bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimizing a Segmented Transmission Line Model for Dynamic Flows in Arbitrarily Tapered Pipelines
Authors: Wiens Travis 
Published: November 2019

Abstract
Previous work by the authors has presented a new method of modeling dynamic laminar flows in pipelines with changing cross sectional area. This method utilizes a number of Transmission Line Models (TLM), each with a single linear taper, as segments to model the pipeline. The Segmented Transmission Line Model (STLM) allows for fast computation, especially with the use of a variable time-step ODE solver for a system-level simulation (typically required for modeling of fluid power components). This paper presents an optimized version, including best practices for segmenting the pipeline based on accuracy and computation time.
Simulation of Dynamic Characteristics of Pneumatic Control Valve With Smart Valve Positioner
Authors: Youn Chongho , Saito Kenji , Furuya Motohiro 
Published: November 2019

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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 &lt; Reb &lt; 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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.