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A STUDY OF OSCILLATING FLOWS OVEr prOpAGATING rIppLES:pArT I. STEADY STrEAMING

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Journal of Hydrodynamics 1999年第4期11卷 16-23页

作者： lu xi yun department of modern mechanics, university of science and technology of china, hefei, 230026, p.r.china department of modern mechanics University of Science and Technology of ChinaHefei 230026 P.R.China

Oscillating flows over periodic ripples are numerically investigated by solving the two dimensional time dependent incompressible Navier Stokes equations in curvilinear coordinates for a wider range of the parameters of KC, re and ε, in particular for the oscillatory flow over propagating ripples. In the oscillating flows over periodic ripples, circulation cells due to the streaming effect are formed, which can help redistribute suspended sediments. In the present study, the circulation patterns for both stationary rigid ripples and propagating ripples are investigated. The energy dissipation in the flow field is also discussed.

关键词： oscillating flow ripple steady streaming separation flow

DIrECT NUMErICAL SIMULATIONS OF TUrBULENT CHANNEL FLOWS WITH CONSIDErATION OF THE BUOYANCY EFFECT OF THE BUBBLE pHASE

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Journal of Hydrodynamics 2011年第3期23卷 282-288页

作者： LIU Nan-sheng CHENG Bao-guo QUE xia lu xi-yun department of Modem mechanics University of Science and Technology of China Hefei 230026 China department of Computer science and technology Hefei University of Technology Hefei 230009 China

Turbulent channel flows with consideration of the buoyancy effect of the bubble phase is investigated by means of the Direct Numerical Simulation （DNS）. This two-phase system is solved by a two-way coupling Lagrangian-Eulerian approach. The reynolds number based on the friction velocity and the half-width of the channel is 194, and the gravitational acceleration varies from -0.5 to 0.5, ranging from the upflow to the downflow cases. This study aims to reveal the influence of buoyancy on the turbulence behavior and the bubble motion. Some typical statistical quantities, including the averaged velocities and velocity fluctuations for the fluid and bubble phases, as well as the flow structures of the turbulence fluctuations, are analyzed.

关键词： Direct Numerical Simulations (DNS) turbulent bubbly flow upflow/downflow turbulence fluctuations bubble statistics turbulence structures

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, Dept. of Mech. and Mech. Eng. Univ. of Sci. and Technol. 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

NUMErICAL SIMULATION OF AN OSCILLATING FLOW pAST A CIrCULAr CYLINDEr IN THE VICINITY OF A pLANE WALL

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Journal of Hydrodynamics 2008年第5期20卷 547-552页

作者： SHAH Syed Bilal Hussain department of modern mechanics University of Science and Technology of China

Oscillating flow around a circular cylinder in the vicinity of a plane wall was investigated by solving the two-dimensional incompressible Navier-Stokes equations with a finite element Galarkin residual method. The effect of the gap G/D between the cylinder surface and the wall on the flow behavior was studied. For the case of G/D 〈 0.25, the periodicity in the flow is attributed to both the outer shear layer instability and the oscillating frequency. As G/D 〉 0.25, vortex shedding occurs and the periodicity in the flow is mainly due to the competition of the oscillating frcqucncy and the vortex shedding frequency from an isolated stationary cylinder.

关键词： finite element method vortex shedding oscillating flow circular cylinder

NUMErICAL　STUDY　ON　THE　VOrTEX　STrUCTUrES　IN　THE　WAKE　OF　AN　OSCILLATING　CIrCULAr　CYLINDEr　IN　A　UNIFOrM　FLOW

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Journal of Hydrodynamics 1994年第1期6卷 12-22页

作者： lu xi-yun Tong Bing-gang Zhuang Li-xian Yin xie-yuan (department of modern mechanics, university of science and technology of china, hefei, Anhui 230026,p. r. china) Univ of science and technology of China Hefei China

Vortex shedding from a circular cylinder subjected to fortal oscillations at arbitrary angles(as shown in Fis. 1 for 0°<β<90°) with respect to the free stream is numerically investigated using the Navier-Stokes equ... 详细信息

Vortex shedding from a circular cylinder subjected to fortal oscillations at arbitrary angles(as shown in Fis. 1 for 0°respect to the free stream is numerically investigated using the Navier-Stokes equations. The emphasis of this study is put on revealing the complicated vortex structures and their evolution in the near wake. In the present study, a number of possible vortex modes are also numerically simulated, and a variety of physical phenomena are duplicated and even renewed numerically. A parameter map indicating the classification of preferred vortex modes is firstly given in the frequency-amplitude plane.

关键词： unsteady flow vortex motion separated flow oscillatory flow.

