bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrodynamics of the Wake of Contra-Rotating Propellers at Different Loading Conditions
Authors: Pereira Francisco Alves , Capone Alessandro , Di Felice Fabio 
Published: October 2020

Abstract
This work presents an experimental study of the wake hydrodynamics of a three-blade contra-rotating propeller system (CRP) at advance ratio J = 0.7, 1 and 1.3. The study is carried out in a cavitation tunnel by employing a mixed hardware-software phase-locked acquisition and processing scheme. Flow measurements are thus phase-averaged based on both the forward and aft propeller angular position, so that the effect of their relative position on the flow features is investigated. Average and fluctuating velocity fields along with vorticity are presented and discussed. Strong interactions take place between the forward and aft propellers’ trailing vorticity with regular patterns of vortex reconnection and break-up which depend on the advance coefficient. Flow visualizations, carried out by inducing cavitation in the vortex cores, show that complex though organized patterns of helical coaxial vorticity occur within the wake.
Non-Equilibrium Thermal Fluctuation in Flow
Authors: Li Wei 
Published: October 2020

Abstract
Non-equilibrium thermal fluctuations present as wave elements in a flow. A wave element is the wave interface between two molecule groups with different temperature; it is generated by density difference which results from temperature difference. Tiny temperature differences always exist everywhere in a fluid. When the fluid is in motion, wave elements are generated among molecule groups. Wave motion and Brownian motion may be the two basic forms of motion of molecules in flow. Brownian motion is controlled by temperature. Wave elements are caused by temperature differences and the motion of the fluid. Wave motion maybe the physical mechanism of convective heat transfer. Non-equilibrium thermal fluctuations exist everywhere among molecule groups in a flow. The theoretical analysis presents that a wave element presents oscillatory behavior along the space and time dimensions simultaneously. The experimental evidence for wave elements can not be directly established at present scientific testing capability because the temperature difference of two molecule groups adjoining to each other in a flow is very small. A series of “enlarged size” experiments of fouling to show the behaviors of wave elements by tracing the movement of molecules are conducted. The experimental study of fouling presents that oscillatory interface along the space and time dimensions simultaneously exists between two densities due to motion of the fluids. The experimental and theoretical analyses are supported to each other.
Wake Patterns in a Dual-Rotor Wind Turbine
Authors: Asfar K. , Mahasneh A. 
Published: October 2020

Abstract
A recently patented novel idea of an adjustable dual-rotor horizontal-axis wind turbine is investigated [1]. The idea behind this proposed design is to continue to extract more mechanical energy from the wind stream which has already passed through the front rotor by having a second identical rotor on the other side of the main shaft of the wind turbine. The complex flow in the dual-rotor is studied using computational fluid dynamics. The optimum performance of this unit is when the wake from each blade in the first rotor passes through the spacing between each two rear rotor blades while the undisturbed part of the wind stream is intercepted by the rear rotor blades. The strength and pattern of the wakes are determined for low and high wind speeds. The numerical study verified the feasibility of the proposed idea. The optimum orientation angle at which no interception of the front rotor wake by any of the rear rotor blades is found to be 60°.
The axial spacing between the front and rear rotors is also investigated. A small scale model was built and tested in a subsonic wind tunnel. The comparison showed that the dual-rotor wind turbine produced nearly 100% more power than the single-rotor wind turbine.
Unified Assessment Approach for Courses With Simulation Component [And Professors in Hurry]
Authors: Milanovic Ivana , Eppes Tom A. , Wright Kamau 
Published: October 2020

Abstract
In support of the digital transformation of our programs, simulation assignments are embedded in undergraduate fluid mechanics and heat transfer lecture-based courses, as well as in the Computational Engineering technical electives. Each course integrates simulations, application building, and inquiry-based learning (IBL) with ten assignments performed outside the class and documented in technical reports. FEA and CFD tools are employed to teach thermo-fluids, and in turn, course material is used to teach CFD and FEA. This new, high-impact practice facilitates a deeper understanding of theoretical concepts, exposes students to modern engineering tools, and develops students’ research capacity while the ‘lecture’ time is dedicated for the fundamental theoretical topics only.
The main goal of this study was to expand on the implementation of simulations and IBL in undergraduate thermo-fluids courses and create a template to do so in other topical threads. This was accomplished by: (1) strategically balancing step-by-step instructions supporting skill-building, with inquiry-based tasks guiding discovery process and developing higher order thinking skills; (2) providing clear and detailed grading criteria guiding students both in the process of gaining skills and performing IBL; (3) designing strategies for the assessment of student work that are easily transported across the curriculum; and (4) assessing students’ understanding and the effect of the overall digital transformation effort based on quantitative and qualitative data indicative of the achievement of learning outcomes.
This study builds on the authors’ previously reported work in the area of simulations and IBL that covered individual courses as well as course sequences. While quantitative data includes assessment of students’ understanding and confidence in comprehension of select concepts using grades, student surveys, and course evaluations, the impact of the described approach is illustrated with qualitative data including several examples of student work and its influence on their professional development.
Large Eddy Simulation of Flow Over a Hemispherical Obstacle Within a Cylindrical Tube
Authors: Sharma Amit , Ghia Urmila , Turkevich Leonid A. 
Published: October 2020

