bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental transient cavitation bubbles in a conical-frustum shaped tube
Authors: Wang Zhichao , Liu Shuhong , Zuo Zhigang , Pan Zhao 
Published: May 2022

Abstract
Extreme flow acceleration in the water can induce large cavitation bubbles in the hydraulic machinery, and cause liquid column separations in the pipeline. The abrupt collapse of these large bubbles produces strong pressure oscillation and causes catastrophic destruction instantaneously. Considering the complexity of the shapes of pipelines in engineering, we experimentally study the transient bubble dynamics in a conical-frustum shaped tube by a modified tube-arrest method in the present paper. Three shapes of cavitation bubbles are observed during the transient processes: (A) conical-frustum shaped bubbles originated from the bottom; (B) hemispherical bubbles originated from the side wall; (C) conical-frustum shaped bubbles originated from the liquid bulk. It is seen that the locations of the cavitation bubbles strongly depend on the geometries and the surface roughness of the tube, and the nucleation status of the bulk liquid.
Investigation on axial thrust behavior of balance piston system for a rocket pump
Authors: Sakai Kento , Iwase Bungo , Matsumoto Keisuke , Miyagawa Kazuyoshi , Kawasaki Satoshi 
Published: May 2022

Abstract
High stability in axial direction is required for rocket pumps operated under extremely low-temperature and high-pressure conditions, turbopumps therefore uses balance piston (BP) system for balancing their axial thrust. The BP system is stable under quasi-static conditions. However, BP system might become dynamically unstable under some condition. Thus it is fundamental for stability evaluation of turbopumps to predict static/dynamic characteristics in axial direction of BP system. Furthermore, we focus on characteristic change by cavitation which often occurs in the pump inlet. In this paper, an experimental study of a model turbopump which had an unshrouded impeller equipped with BP system was carried out. We experimented it with an active magnetic bearing (AMB) test facility in order forcibly to oscillate it with an optional amplitude and frequency. In addition, we examined characteristics of BP system by three-dimensional computational fluid dynamics (3D-CFD) simulations. The results of 3D-CFD simulations were in good agreement with these tendency of BP system, and were effective in predicting its static/dynamic characteristics. Some cases showed that dynamic characteristic of BP system became unstable by growth of cavitation, therefore we suggest that the influence of cavitation must also be considered in the design of turbopump.
Numerical characterization of turbine blade dynamic properties via proper orthogonal decomposition
Authors: Kang S , Kim Y , Song D , Cho H , Shin S 
Published: May 2022

Abstract
Forced vibration analysis is an essential process during the design of a turbine blade and requires enormous computational expense because of its complicated numerical procedures with large size matrices. This paper focuses on the application of the proper orthogonal decomposition (POD). It is under the spotlight for its usefulness on the reduced order model (ROM) construction. POD applications include nonlinear static, modal analysis, and forced vibration (harmonic response) analysis of the turbine blade. Performance of POD-ROM is examined for various operating conditions, and effect of the number of POD modes used is also investigated. With the sufficient number of POD modes, accurate results of turbine blade response are obtained with drastically reduced computational resources.
Motion analysis of a power unit moored with a cable for tidal power generation (2D calculation considering fluid forces acting on the unit and cable)
Authors: Nakanishi Y , Funami Y , Yano T 
Published: May 2022

Abstract
The power unit with counter-rotating propellors has been proposed for a tidal power generation. The unit has the potential to be moored with a cable because of inherent equilibrium of the rotational moments acting on the counter-rotating propellors. On the other hand, the flow condition of a tidal current is not steady, therefore, the motion and the posture of the power unit should be investigated for the stability of the power generation in terms of the fluid dynamics. In this study, the two-dimensional motion of the power unit and the cable modelled with rigid elements connected each other with pivots are analyzed as the combination of translational and rotational motions with the constraint of the connected elements. The time-dependent position, angle and relative velocity of each calculation element were obtained to validate the usefulness of the proposed method.
Power augmentation in H-Type Darrieus wind turbine using wind lens
Authors: Verma Shalini , Mansi  , Paul Akshoy Ranjan 
Published: May 2022

