bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Accurate Thermal Measurement Approach for Determining Fan Efficiencies Based on System Identification
Authors: aus der Wiesche Stefan , Reinker Felix , Wagner Robert , Epple Philipp , Fritsche Manuel , Russwurm Hans Jörg 
Published: November 2019

Abstract
A novel thermal measurement approach is presented for the determination of fan efficiencies. This approach is not resting on a simple direct measurement of the occurring temperature difference but on a system identification based on the transient time signal of the involved temperature measurement device. The values of the system parameters can be identified after recording the transient response of the system to a step input, i. e. the fan is suddenly turned on. By means of a representative case study considering a centrifugal fan, the system identification and its relation to fan efficiency are presented. The outcome of the new thermal approach is compared with results of standardized fan performance tests and with results obtained by the direct temperature measurement method without system identification. It is shown that the direct temperature measurement provides typically poor data whereas the novel thermal approach leads to results which are well comparable with these obtained by standard performance test at the design point.
An Experimental Study of Horizontal Axis Wind Turbine Performance in Artificial Natural Wind by an Active Control Multi-Fan Turbulent Wind Tunnel
Authors: Toshimitsu Kazuhiko , Matsubara Hiroyuki , Kikuchi Haruka , Parnravee Porntisarn 
Published: November 2019

Abstract
Recent developments in wind turbine design research account for the effects of velocity fluctuation and the characteristic turbulence of the installation location site to improve performance. For the design, a low-cost natural wind generator and a laboratory-based performance evaluation of the wind turbine are useful. This paper describes a new actively controlled multi-fan wind tunnel that generates natural wind at a reduced cost. The driving section of its wind tunnel has 100 PC cooling fans that are controlled by an original embedded system. The fluctuating velocity wind is successfully generated with a mean velocity 7m/s, turbulent intensity 2% and turbulent integral scale 5 m, 10 m, 20 m, based on Karman’s power spectrum density function. In particular, the wind satisfies the Kolmogorov’s −5/3 multiplication rule of inertial subrange with the frequency range 0.01∼2.0 Hz. Furthermore, the performance of a wind turbine in steady and natural winds can be investigated. From the results, it is made clear that integral scale has a large effect on the wind turbine performance. The maximum power coefficient in natural wind of the integral scale 5 m and 10m is 124% larger than one of steady wind with the same mean velocity 7 m/s.
Impacts of Storm Surges on Hydrodynamics and Salinity of Sabine Lake and Sabine River Diversion Canal
Authors: Wang Hairui , Zhang Ning 
Published: November 2019

Abstract
In this study, a hydrodynamic and salinity transport model was developed for simulations of Sabine Lake water system located on the Texas-Louisiana border. The target simulation area ranges from Sabine River near Deweyville, TX as the north boundary to the Gulf of Mexico as the south boundary, and from Neches River near Beaumont, TX as the west boundary to part of Gulf Intracoastal Waterway (GIWW) and Sabine River Diversion Canal (SRDC) as the east boundary. The entire area includes several major water bodies, such as Sabine Lake, Sabine River, Sabine Pass, Sabine Neches Canal (Ship Channel), and part of GIWW and SRDC. The SRDC supplies fresh water to the area industry, mainly petrochemical. High salinity in SRDC could significantly affect the daily production of the industry. The major purposes of this study is to use the validated hydrodynamic and salinity transport model to assess and predict the salinity in SRDC under severe weather conditions such as hurricane storm surges. Measurement data from NOAA and USGS were used to calibrate the boundary conditions as well as to validate the model. Two different levels of storm surges each lasting for 24 hours were simulated, 0.5 and 1 meter, respectively, and the salinity in SRDC was monitored and compared to analyze the storm surge threats on SDRC water quality. The result shows that it took about 2 days for the salinity reaching SRDC under the 1m storm surge condition and about 3 days under 0.5m surge condition and the salinity value could reach as high as 5 to 10 ppt.
Development of a Surface Flow Sensor for Measuring Turbulent Drag Force
Authors: Doh Il , Kwon Il-Bum , Chang Jiho , Chun Sejong 
Published: November 2019

