bluuebunny/crossref_metadata_2025_split huggingface dataset:
On Scouring Efficiency of Flush Waves in Sewers: A Numerical and Experimental Study
Authors: Alihosseini Maryam , Thamsen Paul Uwe 
Published: November 2019

Abstract
In sewer sediment management, the removal of depositions using hydraulic flushing gates has recently gotten great attention. Despite numerous investigations, the complex process of sediment transport under flushing waves is not yet well understood. The present work aims to calibrate and validate a coupled computational fluid dynamics and discrete element method (CFD-DEM) to study the fluid-sediment interaction in sewers. The CFD part of the simulation was carried out in the software Ansys Fluent which is two-way coupled to the DEM software EDEM. The multiphase model volume of fluid (VOF) was used to simulate the flushing wave, while the sediments were handled as DEM particles using the discrete phase model (DPM). To validate the 3D model, experimental work has been performed in a circular laboratory pipe with sand and gravel of different size distributions. A construction of a sluice gate was installed to realize the flushing event, which is similar to a dam-break wave. The evolution of the sediment bed and the scouring efficiency of the waves were examined under different flushing conditions. The results showed that the CFD-DEM method could be used to investigate the performance of flushing devices and various features of sediment transport which are not easy to obtain in the laboratory or field.
Visualizing Test on the Distribution Rule of Coarse Particles in a Double Blade Pump
Authors: Wu Xianfang , Tian Xiao , Tan Minggao , Liu Houlin 
Published: November 2019

Abstract
As a typical fluid mechanics problem, pump blockage has always been a hot research topic. The obtaining of the distribution of coarse particles in the solid-liquid two-phase flow pump is the basis of improving its non-blocking performance. High-speed photography technique is applied to do visualizing test and research on the distribution of coarse particles in a double blade pump. The effects of particle concentration, particle density and particle diameter on the distribution of coarse particles in the solid-liquid two-phase flow pump at different phases are studied. Besides, the variation of hydraulic performance of the double blade pump under different parameters is also analyzed. The results show that the particles in the impeller mainly located in the vicinity of the blade pressure surface, and the distribution of the particles in each section of the volute is quite different. The great difference in particle density can result in obviously uneven distribution of particles. With the increase of particle diameter, particle density and particle concentration, the pump head and efficiency both decrease while the shaft power increase on the contrary. This research results can also provide a basis for the optimization design of solid-liquid two-phase flow pumps.
Experimental Investigation on Flow and Breakup of Two-Dimensional Liquid Jets
Authors: Jaberi Amin , Tadjfar Mehran 
Published: November 2019

Abstract
Studying of injectors with non-circular geometries has recently come to the spotlight of researchers as a potential technique to improve the liquid injection characteristics of different systems. In this work, the flow physics and breakup of two-dimensional liquid jets issued from flat slits into still air were experimentally investigated. Three injectors with aspect ratios of 30, 60 and 90 and thickness of 0.35 mm were manufactured to obtain two-dimensional liquid flow at the nozzle exit. The tests were performed for a wide range of volume flow rate, varying from 10 L/h to 240 L/h. Backlight shadowgraphy and high speed photography were employed to capture the flow dynamics of the jets. In order to capture every detail of the flow, photos of the liquid jet were taken from two views with 90° from each other. Using the visualizations, different regimes of the jet flow were explored and a regime map was proposed to distinguish these regimes based on the non-dimensional parameters of the liquid jet. Moreover, quantitative description of the main features of jet flows were obtained using an in-house image processing program. Measurements of different parameters including convergence length, maximum width, breakup length, sheet thickness to name a few, were conducted.
Visualization of Microbubble Distribution Inside Turbulent Boundary Layer Along Flat and Curved Solid Surfaces
Authors: Murai Yuichi , Saito Daichi , Ushiyama Daiki , Park Hyun Jin , Tasaka Yuji 
Published: November 2019

