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Effects of Bulbous Bow on Cross-Flow vortex structures Around a Streamlined Submersible Body at Intermediate Pitch Maneuver： A Numerical Investigation

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Journal of Marine Science and Application 2016年第1期15卷 8-15页

作者： Saeed Abedi Ali Akbar Dehghan Ali Saeidinezhad Mojtaba Dehghan Manshadi Department of Mechanical Engineering Yazd University Yazd 89195-741 Iran Department of Mechanical and Aerospace Engineering Malek Ashtar University of Technology Esfahan 83145-115 Iran

A flow field around a streamlined body at an intermediate angle of incidence is dominated by cross-flow separation and vortical flow fields. The separated flow leads to a pair of vortices on the leeside of the body; therefore, it is essential to accurately determine this pair and estimate its size and location. This study utilizes the element-based finite volume method based on RANS equations to compute a 3D axisymmetric flow around a SUBOFF bare submarined hull. Cross-flow vortex structures are then numerically simulated and compared for a submarine with SUBOFF and DRDC STR bows. Computed results of pressure and shear stress distribution on the hull surface and the strength and locations of the vortex structures are presented at an intermediate incidence angle of 20°. A wind tunnel experiment is also conducted to experimentally visualize the vortex structures and measure their core locations. These experimental results are compared with the numerical data, and a good agreement is found.

关键词： submarine intermediate angle cross-flow separation vortex structures computational fluid dynamics (CFD) wind tunnel experiment

Investigation on the dynamic behavior of cloud cavitation around a flexible hydrofoil

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Journal of Hydrodynamics 2023年第4期35卷 712-723页

作者： Yun-qing Liu Wei Zhao Zhi Pan Zhi-pu Guo Rui Yuan Qin Wu School of Mechanical Engineering Beijing Institute of TechnologyBeijing100081China Wuhan Second Ship Design and Research Institute Wuhan430205China

The objective of this paper is to investigate the dynamic behavior of cloud cavitating flow around a flexible hydrofoil with experimental and numerical *** tightly coupled fluid-structure interaction(FSI)modeling is applied and validated with the experimental *** Q-criterion andω-criterion are applied to illustrate the interaction between the vortex structures and *** flexibility is seen to result in nose-up twist deformation,causing a reduction of the shedding frequency from an increase in the attached cavity *** to the flexibility,the fluctuation of load coefficients of the flexible hydrofoil is larger than that of the rigid ***,the re-entrant jet propagation speed of the flexible hydrofoil is greater than that of the rigid *** shed cloud cavity is observed to be uniform along the flexible hydrofoil span under the combined influence of the strong vibration and the gap flow.

关键词： Cloud cavitation fluid-structure interaction(FSI) vortex structures flexible hydrofoil

Experimental investigation of flow past a circular cylinder with hydrophobic coating

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Journal of Hydrodynamics 2018年第6期30卷 992-1000页

作者： Jun Wen Hai-bao Hu Zhuang-zhu Luo Zhao-zhu Zhang School of Marine Science and Technology Northwestern Polytechnical University Chongqing Institute of Green and Intelligent Technology Chinese Academy of Sciences State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical Physics Chinese Academy of Sciences

A series of experiments are performed in a gravitational low-speed water tunnel to investigate the influence of the hydrophobic coating on the flow past a circular cylinder. The mean velocity and turbulence intensity profiles behind the cylinders are measured using the hot-film anemometer while the separation angles are obtained with the flow visualization technology. For the Reynolds number lower than 3 800, the hydrophobic coatings are in the Cassie state, the velocity deficit and the turbulence intensity in the wake of the hydrophobic cylinders are lower than those of the smooth cylinders which implies the drag reduction effect of the hydrophobic coatings. When the Reynolds number becomes higher than 6 600, the hydrophobic coatings turn into the Wenzel state. Through decomposing the velocity data in the turbulent wake into different scales based on the orthogonal wavelet transform, it is found that the total turbulence intensity in the wake of the hydrophobic cylinders becomes almost the same as in the wake of the smooth cylinders while the intensity of the large scales of vortex components in the wake of the hydrophobic cylinders is still lower. Furthermore, the separation angles show the same trend as a function of the Reynolds number but always take smaller values for the hydrophobic cylinders.