Abstract
A surface flow sensor is needed if turbulent drag force is to be measured over a vehicle, such as a car, a ship, and an airplane. In case of automobile industry, there are no automobile manufacturers which measure surface flow velocity over a car for wind tunnel testing. Instead, they rely on particle image velocimetry (PIV), pressure sensitive paint (PSP), laser Doppler anemometry (LDA), pitot tubes, and tufts to get information regarding the turbulent drag force. Surface flow sensors have not devised yet.
This study aims at developing a surface flow sensor for measuring turbulent drag force over a rigid body in a wind tunnel. Two sensing schemes were designed for the fiber-optic distributed sensor and the thermal mass flow sensor. These concepts are introduced in this paper. As the first attempt, a thermal mass flow sensor has been fabricated. It was flush-mounted on the surface of a test section in the wind tunnel to measure the surface flow velocity. The thermal mass flow sensor was operated by either constant current or constant resistance modes. Resistance ratio was changed as the electric current was increased by the constant current mode, while power ratio was saturated as the resistance was increased by the constant resistance mode. Either the resistance ratio or the power ratio was changed with the flow velocity measured by a Pitot tube, located at the center of test section.
Decay of Turbulence in a Duct With Transverse Magnetic Field
Authors: Zikanov Oleg , Krasnov Dmitry , Boeck Thomas , Sukoriansky Semion 
Published: November 2019

Abstract
Decay of honeycomb-generated turbulence in a duct with a static transverse magnetic field is studied via high-resolution direct numerical simulations. The simulations follow the revealing experimental study [1], in particular the paradoxical observation of high-amplitude velocity fluctuations, which exist in the downstream portion of the flow when the strong transverse magnetic field is imposed in the entire duct including the honeycomb exit, but not in other configurations. It is shown that the fluctuations are caused by the large-scale quasi-two-dimensional structures forming in the flow at the initial stages of the decay and surviving the magnetic suppression. Statistical turbulence properties, such as the energy decay curves, two-point correlations and typical length scales are computed. The study demonstrates that turbulence decay in the presence of a magnetic field is a complex phenomenon critically depending on the state of the flow at the moment the field is introduced.
A New Immersed Stress Method Based on Volume Average
Authors: Fukada Toshiaki , Takeuchi Shintaro , Kajishima Takeo 
Published: November 2019

Abstract
Based on the volume-averaged equations for fluid-solid two-phase flow, an immersed stress method (ISM) is proposed to compute the fluid-solid interaction. As the averaging volume is explicitly defined, the reaction force on the fluid from the solid is related to the surface stress. The size of the averaging volume is comparable to the grid width to capture the flow structure in the grid scale. The reaction force based on the surface stress is computed by assuming the distributions of the velocity and the pressure. Applying the ISM to flows around a particle larger than the grid scale, the drag and lift forces are reasonably represented by computing the surface stress distribution by the ISM.
Wake Characteristics Comparison Between Isolated and Pair Configurations of Marine Hydrokinetic Crossflow Turbines at Low Reynolds Numbers
Authors: Alayeto Iván Hernández , Doan Minh Nhat , Kumazawa Kana , Obi Shinnosuke 
Published: November 2019

Abstract
Wake characteristics and power coefficient of laboratory scaled marine hydrokinetic cross flow turbines were studied both experimentally and numerically. Single and turbine pair configurations were experimentally tested in a 3.5 m long, 0.3 m wide and 0.15 m deep water channel facility. Each turbine was built with three straight NACA0012 blades with chord 2.54 cm and 6.828 cm diameter, corresponding to a solidity of 1.2. The Reynolds number associated with the velocity given by the water pump and blade chord oscillated near 7000. Empirical power measurement was obtained multiplying the average torque by average rotational velocity. These measurements were obtained with a magnetic hysteresis brake utilized as control system and a Hall effect sensor used as speed transducer, respectively. Wake velocity profile was obtained by image processing of Particle Image Velocimetry (PIV) measurements at different positions. The empirical results were contrasted with numerical computational fluid dynamics (CFD) simulations carried out with Salome and OpenFoam. The computational model solved the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations in 2 dimensions using the turbulence models k-ω Shear Stress Transport (SST) and Spallart-Allmaras (SA). The experimental and numerical results show a clear difference of power coefficient and wake shape for both turbine configurations. This influence of two nearby blades on the flow can be exploited to obtain higher ratios of power per land area, leading to an increase of the overall generation of a power plant by a careful arrangement.
Multi-Objective Hydraulic Optimization on Intake Duct of Water-Jet Propulsion Using NSGA-II
Authors: Zhu Rui , Cao Puyu , Wang Yang , Ning Chao 
Published: November 2019