Abstract
The need for clean, sustainable and cost-effective energy sources leads to the installation of wind turbines with advanced technologies. One of the main parameters which govern the productivity of any wind turbine is its power generation capacity. The higher the incoming wind speed, the more the power generation, but the challenges faced by wind turbine is in low wind speeds. Hence, it becomes important to boost the efficiency of wind turbine with modified designs for lower wind urban regions. The prime objective is to boost the power production of a conventional two-bladed VAWT with the application of convergent-divergent type wind lens. Ansys CFX is employed for numerical analysis of flow around the rotor of straight bladed H-Darrieus turbine. Different turbulence models are analysed and SST k-ω model is well validated with experimental result. Power coefficient values are evaluated at a range of 0.5 to 3 tip speed ratios in both cases. Simulation result is validated with experimental results in terms of power coefficient. Computational result is validated with 4% error and 2% error for simple VAWT and VAWT with wind lens respectively. The results show an enhancement of 2.6 times the power coefficient values of conventional VAWT.
Influence of blade leading edge shape on hydraulic and suction performance of a mixed-flow pump
Authors: Kim Yong-In , Yang Hyeon-Mo , Lee Kyoung-Yong , Choi Young-Seok 
Published: May 2022

Abstract
The shape of the blade leading edge (LE) is a design variable that cannot theoretically affect the inlet flow characteristics under the definition of the velocity triangle. However, the LE is the first to encounter the working fluid in terms of streamwise direction. Depending on its shape, not only the local flow characteristics but also the performance can be affected. In this study, a numerical analysis of the hydraulic and suction performance for a mixed-flow pump was performed with different shapes of the blade LE. The blade was prepared with four sets according to the ellipse ratio (ER), including a square (ER=0), round (1), elliptic (2), and parabolic (5) shape. As the shape of the blade LE was square, the flow streamline was immediately separated from the blade surface, showing a significant drop in the hydraulic performance. As the blade LE was designed in a round, elliptic, or parabolic shape instead of a square shape, the hydraulic performance did not show a noticeable difference. On the other hand, in the prediction of suction performance, the square LE obtained the best characteristics. As the LE shape gradually became a parabolic shape, the cavity blockage was reduced, and the suction performance was also improved.
A numerical investigation of cryogenic cavitation flow in LNG submerged pump
Authors: Suh Jun-Won , Yang Hyeon-Mo , Lee Kyoung-Yong , Hong Jin-Hee , Choi Young-Seok 
Published: May 2022

Abstract
The cryogenic centrifugal submersible pump is one of the core equipment of the technology and serves to pressurize and transport the fluid with the centrifugal force generated from the impeller by rotation. Due to the structural characteristics of the working fluid and multi-stage, problems such as cavitation and axial thrust negatively affect the life, noise, vibration, and performance of the pump, so it must be considered. For this reason, this research aimed to investigate a low-pressure LNG pump for an LNG fuel supply system with a general specific speed. The main components were designed based on the previous studies and CFturbo. The numerical analysis method was established and the performance prediction was conducted using commercial CFD packages. The three-dimensional Reynolds-averaged Navier-Stokes equations were discretized to analyze the internal flow field. First, the reliability of the turbulence model was proved through Hord’s experiment in the 0.357-inch ogive. Second, the steady and unsteady simulations were conducted between the single-passage and full-passage conditions in the inducer. Third, the corresponding analysis was investigated to identify problems with existing model features and find improvement directions.
Effect of diffuser vane slit on rotating stall behavior and pump performance in a centrifugal pump
Authors: Takao Shunya , Konno Shinichi , Ejiri Shinichiro , Miyabe Masahiro 
Published: May 2022

