang Hyeon-Mo , Lee Kyoung-Yong
Published: November 2019

This paper describes the numerical optimization of an axial fan focused on the blade and guide vane (GV). For numerical analysis, three-dimensional (3D) steady-state Reynolds-averaged Navier-Stokes (RANS) equations with the shear stress transport (SST) turbulence model are discretized by the finite volume method (FVM). The objective function is enhancement of aerodynamic performance with specified total pressure. To select the design variables which have main effect to the objective function, 2k factorial design is employed as a method for design of experiment (DOE). In addition, response surface method (RSM) based on the central composite design applied to carry out the single-objective optimization. Effects on the components such as bell mouth and hub cap are considered with previous analysis. The internal flow characteristics between base and optimized model are analyzed and discussed.
Visualization of Oil Droplets Distribution in a Rotary Compressor
Authors: Wu Puyuan , Chen Jun , Sojka Paul E.
Published: November 2019

A rotary compressor relies on an eccentric rolling piston, which rotates at high speed, to compress gas in the compression chamber. The oil in the rotary compressor is used for lubricating the bearing and sealing the clearance of sliding parts. However, the oil can exhaust from the rotary compressor by the refrigerant flow and reduce the reliability of the compressor as a result. Thus, studying the behavior of oil droplets distribution in a rotary compressor is a major challenge for manufacturers who rely on CFD tools to predict the multiphase flow. By modifying a rotary compressor, the oil behavior inside the cylinder is observed and recorded by a high-speed imaging system. In the current phase, multiple targeted locations, including the space between the bearing housing and the stator, and the space above the stator are measured in different conditions. The number, size, velocity, and morphology of oil droplets are analyzed based on multiple snapshots. The result can assist designers in improving the CFD analysis of compressors and ultimately reducing the oil discharge rate (ODR).
Detailed Numerical Simulation of Two Impinging Jets With Moderate Injection Velocities
Authors: Ling Yue , Shang Weixiao , Chen Jun
Published: November 2019

Impinging-jet injectors are commonly used in liquid propellant rocket engines. Two cylindrical liquid jets impinge at a certain angle and form a liquid sheet in the plane normal to the jets. When the Reynolds and Weber numbers are large, the liquid sheet becomes unstable and disintegrates into liquid ligaments and droplets. In the present study, we focus on cases with moderate injection velocities so that the liquid sheet remains unbroken. Detailed numerical simulations are performed using the adaptive multiphase flow solver, Basilisk. The volume-of-fluid method is used to resolve the gas-liquid interface. Grid-refinement studies are conducted to verify the formation of the liquid sheet is accurately captured in simulation. The numerical results are compared to the recent experimental measurement of the sheet thickness distribution by partial coherent interferometry and a good agreement is achieved.
The Influence of Flexible Strip Height on Convective Heat Transfer Enhancement
Authors: Yang Yang , Ting David S.-K. , Ray Steve
Published: November 2019

A 12.7 mm wide flexible rectangular strip, made from 0.1 mm-thick aluminum sheet, is experimentally explored as a vortical flow generator for promoting heat convection from a flat plate in a wind tunnel. The strip is positioned normal to the freestream with an incoming velocity of 10 m/s, resulting in a Reynolds number, based on the strip width, of 8,500. The influence of the height of the flexible strip on the convective heat transfer enhancement is of interest. Three strip heights, 25.4 mm, 38.1 mm and 50.8 mm, were investigated. The heat transfer results are expressed in terms of Nusselt number, Nu, normalized by the unperturbed reference Nu0. The shortest, 25.4 mm high flexible strip resulted in the highest peak and overall heat transfer enhancement. The distribution of the local heat transfer enhancement is found to correlate well with the turbulent flow motion detailed using a triple-sensor hot-wire anemometer. Pointedly, the heat transfer rate is most elevated when the local flow is moving toward the hot plate, sweeping across a stretch of the surface before moving away from it. These effective convective motions are most effectively generated by the vortices produced by the shortest strip.
Theoretical Model of a Flow in a Tube With a Slit
Authors: Toda Yuki , Morimatsu Masataka , Nishio Yu , Ogawa Takanobu
Published: November 2019

A tube-type gas burner consists of a straight tube with a slit along it and discharges an air-gas mixture through the slit to produce a flame. The flow velocity from the slit depends on the pressure in the tube and the pressure loss at the slit, and it varies in the longitudinal direction of the tube. The resulting uneven flame degrades the quality of the burner.

