bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Investigation of Choked Flow Conditions for Bubbly Flow
Authors: Shepard Thomas , Garbaly Aleksey 
Published: November 2019

Abstract
In an effervescent atomizer, a bubbly two-phase mixture flows through a convergent section before exhausting from an exit orifice. It is commonly believed that one of the key effects of including bubbles is in the substantial decrease in the speed of sound experienced by the two-phase flow allowing for choked flow conditions at the exit. The existence of choked conditions would result in under-expanded bubbles that would further expand upon exiting the atomizer and provide additional forces to aid in the break-up of the bulk liquid into droplets. This study examines how the homogenous two-phase flow model of speed of sound, and thus critical conditions, compare with experiments in order to better understand the fundamental physics of effervescent atomization. In these experiments, an effervescent atomizer is connected to a vacuum chamber allowing for internal atomizer pressure, liquid flow rate and air flow rate to be monitored as the post-exit pressure is decreased. Experiments reveal that the flow remains subcritical well beyond conditions that the homogenous flow theory might predict being choked. High-speed imaging is used to capture internal atomizer bubble size.
Cavitation-Induced Interface Instability of Droplet Between Plates
Authors: Li Hongchen , Wang Jingzhu , Wang Yiwei 
Published: November 2019

Abstract
Interface instability of droplet and formation of the liquid jet caused by internal volume oscillation are directly related to liquid pumping and mixing of microfluidic devices. Complex morphology jet enables liquid shaping, which is advantageous for industrial applications and biomedical engineering. In this study, the interface instability of cylindrical droplet between plates is investigated. The problem is analyzed through numerical simulation and experimentation. In the experiment, a single-pulse laser is used to generate cavitation at the center of the cylindrical droplet between two polymethyl methacrylate plates, and the physical progress is captured by high-speed photography. A compressible two-phase solver in the open source code OpenFOAM is used to simulate the 3D progress of bubble pulsation and droplet jet in consideration of viscosity and surface tension. Numerical methods adopt large eddy simulation. Results show that the interface density gradient is not collinear with the pressure gradient due to the shock wave impact and the bubble pulsation, that is, the baroclinic effect is the main cause of the instability at the droplet interface. The mechanism of the radial jet formation in the first period of bubble pulsation is closely related to the interface instability. A pair of vortex rings is formed under the influence of instability, thereby causing a stacking phenomenon on the jet head and eventually being cut. Affecting factors of the instability of the droplet interface are discussed. A high instability intensity of the droplet interface can be caused by a large initial bubble energy and a small contact angle. The instability strength of the droplet interface and the mode of jet formation are very sensitive to the curvature of the initial droplet shape. Relevant results may provide a reference for further understanding of interface instability and related engineering applications.
The Effect of the Velocity Ratio on the Diffusion Inhibition of Coaxial Jet
Authors: Akagi Fujio , Etou Takumi , Fukuda Yuito , Yoshioka Ryoya , Ando Youichi , Yamaguchi Sumio 
Published: November 2019

Abstract
The mixing characteristics of a coaxial round jet having inner to outer diameter ratio di/do = 0.67 was investigated to establish the method for mass and energy transport with inhibiting its diffusion. In the present study, the effect of the velocity ratio on the streamwise length of the potential core of the central round jet, the streamwise velocity distribution, and the evolution of vortcies of a coaxial jet was evaluated by using Large Eddy Simulation and experimental flow visualization to clarify diffusion inhibition mechanism of a central jet. Three velocity ratios γ = 0.25, 0.5, and 0.75 were conducted under a single condition of the central jet Reynolds number of 2000. The results show that the potential core length of a central jet become the longest on condition of the velocity ratio of 0.5, and the length was 15 times of the inner nozzle diameter. This value is equivalent to 3.8 times in the case of a general round jet. In other velocity ratio, it was also confirmed that the potential core length of a central jet becomes short by enhancement of vortices generation in the shear layer of annular and central jet. It is concluded that the velocity gradient in the shear layer is the important parameter in determining the diffusion of a central jet.
Numerical Study of Heat Transfer in a Row of Cylinders by 2D Large Eddy Simulation
Authors: Thorstensen Andreas Stengaard , Krogh Andreas , Dueholm Bjørn Christian , Højte Sebastian Bækkel , Thomasen Signe Birkebæk , Jensen Anna Lyhne , Sørensen Henrik , Hærvig Jakob 
Published: November 2019