Abstract
How microbubbles behave inside turbulent boundary layers are investigated experimentally. Water electrolysis is applied for generation of microbubbles in water, of which electrodes are flash mounted on the solid wall in the upstream section of the measurement area. Four kinds of solid surfaces are examined to compare the microbubble distribution. For a circular cylinder of the radius R = 22 mm at Re = 5,000, we found that microbubbles depart from the surface earlier than the liquid boundary layer. For an elliptic cylinder of the curvature radius of R = 60 mm and a hydrofoil of NACA0040, microbubble injection made the separation point move downstream in the range of 9,000 &lt; Re &lt; 90,000. To compare the effect with the cases of flat solid surfaces (R = infinity), we visualized three-dimensional distribution of microbubbles with color-coded volumetric illumination technique. The result has shown formation of microbubble clusters intermittently, which has Coulomb potential due to negative electric charge on bubble interfaces.
A Statistical Approach for Modeling Stochastic Rebound Characteristics of Solid Particles
Authors: Haider G. , Asgharpour A. , Zhang J. , Shirazi S. A. 
Published: November 2019

Abstract
During production of oil and gas from wells, solid particles such as removed scales or sand may accompany petroleum fluids. These particles present in this multiphase flow can impact inner walls of transportation infrastructure (straight pipelines, elbows, T-junctions, flow meters, and reducers) multiple times. These repeated impacts degrades the inner walls of piping and as a result, reduce wall thickness occur. This is known as solid particle erosion, which is a complex phenomenon involving multiple contributing factors. Prediction of erosion rates and location of maximum erosion are crucial from both operations and safety perspective. Various mechanistic and empirical solid particle erosion models are available in literature for this purpose. The majority of these models require particle impact speed and impact angle to model erosion. Furthermore, due to complex geometric shapes of process equipment, these solid particles can impact and rebound from walls in a random manner with varying speeds and angles. Hence, this rebound characteristic is an important factor in solid particle erosion modeling which cannot be done in a deterministic sense. This challenge has not been addressed in literature satisfactorily. This study uses experimental data to model particle rebound characteristics stochastically. Experimental setup consists of a nozzle and specimen, which are aligned at different angles so particles impact the specimen at various angles. Information regarding particle impact velocities before and after the impacts are obtained through Particle Tracking Velocimetry (PTV) technique. Distributions of normal and tangential components of particle velocities were determined experimentally. Furthermore, spread or dispersion in these velocity components due to randomness is quantified. Finally, based on these experimental observations, a stochastic rebound model based on normal and tangential coefficients of restitutions is developed and Computational Fluid Dynamics (CFD) studies were conducted to validate this model. The model predictions are compared with experimental data for elbows in series. It is found that the rebound model has a great influence on erosion prediction of both first and second elbows especially where subsequent particle impacts are expected.
Multi-Objective Optimization of a High Specific Speed Centrifugal Volute Pump Using 3D Inverse Design Coupled With CFD Simulations
Authors: Zhang Luying , Davila Gabriel , Zangeneh Mehrdad 
Published: November 2019

Abstract
This paper presents three different multi-objective optimization strategies for a high specific speed centrifugal volute pump design. The objectives of the optimization consist of maximizing the efficiency and minimizing the cavitation while maintaining the Euler head. The first two optimization strategies use a 3D inverse design method to parametrize the blade geometry. Both meridional shape and 3D blade geometry is changed during the optimization. In the first approach Design of Experiment method is used and the efficiency computed from CFD computations, while cavitation is evaluated by using minimum pressure on blade surface predicted by 3D inverse design method. The design matrix is then used to create a surrogate model where optimization is run to find the best tradeoff between cavitation and efficiency. This optimized geometry is manufactured and tested and is found to be 3.9% more efficient than the baseline with little cavitation at high flow. In the second approach the 3D inverse design method output is used to compute the efficiency and cavitation parameters and this leads to considerable reduction to the computational time. The resulting optimized geometry is found to be similar to the more computationally expensive solution based on 3D CFD results. In order to compare the inverse design based optimization to the conventional optimization an equivalent optimization is carried out by parametrizing the blade angle and meridional shape. Two different approaches are used for conventional optimization one in which the blade angle at TE is not constrained and one in which blade angles are constrained. In both cases larger variation in head is obtained when compared with the inverse design approach. This makes it impossible to create an accurate surrogate model. Furthermore, the efficiency levels in the conventional optimization is generally lower than the inverse design based optimization.
Simulations of Tubular UAV With Vectored Thrust in Near-Hovering Regimes in the Presence of Side Winds
Authors: Matveev Konstantin I. , Wheeler Miles P. 
Published: November 2019