Abstract
In the previous study of a centrifugal pump with a vaned diffuser, it was confirmed that the flowrate at the onset of rotating stall was shifted to the lower flowrate by slitting the diffuser vanes. As the CFD result, it was found that the jet flow from pressure-side to suction-side impinges backflow near the suction surface and it suppresses to expand toward the diffuser inlet. However, it is difficult to say that the optimized shape and slitting position have been sufficiently studied. Therefore, in this study, we investigated the effect of slitting on the pump performance and internal flow by adding another slitting to the diffuser vane with slit. In order to clarify the suppression effect of the jet flow in detail, the effect of adding slits at two locations was verified. The pump performance was compared for these diffusers. The effect of slitting on the diffuser vanes on the occurrence of rotating stall was clarified by the experimental and numerical study.
A study of counter-rotating impulse turbine for wave energy conversion-effect of middle vane thickness on the performance-
Authors: Ogawa T , Takao M , Alam M M A , Okuhara S , Kinoue Y 
Published: May 2022

Abstract
In an oscillating water column (OWC) based wave energy device, a water column that oscillates due to the sea wave motion generates a bi-directional airflow in an air chamber, and finally, the bi-directional airflow driven air turbine converts the pneumatic energy into mechanical energy. The counter-rotating impulse turbine for bi-directional airflow has been proposed by M. E. McCormick of the United States Naval Academy in 1978. In a previous study, the authors investigated the effect of the turbine geometry on the performance of a counter-rotating impulse turbine for bi-directional airflow, and it was clarified that the efficiency of the turbine is higher than an impulse turbine with a single rotor for bi-directional airflow in a range of high flow coefficient. Moreover, this impulse turbine has a disadvantage that the efficiency in a range of low flow coefficient is remarkably low due to the deterioration of the flow between the two rotors. In this study, in order to make the counter-rotating impulse turbine practically compatible, the thickness of the middle vanes installed between the two rotors was changed, and the effect of the thickness on the turbine performance was investigated by the computational fluid dynamics (CFD) analysis. As a result, it was found that the efficiency of the counter-rotating impulse turbine with middle vanes increases as the thickness of the middle vanes decreased.
Analysis of an optimized radial impulse turbine for an OWC wave energy converter
Authors: Saad Mina , García-Diaz Manuel , Pereiras Bruno 
Published: May 2022

Abstract
OWC concept is one of the most spread technologies among wave energy converters due to several reasons. However, this technology has always deal with the problem of the inherent bidirectional flow. Many solutions have been adopted such as a flow rectification system combined with a unidirectional turbine, several types of bidirectional turbines such as Wells turbine or impulse turbine. In this work, it is shown the performance of an optimized geometry for a radial impulse turbine, which improvement is based on the re-designing of the blades and settling angles of the vanes. A CFD model, validated against results from the bibliography, has been used to simulate both a new and a previous geometry taken as reference. The results of both turbines have been analysed in terms of the loss coefficients for each element in order to analyse the advantages of the new geometry. It has been found that the new geometry exceeds the efficiency of the previous geometry by 5%, being this gain based on the fact that sacrificing the rotor’s efficiency could lead to a great improvement in the performance of the guide vanes, reducing their loss and, in turn, lifting the turbine’s efficiency despite reducing the rotor’s one.
Effect of adding ceramic thermal barrier coating on the turbocharger efficiency, external and internal heat transfer
Authors: Mohammad Mahadhir , Chiong Meng Soon , Tan Feng Xian , Rajoo Srithar , Md Sah Muhammad Hanafi 
Published: May 2022