Abstract
Complex flow structures arise as fluids are forced to flow across cylinder rows at moderate Reynolds numbers. In this study a numerical heat transfer analysis of 12 cylinders in an inline configuration is performed using Large Eddy Simulation (LES). The LES is conducted to get a better understanding of changes in the time averaged Nusselt number, 〈Nu〉, and local time averaged Nusselt number, 〈Nuθ〉, for each cylinder in the cylinder row. The simulations are performed at Re = UD/v = 10,000 and Pr = 0.71 with isothermal cylinders and a constant and uniform inflow temperature.
The results show that the time averaged Nusselt number increases slightly between the first and second cylinder due to increased turbulent velocity fluctuations. Beyond the second cylinder, the time averaged Nusselt number decreases until it reaches a near constant value after the fifth cylinder. For all 12 cylinders the local time averaged Nusselt number around the surface is highest at the stagnation point. The first cylinder in the row has the same distribution as the reference simulation conducted for a single cylinder. From the second cylinder and onwards a larger part of the overall heat transfer is in the spanwise direction compared to the first- and reference cylinder.
Effect of Fineness Ratio of 0.5 - 2.0 on the Wake Structure Around a Circular Cylinder Measured Using Time-Resolved PIV
Authors: Yokota Sho , Ochiai Taku , Ambo Takumi , Ozawa Yuta , Nonomura Taku , Asai Keisuke 
Published: November 2019

Abstract
In this study, the wake structure around freestream-aligned cylinder is investigated and its aerodynamic characteristics are discussed. A magnetic suspension and balance system (MSBS) was used to support a model without interference from a mechanical support device. Seven models with the fineness ratio (length to diameter, L/D) of 0.5, 1.0, 1.25, 1.5, 1.75, 2.0, and 2.25 were used. Reynolds number based on the cylinder diameter were 3.2 × 104 and 6.3 × 104. The velocity field was obtained by particle image velocimetry (PIV) in the center plane of the cylinder. In the case of fineness ratio over 1.5, the reattachment of shear layer was observed from the mean velocity field. The characteristic fluctuation of velocity was confirmed in power spectral density of streamwise component and vertical component. The length of the recirculation region is different depending on fineness ratio. The characteristic frequencies of the velocity fluctuation which seems to be due to recirculation bubble pumping and large-scale structure are observed from power spectrum density.
Erosive Wear Behavior of Fiberglass Reinforced Plastic Composite and Polyethylene
Authors: Banazadeh-Neishabouri Nafiseh , Shirazi Siamack A. 
Published: November 2019

Abstract
Effects of particle velocity, impact angle and particle size and shape on erosive behavior of Fiberglass Reinforced Plastic (FRP) and Polyethylene were investigated. Experiments were carried out with two particle velocities (18 and 32 m/s) and different impact angles ranging from 15 to 90 degrees. Silica sands with sizes of 75, 150 and 300 μm was utilized as erodent to study effects of sand shape and size. Results revealed erosion data of FRP and Polyethylene are similar to ductile materials as they display maximum erosion ratio at 30 degrees impact angle. However, Polyethylene showed an interesting behavior at 75 and 90 degrees; sand particles were embedded into the specimen and mass gain of specimen has been observed. 3D scan of wear patterns of specimens was obtained by 3D profilometer in order to evaluate the erosion depth and wear pattern of the surface.
A Tomographic PIV Study and Comparison of Vortex Identification Methods on NACA 63-215 Hydrofoil Wake Structure
Authors: Ziazi Reza M. , Goudarzi Navid 
Published: November 2019