Abstract
An innovative unmanned aerial vehicle with a tubular body and a vectored thruster is considered in this study. In order to optimize the vehicle design and develop effective means for its control, aerodynamic characteristics of this vehicle need to be known. Computational fluid dynamics studies employing STAR-CCM+ software have been carried out for this UAV in near-hovering regimes. Aerodynamic simulations employed the SST k–ω turbulence model, γ transition model, and a virtual actuator disk model. After conducting a validation study with a cylinder in axial flow, modeling of the UAV setup was completed for a range of propulsor orientations and cross winds. The aerodynamic phenomena are found to become more complex with increasing the propulsor angle with respect to the main body axis and in stronger cross winds due to interactions between the incident flow, the propulsor jet, and the body surface. At the propulsor deflection angle of 15°, the horizontal aerodynamic force on the body was augmented by 0.02–0.07 of the propulsor thrust magnitude in various wind conditions, whereas the axial downward force increased by 0.01–0.03 of the thrust. In cross winds with the relative velocity magnitude of 0.65, the horizontal aerodynamic force on the body increased by about 0.25 of the propulsor thrust magnitude, while the axial downward force increased by about 0.05 of the thrust.
Experiments on Turbulent Air-Water Swirling Flow in a Pipe With a Circular Disk
Authors: Tianxing Zhang , Almheiri Ayesha , Khezzar Lyes , Alshehhi Mohamed , Salam Saqib 
Published: November 2019

Abstract
This paper presents an experimental study conducted on turbulent single and two-phase swirling flow in a circular pipe with a bluff body. Laser Doppler Velocimetry (LDV) was used to measure liquid velocity radial profiles. The measurements were performed in a closed water-air loop system with a horizontal test section of length 610 mm and 41 mm internal diameter. The measurement campaign was performed at different axial locations to document the flow field without and with the presence of an air core respectively. The measurements were conducted with water flow rates which corresponded to Reynolds numbers based on pipe diameter and average liquid velocity of 14,500 and 19,450 for single phase and liquid-gas swirling flow, respectively. Analysis of the results reveals a more noticeable reverse flow along the whole pipe intensifying rather than being dampened as expected due to the swirl decay. High-speed photography shows that at a GLR = 0.3% the gas core does not touch the bluff body but breaks down just ahead of the disk surface.
Study on the Influence of Centrifugal Pump Inlet Flow Field Instability and Methods of Adjustment
Authors: Qian Bo , Chen Jinping , Wu Peng , Huang Bin , Wu Dazhuan 
Published: November 2019

