bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of Flow Regimes in Gas-Solid Fluidized Beds via a Data Driven Framework
Authors: Kotteda V. M. Krushnarao , Kommu Anitha , Kumar Vinod 
Published: October 2020

Abstract
Gas-solid fluidized beds are widely used in petroleum, chemical, mineral, pharmaceutical, and power plant applications. The performance of fluidized bed reactors strongly depends on the flow dynamics. Characterization of a particle-laden flow has been one of the challenging issues in fluidization research. The simulation of flow in such processes is challenging as the complex dynamic systems comprised of numerous particles and fluidizing gas confined in specific devices. Nonlinear particle-particle/wall and particle-gas interactions lead to complex flow behavior of the gas-solid flows. We used MFiX to simulate a gas-solid flow in fluidized beds. A data-driven framework is trained with the data from MFiX-PIC simulations. The trained and tested machine learning model is used to characterize the flow regimes in fluidized beds. In the present study, the void fraction is used to characterize the flow regimes. However, others in the literature have used pressure, temperature, heat transfer coefficient, acoustic emission, vibration, and electrostatic charge for the characterization of flow regimes.
The Unsteady Behavior of Diffuser Stall in a Centrifugal Compressor With Vaneless Diffuser
Authors: Miida Hiroshi , Tajima Kenta , Fujisawa Nobumichi , Ohta Yutaka 
Published: October 2020

Abstract
The unsteady diffuser stall behavior in a centrifugal compressor with a vaneless diffuser was investigated by experimental and computational analyses. The diffuser stall generated as the mass flow rate decreased. The diffuser stall cell rotated at 25–30% of the impeller rotational speed, with diffuser stall fluctuations observed at 180° from the cutoff. The diffuser stall fluctuation magnitude gradually increased near the cutoff. Based on diffuser inlet velocity measurements, the diffuser stall fluctuations generated near both the shroud and hub sides, and the diffuser stall appeared at 180° and 240° from the cutoff. According to the CFD analysis, the mass flow fluctuations at the diffuser exit showed a low mass flow region, rotating at approximately 25% of the impeller rotational speed. They began at 180° from the cutoff and developed as this region approached the cutoff. Therefore, the diffuser stall could be simulated by CFD analysis. First, the diffuser stall cell originated at 180° from the cutoff by interaction with boundary separation and impeller discharge vortex. Then, the diffuser stall cell further developed by boundary separation accumulation and the induced low velocity area, located at the stall cell center. The low velocity region formed a blockage across the diffuser passage span. The diffuser stall cell expanded in the impeller rotational direction due to boundary separation caused by a positive flow angle. Finally, the diffuser stall cell vanished when it passed the cutoff, because mass flow recovery occurred.
Comparison of Different On-Site Measurement Methods and Their Practical Accuracy
Authors: Benigni Helmut , Leithner Stefan , Jaberg Helmut , Guggenberger Mark 
Published: October 2020

Abstract
Turbines or pumps in hydropower plants achieve peak efficiencies of far more than 90% depending on the specific speed and the type of machine. Based on model tests or numerical simulations, the efficiency of a prototype machine has to be guaranteed and measured with the best measurement technique available. The choice of the appropriate efficiency measurement method does not only depend on the expected measurement uncertainties and tolerances set in a contract, it is also a question of the effort required for such a measuring campaign and of technical challenges, e.g., limitations imposed by plant operating conditions as draining of the system or constant load operation. Concerning hydraulic turbomachines, modern measuring technology offers different methods for efficiency measurements at a turbine unit. Primarily through the development of real-time capable data acquisition systems, it is possible to perform high-precision measurements rather quickly, whereby minimal downtimes can be achieved.
In the first part, the specific measurement methods available in different standards are presented in an overview, and then in the second part, the achieved accuracies of a very complex thermodynamic measurement are compared with a low-cost clamp-on acoustic Doppler measurement using a concrete example.
Continuous Blowing Jet Flow Control Optimization in Dynamic Stall of NACA0012 Airfoil
Authors: Tadjfar M. , Kasmaiee Saman , Noori S. 
Published: October 2020

