bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pore-Scale Study of the Thermochemical Process in Porous Media With Immiscible Phase by Lattice Boltzmann Method
Authors: Xu Zhiguo , Zhou Xiao 
Published: October 2020

Abstract
Reactive flow happens in carbonate rocks which are porous media during acidification. In this study, a thermochemical dissolution model based on the lattice Boltzmann method (LBM) is established to investigate the complex thermochemical process in porous media with immiscible phase at pore scale. In the model, the immiscible fluid flow, solute transport, and heat transfer are solved by Shan–Chen multicomponent LB model, mass transport LB model, and multicomponent thermal LB model, respectively. The porous media is generated by the quartet structure generation set, and the evolution of solid phase is addressed by volume of pixel (VOP) method. The detailed thermochemical process in porous media with immiscible phase is revealed, and the effects of velocity, concentration, and temperature on mass and heat transfer are further analyzed. The results show that increasing inlet velocity, inlet concentration, and temperature accelerates acidizing process and influences the temperature evolution in porous media significantly.
Reconfigurable Acoustic Arrays With Deployable Structure Based on a Hoberman–Miura System Synthesis
Authors: Zhao Ningxiner , Harne Ryan L. 
Published: October 2020

Abstract
Curved surfaces are often used to radiate and focus acoustic waves. Yet, when tessellated into reconfigurable surfaces for sake of deployability needs, origami-inspired acoustic arrays may be challenging to hold into curved shape and may not retain flat foldability. On the other hand, deployable mechanisms such as the Hoberman ring are as low-dimensional as many origami tessellations and may maintain curved shape with ease due to ideal rigid bar compositions. This research explores an interface between a Hoberman ring and Miura-ori tessellation that maintain kinematic and geometric compatibility for sake of maintaining curved shapes for sound focusing. The Miura-ori facets are considered to vibrate like baffled pistons and generate acoustic waves that radiate from the ring structure. An analytical model is built to reveal the near field acoustic behavior of acoustic arrays resulting from a Hoberman–Miura system synthesis. Acoustic wave focusing capability is scrutinized and validated through proof-of-principle experiments. Studies reveal wave focusing phenomena distinct to this manifestation of the acoustic array and uncover design and operational influences on wave focusing effectiveness. The results encourage exploration of new interfaces between reconfigurable mechanisms and origami devices where low-dimensional shape change is desired.
Uncertainty Quantification With Sparsely Characterized Parameters: An Example Applied to Femoral Stem Mechanics
Authors: Wanki Godlove , Ekwaro-Osire Stephen , Dias João Paulo , Cunha Americo 
Published: October 2020

Abstract
The advent of state-of-the-art additive manufacturing (AM) processes has facilitated the manufacturing of complex orthopedic metallic implants such as femoral stems with porous portions based on lattice structures. These struts often have rough and not smooth textured surfaces, for which the irregularities may influence mechanical properties. To make robust predictions about the behavior of this kind of system, the variability effect of its parameters on the stem stiffness must be considered in the processes of modeling and design of porous femoral stems. Also, to improve the credibility of computational models used for hip implant analysis, which involves numerous uncertainties, there is a need for rigorous uncertainty quantification (UQ) framework for proper model assessment following a credible-modeling standard. This work proposes a UQ framework in the presence of sparsely characterized input parameters using the maximum entropy principle for analyzing a femoral stem implant model and thus to clarify how uncertainties impact the key properties of a porous femoral stem. In this study, uncertainties in the strut thickness, pore size, Young's modulus, and external forcing are considered. The UQ framework is validated using experimental results available from literature, following the guidelines set in an ASME standard.
Code Verification of a Pressure-Based Solver for Subsonic Compressible Flows
Authors: Muralha João , Eça Luís , Klaij Christiaan M. 
Published: October 2020