Abstract
Flow distortions occur at the outlet section of the intake duct owing to its shape properties, which is a component of water-jet propulsion. Since the noticeable influence of intake’s flow characteristics upon propulsive efficiency, it’s necessary to focus on intake duct redesign. In this paper, a systematic methodology for reducing flow distortions and power losses within the intake duct through a shape optimization process was obtained. In addition, the mechanism of flow distortions was also developed.
The flush type inlet applied in the marine vessel with the speed of 30 knots was chosen as research project. Four characteristic parameters were set as optimization variables depending on the geometrical relationship of thirteen characteristic parameters referred to the duct longitudinal midsection, which were the ramp angle α, the radius of the upper lip R3, the radius of the lower lip R4 and the lip height h respectively.
Subsequently, a sample space was built by Latin Hypercube Sampling (LHS) and the parameters were normalized in the range of 0 to 1. With the commercial software CFX, the numerical simulation was accomplished driven by SST k-ω turbulence model. Multi-objective optimization based on the Non-Dominated Sorting Genetic Algorithm II (NSGA-II) was utilized to minimize the non-uniformity at outlet section and maximize the minimal pressure at lip simultaneously. Moreover, the Radial Basis Function (RBF) neural network was employed to approximate the functional relationship between variables and objectives, which could be applied in the NSGA-II to get the Pareto Front.
The minimum non-uniformity point and the trade-off point (The point both satisfies the minimum non-uniformity and the maximum minimal pressure at lip strategically) were selected from the Pareto Front. With regard to the characteristic parameters of the trade-off point, the ramp angle, the radius of the upper lip, the radius of the lower lip and the lip height are 31.91°, 11.42 mm, 400.97 mm and 55.43 mm respectively.
Meanwhile, the characteristic parameters of the minimum non-uniformity point are 30.22°, 25.59 mm, 166.65 mm and 89.90 mm respectively. Ultimately, the duct outflow characteristics of prototype and optimization are compared. In terms of the trade-off point, the minimal pressure at lip increases 66.40% to −24488.93 Pa and the non-uniformity has a drop of 4.56% to 0.1571. The non-uniformity of the minimum point is 0.1481 which is reduced by 10.02%. Through the optimization of duct shape, the secondary flow (Dean vortices) is suppressed effectively. This paper is expected to provide a better comprehension of the flow field within the intake duct of water-jet propulsion.
Numerical Simulation of a Gas Bubble Rising in Power-Law Fluids Using a Sharp Surface Force Implementation
Authors: Kumar Purushotam , Jin Kai , Vanka Surya Pratap 
Published: November 2019