Abstract
Use of active flow control techniques has become important in flow separation control. Continuous blowing jet is one of the most effective methods that can be used to improve aerodynamic performance of an airfoil. In the present work, different operational parameters of a continuous blowing jet were optimized to improve the aerodynamic performance of an oscillating NACA0012 airfoil. The airfoil underwent a sinusoidal motion about its quarter-chord between −5 and 25 degrees at the Reynolds number of 1.35 × 105. Unsteady Navier-Stokes equations were solved with k-ω SST turbulence model. Due to the time-consuming nature of large number of numerical simulations required during the optimization process, two neural networks were employed to reduce the number of simulations required. The optimization was carried out with the use of a genetic algorithm. The objective function was defined as the lift-to-drag ratio. In these networks, the relationship between the jet operational characteristics and the aerodynamic coefficients were trained. The jet operational parameters that were considered in this study, included jet location (at 1–60 percent of chord length), jet-opening length (0.05 to 0.3 percent of chord length), blowing jet velocity magnitude (0 to 5U∞), and blowing jet incident angle (0 to 180 degrees). Obtained results indicated that jet-opening length and blowing velocity magnitude have a greater effect on the aerodynamic performance when reached their upper values. Concerning the jet location, it was observed that the best jet location was about 2 to 5 percent of the chord Jet angle (θ) was found to results in the best performance when oriented at range 55 to 70 angle. Results indicated a significant improvement of the aerodynamic performance at the optimum blowing jet configuration.
Diversion of Pulsatile Flow Over a Rectangular Sidewall Cavity Using Superhydrophobic Mesh
Authors: Eichholz Benjamin , Zhang Ruihang , Zhang Yan 
Published: October 2020

Abstract
Pulsatile flow over open cavity represents one type of physiological phenomenon related to a few common cardiovascular diseases, such as cerebral sidewall aneurysm and arrhythmia-induced thromboembolism in the left atrium appendage (LAA). In recent years, endovascular treatments using mesh-based implants have become increasingly popular. In this paper, we study the characteristics of pulsatile flow over a simplified sidewall cavity under two Reynolds/Womersley number conditions using Particle Image Velocimetry. The impacts of a regular mesh and a superhydrobobically-coated mesh on the cavity flow are investigated. Our results quantify the phase-to-phase changes of the flow fields and reveal the formation and the transport of the primary vortex over the ostium of the rectangular cavity. Results suggest the meshes diverted the main flow away from the cavity and prohibited the development of the primary vortex. A penetrated jet flow was formed near the front side of the cavity due to the presence of the mesh. The superhydrophobic mesh dramatically reduced the kinetic energy of the penetrated jet into the cavity. It indicates the mesh flow diversion is effective because of the destruction of the shear-induced vortex dynamics that causes flow stagnation on the rear cavity wall. Our results also indicate the superhydrophobic coating is potentially beneficial in terms of reducing the hemodynamic loading inside the cavity.
Noise Source Identification and Noise Directivity Analysis of Bladeless Fans by Combined CFD and CAA Method
Authors: Li Ang , Chen Jun , Liu Yangfan , Bolton J. Stuart , Davies Patricia 
Published: October 2020