In this study, we develop a one-dimensional theoretical model of the flow in a tube with a slit. To validate the result of the theoretical model, we also conduct experiments and numerical simulations for the same flow field. We applied this theoretical model to a flow in a tube, 1 m length, 40 mm in diameter, with a slit 2.5 mm wide. The end of the tube is closed. We also discuss the effect of the length of the burner on the unevenness.
Optimal Design for Impeller of a Sludge Pump Using Design of Experiment
Authors: Jin Jeong-Min , Ji Hyo-Geun , Kim Youn-Jea
Published: November 2019

Recently, many studies carried out to improve the performance of the pump with shape changes. In this paper, impeller optimization is performed to improve the pump performance. Design optimization techniques for the sludge pump impellers have been developed by using computational fluid dynamics (CFD) and optimal design theory. This paper describes the design optimization of a sludge pump impeller based on Response Surface Method (RSM) coupled with Navier-Stokes flow analysis. In particular, RSM which was based on the results of the design of experiment (DOE) helps to achieve the optimum point. In order to optimize the shape of the impeller, the thickness and the height of the blade were set as design factors. As a result, it was confirmed that the efficiency and the head were improved by 11.2% and 6.67%, respectively, compared to the referenced model.
Large Scale Wettability Quantification in Porous Media Using Tracers
Authors: Singh Deepshikha , Pant Harish J. , Phirani Jyoti , Roy Shantanu
Published: November 2019

Tracers are widely used to study physical phenomena taking place inside the porous medium such as hydrodynamics of the reactor by residence time distribution, and characterizing the oil reservoirs for heterogeneity and residual oil saturation. In this work, we use tracer techniques to characterize oil phase tracers to quantify the wettability of a fluid in a multi-phase flow in a porous medium. The wetting fluid will have more contact area with the sediments. The quantification of contact area of a fluid with sediments during flow will give us insights into the wettability and wettability alteration. A two tracer method is used to quantify the wetted area by one fluid in the porous medium. We first find the adsorption characteristics of the tracers for non-aqueous-phase tracers on the sediments. Subsequently flow experiments are performed to conduct residence time distribution (RTD) analysis using single phase flow. The adsorption characteristics during flow are identified for various flow rates. The difference in RTD curves of the two tracers of a phase is used to estimate the area in contact with the fluids with the sediment surface.
Development of Rotating Stall Cell Under Coexisting Phenomena of Surge and Rotating Stall in an Axial-Flow Compressor
Authors: Sakata Yuu , Ando Shuji , Fujisawa Nobumichi , Ohta Yutaka
Published: November 2019

The relationship between the growth of the stall cell and variation in the surge behavior was experimentally investigated. The aim of this study was to reveal the effect of the stall cell on the surge behavior from the viewpoint of the inner flow structure. In the experiment, the unsteady compressor characteristics during the surge and rotating stall were obtained by using a precision pressure transducer and a one-dimensional single hotwire anemometer. Under the coexisting states of surge and rotating stall, various surge behaviors were observed by throttling the mass flow rate. When the flow rate was set such that the surge behavior switched, an irregular surge was observed. During the irregular cycle, two different cycles were selected randomly corresponding to the stall behavior. When the amplitude of the plenum pressure is relatively large among the measurement results, the absolute value of the time-change rate in the flow coefficient and the static pressure-rise coefficient tend to be high. This shows that the flow field during stable operation near the peak point of the unsteady characteristics changes rapidly. In this case, an auto-correlation function of the wall-pressure fluctuation data showed that the stall inception of the compressor was induced earlier in the large cycle compared with the case of the top cycle. When studying the growth of the stall cell during the stalling process of the large cycle, the wall-pressure fluctuation data showed that the stall cell rapidly grew by gathering more than one spike-type disturbance into one stall cell. In this case, the stall cell fully expanded along the circumferential direction and developed into a deep stall. Therefore, the key factors that determine the surge behavior are the sudden change in the flow field near the peak point of the unsteady characteristics and the rapid growth in the stall cell during the stalling process.
Experimental Study on the Effects of Radial Dispersion of Spherical Particles on the Suspension Rheology
Authors: Kawaguchi Misa , Fukui Tomohiro , Funamoto Kenichi , Miyauchi Suguru , Hayase Toshiyuki
Published: November 2019

Experimental studies were performed to characterize the effects of the microstructure on the rheology of suspension. We focused on the change in the dispersion of the suspended particles under different particle Reynolds number conditions. Suspension flow through a microchannel with a circular cross-section was measured, and the radial dispersion of suspended particles and the velocity profiles were obtained. It was suggested that the particle dispersion could be changed owing to the difference in inertial force acting on the particles.
Inducer Design Optimization to Improve its Suction Performance
Authors: Nakamura Yushi , Lubieniecki Marek , Hayashi Kentarou , Kawata Yutaka , Miyabe Masahiro , Lettieri Claudio
Published: November 2019