TUrBULENT OpEN CHANNEL FLOW SUBJECTED TO THE CONTrOL OF A SpANWISE TrAVELING WAVE

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Journal of Hydrodynamics 2009年第1期21卷 65-70页

作者： LIU Nan-sheng WANG Lei lu xi-yun department of Modem mechanics University of Science and Technology of China Hefei 230026 China

Turbulent open channel flows subjected to the control of a spanwise traveling wave have been investigated by means of Direct Numerical Simulation （DNS）. The objective of this study is to reveal the response of the near-wall and surface-influenced turbulence to the spanwise traveling wave control. Three typical frequencies of the spanwise traveling wave, i.e., high-, middle- and low-frequency, corresponding to the exciting periods at 25, 50 and 100, are considered to study the turbulence dynamics in the wall and surface regions. To elucidate the behaviors of turbulence statistics, some typical quantities, including the mean velocity, velocity fluctuations and the structures of turbulence fluctuations, are exhibited and analyzed.

关键词： turbulent open channel flow traveling wave Direct Numerical Simulation (DNS) turbulence statistics turbulence structures

AN INVESTIGATION OF TUrBULENT HEAT TrANSFEr IN CHANNEL FLOWS BY LArGE EDDY SIMULATION

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Journal of Hydrodynamics 2002年第2期14卷 29-35页

作者： Dong Yu-hong, Zhong Feng-quan, lu xi-yun, Zhuang Li-xian department of mechanics and Mechanical Engineering, university of science and technology of china, hefei 230026, china Dept. of Mech. and Mech. and Eng. Univ. of Sci. and Technol. of China Hefei 230026 China

Large Eddy Simulation (LES) of fully developed turbulent channel flow with heat transfer was performed to investigate the effects of the reynolds number on the turbulence behavior. In the present study, the bottom wall of the channel was cooled and the top wall was heated. The reynolds numbers, based on the central mean-velocity and the half-width of the channel, were chosen as 4000, 6000, 10 4 and 2×10 4, and the prandtl number as 1.0. To validate our calculations, the present results were compared with available data obtained by Direct Numerical Simulation (DNS), which proves to be in good agreement with each other. To reveal the effects of the reynolds number, some typical quantities, including the velocity fluctuations, temperature fluctuation, heat fluxes and turbulent prandtl number, were studied.

关键词： Large Eddy Simulation (LES) turbulent channel flow Subgrid Scale (SGS) model heat transfer stratified turbulence

ANALYSIS OF HYDrODYNAMICS FOr TWO-DIMENSIONAL FLOW ArOUND WAVING pLATES

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Journal of Hydrodynamics 2007年第1期19卷 18-22页

作者： ZHANG Cheng ZHUANG Li-xian lu xi-yun department of mechanics and Mechanical Engineering University of Science and Technology of China Hefei 230026 China

Hydrodynamic characteristics for two-dimensional flow around a waving plate are investigated. Under large reynolds number approximation, the flow is assumed to be a combination of the outer potential flow and a thin vortex layer, which consists of a boundary layer and a shed free shear layer. A nonlinear mathematical formulation for describing the outer unsteady potential flow coupled with an unsteady boundary layer equation for the inner viscous flow adjacent to the waving plate is developed. A semi-analytical method with a nonlinear Kutta condition imposed at the trailing edge is used to solve the velocity field of the outer flow and the evolution of wake vortex induced by a large-amplitude waving plate. The unsteady boundary layer equation is solved by extending pohlhausen＇s method to its unsteady counterpart. The thrust and viscous drag coefficients, propulsive efficiency, and the pattern of wake vortex sheet are discussed.

关键词： waving plate fish swimming unsteadyboundary layer vortex shedding

Capture Efficiency Analysis in the Circular restricted Three-body problem

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research in Astronomy and Astrophysics 2024年第5期24卷 198-210页

作者： Yu-Xuan Miao xi-yun Hou department of Astronomy and Space science Nanjing UniversityNanjing 210023China Institute of Space Environment and Astrodynamics Nanjing UniversityNanjing 210023China Key Laboratory of modern Astronomy and Astrophysics Ministry of EducationNanjing 210023China

Temporary capture efficiency is studied in the framework of the circular restricted three-body problem in two ***, a non-uniform distribution of test particles around the secondary's orbit is obtained by fully accounting the secondary's gravitational influence. Second, the capture efficiency is computed based on the non-uniform distribution. Several factors influencing the result are discussed. By studying the capture efficiency in the circular restricted three-body problem of different mass ratios, a power-law relation between the capture efficiency(p) and the mass ratio(μ) is established, which is given by p ≈ 0.27 × μ^(0.53), within the range of 3.0035 ×10^(-6)≤ μ ≤ 3.0034 × 10^(-5). Taking the Sun–Earth system as an example, the influence from the orbit eccentricity of the secondary on the non-uniform distribution and the capture efficiency is studied. Our studies find that the secondary's orbit eccentricity has a negative influence on the capture efficiency.

关键词： methods numerical-celestial mechanics-planets and satellites dynamical evolution and stability