Abstract
In this paper, we have applied a recently-developed numerical technique to study the three-dimensional dynamics of a confined air bubble rising in shear thinning and shear-thickening power-law fluids. The method is a blend of Volume of Fluid and Level Set methods and incorporates a Sharp Surface Force Method (SSF) for surface tension forces by solving a second Pressure Poisson Equation (PPE). The gas-liquid interface is captured by an equation for the liquid volume fraction and advected using the geometry reconstruction method. The interface normal and curvature are computed using level-set and height function methods. The accurate representation of the interface and interfacial forces significantly suppressed the spurious velocities commonly observed with conventional volume of fluid method and the Continuum Surface Force (CSF). The algorithm is implemented in a in-house code called CUFLOW and runs on multiple GPUs platform.
We explored the effects of fluid rheology, Bond number, and wall confinement on bubble’s transient shape, rise velocity, rise path, and generated vortex structures. The power-law index is varied from 0.25 to 1.50 covering shear-thinning and shear-thickening regimes. Three Bond numbers (Bo = 2, 10 and 50) and three confinement ratios (Cr = 4, 6 and 8) are considered, and their impacts on bubble’s dynamics are analyzed. For the range of parameters examined here, bubble motion in a shear-thinning fluid is seen to be unsteady with significant shape oscillations. The bubble rises with a secondary motion in the cross-sectional plane along with its primary vertical rise. However, in the Newtonian and shear-thickening fluids, the bubble’s shape is seen to reach a steady-state in a relatively short time and rise with only minor deviations from the vertical path.
Experimental Investigation of Turbulent Cavitating Flows in a Small Venturi Nozzle
Authors: Zhang Guangjian , Khlifa Ilyass , Coutier-Delgosha Olivier 
Published: November 2019

Abstract
The cavitating flows created in a small Venturi tube with throat cross section 4 × 15.34 mm2 are investigated based on ultra-fast x-ray imaging. The instantaneous velocities of the liquid and vapor are measured simultaneously by tracking seeding particles and vapor structures respectively while the vapor volume fraction is derived from the different x-ray attenuation. Wavelet decomposition with appropriate thresholds is used to separate seeding particles from vapor structures, so that image cross-correlations could be applied on the two phases separately. This study presents data on mean velocity and void ratio field, statistical turbulent quantities in three different cavitation levels with the same reference velocity. A type of cavitation associated with a weak but persistent re-entrant jet is described. The comparison between the cavitation and the noncavitating flow shows that the averaged flow field is significantly altered by the presence of cavitation and the vapor formation near the throat area is observed to suppress velocity fluctuations.
Effect of Interface Condition on the Hydraulic Performance of a Pump-Turbine at Various Guide Vane Opening Conditions in Pumping Mode
Authors: Suh Jun-Won , Kim Seung-Jun , Choi Young-Seok , Kim Jin-Hyuk , Joo Won-Gu , Park Jungwan 
Published: November 2019

Abstract
Nowadays, pumped-storage power stations require high flexibility and reliability in operation under off-design conditions, especially in the pump mode. When a pump-turbine operates under various part load conditions in pump mode, highly dynamic phenomenon such as stationary vortex and rotating stall occur. Therefore, the performance characteristics in pump mode are vital for the safe and effective operation. A number of studies have been conducted to investigate the flow characteristics in turbine or pump mode under different GVOs through numerical simulations. However, the studies about influence of the position of interface and interface condition on the pump characteristics of pump-turbines are not completely clear.
In this paper, the three-dimensional steady and unsteady Reynolds-averaged Navier–Stokes equations were solved for a detailed analysis of the influence of interface conditions with various guide vane opening conditions in pump mode. To ensure the reliability of the numerical analysis, the numerical results were validated in comparison with the experimental data.
Multiphase Flow Simulation of In-Line Gas-Liquid Separator for Multiphase Metering
Authors: Seo Nakyeong , Kharoua Nabil , Khezzar Lyes , Alshehhi Mohamed , Meribout Mahmoud 
Published: November 2019

