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Numerical investigation on vortex dynamics of flow around a pitching hydrofoil via the finite-domain impulse theory

Acta Mechanica Sinica 2025年第1期41卷 82-94页

作者： Hui-Yun Hao Yun-Qing Liu Qin Wu Ying Liu School of Mechanical Engineering Beijing Institute of TechnologyBeijing 100081China

The behaviors of unsteady flow structures and corresponding hydrodynamics for a pitching hydrofoil are investigated numerically and theoretically in the present *** aims are to derive the total lift by finite-domain impulse theory for subcavitating flow(σ=8.0)and cavitating flow(σ=3.0),and to quantify the distinct impact of individual vortex structures on the transient lift to appreciate the interplay among cavitation,flow structures,and vortex *** motion of the hydrofoil is set to pitch up clockwise with an almost constant rate from 0°to 15°and then back to 0°,for the Reynolds number,7.5×105,and the frequency,0.2 Hz,*** results reveal that the presence of cavities delays the migration of the laminar separation bubble(LSB)from the trailing edge(TE)to the leading edge(LE),consequently postponing the hysteresis in the inflection of lift *** eventual stall under the sub-cavitation regime is the result of LSB *** the instabilities within the leading-edge LSB induce the convection of cavitation-dominated vortices under the cavitation regime *** validated the lift coefficients on the hydrofoil through the finite-domain impulse theory using the standard force expression,the Lamb vector integral emerges as the main contribution to the generation of unsteady ***,the typical vortices’contributions to the transient lift during dynamic stall are accurately *** analysis indicates that the clockwise leading-edge vortex(−LEV)contributes positively,while the counterclockwise trailing-edge vortex(+TEV)contributes *** negative influence becomes particularly pronounced after reaching the peak of total lift,as the shedding of the concentrated wake vortex precipitates a sharp decline due to a predominant negative lift contribution from the TEV ***,the vortices’contribution is relatively modest in sub-cavitating flow,but it is notably more significant in the context of incipient ca

关键词： Cavitation vortex dynamics Finite-domain impulse theory Pitching hydrofoil Laminar separation bubble Dynamic stall

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vortex dynamics and entropy generation in separated transitional flow over a compressor blade at various incidence angles

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Chinese Journal of Aeronautics 2022年第3期35卷 42-52页

作者： Mingyang WANG Ziliang LI Ge HAN Chengwu YANG Shengfeng ZHAO Yanfeng ZHANG Xin’gen LU Key Laboratory of Light-Duty Gas-Turbine Institute of Engineering ThermophysicsChinese Academy of SciencesBeijing 100190China University of Chinese Academy of Sciences Beijing 100049China

The transition process within a Laminar Separation Bubble(LSB)that formed on a compressor blade surface was investigated using Large Eddy Simulations(LESs)at a Reynolds number of 1.5×10;and incidence angles of 0°,+3°,and+5°.The vortex dynamics in the separated shear layers were compared at various incidence angles and its effects on the loss generation were clarified through entropy *** showed that transition onset,which was accurately identified by the Linear Stability Theory(LST),was significantly promoted at the increased incidence *** such,the development of LSB was suppressed and the relative role of viscous instability played in the transition process was *** the incidence angle of 0°,two-dimensional spanwise vortices detached from the blade surface and roiled up periodically,which were further stretched and eventually evolved into large-scale hairpin *** time passed,the fully developed hairpin vortices broke down into small-scale ***,the flow near the wall reversely ejected into the outer separated shear layers and a sweeping process happened subsequently,forcing the separated shear layers to reattach and accelerating the generation of turbulent *** comparison,the strength of vortex rolling-up was weakened at higher incidence angles,and the vortex pairing and breakdown of large-scale vortices were less ***,the level of turbulent fluctuations that generated in the separated shear layers was *** entropy analysis showed that the turbulent dissipation effect related to the Reynolds shear stresses determined the largest amount of positive entropy generation,which declined to a lower level as the incidence angle increased from 0°to+5°.Correspondingly,the profile loss was reduced by 50.4%.

关键词： Aerodynamic performance Compressor airfoil Entropy Incidence angle Separation bubble vortex dynamics

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vortex dynamics OF THE ANISOTROPIC GINZBURG-LANDAU EQUATION

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Acta Mathematica Scientia 2010年第3期30卷 949-962页

作者：温焕尧丁时进 School of Mathematical Sciences South China Normal University

In this article, using coordinate transformation and Gronwall inequality, we study the vortex motion law of the anisotropic Cinzburg-Landau equation in a smooth bounded domain Ω （R^2,that is ,Эtuε=j,k=1∑2（ajkЭxkuε）xj＋ε^2^-b（x）（1-｜uε｜^2）uε,x∈Ω,and conclude that each vortex,bj（t）（j=1,2,…,N）satisfies dt^-dbj（t）=-（a（bj（t））^-a1k（bj（t））Эxka（bj（t））,a（aj（t））^-a2k（bj（t））Эxka（bj（t）））,where a（x）=√a11a22-a12^2. We prove that all the vortices are pinned together to the critical points of a（x）. Furthermore, we prove that these critical points can not be the maximum points.