Abstract
The unsteady flow field in the vicinity of a NACA 63-215 hydrofoil in a closed-loop water channel at Reynolds number of Re ≈ 29103 is investigated experimentally. A Tomographic Particle Image Velocimetry (TomoPIV) is used to determine the velocity field in the near-wake region of the studied hydrofoil. The manufactured hydrofoil was mounted on the 3D traverse and installed vertically in the water tunnel test section. The TomoPIV measurement volume was performed in a voxel with the volume of 164 × 168 × 82 mm3 (X, Y, Z). Vortex identification techniques including Q-criterion and λci criterion, together with helicity of flow are evaluated in the wake of the hydrofoil. Vorticity and swirling strength are used to further understand the location and behavior of the dynamic pattern of the vortex shedding in the trailing edge of the hydrofoil. The vorticity magnitudes as they transport downstream is explored to dissipate their energy in the wake. The flow pattern reflects a turbulent behavior required for higher efficiency of the designed hydrofoil. The results are compared with literature. This work obtains a validated model for the wind farm case and will be a basis of the ocean current turbine arrays wake structure analysis.
In-Line Testing of Novel Filter Media for Oil-Water Mixtures
Authors: Mule Anisha , Dabirian Ramin , Kolla Srinivas Swaroop , Mohan Ram , Shoham Ovadia 
Published: November 2019

Abstract
A novel non-fibrous filter media is evaluated for in-line oil-water separation. Outside-in-crossflow configuration incorporating the filter media is utilized in order to test the filter. All experiments are conducted with a hydrophilic-olephobic filter for water-continuous flow with low oil concentrations.
The collected experimental data include permeate flow rate and purity as well as pressure drop. Values of permeate flow rate and pressure drop are averaged over the duration of the experiments, which is about 5 minutes, constituting the “initial average” of the permeate flow rate and the corresponding pressure drop. Totally twelve experimental runs are conducted for mixture velocities of 0.038 m/s, 0.055 m/s and 0.066 m/s, and oil concentrations of 0.6%, 0.83%, 1.1%, 7.9% and 9.1%. Permeate samples are analyzed for oil content, demonstrating a high separation efficiency of 98 ± 2%.
The permeate flux across the filter cartridge ranges between 0.0739 (L/h)/cm2 to 0.216 (L/h)/cm2 owing to the low pressure drop across to filter. Oil concentration in to permeate water samples shows consistently increasing trend with an increase in inlet oil content, while maintaining high separation efficiency for all runs. The pressure drop across the membrane under flowing conditions ranges from 0.35 psid to 0.6 psid for flow rates between 0.1 L/min and 0.29 L/min, respectively. Also the data confirm that the filter membrane breakthrough pressure is 0.35 psid.
Reynolds Averaged Navier-Stokes Simulation of Highly Turbulent, Under-Expanded Jets and Effects of Impingement at Elevated Injection Pressure
Authors: Riglin Jacob , Wachtor Adam , Morgan Robert , Holguin Ryan , Bernardin John 
Published: November 2019

Abstract
Under-expanded jets have wide range of application from fuel injection to rocket propulsion. In the present work, a numerical model was generated to investigate the fluid mechanics behavior of under-expanded jet formation and wall interaction of a jet produced by exhausting a high pressure cylinder through a narrow tube into a low pressure cylinder. Axisymmectic, Reynolds Averaged Navier Stokes simulations were conducted employing the ANSYS FLUENT explicit, Coupled Pressure-Velocity solver to determine the stagnation pressure at the wall downstream of the orifice. Transient cases were conducted using timestep sizes of 1.0 × 10−8 s and 5.0 × 10−9 s. Various gases were investigated with Hydrogen being the primary working fluid with pressure ratios ranging from 10 to 100. This paper will focus primarily on the Hydrogen jets for pressure ratios of 10, 20, and 70. Numerical results were validated from both experimental results and higher fidelity Large Eddy Simulation results specifically analyzing the jet formation. Error between Mach disk height, Mach disk width, and Prandtl-Meyer expansion fan angles of the jet for pressure ratios of 10 and 70 were kept below 5%. The peak stagnation pressures at the center of the far wall for pressure ratios of 10, 20, and 70 were observed to be 86,843 Pa, 127,786 Pa, and 315,843 Pa, respectively. The predicted peak pressures show a linear relationship with respect to the initial pressure ratio existing between the high pressure and low pressure regions when the ratios are bounded between 10 and 70.
Evaluation of the Effect of Particle Size on Erosion Calculations Utilizing CFD and Comparison With Submerged Slurry Jet Experiments
Authors: Karimi Soroor , Zhang Jun , Shirazi Siamack A. , McLaury Brenton S. 
Published: November 2019