Abstract
Although most flows in maritime applications can be modeled as incompressible, for certain phenomena like sloshing, slamming, and cavitation, this approximation falls short. For these events, it is necessary to consider compressibility effects. This paper presents the first step toward a solver for multiphase compressible flows: a single-phase compressible flow solver for perfect gases. The main purpose of this work is code verification of the solver using the method of manufactured solutions. For the sake of completeness, the governing equations are described in detail including the changes to the SIMPLE algorithm used in the incompressible flow solver to ensure mass conservation and pressure–velocity–density coupling. A manufactured solution for laminar subsonic flow was therefore designed. With properly defined boundary conditions, the observed order of grid convergence matches the formal order, so it can be concluded that the flow solver is free of coding mistakes, to the extent tested by the method of manufactured solutions. The performance of the pressure-based SIMPLE solver is quantified by reporting iteration counts for all grids. Furthermore, the use of pressure–weighted interpolation (PWI), also known as Rhie–Chow interpolation, to avoid spurious pressure oscillations in incompressible flow, though not strictly necessary for compressible flow, does show some benefits in the low Mach number range.
Comparison of Neutron-Gamma Separation Qualities of Various Organic Scintillation Materials and Liquid Scintillator LSB-200
Authors: Matěj Zdeněk , Mravec Filip , Jančár Aleš , Košťál Michal , Kučera František , Cvachovec František , Prenosil Václav , Kopecký Zdeněk , Čulen Jiří , Pecák Oldřich 
Published: October 2020

Abstract
In this work, we compare the pulse-shape discrimination (PSD) properties of newly developed liquid scintillator LSB-200, EJ-299-33A, BC-501A, stilbene, p-terphenyl, and Hidex Aqualight in neutron field generated by the LVR-15 reactor with silicon filter utilization. Pulses from the scintillators are processed by the Neutron-Gamma spectrometer. This spectrometric system with fast digitizer card contains two analog–digital converters with a resolution of 12 bits and sampling frequency 500 × 106 Hz. For photomultiplier linearity improvement, the active divider has been used. Measured data from scintillators have been processed using the integration method and compared. The results are presented.
Analysis of a FAME/MLL Screw Multi-Stage Compressor for High Temperature, High Pressure Vapor Compression Refrigeration Cycle
Authors: Anderson Kevin R. , Steele Trevor 
Published: October 2020

Abstract
This paper presents the analysis and design of a compressor for application to a Fatty Acid Methyl Ester (FAME) Methyl Linoleate (MLL) bio-refrigerant cascade working cycle. This working fluid is being used in the topping cycle of an active electronics payload cooling system design to operate at elevated temperatures and pressures such as those witnessed by a Venus lander. The twin-screw, three-stage compressor operates at escalated temperatures of approximately 520 °C (960 °F). The total compressor power of 143.4 W is shared as 43.5 W, 47.7 W, and 53.3 W over stages 1, 2, and 3, respectively. The screw compressor is baselined with a D = 1 inch diameter rotor and an L/D (stroke/bore) ratio of L/D = 2 per stage. The compression ratio corresponds to a volume ratio of 6.5. The swept volume for a 4+6 rotor configuration is estimated to be 1.13 CFM at 2000 RPM with an asymmetric profile and no leakage. The volumetric efficiency of the compressor is estimated to be on the order of 80% due to the higher molecular weight of the FAME/MLL working fluid. The SCORG turbomachinery software is used to verify the thermodynamics analysis and affords a volumetric displacement of 0.025 L/rev at 2000 RPM and 80% adiabatic efficiency.
Numerical Simulation of Twin-Parachute Inflation Process for Aircraft Ejection Escape
Authors: Wang Liwu , Tang Mingzhang , Zhang Sijun 
Published: October 2020