关键词： Anisotropic Ginzburg-Landau equation Gronwall inequality vortex dynamics

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Flow Separation and vortex dynamics in Waves Propagating over A Submerged Quartercircular Breakwater

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China Ocean Engineering 2018年第5期32卷 514-523页

作者： JIANG Xue-lian YANG Tian ZOU Qing-ping GU Han-bin Tianjin Key Laboratory of Soft Soil Characteristics & Engineering Environment Tianjin Chengjian University State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin University The Lyell Centre for Earth and Marine Science and Technology Institute for Infrastructure and EnvironmentHeriot-Watt University School of Naval Architecture &Mechanical-Electrical Engineering Zhejiang Ocean University

The interactions of cnoidal waves with a submerged quartercircular breakwater are investigated by a ReynoldsAveraged Navier–Stokes(RANS) flow solver with a Volume of Fluid(VOF) surface capturing scheme(RANSVOF) model. The vertical variation of the instantaneous velocity indicates that flow separation occurs at the boundary layer near the breakwater. The temporal evolution of the velocity and vorticity fields demonstrates vortex generation and shedding around the submerged quartercircular breakwater due to the flow separation. An empirical relationship between the vortex intensity and a few hydrodynamic parameters is proposed based on parametric analysis. In addition, the instantaneous and time-averaged vorticity fields reveal a pair of vortices of opposite signs at the breakwater which are expected to have significant effect on sediment entrainment, suspension, and transportation,therefore, scour on the leeside of the breakwater.

关键词： submerged quartercircular breakwater cnoidal wave flow separation vortex dynamics scour

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Liutex-based vortex dynamics:A preliminary study

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Journal of Hydrodynamics 2020年第6期32卷 1217-1220页

作者： Hai-dong Yu Yi-qian Wang School of Aerospace Engineering Tsinghua UniversityBeijing100084China School of Mathematical Science Soochow UniversitySuzhou215006China

vortex dynamics,with the possibility of efficient flow control,is explored in this study based on the new introduced vortex definition and identification system of *** the six core elements of vortex identification,including(1)absolute strength,(2)relative strength,(3)local rotational axis,(4)global rotational axis,(5)vortex core size and(6)vortex boundary,provided by the Liutex system,it is possible to numerically devise strategies,primarily by introducing additional source terms in Navier-Stokes equations,which we call Liutex force field model here,to control the vortex *** methodologies of centripetal force model and counter-rotation force model are preliminarily investigated in a cavitating flow around two-dimensional Clark-Y *** is found that Liutex based models are capable of illustrating the vortex dynamics and possibly strengthening or weakening the vortices.

关键词： vortex dynamics Liutex vector flow control

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THE NONLINEAR INTERACTION OF vortex RINGS WITH A FREE SURFACE

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Acta Mechanica Sinica 1997年第2期13卷 120-129页

作者：叶取源 C.K.Chu Dept.of Engineering Mechanics Shanghai Jiao Tong UniversityShanghai 200030China Dept.of Applied Physics Columbia UniversityNew YorkNY 10027USA

Nonlinear interactions of vortex rings with a free surface are considered in an incompressible, ideal fluid using the vortex contour dynamics technique and the boundary integral equation method. The flow is axisymmetric and the vorticity is linearly distributed in the vortex. Effects of the gravity and the surface tension as well as the initial geometric parameter of the vortex on the interaction process are investigated in considerable detail. The interaction process may be divided into three major stages: the vortex free-traveling stage, the collision stage, and the vortex stretching and rebounding stage. Time evolutions of both the vortex and free surface under various conditions are provided and analyzed. Two kinds of waves exist on the free surface during interaction. In a special case where the gravity and surface tension are very weak or the vortex is very strong, an electric-bulb-like 'cavity' is formed an the free surface and the vortex is trapped in the 'cavity' for quite a. long time, resulting in a large amount, of fluid above the mean fluid surface.

关键词： vortex ring vortex dynamics contour dynamics nonlinear free surface

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Liutex-based vortex control with implications for cavitation suppression

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Journal of Hydrodynamics 2021年第1期33卷 74-85页

作者： Yi-qian Wang Hai-dong Yu Wei-wen Zhao De-cheng Wan School of Mathematical Science Soochow UniversitySuzhou 215006China School of Aerospace Engineering Tsinghua UniversityBeijing 100084China Computational Marine Hydrodynamics Lab(CMHL) State Key Laboratory of Ocean EngineeringSchool of Naval ArchitectureOcean and Civil EngineeringShanghai Jiao Tong UniversityShanghai 200240China

Viewed as sinews and muscles of fluid motion,coherent vortical structures with their interactions are key to understanding the flow *** upon this observation,we explore the possibility of efficient flow control by directly manipulating vortices numerically inside the flow field based on the vortex definition and identification system of *** objective is twofold:(1)to study the vortex dynamics,for example,by observing the response of the flow to strengthening or weakening of certain vortices,and(2)to obtain efficient vortex-based control strategies which might lead us to practical *** the present numerical study,the manipulating of vortices is achieved by introducing additional source(force)terms to the Navier-Stokes equations,which hereafter will be collectively called Liutex force field *** including controlling the rotation strength and centripetal force of particular vortices are detailed in a flow past a cylinder with different control purposes at Reynolds number of *** examples are provided with a cavitating flow around two-dimensional Clark-Y hydrofoil,with particular interests on cavitation *** is illustrated particular vortex with cavitation encircled could be effectively suppressed.