Abstract
Motivated by recent experiments on the dustiness of nanoscale powders, this research addresses the modeling of powder aerosolization within the Venturi Dustiness Test (VDT) apparatus. As a first step in such modeling, we investigate the flow over a hemispherical (powder) hill, at the operating Reynolds number Re ∼ 20,000, in the powder holding tube attached to the VDT. The powder holding tube is idealized as a cylindrical tube, obstructed by a hemispherical (powder) hill.
The upstream flow field is characterized by the presence of a horse-shoe vortex, formed due to the separation of the boundary layer from the wall of the tube. A stagnation point occurs at the lower front surface of the bump. Strong near-wall vorticity is generated midway up the bump, and the flow is separated near the top of the bump. Kelvin-Helmholtz vortices are produced due to the strong shear-layer vorticity, and these then travel downstream with the flow. The upstream near-wall flow is dominated by a horseshoe vortex forming a necklace pushed out into the wake area. The flow detaches from the bump at the separation line, leading to vortex ‘roll-up’. These rolled-up vortices merge with the horseshoe vortices to form a large entangled hairpin vortex. The arch-type vortices shed with a frequency consistent with the Strouhal estimate fSt ∼ 6700 Hz.
A Phase Field Method for Numerical Simulation of Boiling Heat Transfer
Authors: Wang Zhicheng , Zheng Xiaoning , Karniadakis George 
Published: October 2020

Abstract
The Cahn-Hilliard phase field method for two-phase flow has gained particular attention due to its unique features including its flexibility for complex morphological and topological changes, the intrinsic property of conserving mass, and the natural approach to account for the surface tension. The essential idea of the method is to use a phase field function to describe the two-phase system, while a thin smooth transition layer (interfacial area) connects the two immiscible fluids, where the value of phase field function varies continuously. The application of phase field method to two-phase flows has become more widespread recently, but to the best of our knowledge, very little progress has been made for the method being applied to the two-phase flows with phase change. This includes evaporation, condensation and boiling, which plays an important role in enhanced heat transfer in power electronics, energy, and aerospace engineering. In previous work, in order to face the challenge of large density contrast and high Reynolds number of practical engineering problems, we developed a stabilized phase field method that can handle two-phase flow with density ratio over 1000, at high Reynolds number over 10,000, and applied the method to simulate slug initiation in a long circular pipe. In this paper, inspired by the boiling model widely used in the level-set method, we propose a new boiling model that assumes that boiling takes place in the whole interfacial layer. The method is then used to solve the non-solenoidal Navier-Stokes equations. The boiling model is validated by simulating a vapor bubble growing in super-heated liquid. For this case, the growth rate of the bubble has an analytical solution, and it is used as a benchmark case in volume of fluid (VOF) and level-set methods extensively. For three different refrigerants, namely water, R134a and HFE7100, our phase field method with the boiling model can obtain accurate simulation results. Moreover, the method and model are applied to predict the three-dimensional boiling heat transfer in a rectangular micro-channel that contains a water vapor bubble with various inlet super-heat conditions. We found that the predicted bubble shape is very similar to that visualized in existing experiment. From our simulation of boiling flow using the phase field method, We have found that the required mesh resolution for the phase field method is comparable with that of VOF and level-set methods.
Experimental Validation of Fluid-Structure Interaction Co-Simulations Using ANSYS via Wind Tunnel Testing of Cantilevered Plate
Authors: Shepard Thomas G. , Schneider Kyle , Baxter Sarah , Schwartz William 
Published: October 2020

