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HYDRODYNAMICS OF A FLAPPING FOIL IN THE WAKE OF A D-SECTION CYLINDER

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Journal of Hydrodynamics 2011年第4期23卷 422-430页

作者： shao xue-ming PAN Ding-yi State Key Laboratory of Fluid Power Transmission and Control Department of Mechanics Zhejiang University Hangzhou 310027 China

The water environment of swimming fish in nature is always complex which includes various vortices and fluctuations. In order to study the interaction between the fish and its surrounding complex flow, the physical model with a D-section cylinder placed at the front of a flapping foil is employed. The D-section cylinder is used to produce vortices to contact with the foil as well as the vortices shed from the foil. According to the experimental work of Gopalkrishnan et al., there are three interaction modes between vortices shed from the cylinder and the flapping foil, which are expanding wake, destructive interaction and constructive interaction. Here in this article, three of those typical cases are picked up to reproduce the vortices interaction modes with the modified immersed boundary methods and their hydrodynamic performances are studied further. Results show that, for expanding wake mode and destructive interaction mode, the incoming vortices contact with the foil strongly, inducing relative low pressure domains at the leading-edge of the foil and enlarging the thrust of foils. For constructive mode, the foil slalom between the shed vortices from the D-section cylinder do not contact with them obviously and the foil＇s thrust is only enlarged a little.

关键词： flapping foil fish propulsion vortices interaction thrust enlargement

NUMERICAL STUDY ON PROPULSIVE PERFORMANCE OF FISH-LIKE SWIMming FOILS

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Journal of Hydrodynamics 2006年第6期18卷 681-687页

作者： DENG Jian shao xue-ming REN An-lu Department of Mechanics State Key Laboratory of Fluid Power Transmission and Control Zhejiang UniversityHangzhou 310027 China

Two-dimensional numerical simulations are performed to study the propulsive performance of fish-like swimming foils using the immersed-boundary method. A single fish as well as two fishes in tandem arrangement are studied. First, the effect of the phase speed on the propulsive performance of a single fish is analyzed. The wake structures and pressure distribution near the wavy fish are also examined. The results show good correlation with those by previous researchers. Second, two tandem fishes with the same phase speed and amplitude are studied. The results show that the fish situated directly behind another one endure a higher thrust than that of a single one.

关键词： biomechanics fish-like swimming traveling wavy foil immersed-boundary method

VANISHING OF THREE-DIMENSIONALITY IN THE WAKE BEHIND A ROTATIONALLY OSCILLATING CIRCULAR CYLINDER

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Journal of Hydrodynamics 2007年第6期19卷 751-755页

作者： DENG Jian shao xue-ming REN An-lu State key Laboratory of Fluid Power Transmission and Control Department of MechanicsZhejiang University Hangzhou 310027 China

The flow behind a three-dimensional rotationally oscillating circular cylinder was studied by a numerical method. The computations were performed at a Reynolds number of 260, which is at a level that the flow wake has developed into a three-dimensional state called Mode-B. The purpose of this paper is to examine the influence of various rotational amplitudes （0.1-0.7） on the wake instability of the flow, while the oscillation frequency is fixed to the value of that measured in the wake of a stationary cylinder. The results show that the rotation with sufficiently high amplitude brings the flow back to its nominal two-dimensional state. Moreover, it is found that the value of the time-averaged drag and the RMS value of the lift are larger than those of a stationary circular cylinder.

关键词： rotationally oscillating circular cylinder wake instability oscillation frequency

A PRESSURE-BASED ALGORITHM FOR CAVITATING FLOW COMPUTATIONS

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Journal of Hydrodynamics 2011年第1期23卷 42-47页

作者： ZHANG Ling-xin ZHAO Wei-guo shao xue-ming Department of Mechanics State Key Laboratory of Fluid Power Transmission and Control Zhejiang UniversityHangzhou 310027 China

A pressure-based algorithm for the prediction of cavitating flows is *** algorithm employs a set of equations including the Navier-Stokes equations and a cavitation model explaining the phase change between liquid and vapor.A pressure-based method is used to construct the algorithm and the coupling between pressure and velocity is *** pressure correction equation is derived from a new continuity equation which employs a source term related to phase change rate instead of the material derivative of density Dρ/*** pressure-based algorithm allows for the computation of steady or unsteady,2-D or 3-D cavitating *** 2-D cases,flows around a flat-nose cylinder and around a NACA0015 hydrofoil,are simulated respectively,and the periodic cavitation behaviors associated with the re-entrant jets are *** algorithm shows good capability of computating time-dependent cavitating flows.

关键词： cavitating flow pressure-based algorithm cavitation model numerical simulation

FULLY RESOLVED NUMERICAL SIMULATION OF TURBULENT PIPE FLOWS LADEN WITH LARGE NEUTRALLY-BUOYANT PARTICLES

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Journal of Hydrodynamics 2011年第1期23卷 21-25页

作者： WU Teng-hu shao xue-ming YU Zhao-sheng State Key Laboratory of Fluid Power Transmission and Control Department of Mechanics Zhejiang UniversityHangzhou 310027 China

In this article,we employ a fully-resolved numerical simulation method（the fictitious domain method）to investigate the effects of large neutrally-buoyant particles on the turbulent flow in a pipe at low Reynolds number and non-dilute *** tube Reynolds number is fixed to be 4 900,the particle-pipe diameter ratio is 0.1,and the particle volume fraction ranges from 0.33%to 10%.Our results indicate that the presence of large particles decreases the maximum root-of-mean-square（rms）of the streamwise velocity fluctuation near the wall by weakening the intensity of large-scale streamwise vortices,although in the region very close to the wall the particles increase the rms of streamwise velocity *** the other hand,the particles induce small-scale vortices in the near-wall region,resulting in the enhancement of the rms of radial and circumferential velocity fluctuations there.