Abstract
The bladeless fan is a new concept of fan that does not have visible impellers. It features low noise level, uniform airflow, and improved safety. It has been widely applied in household appliances. Since the customers are particularly sensitive to the noise generated by the fan, the aeroacoustics performance of the fan needs to be accurately characterized in the design stage. In this study, computational fluid dynamic (CFD) and computational aeroacoustics (CAA) are applied to investigate the aeroacoustics performance and identify the major noise source of the bladeless fan. A prototype of the bladeless fan, including a wind channel, a base cavity, a rotor and a stator inside the base, is set in a computational domain of 4m × 2m × 2m and the airflow through the fan is simulated. The hybrid mesh is generated, the unstructured mesh in the near field, and the structured at the far field. To compute the flow field, steady RANS simulation (standard k–ε turbulence model) and Large Eddy simulation (Smagorinsky-Lilly model) are carried out. Ffowcs Williams and Hawkings (FW-H) analogy is used to predict the acoustic field. Experiments, including air velocity measurement and sound pressure measurement, are conducted to validate simulation results. Sound pressure level results at the near-field receiver illustrate that the blade passage frequency can be captured by combined CFD and CAA method. Noise source analysis shows that the combination of the rotor and stator contributes most to the noise produced by the bladeless fan. The wind channel is the secondary source. Sound pressure level contours at different distances and different heights are generated to investigate the directivity pattern of the noise generated by the bladeless fan. At the near field, the produced noise at the front and the back of the bladeless fan are louder than those at left and right; at the far field, the noise at the front is much larger than the other three sides. In addition, at the near field, with the increase of the height, two separated hotspots appear over 2,500Hz and the sound pressure level at these two hotspots increases; at the far field, the noise distribution at different heights is similar and the peak near 3,000Hz can be estimated. A possible reason to cause this peak is vortex shedding at the trailing edge of the rotor’s blades. The aeroacoustics analysis is helpful to develop strategies to reduce noise and guide the improved design of the bladeless fan.
Analysis of the Vortex Dynamics and Instability Mechanisms for a Lobed Nozzle Jet
Authors: Sekaran Aarthi , Amini Noushin 
Published: October 2020

Abstract
The application of radially lobed nozzles has seen renewed challenges in the recent past with their roles in combustion chambers and passive flow control. The free jet flow from such nozzles has been studied for different flow conditions and compared to jets from round nozzles, verifying their improved mixing abilities. The precise mixing mechanisms of these nozzles are, however, not entirely understood and yet to be analyzed for typical jet parameters and excitation modes. While past studies have proposed the presence of spanwise Kelvin-Helmholtz instability modes, the roll-up frequencies of the structures indicate more than one primary structure, which is challenging to resolve experimentally.
The present study carries out three dimensional CFD simulations of the flow from a tubular lobed nozzle to identify instability mechanisms and vortex dynamics that lead to enhanced mixing. We initially validate the model against existing hotwire and LDV data following which a range of Large Eddy Simulations (LES) are carried out. The free jet flow was at a Reynolds number of around 5 × 104, based on the effective jet diameter. Initial results are compared to that of a round nozzle to demonstrate changes in mixing mechanisms. The lobed nozzle simulations confirmed the presence of K-H-like modes and their evolution. We also track the formation and the transport of coherent structures from the tubular part of the nozzle to the core flow, to reveal the evolution of the large-scale streamwise modes at the crests and corresponding horseshoe-like structures at the troughs.
Investigating the Effect of Configuration and Reduced Frequency on SD7003 Airfoils Performance in Tandem
Authors: Hosseini Niloofar , Tadjfar Mehran 
Published: October 2020

Abstract
The effect of placing a stationary airfoil downstream of a pitching airfoil in a tandem configuration was investigated using computational fluid dynamics. A finite-volume URANS solver was employed to simulate the flow field. An optimization study was performed at the low Reynolds number of 30,000 for SD7003 airfoils using a genetic algorithm. Three artificial neural networks were coupled with the genetic algorithm to reduce the computational cost. The optimization process was used to find the optimum design parameters in order to maximize lift to drag ratio of airfoils together in addition to the thrust coefficient of the hindfoil. It was found that a significant improvement of 174% and 15% could be achieved for the thrust coefficient of static hindfoil and L/D of the combined airfoils respectively in tandem configuration over single airfoils at optimum values of design parameters.
Numerical Investigation of a Square Back Vehicle Equipped With a Single Cavity and Multi-Cavity
Authors: Koppa Shivanna Naveen , Ranjan Pritanshu , Clement Shibu 
Published: October 2020