关键词： vortex dynamics Liutex vector flow control cavitation Introduction

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Cascade excitation of vortex motion and reentrant superconductivity in flexible Nb thin films

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Chinese Physics B 2023年第4期32卷 613-621页

作者：张丽萍徐祖雨黎晓杰张旭秦明阳张若舟徐娟程文欣袁洁王华兵 Alejandro V.Silhanek 朱北沂苗君金魁 School of Materials Science and Engineering University of Science and Technology BeijingBeijing 100083China Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China Research Institute of Superconductor Electronics School of Electronic Science and EngineeringNanjing UniversityNanjing 210023China Department of Materials Science and Engineering Southern University of Science and TechnologyShenzhen 518055China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100049China Key Laboratory of Vacuum Physics School of Physical SciencesUniversity of Chinese Academy of SciencesBeijing 101408China Purple Mountain Laboratories Nanjing 211111China Experimental Physics of Nanostructured Materials Q-MATCESAMUniversit´e de Li`egeB-4000 Sart TilmanBelgium Songshan Lake Materials Laboratory Dongguan 523808China

High quality Nb films were successfully prepared on both flexible polyimide(PI)and rigid Al2O3substrates and their transport properties were systematically studied at various applied currents,external magnetic fields,and sample *** is found that a curved Nb/PI film exhibits quite different superconducting transition and vortex dynamics compared to the flat Nb/*** the curved Nb/PI film,smooth superconducting transitions were obtained at low currents,while unexpected cascade structures were revealed in theρ(T)curves at high *** attribute this phenomenon to the gradient distribution of vortex density together with a variation of superconductivity along the curved *** addition,reentrant superconductivity was induced in the curved Nb/PI thin film by properly choosing the measurement *** attribute this effect to the vortex pinning from both in-plane vortices and out-of-plane *** work reveals the complex transport properties of curved superconducting thin films,providing important insights for further theoretical investigations and practical developments of flexible superconductors.

关键词： vortex dynamics flexible superconducting films transport properties superconducting films

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FORCE CHARACTERISTICS AND vortex SHEDDING OF A PITCHING FOIL IN SHEAR FLOWS

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Journal of Hydrodynamics 2005年第1期17卷 27-33页

作者： LIDan-yong LIUNan-sheng LUXi-yun YINXie-zhen DepartmentofMechanicsandMechanicalEngineering UniversityofScienceandTechnologyofChinaHefei230026China

The objective of this study is to deal with unsteady force acting on a pitching foil in shear flow and to study the relation of the force characteristics with vortex shedding near the foil. The two dimensional incompressible Navier Stokes equations in the vorticity and stream function formulation were solved with the fourth order essentially compact finite difference schemes for the space derivatives and a fourth order Runge Kutta scheme for the time advancement. The force characteristics and vortex shedding of the pitching foil in shear flows were investigated. The effects of some typical factors, including the incoming flow shear, the oscillating frequency and amplitude, on the vortex shedding and force behavior were analyzed and discussed.

关键词： vortex dynamics vortex shedding force unsteady flow locomotion biomechanics

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PROPULSIVE PERFORMANCE AND vortex SHEDDING OF A FOIL IN FLAPPING MOTION

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Journal of Hydrodynamics 2003年第5期15卷 7-12页

作者： Yang Yan, Lu Xi yun, Yin Xie zhen Department of Mechanics and Mechanical Engineering, University of Science and Technology of China, Hefei 230026, China, Department of Mechanics and Mechanical Engineering University of Science and Technology of China Hefei 230026 China

The propulsive performance and vortex shedding of oscillating foil, whichmimics biological locomotion, were numerically investigated. The objectives of this study were todeal with unsteady force, in particular thrust force, exerted on the foil in pitching and plungingmotions, and to explore the relation of the propulsive performance with vortex structures near thefoil and vortex shedding in the near wake. The two-dimensional incompressible Navier-Stokesequations in the vorticity and stream-function formulation were solved by fourth-order essentiallycompact finite difference schemes for the space derivatives and a fourth-order Runge-Kutta schemefor the time advancement. To reveal the mechanism of the propulsive performance, the unsteady forceand the shedding of the trailing- and leading-edge vortices of the foil were analyzed. The effectsof some typical factors, such as the frequency and amplitude of the oscillation, the phasedifference between the pitching and plunging motions, and the thickness ratio of the foil, on thevortex shedding and unsteady force were discussed.

关键词： vortex dynamics vortex shedding thrust force unsteady flow flappingmotion

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