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Experimental and numerical investigations on the vortical structures of an impinging jet in crossflow

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Journal of Shanghai University(English Edition) 2006年第3期10卷 279-280页

作者：张燕 Shanghai Institute of Applied Mathematics and Mechanics Shanghai University Shanghai 200072 P.R. China

The objective of this dissertation is to investigate the impinging jet under the influence of crossflow. It has been known that there exist jet shear layer, impingement on the bottom wall, interactions between the induced wall jet and the ambient crossflow in near field. There are few intensive studies of the impinging jet in crossflow at home and abroad due to the complexities of flow, such as the formation and evolution of the vortical structures, interactions among vortices, while researches on the temporal and spatial evolution of these vortical structures can promote the practical applications in environment engineering, hydroelectricity engineering, etc., and provide the basis for flow control and improvement through revealing the inherent mechanism and development of the vortical structures.

关键词： vortical structure impinging jet crossflow PIV measurement LES.

Imaging of the Space-time structure of a Vortex Generator in Supersonic Flow

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Chinese Journal of Aeronautics 2012年第1期25卷 57-63页

作者： WANG Dengpan XIA Zhixun ZHAO Yuxin WANG Bo ZHAO Yanhui Science and Technology on Scramjet Laboratory National University of Defense TechnologyChangsha 410073China

The fine space-time structure of a vortex generator （VG） in supersonic flow is studied with the nanoparticle-based planar laser scattering （NPLS） method in a quiet supersonic wind tunnel. The fine coherent structure at the symmetrical plane of the flow field around the VG is imaged with NPLS. The spatial structure and temporal evolution characteristics of the vortical structure are analyzed, which demonstrate periodic evolution and similar geometry, and the characteristics of rapid movement and slow change. Because the NPLS system yields the flow images at high temporal and spatial resolutions, from these images the position of a large scale structure can be extracted precisely. The position and velocity of the large scale structures can be evaluated with edge detection and correlation algorithms. The shocklet structures induced by vortices are imaged, from which the generation and development of shocklets are discussed in this paper.

关键词： vortex generator nanoparticle-based planar laser scattering vortical structure evolution characteristic shocklet

A hybrid RANS/LES model for simulating time-dependent cloud cavitating flow around a NACA66 hydrofoil

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Science China(Technological Sciences) 2016年第8期59卷 1252-1264页

作者： ZHANG GuangJian SHI WeiDong ZHANG DeSheng WANG Chuan ZHOU Ling Research Center of Fluid Machinery Engineering and Technology Jiangsu University Zhenjiang 212013 China

Cloud cavitating flow is highly turbulent and dominated by coherent large-scale anisotropic vortical structures. For the numer- ical investigation of such a class of flow, large eddy simulation （LES） is a reliable method but it is computationally extremely costly in engineering applications. An efficient approach to reduce the computational cost is to combine Reynolds-averaged Navier-Stokes （RANS） equations with LES used only in the parts of interest, such as massively separated flow regions. A new hybrid RANS/LES model, the modified filter-based method （FBM）, is proposed in the present study which can perform RANS or LES depending on the numerical resolution. Compared to the original FBM, the new method has three modifications： the state-of-the-art shear stress transport （SST） model replaces the k-c model as a baseline RANS model. A shielding function is introduced to obviate the switch from RANS to LES occurring inside the boundary layer. An appropriate threshold controlling the switch from RANS to LES is added to achieve an optimal predictive accuracy. The new model is assessed for its predictive capability of highly unsteady cavitating flows in a typical case of cloud cavitation around a NACA66 hydrofoil. The new mod- el results are compared with data obtained from the Smagorinsky LES and SST model based on the same homogeneous Zwart cavitation model. It is found that the modified FBM method has significant advantages over SST model in all aspects of pre- dicted instantaneous and mean flow field, and its predictive accuracy is comparable to the Smagorinsky LES model even using a much coarser grid in the simulations.

关键词： hybrid RANS/LES model eddy viscosity vortical structure cloud cavitation hydrofoil

Large Eddy Simulation of a Vortex Ring Impacting a Bump

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Advances in Applied Mathematics and Mechanics 2014年第3期6卷 261-280页

作者： Heng Ren Ning Zhao Xi-Yun Lu Department of Modern Mechanics University of Science and Technology of ChinaHefei 230026AnhuiChina Department of Aerodynamics Nanjing University of Aeronautics and AstronauticsNanjing 210016JiangsuChina

A vortex ring impacting a three-dimensional bump is studied using large eddy simulation for a Reynolds number Re=4×104 based on the initial diameter and translational speed of the vortex *** effects of bump height and vortex core thickness for thin and thick vortex rings on the vortical flow phenomena and the underlying physical mechanisms are *** on the analysis of the evolution of vortical structures,two typical kinds of vortical structures,i.e.,the wrapping vortices and the hair-pin vortices,are identified and play an important role in the flow state *** boundary vorticity flux is analyzed to reveal the mechanism of the vorticity generation on the bump *** circulation of the primary vortex ring reasonably elucidates some typical phases of flow ***,the analysis of turbulent kinetic energy reveals the transition from laminar to turbulent *** results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the flow evolution and the flow transition to turbulent state.