Abstract
This work aims to investigate the comparative effect of two passive flow controls in modifying the mean wake topology around a simplified square back vehicle model. The two passive flow controls are (i) Single cavity and (ii) Multi-cavity. A straight cavity with an optimum depth at the rear base of a vehicle is a well-known technique used to alter the mean wake topology and achieve drag reduction[1]. For two dimensional bluff bodies, a multi-cavity is known to deliver better drag reduction at shorter cavity depths in comparison to a single cavity[2]. With this viewpoint, a numerical investigation is carried out to examine the performance of a multi-cavity over a single cavity in drag reduction for a three-dimensional bluff body vehicle model. The numerical simulations are performed at Reynolds Number (Re) = 1 × 105 using the k-ω SSTSAS turbulence model in a Finite volume open-source code OpenFOAM. The investigations revealed, for any cavity depth, a single cavity always performed better than multi-cavity in reducing drag. However, at optimum cavity depth equal to 33% of the body height, the drag reduction magnitude was identical for both the flow controls. The plausible mechanisms responsible for their relative difference in performance will be explored by analyzing the base pressure distribution, wake mean topology, and the temporal behavior of the wake.
Vortex Induced Vibrations Analysis of a Cantilevered Blunt Plate by Proper Orthogonal Decomposition of TR-PIV and Structural Modal Analysis
Authors: Watine Yann , Gabillet Céline , Astolfi Jacques-André , Pernod Laetitia , Lossouarn Boris , Deü Jean-François 
Published: October 2020

Abstract
The present work focuses on the experimental characterization of the vortex shedding and on the induced vibrations of a cantilevered blunt rectangular aluminum plate of chord to thickness ratio 16, immersed in a uniform water flow in the hydrodynamic tunnel of the French Naval Academy Research Institute. Experiences have been conducted for Reynolds numbers Re (based on chord length) ranging from 2.5 × 105 to 10.5 × 105 at zero degrees incidence. Special attention has been paid to the interaction of the structural response and the flow dynamics at the twisting resonance. For this purpose, wake structures have been analyzed by Time Resolved Particle Image Velocimetry (TR-PIV) and the structural response of the plate has been examined by laser vibrometry. The von Karman vortex street has been characterized by statistical analysis and Proper Orthogonal Decomposition of PIV velocity fields and the structure is analyzed through modal analysis. The near-wake’s structure has been examined for three different Reynolds numbers: (i) at Re = 3.0 × 105, corresponding to vortex induced structural response at constant Strouhal number; (ii) at Re = 4.5 × 105, corresponding to mechanical resonance but dissociated vortex shedding and (iii) at Re = 5.4 × 105, corresponding to lock-in of the vortex shedding at the mechanical resonance. At Re = 4.5 × 105, at mechanical resonance, it reveals the occurrence of an energy transfer between the shear layer and the bubble wake vortex which cancels synchronization of the structural vibration with the von-Karman vortex street.
The Effect of Varying Viscosity in Turbulent Channel Flow
Authors: Coppo Leite Victor , Merzari Elia 
Published: October 2020