Abstract
In order to study the safe distance between twin-parachute during their inflation process for fighter ejection escape, the fighter was equipped with two canopies and two seats, two types of parachute were used to numerically simulate their inflation process, respectively. One of them is C-9, the other a slot-parachute (S-P). Their physical models were built, then the meshes inside and around both parachutes were generated for fluid-structure interaction (FSI) simulation. The penalty function and the arbitrary Lagrangian-Eulerian (ALE) method were employed in the FSI simulation. To validate the numerical model for FSI simulation, at first the single parachute of the twin-parachute was used for the FSI simulation, the predicted inflation times for both types of parachute were compared with the experimental data. The computed results are in good agreement with experimental data. As a result, the inflation times were predicted with twin-parachute for both kinds of parachute. On the basis of the locations of ejected seats after the separation of seat and pilot, the initial locations and orientations of twin-parachute were also obtained. The numerical simulations for both kinds of parachute were performed by the FSI method, respectively. Our results illustrate that when the interval time for two seats ejected is greater than 0.25s, two pilots attached the twin-parachute are safe, and the twin-parachute would not interfere each other. Moreover, our results also indicate that the FSI simulation for twin-parachute inflation process is feasible for engineering applications and have a great potential for wide use.
Machine Learning for Turbulence Modeling and Predictions
Authors: Bhushan S. , Burgreen Greg W. , Martinez D. , Brewer Wes 
Published: October 2020

Abstract
A stand-alone machine learned turbulence model is applied for the solution of integral boundary layer equations, and issues and constraints associated with the model are discussed. The results demonstrate that grouping flow variables into a problem relevant parameter for input during machine learning is desirable to improve accuracy of the model. Further, the accuracy of the model can be improved significantly by incorporation of physics-based constraints during training. Data driven machine learning training requires trial-and-error approach, shows oscillations in a posteriori predictions, and shows unphysical results when used with arbitrary initial condition, as the query is essentially extrapolations. Physics informed machine learning addresses the above limitations, and is identified to be a viable approach for development of machine learned turbulence model.
Blood Flow Simulations of Particle Trapping in Models of Arterial Bifurcations
Authors: Xu Qihang , Agarwal Ramesh K. 
Published: October 2020

Abstract
This paper describes the particle trapping mechanism in blood flow in different arterial bifurcation models. For validation of CFD calculations, a T-junction model and a Y-junction model are analyzed. In both the models, there is one inlet pipe with two outlet pipes creating a symmetric bifurcation at some angle from the centerline of the inlet pipe. Naiver-Stokes (RANS) equations are solved for single phase laminar flow using the commercial CFD software ANSYS Fluent. After validation, Eulerian simulations are performed by using the Discrete Phase Model (DPM) for two-phase flow with particles injected in different bifurcation models with bifurcation angle of an outlet pipe varying from 80° to 100° w.r.t the centerline of the inlet pipe (90° being the bifurcation angle of T-junction). By changing the average Reynolds number of the flow and the injected particle diameters, the mechanism of particle trapping is investigated in laminar flow. The contours of velocity magnitude, pressure and wall shear stress are also obtained and analyzed. It is found that the particle trapping increases as the bifurcation angle decreases from 90° and becomes negligible as the bifurcation angle increases from 90°. This is a very important result which has never been reported in the previous literature. In addition, turbulent flow computations for T-junction flow are performed using the SST k-ω and Wray-Agarwal turbulence models. Finally, the influence of stenosis in Y-junction is studied and analyzed. The results have implications in understanding the hemodynamic flows in arterial bifurcations without and with stenosis.
Using Liquid Spray Formations to Improve Aerodynamic Performance of Airfoils
Authors: Loubimov George , Fontes Douglas , Loving Garett , Kinzel Michael 
Published: October 2020

Abstract
Previous research on firefighting aircraft which employ dumping water from their lower surface to extinguish flames has shown that there are added lift benefits during dumping maneuvers which do not directly correlate to the exchange in water mass. In this case study, the effects of liquid spray formations on two dimensional aerodynamics are investigated by use of a numerical approach. Studies include chord-wise variation of liquid-jets and variation of spray momentum ratios. Comparisons are also made to previous, single-phase, jet-flap numerical experiments and show favorable agreement. Findings show that increases in lift coefficient and decreases in drag coefficient are observed with the presences of liquid jets located on the lower surface.
Part Load Instability and Rotating Stall in a Multistage Low Specific Speed Pump
Authors: Vermunt E. M. A. , Bruurs K. A. J. , van der Schoot M. S. , van Esch B. P. M. 
Published: October 2020