关键词： Hydrophobic coating drag reduction vortex structures separated flows

Self-propelled swimming of a flexible fllament driven by coupled plunging and pitching motions

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Journal of Hydrodynamics 2021年第1期33卷 157-169页

作者： Bing-lin Li Yi-wei Wang Bo Yin Xiang Zhang Xing Zhang The State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China Key Laboratory for Mechanics in Fluid Solid Coupling Systems Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Science University of Chinese Academy of SciencesBeijing 100049China

This paper numerically investigates the self-propelled swimming of a flexible filament driven by coupled pitching and plunging motions at the leading *** influences of bending rigidity and some actuation parameters(including the phase offset between pitching and plunging,and the amplitudes of pitching and plunging motions)on the swimming performance are *** is found that with increasing rigidity,the swimming style gradually transits from the undulatory mode to the oscillatory *** plunging-pitching actuation is found to be superior to the plunging-only actuation,in the sense that it prevents the decrease of speed at high rigidity and achieves a higher efficiency across a wide range of *** comparison of the body kinematics with those of animal swimmers,and the classification of the wake structures are *** results of this study provide some novel insights for the bio-inspired design of autonomous underwater vehicles.

关键词： Self-propelled swimming flexible filament fluid-structure interaction(FSI) vortex structures immersed boundary method

3D Flow Past Transonic Turbine Cascade SE 1050-Experiment and Numerical Simulations

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Journal of Thermal Science 2013年第4期22卷 311-319页

作者： D.imurda J.Fürst M.Luxa Institute of Thermomechanics AS CR v.v.i.Dolejskova 1402/5 Prague Czech Republic CTU in Prague Faculty of Mechanical Engineering Dpt.of Technical MathematicsKarlovo Náměstí 13 Prague Czech Republic

This paper is concerned with experimental and numerical research on 3D flow past prismatic turbine cascade SE1050 （known in QNET network as open test case SE1050）. The primary goal was to assess the influence of the inlet velocity profile on the flow structures in the interblade channel and on the flow field parameters at the cascade exit and to compare these findings to results of numerical simulations. Investigations of 3D flow past the cascade with non-uniform inlet velocity profile were carried out both experimentally and numerically at subsonic （M2 = 0.8） and at transonic （M2 = 1.2） regime at design angle of incidence. Experimental data was obtained using a traversing device with a five-hole conical probe. Numerically, the 3D flow was simulated by open source code OpenFOAM and in-house code. Analyses of experimental data and CFD simulations have revealed the development of distinctive vortex structures resulting from non-uniform inlet velocity profile. Origin of these structures results in increased loss of kinetic energy and spanwise shift of kinetic energy loss coefficient distribution. Differences found between the subsonic and the transonic case confirm earlier findings available in the literature. Results of CFD and experiments agree reasonably well.

关键词： blade cascade vortex structures transonic flow CFD

Numerical investigation of the effect of wedge-type cavitating-bubble generator on attached unsteady cavitating flows using proper orthogonal decomposition method

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Journal of Hydrodynamics 2023年第2期35卷 314-329页

作者： Bo-jie Hong Chang-li Hu Zhi-ying Wang Hao-jie Xing School of Energy and Power Engineering Nanjing University of Science and TechnologyNanjing210094China Key Laboratory for Mechanics in Fluid Solid Coupling Systems Institute of MechanicsChinese Academy of SciencesBeijing100190China

The objective of this work is to reveal the effect of a passive control method called wedge-type cavitating-bubble generator(WCG)on the cloud cavitation dynamics of National Advisory Committee for Aeronautics(NACA)66 *** simulations are performed using the Partially-averaged Navier-Stokes(PANS)method coupled with the Zwart cavitation *** proper orthogonal decomposition(POD)method is applied to extract the dominant flow *** results show that the WCG can induce the attached cavity to occur just behind the WCG instead of the hydrofoil leading *** the periodical time-evolution process of the unsteady cavity,it is found that the attached cavity with a larger scale around the hydrofoil with WCG has a rougher surface,accompanied with more shedding behaviors of small *** is further illustrated by the POD modes,that is,the mode 1 and modes 2–4 present the large and small cavity vortex structures ***,the dominant frequencies of 50 Hz,47.5 Hz are given by the POD method respectively for the hydrofoils without and with WCG,which is in good agreement with that of FFT *** addition,the correlation distribution of POD modal coefficients shows that the WCG can strengthen the vortex energy as well as the turbulence intensity.