Abstract
Turbocharger is a device installed on an internal combustion engine to boost its thermal efficiency. A turbocharger consists of three main components, namely the turbine, central housing, and compressor. The common material for commercial turbine housing is cast iron, for its lower cost yet resilience at elevated temperature. Given the high exhaust temperature a turbocharger is exposed to, energy loss in the form of heat transfer is inevitable. It is known to H turbine efficiency by up to 30%. This research aims to determine the turbocharger efficiency in the presence of thermal barrier coating (TBC) on the inner surface of turbine volute. Particularly, this work will focus on the internal and external heat transfer of the turbine and its impact on efficiency. The subject turbocharger is a commercial single-scroll vaneless unit commonly used in gasoline passenger vehicle. Yttria-Stabilized Zirconia (YSZ) is chosen as the TBC material, due to high melting point (around 2700°C), good thermal insulation property and very low thermal expansion compared to other ceramic materials. The YSZ was applied to the inner surface of turbine volute via plasma coating technique. However, due to the large disparity in thermal expansion between YSZ and cast iron, the TBC is prone to cracking at elevated exhaust temperature. Thus, an Inconel 718 turbine housing, with closer thermal expansion to YSZ, was refabricated for the use of this study The turbocharger performance was experimentally measured on the LoCARtic turbocharger gas stand. The turbine inlet temperature (TIT) was varied at 150, 350, 550, 650 and 750°C, while the compressor operating condition was maintained throughout the testing for equivalent comparison. From the result, the turbocharger efficiency drops when TIT is increased, and the turbine pressure ratio becomes lower. Overall, the external heat transfer loss is found to reduce 7% to 40% and no significant difference noticed on the internal heat transfer.
Research on the application of ADN propulsion module for satellites
Authors: Ji Jialong , Liu Guoxi , Fang Zhongjian , Song Fei 
Published: May 2022

Abstract
The novel technology of the liquid Ammonium Dinitramide(ADN) propulsion is researched for its higher working performance and safer characteristics. Based on the safe performance, the design of ADN propulsion system for satellites is also presented in this paper. At the same time, the research on ADN propulsion system module is presented in this paper, including the developing processes method, the interface analysis, and the assemblage in satellites. Two examples are described here besides an ADN propulsion module applied in orbit. From the research we can know that ADN propulsion technology is fit for satellites, and the modularization of ADN propulsion system is a better developing mode for small satellites, which can simplify the developing process of propulsion system and crafts. In the end, the further application object and further work of ADN propulsion module for satellites is stated.
Evaluation of the multiple sensor optical fiber probe methods for the measurement of local bubble parameters accordng to bubble shape
Authors: Moon Jeongmin , Kim Taeho , Jeong Jae Jun , Yun Byongjo 
Published: May 2022

Abstract
It is necessary to evaluate a multiple sensor probe methods according to the bubble shape for the measurement of local bubble parameters. For this, numerical simulation and air-water benchmark experiments were performed with the double-sensor and four-sensor probes. It was found that the velocity measurement errors of the probes were 5.3% and 4.2%, respectively. In terms of Sauter mean diameter (D
32), its measurement performance is affected by the type of the probe and bubble shape. The double-sensor probe showed reasonable measurement accurancy of the D
32 for the spherical shape bubble. However, as the bubble shape is distorted from the sphere, the D32 measurement error increases. The four-sensor probe has a relatively large error compared to that of the double sensor probe under the bubbly flow with small size. While, when the D
32 is larger than 2 mm, the four sensor probe shows excellent measurement performance regardless of the bubble shape.
Characteristics of non-equilibrium condensing flow in three-dimensional supersonic rectangular nozzles
Authors: Haque S , Matsuo S , Kaeriyama H 
Published: May 2022