Abstract
A new diffuser design is developed for a low specific speed, multistage pump. In this design the diffuser and the de-swirl vanes are integrated into single vanes. This creates diffuser channels that extend from behind the impeller exit through the cross-over, up to the eye of the next stage impeller. Experiments show the occurrence of a saddle type instability in the head curve. At a critical flow rate of close to 50% of the flow rate at Best Efficiency Point (BEP), the head drops by 7% of the head at BEP. In this study Computational Fluid Dynamics (CFD) are used in an effort to understand the underlying flow phenomena.
The head curve that is obtained with the transient CFD simulations contains a saddle type instability at a flow rate that is approximately the same as in the experiments, but with a lower magnitude. At flow rates higher than the critical flow rate, the predicted head and power are in very good agreement with the experimental data. At flow rates lower than the critical flow rate, the head and power are slightly over-predicted. An analysis of the pressure distribution in the pump reveals that the head loss at different flow rates in the diffuser shows a discontinuity at the critical flow rate. Since both the impeller head and the head loss in the vaneless gap increase continuously for decreasing flow rate, this is an indication that the cause of the head instability lies in the diffuser. Moreover, a strong increase in the variability of head and power at flow rates below the critical flow suggests that the phenomenon is unsteady.
Flow patterns in the impeller and in the diffuser, as calculated by CFD, show a high degree of periodicity and are very similar for flow rates down to the critical flow rate. However, for lower flow rates the flow pattern changes completely. A single rotating stall cell is observed that causes two or three neighboring diffuser channels to stall, leading to a significantly lower flow rate or even a reversed flow. This stall pattern rotates in the direction of impeller rotation at a very low frequency of approximately 3.3% of the impeller rotation frequency.
Evaluation of Reattaching Shear-Layer in Compressible Turbulent Flows: A Large Eddy Simulation Approach
Authors: Zangeneh Rozie 
Published: October 2020

Abstract
The boundary-layer separation and subsequent reattachment due to the free shear-layer and Shockwave interaction have a significant impact on the aerothermal design of supersonic aerospace systems. This problem is prevalent in high-speed flights and can significantly affect the skin friction, aerodynamic loads, and heat transfer. In recent years, considerable progress has been achieved in the prediction of turbulent compressible flows using high-fidelity models. However, the prediction of reattaching free shear-layer and shockwave interactions still needs to be modified for accurate predictivity. The objective of this study is to investigate the ability of a new computational fluid dynamics model to predict these critical flow phenomena accurately. The new high-fidelity model is based on a collocated central scheme, which has the advantage of being a Riemann free solver, and therefore easy to implement on unstructured grids. It is developed to capture any discontinuities at shocks while it is able to capture broadband spatial and temporal variations in turbulent flows with minimal dissipation and dispersion. Large Eddy Simulation is performed on a compression corner at a Mach number of 2.92 and a high Reynolds number. The geometry of the model is specifically designed to isolate the reattachment process of a high-speed separated flow. To examine the accuracy of the predicted results, results of velocity profiles in the free shear-layer, boundary layer development, turbulent fluctuations, and pressure are compared to an experimental effort by Princeton. Excellent agreement is observed, and it is recommended that the model can be used to investigate the physics of the shock unsteadiness due to interaction with a free shear-layer.
Visualization of R410A Flowing in Copper and Stainless Steel Dimpled Tubes Enhanced by Petal-Shaped Patterns Under Evaporation Conditions
Authors: Tang Weiyu , Sun Zhichuan , Luo Yang , Li Wei 
Published: October 2020

Abstract
Experimental investigations were conducted to study the heat transfer characteristics and flow patterns of R410A during evaporation in three horizontal tubes having the same outside diameter of 12.70 mm and 180 mm in length. The tested tubes contain two tubes with three-dimensional enhanced surface structures (Cu-1EHT and SS-1EHT), and one equivalent smooth tube. This experiment was done at an evaporation temperature of 6 °C and mass flux from 100 to 200 kg/(m2·s) for vapor qualities varying from 0.2 to 0.8. For all the tube tested, flow pattern observations were obtained using a high-speed camera, and the impact of the actual flow regime on heat transfer was discussed. Results indicated that the transition from annular flow to intermittent flow began at a lower vapor quality for two enhanced tubes when compared to the smooth tube. Accordingly, both the Cu-1EHT tube and the SS-1EHT tube exhibited a superior performance than the smooth tube. In addition, the heat transfer coefficient of Cu-1EHT tube is higher than that of the stainless steel one, mainly due to the larger thermal conductivity of wall material.
Investigation on the Modeling of Tire Rotating Using Computational Fluid Dynamics
Authors: Fu Gen , Untaroiu Alexandrina 
Published: October 2020