Abstract
The effects of particle size on erosion magnitude and erosion profiles are investigated experimentally in a submerged slurry jet impingement facility. The slurries were diluted to avoid concentration effects on the flow field and the resulting erosion. The experiments are performed with particle sizes of 25, 75, 150, 300, and 600 μm. Experimental results demonstrate different erosion severity and pattern for the various particle sizes. It is critical to have a reliable and accurate tool to predict erosion for different particle sizes. Previously, a comprehensive CFD-based procedure to predict erosion for various particle sizes was proposed by investigators at the Erosion/Corrosion Research Center (E/CRC). A feature of this procedure is that it can account for particle size in more detail than previous methods. In this study, the computational procedure is applied to conditions of the present experimental data. Particle impact parameters are extracted to explain the effect of particle size on the resulting erosion. The predicted results are compared with data which demonstrate possible shortcomings of the available CFD based techniques for predicting solid particle erosion. The results indicate that with proper use of grid spacing near the wall, the CFD-based erosion calculation method with existing erosion models can predict the trend of the experimental data, though improvements are still needed to the models to accurately account for particle size effects.
Numerical Simulation of Deposition Phenomena on High-Pressure Turbine Vane Using UPACS
Authors: Mizutori Kenta , Fukudome Koji , Yamamoto Makoto , Suzuki Masaya 
Published: November 2019

Abstract
We performed numerical simulation to understand deposition phenomena on high-pressure turbine vane. Several deposition models were compared and the OSU model showed good adaptation to any flow field and material, so it was implemented on UPACS. After the implementation, the simulations of deposition phenomenon in several cases of the flow field were conducted. From the results, particles adhere on the leading edge and the trailing edge side of the pressure surface. Also, the calculation of the total pressure loss coefficient was conducted after computing the flow field after deposition. The total pressure loss coefficient increased after deposition and it was revealed that the deposition deteriorates aerodynamic performance.
Analysis of a Centrifugal Pump Equipped With an Axial Rotor With Variable Speed
Authors: Bosioc Alin Ilie , Moş Daniel Călin , Muntean Sebastian , Anton Liviu Eugen 
Published: November 2019

Abstract
In the last two decades the energy market policy was focused on development of renewable energy. The renewable energy (solar and wind power) induces a fluctuating component of the electrical grid. The solution to compensate fluctuating energy is provided by the hydraulic turbines in order to produce energy in a short time and the pumps units in order to use the energy excess.
In order to ensure higher flow rate for the storage pumps, the units have constructive differences besides regular. Consequently, the complex shape of the suction-elbow with symmetrical geometry generates unsteady flows which are ingested by the impeller. These phenomena induce stronger unsteady flow conditions, such as stall, wakes, turbulence and pressure fluctuations, which affect the overall behavior of the pump providing vibration, noise and radial and axial forces on the rotor.
Alternatively, an axial rotor can be installed in front of the impeller. In this case, the flow non-uniformity will be decreased and the static pressure will be increased at the pump impeller inlet. Consequently, the efficiency behavior practically remains unchanged while the cavitational behavior is improved. Recently, a new concept was explored in order to assess the cavitational behavior on a wide range operation of the pump. The new concept proposes variable speed for the axial rotor, while the speed of the pump impeller remains constant. Accordingly, this new concept is experimentally and numerically investigated in the paper. First, the paper presents the 3D numerical investigation of the pump impeller combined with an axial rotor. The axial rotor is investigated at variable speed (between 2000 and 3000 rpm) while the pump impeller has constant speed of 2500 rpm. The minimum static pressure and the static pressure coefficient are analyzed in order to assess the new method. Second the mechanical design of the solution, for testing on the laboratory is presented. The solution contains an innovative clutch for controlling the variable speed of the axial rotor using magneto-rheological (MR) fluids. Thirdly, the experimental results concentrates on MR clutch operating regimes and the pump efficiency analysis. The MR clutch was installed between the driven electrical motor and the pump, three regimes were investigated: runaway speed for the axial rotor, clutch with MR fluid inside with and without magnetic field applied on it. The conclusions are drawn in the last section.
Fundamental Study on Injector Flow Characteristics of Self-Pressurizing Fluid for Small Rocket Engines
Authors: Yasuda Kazuki , Nakata Daisuke , Uchiumi Masaharu , Okada Kugo , Imai Ryoji 
Published: November 2019