Abstract
Validation of numerical simulations is a key step in gaining confidence in the fidelity of computational models for a given application. These simulations take on additional complexity in fluid structure interactions when the body being studied experiences flow-induced deformation. In this study, experiments are conducted on a cantilevered aluminum plate mounted in a wind tunnel. Experimentally, deflections are measured using Digital Image Correlation and axial bending strains are measured using strain gages and. These values are compared to a coupled fluid-structure interaction simulation, which co-simulated the structural (Lagrangian FEA) and fluid (Navier-Stokes CFD) computational methods. Within the simulations, FEA parameters including mesh size, mapping method, and mesh type were varied; CFD parameters that were varied include turbulence theory, mesh sizing, inflation layer, mapping method, and Courant Number. Values were varied to study their effects on the simulation solution, as well as to ensure mesh independence of the solution relative to both simulation domains. Experiments were conducted on an Aluminum (6061-T6) plate measuring 152.4 × 50.8 × 0.61 mm. The plate was positioned in the wind tunnel at two different angles relative to the oncoming flow and Reynolds numbers of 98,000–247,000 were considered. The numerical simulation demonstrates agreement with DIC displacements and good agreement with measured strains with deflections up to ∼ 11 mm. Future steps are discussed.
Investigation of the Flow Instabilities of a Low Specific Speed Pump-Turbine: Part 1 — Experimental and Numerical Analysis
Authors: Deniz Sabri , Del Rio Armando , von Burg Martin , Tiefenthaler Manuel 
Published: October 2020

Abstract
This is the first part of a two-part paper focusing on the flow instabilities of low-specific pump turbines. In this part, results of the CFD simulations and experiments of the research carried out on a low specific speed model pump-turbine at HSLU (Lucerne University of Applied Sciences) Switzerland are presented.
The requirements of a stable and reliable pump-turbine operation under continuously expanding operating ranges, challenges the hydraulic design and requires new developments. Previous research at the HSLU [1] analyzed the instabilities of a medium specific speed (i.e. nq = 45) pump turbine. This paper presents the results of experimental (model pump-turbine at the test rig) and numerical (CFD) investigations of the pump-turbine instabilities of a low specific speed (nq = 25) pump-turbine in the turbine operating mode in the region of S-shaped characteristics (that is where the pump-turbine is synchronized and oscillations may occur during load rejection). The four-quadrant characteristics of a low specific speed model pump-turbine with two similar runners differentiating in the size (diameter) are measured. Testing of both runners with the same guide vane system provided information about the effects of the increased vaneless space (the distance between the guide vanes and runner) on the pump-turbine performance and stability both in turbine- and pump operating modes.
A CFD methodology by using different numerical approaches and applying several turbulence models is developed in order to accurately predicting the characteristics of the reversible pump-turbines in the S-shaped region (speed no load conditions) as well as analyzing the flow features especially at off-design conditions. This CFD model is validated against the experimental data at 6° and 18° guide vane openings in turbine operating mode.
With the measured data of the unsteady pressure measurements and detailed investigation of unstable ranges on the pump-turbine characteristics, flow instabilities in the low-specific speed model pump-turbine are analyzed. Relevant frequencies such as rotating stall, steady and unsteady vortex formations are determined. Based on the analysis of the experimental data and CFD results focusing especially on the flow features in the vaneless space and at the runner inlet, the onset and development of the flow instabilities are explored.
Numerical Investigation and Performance Characterization of Oscillating Foil Energy Harvesting
Authors: Pannell James , Walters D. Keith 
Published: October 2020

Abstract
Oscillating foil energy harvesting devices are increasingly being considered as a sustainable energy alternative, especially in rivers and tidal areas. This paper applies CFD to an oscillating foil power generation device in order to explore the effects of pitching amplitude, the ratio of heaving amplitude to chord length, and the reduced frequency to the energy harvesting efficiency. Ansys Fluent 17.2 was used for this study, and the results are compared to experimental results that have been previously documented in the open literature. Configurations examined included pitching amplitudes of 65, 70, 75, and 80 degrees; heaving ratios of 0.4, 0.6, and 0.8; and reduced frequencies of 0.1, 0.12, 0.14, and 0.16. Results seems to indicate that the optimal reduced frequency is related to the heaving ratio, with the pitching amplitude only creating slight variations in the power produced by the foil. In the data, configurations with a heaving ratio of 0.4 have highest efficiency at reduced frequencies of either 0.14 or 0.16, but efficiency remains high at both points, which indicates the possibility of a peak in between the two points. Configurations with heaving ratio of 0.6 peak at reduced frequency 0.14 with a significant drop off at reduced frequency of 0.16. Finally, configurations with a heaving ratio of 0.8 show a peak at 0.12 reduced frequency and a significant drop at 0.14 and 0.16. These results suggest that OFEH devices can be effectively optimized for different and potentially varying operating conditions that may be encountered during practical implementation of OFEH technology.
A Solution for Experimental Modeling the Axial Fans With High Efficiency and Reduced Noise
Authors: Radulescu Victorita 
Published: October 2020