Abstract
In this article we examine channel flow subject to spatially varying viscosity in the streamwise direction. The Reynolds number is imposed locally with three different ramps. The setup is reminiscent of transient channel flow, but with a space-dependent viscosity rather than a time dependent viscosity. It is also relevant to various applications in nuclear engineering and in particular in test reactors, where the viscosity changes significantly in the streamwise direction, and there is a severe lack of Direct Numerical Simulation (DNS) data to benchmark turbulence models in these conditions.
As part of this work we set up a novel benchmark case: the channel is extended in the stream-wise direction up to 20π. The viscosity is kept constant in the first 4π region. This inlet region is used as a cyclic region to obtain a fully developed flow profile at the beginning of the ramping region. In the ramping region the Reynolds number is linearly increased along the channel. The flow is homogenous in the spanwise direction, while it is non-homogenous in the stream-wise and wall-normal direction. We perform here Direct Numerical Simulation (DNS) with Nek5000, a spectral-element computational fluid dynamics (CFD) code developed at Argonne National Laboratory.
In this study, specific focus is given to the investigation of turbulence properties and structures in the near-wall region along the flow direction. Turbulent statistics are collected and investigated. Similarly to transient channel flow, the results show that a variation in the Reynolds across a channel does not cause an immediate change in the size of turbulent structures in the ramp region and a delay is in fact observed in both wall shear and friction Reynolds number. The results from the present study are compared with a correlation available in the literature for the friction velocity and as a function of the Reynolds number.
Retracted: “Experimental Investigation of the Fluctuating Static Pressure in a Subsonic Axisymmetric Jet” [ASME 2020 Fluids Engineering Division Summer Meeting, Volume 2: Fluid Mechanics; Multiphase Flows, Virtual, Online, July 13–15, 2020, Conference Sponsors: Fluids Engineering Division, ISBN: 978-0-7918-8372-3, Copyright © 2020 by ASME. Paper No. FEDSM2020-20242, V002T03A040; 15 pages; doi: 10.1115/FEDSM2020-20242]
Authors: ASME  
Published: October 2020

Abstract
This paper was removed from publication at the author’s request. December 9, 2020.
Copyright © 2020 by ASME
Using Computational Fluid Dynamics to Analyze Convection in Pin-to-Plane Plasma Discharge
Authors: Galvez Robert , Wright Kamau , Milanovic Ivana 
Published: October 2020

Abstract
Multiphysics simulations were conducted to model the role of naturally induced convection in heat and mass transport within a non-isothermal plasma discharge chamber. A pin-to-plane discharge into chamber containing carbon dioxide can be used to possibly decompose carbon dioxide. The present study characterizes the role that convection plays in the diffusion of various products such as ions and excited-state species throughout the test chamber. Multiphysics software including computational fluid dynamics was employed in a two-dimensional transient simulation of a closed reactor with a large pin serving as the cathode and a bottom plate serving as the anode. The mesh was adjusted to best capture important discharge phenomena, while the simulated time was varied to best characterize the chemical processes.. Mesh validation was undertaken using the relevant minimum sizes required by the plasma, fluid flow, and heat transfer solvers. The flow induced by natural convection from the discharge was then compared to the flow induced by natural convection around a resistance heater operating with the same power input as the plasma. The results of this simulation are used to inform improvements on a parallel experimental system used to study the discharge, such as placement of gas concentration sensors and to better understand the heat and mass transfer through the discharge.
Experimental Hydraulic and Mechanical Characterisation of a Double-Flow Implantable Blood Pump
Authors: Strauch Carsten , Thamsen Paul Uwe , Escher Andreas , Granegger Marcus 
Published: October 2020

Abstract
The considerable contribution of parasitic measurement effects in fluid flow machines of small performance classes remains a major challenge in the assessment of corresponding hydraulic characteristics such as hydraulic losses and efficiencies. However, a standardized experimental approach to accurately quantify such properties is of paramount importance for the design of rotary blood pumps with low hydraulic power and torque.
This study proposes a novel test bench to accurately assess hydraulic and mechanical characteristics of pumps designed for a mechanical power input of up to 20,9W, a maximum rotational speed of 7000min−1 and a maximum torque of 10mNm. Key feature of the iteratively optimized test bench is a torque measuring shaft combined with ceramic bearings and seals that minimizes the friction torque to 0.66–0.69mNm.
Preliminary measurements for a double-inflow, double-outflow circulatory support pump with maximum torque of 1.71mNm and hydraulic power of 0.15W, demonstrated both the feasibility of the hydraulic and mechanical design of the test bench and the reproducibility of the measured data. These results warrant the applicability of the presented test-bench for the investigation of typical cardiac assist systems as well as for all other hydraulic flow machines of the equivalent performance class.