Abstract
Fuel efficiency is very important when designing new vehicles. There is a continuous demand for lower fuel cost to customers. Many researchers have started to investigate the aerodynamics of tires. Since the experimental approaches are time consuming and costly, numerical methods have been developed to model the air flow around the tire. One of the challenges for modeling the tire is rotating boundary and contact patch. In the CFD model, both rotating and tire deformation have to be considered to get accurate predictions. However, most of the current methods neglect the tire deformation and contact patch. Therefore, in this study, three modeling approaches are compared for the modeling of tire rotation. They include rotating wall, multiple reference frame and sliding mesh. In CFD simulation, another challenge is mesh generation due to the sharp edge and large curvature around the contact patch. In order to generate mesh efficiently. A hybrid mesh which combines hex elements and polyhedral elements is used in this study. In addition, three different tire designs are investigated, including smooth tire, smooth tire with grooves and grooved tire with open rim. The results show that tire with open rim has the highest drag. Sliding mesh provides the most accurate predictions regarding of aerodynamic drag.
Experimental Study on Effective Operating Envelops of Nozzle to Mitigate Liquid Loading in Gas Wells
Authors: Xie Chuan , Liu Yonghui , Luo Chengcheng 
Published: October 2020

Abstract
The downhole liquid atomization by supersonic nozzle is an economic and efficient way to alleviate the liquid loading, but the optimal efficiency conditions are still not clear. In this paper, experimental studies were conducted in a 6-m long and 30-mm inner diameter vertical Perspex pipe to evaluate the performance of supersonic nozzle in different conditions. Camera was employed to record the characteristic of fluid flow downstream the nozzle, and the MATLAB was used in combination with DIP-image technology to determine the diameter of droplets. The experimental results show that mist is easy to be captured by the liquid bulk due to the liquid loading downstream the nozzle when the gas-liquid two phase flow pattern downstream nozzle is non-annular flow, thus leading to a failure of this technology. Due to the huge temperature drop in the annular flow condition, small fraction of mist is condensed into droplets and then attaches onto the pipe wall, forming liquid film. The remaining mist can still flow upwards. In this article, when the gas velocities upstream the nozzle range from 2.4m/s to 3.2m/s, the size of droplets range from 50μm to 1000μm correspondingly. Field application indicates that this technology under the effective operating envelops are able to be efficient to remove the liquid-loading, and the gas wells can maintain a long-term stable production.
Interactions of Two UAV Rotors at Low Reynolds Number
Authors: Tomar Yashvardhan , Shukla Dhwanil , Komerath Narayanan 
Published: October 2020

Abstract
Vertical takeoff and landing vehicle platforms with many small rotors are becoming increasingly pertinent for small Unmanned Aerial Vehicles (UAVs) as well as distributed electric propulsion for larger vehicles. These rotors operate at low Reynolds number unlike large rotors for which the existing prediction methods were developed. Operating at very low Reynolds number essentially means that viscous effects are more dominant; and their spatial spread is significant with respect to the rotor dimensions. This impacts the nature of inter-rotor aerodynamic interactions which become more difficult to predict and characterize. In the present research, two nominally identical commercial UAV rotors are studied for a range of separations in hover and forward flight, both experimentally and computationally, in parallel with ongoing vehicle flight tests with 4 and 8 rotors. Bi-rotor tests in tandem in-plane configuration were performed in Georgia Tech’s 2.13m × 2.74m test section wind tunnel. Rotor simulations were done using the RotCFD Navier-Stokes solver. In hover, rotor performance is sensitive to the distance between rotors at low rotation speeds, indicating the presence of greater inter-rotor interactions at low Reynolds number. In forward flight, the performance of the downstream rotor gets negatively affected by the upstream rotor wake.