Abstract
Present paper describes some experimental results obtained for modeling an axial fan with newly designed blade profiles, having high efficiency, low vibrations and noise. The axial fan was firstly designed by computational method, during a research project with our industrial partner SAVEB SA. One of the company objectives is represented by the production of the axial industrial fans, dedicated to different users to eliminate the smoke and the air pollutants from industrial halls, according to their specific needs. In the beginning, are presented some aspects of the theoretical aspects used in the numerical modeling for designing the rotor blades. Some considerations concerning the selection of the incidence angles of 10°, 15°, and 20° are mentioned. The profiles were selected from the recommended schemes, for different industrial applications, as the industrial halls for the air or gas circulation without corrosive, abrasive, or toxic agents, metallic dust, or with crowding/sticking suspensions contents. For this type of axial fan, the content of suspensions should not exceed 50 mg/m3. Further is presented the experimental stand, in conformity with actual standards, STAS 7466-84 and DIN 24163, equipped with a hydrometer with an error less than 3%, barometer with an error less than 1 mm Hg, stroboscope and tachometer with an error less 0,5% from the total rotation velocity, two voltmeters, with an error less 0,5, two wattmeters, etc. For the experimental tests was selected a fan with a diameter of 630 mm, which as standard execution has a maximum efficiency of 56%, in six different constructive variants: a rotor with 12 profiles and directory device with 11 blades, with 6 blades and directory device, etc. As the first variant of the rotor’s profiles has been used two solutions for the realization as two technological options, both of them tested in the laboratory. There are detailed some schemes adopted for the measurements and tests, and finally the adopted solution for measuring different characteristic parameters like efficiency, noise, and vibrations produced by the axial fan. Next are illustrated part of the measurement reports and the corresponding charts. Of the total amount of experimental results were selected for measuring scheme III and IV for their optimum energetic characteristics and high efficiency. All four diagrams are presented for both selected solutions used in the realization of the fan rotor blades. Finally, some conclusions and references are presented.
Flow Boiling on Heterogeneous Wetting Surface in a Vertical Narrow Microchannel
Authors: Lin Yuhao , Li Junye , Zhou Kan , Li Wei , Sheng Kuang , Shao Shuai 
Published: October 2020

Abstract
The micro structured surfaces have significant impact on the flow patterns and heat transfer mechanisms during the flow boiling process. The hydrophobic surface promotes bubble nucleation while the hydrophilic surface supplies liquid to a heating surface, thus there is a trade-off between a hydrophobic and a hydrophilic surface. To examine the effect of heterogeneous wetting surface on flow boiling process, an experimental investigation of flow boiling in a rectangular vertical narrow microchannel with the heterogeneous wetting surface was conducted with deionized water as the working fluid. The heat transfer characteristics of flow boiling in the microchannel was studied and the flow pattern was photographed with a high-speed camera. The onset of flow boiling and heat transfer coefficient were discussed with the variation of heatfluxes and mass fluxes, the trends of which were analyzed along with the flow patterns. During the boiling process, the dominated heat transfer mechanism was nucleate boiling, with numerous nucleate sites between the hydrophilic/hydrophobic stripes and on the hydrophobic ones. In the meantime, after the merged bubbles were constrained by the channel walls, it would be difficult for them to expand towards upstream since they were restricted by the contact line between hydrophilic/hydrophobic stripes, thereby reduce the flow instability and achieve remarkable heat transfer performance.
Trends in match injury risk in professional male rugby union: a 16-season review of 10 851 match injuries in the English Premiership (2002–2019): the Professional Rugby Injury Surveillance Project
Authors: West Stephen W , Starling Lindsay , Kemp Simon , Williams Sean , Cross Matthew , Taylor Aileen , Brooks John H M , Stokes Keith A 
Published: October 2020

Objectives
The Professional Rugby Injury Surveillance Project is the largest and longest running rugby union injury surveillance project globally and focuses on the highest level of rugby in England.

Methods
We examined match injuries in professional men’s rugby over the period 2002/2003 to 2018/2019 and described trends in injuries over this time.

Results
Over the period 2002/2003–2018/2019, 10 851 injuries occurred in 1 24 952 hours of match play, equating to a mean of 57 injuries per club per season and one injury per team per match. The mean incidence, severity (days absence) and burden (days absence/1000 hours) of injury were 87/1000 hours (95% CI 82 to 92), 25 days (95% CI 22 to 28) and 2178 days/1000 hours (95% CI 1872 to 2484), respectively. The tackle accounted for 43% injuries with running the second most common activity during injury (12%). The most common injury location was the head/face with an incidence of 11.3/1000 hours, while the location with the highest overall burden was the knee (11.1 days/1000 hours). Long-term trends demonstrated stable injury incidence and proportion of injured players, but an increase in the mean and median severity of injuries. Concussion incidence, severity and burden increased from the 2009/2010 season onwards and from 2011 to 2019 concussion was the most common injury.

Conclusion
The rise in overall injury severity and concussion incidence are the most significant findings from this work and demonstrate the need for continued efforts to reduce concussion risk as well as a greater understanding of changes in injury severity over time.