关键词： Large eddy simulation vortex ring vortical structure turbulent state.

Numerical Study of Two-Winged Insect Hovering Flight

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Advances in Applied Mathematics and Mechanics 2009年第4期1卷 481-509页

作者： Yanjun Liu Nansheng Liu Xiyun Lu Department of Modern Mechanics University of Science and Technology of ChinaHefeiAnhui 230026China

The two-winged insect hovering flight is investigated numerically using the lattice Boltzmann method(LBM).A virtual model of two elliptic foils with flapping motion is used to study the aerodynamic performance of the insect hovering flight with and without the effect of ground *** studies have been carried out by changing some parameters of the wing kinematics,including the stroke amplitude,attack angle,and the Reynolds number for the insect hovering flight without ground effect,as well as the distance between the flapping foils and the ground surface when the ground effect is *** influence of the wing kinematic parameters and the effect of the ground surface on the unsteady forces and vortical structures are *** unsteady forces acting on the flapping foils are verified to be closely associated with the time evolution of the vortex structures,foil translational and rotational accelerations,and interaction between the flapping foils and the existed vortical *** unsteady mechanisms of lift production are identified by examining the vortical structures around the flapping *** results obtained in this study provide some physical insight into the understanding of the aerodynamics and flow structures for the insect hovering flight.

关键词： Insect hovering flight lattice Boltzmann method ground effect unsteady force vortical structure

Numerical investigation on convective heat transfer over two heated wall-mounted cubes in tandem and staggered arrangement

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Theoretical & Applied Mechanics Letters 2018年第3期8卷 171-183页

作者： S.M.Mousazadeh M.M.Shahmardan T.Tavangar Kh.Hosseinzadeh D.D.Ganji Department of Mechanical Engineering Shahrood University of Technology Department of Mechanical Engineering Babol Noushirvani University of Technology

In this study, laminar convective heat transfer over two heated wall-mounted cubes is *** cubes, which are under constant heat flux, are placed in different tandem and staggeredarrangements on a base plate. This problem is studied for different streamwise and spanwisedistances between two cubes in different Renolds number （Re）, by using finite-volume *** of these parameters are considered on flow and heat transfer characteristics. The resultsshow that the temperature distribution is strongly dependent on flow structure and varies with anychange of flow pattern in different arrangements of cubes. In addition, it is observed that the dragcoefficient, which is influenced more by pressure forces, in staggered arrangement, is greater thantandem arrangement. Results show that by increasing the spanwise distance the amount of meanNusselt number （Nu） of Cube 2 becomes the same as Cube 1.

关键词： Steady laminar flow vortical structure Convective heat transfer Constant heat flux

Large eddy simulation of a vortex ring impinging on a three-dimensional circular cylinder

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Theoretical & Applied Mechanics Letters 2013年第3期3卷 46-50页

作者： Heng Ren Xiyun Lu Department of Modern Mechanics University of Science and Technology of China

Abstract A vortex ring impacting a three-dimensional circular cylinder is studied using large eddy simulation （LES） for a Reynolds number Re = 4 × 10^4 based on the initial translation speed and diameter of the vortex ring. We have investigated the evolution of vortical structures and identified three typical evolution phases. When the primary vortex closely approaches to the cylinder, a secondary vortex is generated and its segment parts move inward to the primary vortex ring. Then two large-scale loop-like vortices are formed to evolve in opposite directions. Thirdly, the two loop-like vortices collide with each other to form complicated small-scale vortical structures. Moreover, a series of hair-pin vortices are generated due to the stretching and deformation of the tertiary vortex. The trajectories of vortical structures and the relevant evolution speeds are analyzed. The total kinetic energy and enstrophy are investigated to reveal their properties relevant to the three evolution phases.

关键词： large eddy simulation vortex ring circular cylinder vortical structure high Reynoldsnumber

Three-dimensional numerical simulation of a vortex ring impacting a bump

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Theoretical & Applied Mechanics Letters 2014年第3期4卷 42-48页

作者： Heng Ren Changyue Xu China Electronics Technology Group Corporation No.38 Research Institute College of Aerospace Engineering Nanjing University of Aeronautics and Astronautics

A vortex ring impinging on a three-dimensional bump is studied using large eddy simulation for a Reynolds number Re = 4 × 104 based on the initial translation speed and diameter of the vortex ring. The effects of bump height on the vortical flow phenomena and the underlying physical mechanisms are inves- tigated. Based on the analysis of the evolution of vortical structures, two typical kinds of vortical structures, i.e., the wrapping vortices and the hair-pin vortices, are identified and play an important role in the flow state evolution. The circu- lation of the primary vortex ring reasonably elucidates some typical phases of flow evolution. Furthermore, the mechanism of flow transition from laminar to turbulent state has been revealed based on analysis of turbulent kinetic energy.

关键词： large eddy simulation vortex ring bump vortical structure turbulent state

Experimental and Large-Eddy Simulation Studies on Three-Dimensional Vortices Produced by an Impinging Transverse Jet

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Experimental and Large-Eddy Simulation Studies on Three-Dime...