关键词： fully-resolved direct numerical solution particulate turbulent pipe flow large particles particle-turbulence interactions

NUMERICAL STUDIES ON THE PROPULSION AND WAKE STRUCTURES OF FINITE-SPAN FLAPPING WINGS WITH DIFFERENT ASPECT RATIOS

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Journal of Hydrodynamics 2010年第2期22卷 147-154页

作者： shao xue-ming PAN Ding-yi DENG Jian YUZhao-sheng Department of Mechanics State Key Laboratory of Fluid Power Transmission and Control Zhejiang UniversityHangzhou 310027 China

An immersed-boundary method is used to investigate the flapping wings with different aspect ratios ranging from 1 to *** numerical results on wake structures and the performance of the propulsion are *** the case of the two-dimensional flapping foil,the wing-tip vortices appear for the flow past a three-dimensional flapping wing,which makes the wake vortex structures much *** results show that the leading edge vortex merges into the trailing edge vortex,connects with the wing tip vortices and then sheds from the wing.A vortex ring forms in the wake,and exhibits different patterns for different foil aspect *** of hydrodynamic performances shows that both thrust coefficient and efficiency of the flapping wing increase with increasing aspect ratio.

关键词： bionic mechanics finite-span flapping wing aspect ratio immersed-boundary method

NUMERICAL SIMULATION OF CAVITATION FLOW UNDER HIGH PRESSURE AND TEMPERATURE

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Journal of Hydrodynamics 2011年第3期23卷 289-294页

作者： ZHAO Wei-guo ZHANG Ling-xin shao xue-ming Department of Mechanics Zhejiang University Hangzhou 310027 China State Key Laboratory of Fluid Power Transmission and Control Zhejiang University Hangzhou 310027 China

The numerical simulation of cavitation flow on a 2D NACA0015 hydrofoil under high pressure and temperature is performed. The Singhal＇s cavitation model is adopted combined with an improved RNG k-ε turbulence model to study the cavitation flow. The thermal effect in the cavitation flow is taken into account by introducing the energy equation with a source term based on the latent heat transfer. The code is validated by a case of a hydrofoil under two different temperatures in a comparison between the simulation and the experiment. Computational results show that the latent heat of vaporization has a significant impact on the cavitation process in the high temperature state, and the cavity in the high temperature state is thinner and shorter than that in a normal state with the same cavitation number, due to the fact that the heat absorption in the cavitation area reduces the local temperature and the saturated vapor pressure. This numerical study provides some guidance for the design of machineries in the High Pressure and Temperature （HPT） state.

关键词： cavitation NACA0015 thermodynamic CFD high pressure and temperature

THREE-DIMENSIONAL PAIRING OF COHERENT STRUCTURES IN A PLANE MIXING LAYER

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Journal of Hydrodynamics 2002年第2期14卷 1-6页

作者： Lin, Jian-Zhong Shi, Xing Yu, Zhao-Sheng shao, xue-ming Dept. of Mech. Lab. of Fluid Power Trans. Zhejiang Univ. Hangzhou 310027 China

The three-dimensional (3D) pairing process of coherent structures in a plane mixing layer was simulated numerically with the pseudo-spectral method. The behaviors of spanwise cup-shaped vortices, streamwise rib-shaped vortices and quadrupoles were obtained in terms of their iso-surfaces. The results show that three-dimensional structures are strongly influenced by the initial amplitude of the 3D disturbance, and that in most cases the local pairing finishes in a roughly two-dimensional manner. In pairing region, the streamwise vortices are chaotic after pairing due to the breakdown of the engulfed ribs and especially the subsequent breakdown of the quadrupoles. The surviving ribs extend to the top (or bottom) of the paired vortices under the stretch of them. In addition, it is revealed that three dimensional vortices pairing can enhance the mixing of fluid. Finally, some patterns of numerical flow visualization are presented by computing the passive scalar.

关键词： Flow of fluids Flow visualization Mixing Numerical analysis Three dimensional

DIRECT NUMERICAL SIMULATION OF PARTICULATE FLOWS

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Journal of Hydrodynamics 2003年第3期15卷 89-95页

作者： shao xue-ming Department of Mechanics, Zhejiang University, Hangzhou 310027, China, Department of Mechanics Zhejiang University Hangzhou 310027 China

In this paper, a new method-Distributed La-grange Multiplier/fictitiousdomain (DLM) method for partic-ulate flows was improved. A rectangular mesh was introduced todiscretize the domain, and the buoyant force was considered for predicting the positions ofparticles. In order to validate the presented algorithm, the sedimentation of a single circularparticle was simulated using different mesh sizes and time steps firstly. The results show that thesimulation is independent of the mesh size as well as the time step. And then, the interactionsbetween two falling particles, including drafting, kissing and tumbling, and the sedimentation of 18particles also have been simulated with the code.

关键词： distirbuted lagrange multiplier/fictitious domain method paniculate flow sendimentation of circular particle