Abstract
Nitrous oxide (N2O) is a suitable propellant for small rocket engines (mostly kN class), and has been widely used in various countries given its high saturated vapor pressure (i.e., 6 MPa at 300 K), which enables self-pressurization. Because nitrous oxide exists with gas-liquid equilibrium in tanks, cavitation occurs when the pressure in the tanks and feed lines drops slightly, which easily forms a gas-liquid two-phase flow. Since accurately estimating the performance of rocket engines requires ascertaining the characteristics of their propellant flows, flow tests with self-pressurization using nitrous oxide were conducted, as were firing tests of hybrid rocket engines using nitrous oxide as a liquid oxidizer and acrylic as a solid fuel. This paper presets the results of those tests, along with findings obtained regarding the characteristics of the gas-liquid two-phase injector flow with self-pressurization. In the N2O flow test, the injector upstream pressure was approximately 1.5 MPa, while the injector downstream pressure was approximately 0.1 MPa. At 0.070, the ratio of upstream to downstream pressure of the injector was thus extremely large, which suggested that the gas-liquid two-phase flow was choked with the injector. By contrast, in the firing test with a chamber pressure of approximately 1.0 MPa and a thrust of approximately 650 N, the ratio of the injector downstream pressure (i.e., chamber pressure) and its upstream pressure was approximately 0.56. Although that ratio was relatively large, because the injector upstream pressure is relatively low (i.e., approximately 1.8 MPa) and the backpressure fluctuated due to combustion, it remains unclear whether the gas-liquid two-phase flow was choked.
Inclusion of Heat Transfer on Settling Behavior of Elliptical Particles: Immersed Boundary-Thermal Lattice Boltzmann Method
Authors: Karimnejad Sajjad , Amiri Delouei Amin , Nazari Mohsen , Shahmardan Mohammad Mohsen , Ahmadi Goodarz , Mofakham Amir A. 
Published: November 2019

Abstract
In this study, the hybrid immersed boundary-thermal lattice Boltzmann method was developed and applied to assess the inclusion of heat transfer in flows containing non-circular particles. The direct forcing/heating immersed boundary method was used for determining the hydrodynamic forces and energy exchange. A complementary method was also implemented to treat non-circularity. The accuracy of the computational model and the employed complementary method were properly validated. Two cases for the falling ellipse were considered. A set of comprehensive simulations were performed and the effects of geometry, Grashof number, repulsive force, and heat transfer were analyzed. The findings of this study would be useful for a better understanding of settling non-circular particles in a thermal field.
Dynamic Performance Analysis of Large-Scale Packed Bed Truncated Conical Thermal Energy Storage
Authors: Singh Shobhana , Sørensen Kim 
Published: November 2019

Abstract
In the present paper, a high-temperature packed bed energy storage system of volume 175,000m3 is numerically investigated. The system is a underground packed bed of truncated conical shape, which comprises of rocks as a storage medium and air as a heat transfer fluid. A one-dimensional, two-phase model is developed to simulate the transient behavior of the storage. The developed model is used to conduct a parametric study with a wide range of design parameters to investigate the change in performance during both charging and discharging operation. Results show that the model satisfactorily predicts the dynamic behavior, and the truncated conical shaped storage with a rock diameter of 3cm, insulation thickness up to 0.6m and charging-discharging rate of 553kg/s leads to lower thermal losses and higher energy efficiencies. The paper provides useful insight into the transient performance and efficiency of a large-scale packed bed energy storage system within the range of parameters investigated.
Embedded RIOTS: Model Predictive Control Towards Edge
Authors: Viola Jairo , Dehghan Sina , Chen YangQuan 
Published: November 2019

Abstract
RIOTS is a general purpose optimal problem solver written as a MATLAB toolbox with mixed-language programming (C, Fortran, Matlab, Simulink). This first paper introduces how to make RIOTS run under an embedded platform RP3B (Raspberry Pi 3 B) with Windows 10. We presented the system architecture and a complete demo on running RIOTS as the inner kernel for MPC, using a house made thermal control system based on Peltier modules.