Abstract
The present study addresses itself to the performance assessment of a novel in-line gas-liquid separator. The separator is developed by FRAMES company under the name of SwirlSep based on the interaction of a swirling flow, generated by an innovative devise called swirl cage, and a hollow conical bluff body designed to deviate the gaseous phase internally.. The separator is intended to be implemented within a multiphase flow metering system in oil field gathering stations in the Gulf region. The study represents a preliminary step among a design process including elaborate lab-scale and filed tests.
The flow in the gas-liquid separator is studied using Computational Fluid Dynamics CFD. The Shear Stress Transport (SST) k-ω turbulence and Eulerian-Eulerian multiphase models, under different flow conditions, were used to simulate real flow scenarios. The scenarios were chosen to replicate flow conditions that could exist during the operation of oil wells over their lifetime with the aim to provide guidance for proper control of the separator valves. The fraction of the total flow is prescribed at each outlet, using an outflow boundary condition, to mimic the action of the control valves. At the inlet, the phase velocity and volume fraction were prescribed.
The outlet streams and their phase’s content were, then, analyzed together with the distribution of the velocity and concentration fields inside the separator. Velocity and pressure drop were found to increase with the increase of the outflow in one outlet when changing the flow split. Flow control, at the outlets, caused an increase of the oil-in-gas entrainment when trying to minimize gas-in-oil entrainment which is a non-trivial task. The effects of the flow split specified appeared downstream of the conical bluff body only when the inflow conditions were kept constant whereas the flow field remained identical upstream of the cone. A recirculation zone was generated in the annular space downstream of the cone and affected the separator performance considerably. The recirculation zone was due to the effect of the higher flow rate towards the gas outlet and disappeared when the flow rate towards the oil outlet tended to be equal or higher. The phase distribution was identical upstream of the cone and depended on the flow split downstream of the cone.
The cases considered served as an assessment of the separator performance under different multiphase flow conditions replicating realistic scenarios.
Flow Characteristics of Rectangular Liquid Jets Injected Into Low Subsonic Crossflow
Authors: Tadjfar M. , Jaberi A. , Shokri R. 
Published: November 2019

Abstract
Perpendicular injection of liquid jets into gaseous crossflow is well-known as an effective way to obtain good mixing between liquid fuel and air crossflow. Mostly, injectors with circular holes were used as the standard method of fuel spraying. However, recently a great attention to injectors with non-circular holes has emerged that aims to improve the quality of fuel mixing and consequently combustion efficiency. In the present work, rectangular injectors with different aspect ratios varying from 1 to 4 were experimentally studied. Using a wind tunnel with maximum air velocity of 42 m/s, tests were performed for a wide range of flow conditions including liquid-to-air momentum ratios of 10, 20, 30 and 40. Backlight shadowgraphy and high speed photography were employed to capture the instantaneous physics of the liquid jets discharged into gaseous crossflow. The flow physics of the rectangular liquid jets were investigated by means of flow visualizations. Different regimes of flow breakup including capillary, arcade, bag and multimode were observed for rectangular jets. Moreover, a new technique was used to calculate the trajectory of the liquid jets. It was shown the nozzle’s shape has no significant effect on jet trajectory. Also, the momentum ratio was found to has a profound effect on jet trajectory.
A New Vacuum System for Steam Plant Condenser
Authors: Hegazy Ahmed , Yousef Khaled , Engeda Abraham 
Published: November 2019

Abstract
In the current work, a simple and low energy consuming system is proposed for holding on the vacuum in the steam power plant system. In this system, vacuum is created at the tip of an inverted U-pipe through which water flows by siphon effect. The stream of water through this pipe is brought about from a reservoir to another one whose water surfaces are at certain height difference. This height difference along with the height of the inverted U-pipe tip defines the value of the vacuum that can be produced. At this tip, the U-pipe is linked to the discharge pipe of a compressor which draws a mixture of air, non-condensable gases and some water vapor from the steam condenser and raises their pressure a little higher than that of the inverted U-pipe tip so that the resistance of connecting pipe is overcome and the pressure at exit of this pipe is equal to that at the inverted U-pipe tip. The mixture flows along with the water down the inverted U-pipe till it leaves the pipe with the water. A thermodynamic and fluid flow analysis is developed for predicting the performance of the proposed system. The results of this analysis show that the right selection of the mass flow rates ratio of water flowing in the inverted U-pipe and air and water vapor mixture sucked by the compressor from the steam plant condenser, in the range of 25000, the height of the inverted U-pipe summit from the water level of the higher water tank greater than 9.2 m and the height difference of the water levels in the two water tanks small enough, in the range of 0.1m saves the power of vacuum system by 80% less than that consumed when using compressor alone for venting the steam plant condenser.