关键词： Cavitating-bubble generator proper orthogonal decomposition(POD) attached cavity vortex structures

Optimal dynamical systems of Navier-Stokes equations based on generalized helical-wave bases and the fundamental elements of turbulence

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Science China(Physics,Mechanics & Astronomy) 2016年第11期59卷 61-69页

作者： NaiFu Peng Hui Guan ChuiJie Wu State Key Laboratory of Structural Analysis for Industrial Equipment School of Aeronautics and AstronauticsDalian University of Technology State Key Laboratory for Turbulence and Complex Systems Center for Applied Physics and TechnologyCollege of Engineering Peking University College of Meteorology and Oceanography PLA University of Science and Technology

In this paper, we present the theory of constructing optimal generalized helical-wave coupling dynamical systems. Applying the helical-wave decomposition method to Navier-Stokes equations, we derive a pair of coupling dynamical systems based on optimal generalized helical-wave bases. Then with the method of multi-scale global optimization based on coarse graining analysis, a set of global optimal generalized helical-wave bases is obtained. Optimal generalized helical-wave bases retain the good properties of classical helical-wave bases. Moreover, they are optimal for the dynamical systems of Navier-Stokes equations, and suitable for complex physical and geometric boundary conditions. Then we find that the optimal generalized helical-wave vortexes fitted by a finite number of optimal generalized helical-wave bases can be used as the fundamental elements of turbulence, and have important significance for studying physical properties of complex flows and turbulent vortex structures in a deeper level.

关键词： optimal dynamical systems helical-wave decomposition fundamental elements of turbulence vortex structures

The effects of attached flexible tail length on the flow structure of an oscillating cylinder

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Science China(Physics,Mechanics & Astronomy) 2013年第2期56卷 340-352页

作者： HU Ye WANG JinJun Key Laboratory of Fluid Mechanics Ministry of EducationBeihang University

Particle Imaging Velocimetry （PIV） is utilized to investigate the flow structures of an oscillating cylinder attached to a flexible tail. At the same oscillation frequency and amplitude, the mean streamwise velocity along the wake central-line and the mean vertical velocity around the trailing edge of the flexible tail can be greatly increased with the tail length. Meanwhile, the longer the flexible tail is, the larger its deformation is. In order to study the influence of flexible tail length on the wake pattern of the experimental model, the relationships between the swirling strength Aci of vortex structure near the tail end and the velocity of tail trailing edge have been revealed. Moreover, the convection tracks and the Aci of vortex cores for different flexible tails are discussed.

关键词： oscillating cylinder flexible tail tail deformation vortex structures mean flow characteristics

Physical and numerical investigation on transient cavitating flows

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Science China(Technological Sciences) 2013年第9期56卷 2207-2218页

作者： HUANG Biao WANG GuoYu ZHAO Yu WU Qin School of Vehicle and Transportation Engineering Beijing Institute of Technology

The objective of this paper is to investigate transient cavitating flows around a hydrofoil via combined physical and numerical studies. The aims are to 1) investigate the periodic formation, breakup, shedding, and collapse of the sheet/cloud cavities, 2) provide a better insight in the physical mechanism that governs the dynamics and structures of the sheet/cloud cavitation, 3) quantify the influence of cavitation on the surrounding flow structures. Results are presented for a Clark-Y hydrofoil fixed at an angle of attack of a=8° at a moderate Reynolds number, Re=7×105 , for sheet/cloud cavitating conditions. The experimental studies were conducted in a cavitation tunnel at Beijing Institute of Technology, China. The numerical simulations are performed by solving the incompressible, multiphase unsteady Reynolds-averaged Navier-Stokes (URANS) equations via the commercial code CFX using a transport equation-based cavitation model; a filter-based density corrected model (FBDCM) is used to regulate the turbulent eddy viscosity in both the cavitation regions near the foil and in the wake. The results show that numerical predictions are capable of capturing the initiation of the cavity, growth toward the trailing edge, and subsequent shedding in accordance with the quantitative features observed in the experiment. Regarding vapor shedding in the cavitating flow around the three-dimensional foil, it is primarily attributed to the effect of the re-entrant flow, which is formed due to the strong adverse pressure gradient. The results show strong correlation between the cavity and vorticity structures, demonstrating that the inception, growth, shedding, and collapse of sheet/cloud cavities are important mechanisms for vorticity production and modification.

关键词： unsteady cavitating flows cavity shedding baroclinic torque vortex structures