Abstract
The quality of centrifugal pump inlet flow field is an important factor that affecting the performance of pump. Studies have proved that the vortex in the inlet area can also bring an extra flow instability to pump, which results in a hydro-induced vibration. This phenomenon is more common and significant in the pumps with an elbow tube, which is often applied to minimize installation size, before pump inlet. Therefore, it is necessary to look into the influence of inlet flow field instability on pump performance especially the vibration performance. The methods of adjusting pump inlet flow field is also worthy of being studied in the meantime. In this study, the influence of inlet vortex on the performance of centrifugal pump with an elbow inlet tube is investigated by means of CFD analysis. The flow is significantly affected when going through the elbow tube inlet and then turbulence is generated as a result, which enters the impeller at the next moment. The turbulence brings an asymmetrical flow condition at the impeller suction area, which can intensify pressure pulsation and hydro-induced vibration. In order to reduce the turbulence, two modifications on the elbow inlet tube are investigated in this study. A specially designed vane is deployed inside the inlet tube in the MOD1, and the MOD2 is added with two splitter vanes on the basis of the MOD1. The turbulent flow in the elbow inlet tube can be reordered as it is controlled by the vanes. The difference on pump performances that the inlet vane has made is specifically simulated and compared. The flow fields of the inlet tube influenced by the vane is also investigated on the vortex distribution and velocity vector distribution. The MOD1 has a generally smaller pressure fluctuation amplitude than the prototype in the impeller inlet area while the pressure fluctuation amplitude of the MOD2 in the impeller inlet area is stronger than the prototype. It is considered as a consequence of multiple effects, which are, the rise of velocity because of flow area replacement by the vanes making the flow field less stable as well as the wake flow induced by the vanes increasing the instability of the flow field. Therefore, although the flat vanes can help adjusting the flow field, their negative influences also act in the opposite way. It is worthwhile to find the balance between the benefits and the costs in flow field stability of installing adjusting vanes. The selection of parameter, number and installation position needs to be further investigated. The numerical results of the MOD1 are also validated through experimental investigations.
Theoretical and Numerical Studies on the Performance of Shock Vector Control
Authors: Wu Kexin , Kim HeuyDong 
Published: November 2019

Abstract
The transverse injection into a supersonic flow is a significant application that appeared in numerous aerodynamic applications, such as drag reduction and fluidic thrust vectoring control. Nowadays, fluidic thrust vector control is gradually replacing mechanical thrust vector control to redirect various air vehicles. Shock vector control is very popular in fluidic thrust vector control field due to lots of advantages, such as simple structure, more integrated control effect, and quick vectoring response. In present works, numerical simulations and theoretical analyses were conducted to investigate the shock vectoring performance in a three-dimensional rectangular nozzle. To validate the reliability and accuracy of the present numerical methodology, static pressure distributions along upper and lower nozzle surfaces in the symmetry plane were compared with experimental data published by NASA. It was evident that present numerical results present great approximations with experimental data. Control variables of the slot injector were studied, which not only include slot length and slot width but also contain uniform mass flow ratio and injection pressure ratio. Performance variations were illustrated clearly, such as static pressure distributions along upper and lower nozzle surfaces, deflection angle, resultant thrust coefficient, and thrust efficiency. Useful conclusions were obtained for further investigations on shock vector control.
Experimental Investigations of a Comb-Like Film Cooling Scheme
Authors: Li Hao-Ming , Ghaly Wahid , Hassan Ibrahim 
Published: November 2019

Abstract
The performance of a simple slot is perfect, but it does not have structural integrity. A new advanced cooling scheme with perfect performance and practical structural integrity is presented. Based on the crucial effect of the counter-rotating vortex pair (CRVP) on the film cooling effectiveness (η), the new scheme is composed of a comb-like structure and a blind slot, in which the comb structure maintains the mechanical strength, and the blind slot is intended to eliminate the CRVP and produce a smooth coolant film. The new scheme is investigated experimentally with the transient thermochromic liquid crystal (TLC) technique. Two classic geometries, the cylindrical hole and the simple slot, were also measured. The agreement of their results with the published data validated the present experimental facilities. The experimental results of the Comb scheme demonstrated that, with practical structural integrity, the new scheme has perfect performance, which bears comparison with the simple slot. Consequently, the success of the Comb scheme proved the crucial CRVP effect on η.
Experimental Study of Thermal Performance and Flow Behaviour With Winglets Vortex Generators in a Circular Tube
Authors: Nurizki A. , Islam Md. , Alam Md. 
Published: November 2019