Abstract
Fluid flow inside a supersonic nozzle with a rectangular cross-section induces secondary flow due to the shape of the upper wall curvature. The secondary flow forms longitudinal vortices near the wall of the nozzle corner which destabilizes the nozzle outlet flow due to the early transition of the flow from laminar to turbulent. It is known that non-equilibrium homogeneous condensation occurs in a supersonic rectangular nozzle due to the rapid expansion of the condensable fluid with large latent heat such as water vapor. Homogeneous condensation takes place through the formation of water nuclei from its vapor when foreign nuclei are absent in the flow. The irreversibility of the non-equilibrium condensation process causes loss in flow transportation energy in the form of total pressure loss. Although numerous researches have been conducted about the effect of non-equilibrium condensation process in supersonic nozzles, however, the interactions between nozzle shape, non-equilibrium condensation, and longitudinal vortices have not been studied convincingly. Therefore, numerical simulations have been carried out for two supersonic three-dimensional rectangular nozzles in order to understand the effect of nozzle shape and non-equilibrium condensation on the longitudinal vortices at the nozzle corner. Furthermore, total pressure distribution in the nozzle was analysed to understand the effect of degree of supersaturation and expansion rate on the total pressure loss. In this research, characteristics of simulated flow fields including total pressure loss were in good agreement with the published literature.
Design and Simulation Analysis of Wide-range Current Transformer with Adaptively Adjustable Air Gap Length
Authors: Lu Bing , Chen Xiwen , Xu Zhongda , Nie Gaoning , Tang Xiaojun 
Published: May 2022

Abstract
This paper proposes a wide-range current transformer structure with adaptively adjustable air gap length. The length of the air gap of the iron core of this structure can be automatically adjusted with the current harmonic ratio of the secondary side of the current transformer, so that the current transformer has good anti-saturation characteristics; on the other hand, the output voltage value of the detection winding can be adjusted after proportional calculation. The secondary side current is compensated to ensure the accuracy of its measurement. At the end of the article, the structure of the current transformer is simulated and analyzed. The calculation results show that the measurement error of the secondary side current after compensation can reach the design requirements of the 0.2-level standard current transformer during the change of the primary current from 100% to 350%. This structure can effectively broaden the range of the current transformer and improve its measurement accuracy.
Matched Interface and Boundary Method for the Helmholtz Equation with a Discretization by 4th-order 17-point FD Scheme
Authors: Zhu Xiaoling , Cheng Dongsheng , Long Guangqing 
Published: May 2022

Abstract
We generalize the MIB (matched interface and boundary) method for solving the Helmholtz equation with a rotated 17-point 4th-order FD(finite difference) scheme, which is non-compact, and has to use the points outside of the computational region. An optimal combination of difference schemes are employed to discretize the Helmholtz equation both on the standard coordinate system and the 45° rotated one. The combination weights are obtained via minimizing the numerical dispersion. Numerical experiments show that the rotated 17-point FD scheme with the MIB method is 4th-order in accuracy, and is effective in supressing numerical dispersion.
Effect of Gap and Diameter Ratio on Vortex-induced Forces for Cylinders in Tandem at Re=100
Authors: Annapeh H F , Kurushina V 
Published: May 2022

Abstract
The article investigates fluctuations of the vortex-induced loads related to the effects of gap and diameter ratio on the mean drag and lift coefficients of the downstream cylinder, when two circular stationary cylinders of different diameters are arranged in a tandem configuration. The study is performed with the method of computational fluid dynamics for the low Reynolds number of 100. The benchmarking of the numerical model is followed by the parametric investigation with the variation of: a) the ratio of diameters of the upstream to downstream cylinder (d/D), in order to observe the effects associated with relative sizes of structures; b) the gap-to-diameter ratio (G/D), in order to observe the combined effects of varying these geometrical quantities. The results demonstrate a rapid change in the mean drag and lift coefficient values at the gap-to-diameter ratio between 2.0 and 3.0 at the diameter ratios of 0.7 and 1.0.
Solitary Wave Solutions for a Generalized KdV Equation with High Power Nonlinearities
Authors: Wu Rui , Cheng Qian , Xu Yinan , Zhu Minting , Yan Yongsheng , Li Rui , Zhang Xiao , Shen Wanqing 
Published: May 2022

Abstract
In current paper, a generalized KdV equation with high order nonlinearities has been investigated by the expansion and the ansatz method. The obtained solutions can be classified as periodic soliton solution, kink solution, triangular soliton solution, Bell-shaped soliton solution and multi-soliton solution. Finally, by selecting some appropriate parameters, the results are demonstrated graphically that can be applied to describe the real world phenomenon.
2010 MSC: 35C07, 35C08, 35G20, 35Q53.