The purpose of this paper is to present optimization method of an inducer blade shape to improve its suction performance and clarify the relationship between pump performance and design parameters. In order to conduct the optimization process a response surface based optimization framework was established. Baseline was designed in previous research [1]. The inducers were 3Dprinted in ABS plastic and their wetted and cavitating characteristics were measured. It was confirmed that the optimized inducer can maintain its wetted performance at lower cavitation numbers. A response surface is a mathematical model that approximates the relationship between the input parameters and the objective function from a finite number of learning points within the design space. The design space was defined by four parameters: sweep angle, sweep radius, incidence angle and blade solidity at the tip that controlled the blade shape. The performance of each design was evaluated with a CFD simulation established in a commercial solver. The optimization goal was to minimize the critical cavitation number that corresponds to a 5% drop of pressure increase through the pump due to cavitation.

A starting point of the optimization was the industrial pump designed by a Japanese company Teral [1]. The results of the numerical optimization show that the critical cavitation number was decreased by 17.6% with respect to the baseline design. In the experimental results, an average improvement of 15.4% was achieved.
Deposition of Ellipsoidal Fibers in Nasal Cavity: Influence of Non-Creeping Flow Conditions
Authors: Tash Mehdi Aboulhasan , Tavakol Mohammad Mehdi , Abouali Omid , Ahmadi Goodarz
Published: November 2019

In this study, deposition fraction of ellipsoidal particles in a 3D-Model of the nasal cavity (right airway) of a 24-year-old healthy woman was simulated for laminar and turbulent inhalation flow rates. The geometry used included the main nasal cavity from the nostril to the beginning of nasopharynx and was constructed in the Ansys-ICEM software from a CT scan image. The numerical simulations of governing equations were obtained using the Ansys-Fluent software. The mean airflow was assumed to be incompressible and steady. For turbulence modeling, the Realizable k-ε model was employed and the Lagrangian trajectory analysis method was used for particle tracking. For evaluating the ellipsoidal particle motions, several user-defined functions (UDFs) were developed and linked to the discrete phase model of the Ansys-Fluent code. The developed UDFs solve for the coupled translational and rotational equations of motion for ellipsoidal fibers and also accounts for the stochastic modeling of turbulence velocity fluctuations. The hydrodynamic forces and torques were calculated based on the non-creeping formulations for various ellipsoidal fibers. Laminar flow condition was assumed for breathing rate of 5.0 lit/min for the rest or light physical activities and turbulent flow condition was assumed for airflow rate of 20 lit/min for high physical activities. To investigate the dispersion and deposition of particles in the model of the human nasal cavity, various fibers with a semi-minor axis of 1, 3, 5 and 10 μm and various aspect ratios were considered.

Using the non-creeping flow formulation for hydrodynamic forces and torques, the simulation results showed slight differences in the total deposition fraction of ellipsoidal fibers compared with the corresponding creeping flow model. Small fibers deposit roughly uniformly in the nasal cavity with no hotspot region. For the large inertial fibers, however, the nasal valve is a hot spot region, where the deposition rate reaches to its peak.
Numerical Simulation of Torque Converter With Different Pump Blade Camber
Authors: Ke Zhifang , Liu Cheng , Wei Wei , Yan Qingdong , Meng Xianglu
Published: November 2019

The main function of the torque converter pump is to transfer mechanical power into fluid dynamic energy. It has been proved that the pump blade shape, especially pump blade camber peak, is crucial to torque converter hydrodynamic performance. However, it remains unclear how this parameter affects internal flow characteristics, and how it leads to the difference in performance. Thus, the relationship between the pump blade camber and the performance of torque converter and the flow mechanism were explored in this study.

Torque converters with different pump blade camber were tested. Meanwhile, the corresponding numerical models were also established and their internal flow fields were investigated through steady-state simulations. The influence of the pump blade camber on the hydrodynamic performance was studied using both numerical and experimental methods, and the flow mechanism was also revealed and elaborated by exploring the numerical flow fields.

The results from both experiments and simulations showed that larger pump blade camber peak led to higher pump capacity, higher maximum efficiency and lower stall torque ratio. The flow field simulation revealed that larger pump camber peak would lead to higher total pressure in pump channel. And the pressure distribution between the suction and pressure surface showed a similar pattern; however, their difference, especially near the leading and tailing edge, depends on the camber peak. Besides, higher camber peak blade absorbed more power, also induced more complex vortex, but there always existed the most efficient speed ratio when pump efficiency can reach to peak, at this moment, the difference between angle of attack and entrance angle reach the zero, which can be used to guide the design of pump blade.