Abstract
Vortex generator (VG) is one of the passive techniques which could improve the heat transfer with relatively low pressure drop. Vortex generators create streamwise longitudinal vortices which does not decay until far downstream that leads to have higher heat transfer with a lower pressure drop. The objectives of this experiment were to study the heat transfer and flow characteristics of fully developed turbulent flow due to different arrangement of VGs in a tube. The experiments were performed by using delta winglet vortex generators in a 52 mm circular copper tube. The flow regime varied from 6000 to 27000 Reynolds number. Four vortex generators with 45° angle of attack were used inside the circular tube. Different parameters of the VGs studied in this experiment such as lengths (L = 10, 15, and 20 mm) and arrangements (R = 0° to −15°). The results indicate that the length affected friction factor (f) and Nusselt number (Nu) significantly. L20 reached the highest f and Nu. The staggered arrangement concludes a significant drop on friction factor and a significant increase on Nusselt number. Consequently, the thermal performance of all staggered arrangement cases could reach a significant rise compared to the inline arrangement. The oil flow visualization could track down the trace of vortex behind the VG. The inline arrangement showed a strong vortex formed as a result of VG which was related to higher f while the staggered arrangement indicated a weak vortex.
Numerical Method for Studying Bearing Gap Pressure Wave Development and Subsequent Performance Mapping of Externally Pressurized Gas Journal Bearings
Authors: Lawrence Tom M. , Kemple Marvin D. 
Published: November 2019

Abstract
In previous work, numerical methods were developed to determine the pressure waves (pressure distribution) in the bearing gap of round externally pressurized gas bearings (EPB’s) that were pressurized through porous liners (PL bearings) or through liners with rows of feedholes (FH bearings). When integrated and differentiated these pressure portraits yield the net hydrodynamic force (FH) between the shaft and the bushing and the mass flow rates through the bearing gap. These results successfully replicated force-deflection curves and mass flow rate data for experimentally tested prototype FH and PL bearings over a wide range of mass flow constriction and clearances. Subsequently the numerical study was expanded to a broader design space of clearance and mass flow compensation. Also, a bearing performance mapping method of mapping the normalized bearing load over the clearance-eccentric deflection plane was developed for different levels of mass compensation. These performance maps produced a very interesting result as they indicated certain areas in the design space of FH bearings where static instability (negative stiffness) would be encountered. This static instability was not observed in the experimental data but is noted in references as known to occur in practice. Because this numerical method is based on the development of pressure wave portraits, the FH pressure wave could then be “dissected” in the areas of the onset of static instability which gave much insight as to the possible causes of static instability. This initial work, then, was perhaps the first to predict where in design space static instability would occur and yield some insight via examination of the corresponding pressure waves as to the cause. The numeric techniques developed, however are in no way limited to non-rotating bearings but are extensible to rotating bearings. The method is also easily extensible to examination of any configuration of feedholes or orifices. Nor is it limited to parallel deflections but can yield results for unbalanced loads. The method is also not limited to round bearings but can be applied to any cross-section configuration of bearing gap cross section such as a 3 lobed bearing or a slotted 3 lobed bearing. Examination of the resulting pressure wave development patterns for different scenarios can be examined to garner insight as to the causes of differing performance that can be applied to alterations towards optimization. Thus sharing in detail the developed numerical method underlying these studies seems worthwhile.
Experimental Study on the Friction Drag Reduction of Hydrogel Paint in a Boundary Layer on Flat Plate
Authors: Takagi Youhei , Hino Takanori , Nishimura Masanari , Aso Hiromi 
Published: November 2019

Abstract
The drag reduction effect of hydrogel paint was experimentally investigated with the resistance test in a circular water tank. The hydrogel and non-hydrogel paints were coated on the 1.7-meters flat plate and the total drag force was measured with a one-component force meter up to the middle Reynolds number of 1.5 × 106. The attachment of turbulence stimulator at the leading edge on the plate was also considered. The remarkable drag reduction was observed at the low Reynolds number of laminar-turbulent transition region and the hydrodynamic mechanism of its drag reduction was discussed.