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Simulation of vortex shedding behind a bluff body flame stabilizer using a hybrid U-RANS/PDF method

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Acta Mechanica Sinica 2012年第2期28卷 348-358页

作者： Min-Ming Zhu Ping-Hui Zhao Hai-Wen Ge Yi-Liang Chen Department of Thermal Science and Energy Engineering University of Science and Technology of China230027 HefeiChina Engine Research Center University of Wisconsin-Madison1500 Engineering DriveMadisonWI 53706USA

The present study aims at the investigation of the effects of turbulence-chemistry interaction on combus- tion instabilities using a probability density function （PDF） method. The instantaneous quantities in the flow field were decomposed into the Favre-averaged variables and the stochastic fluctuations, which were calculated by unsteady Reynolds averaged Navier-Stokes （U-RANS） equations and the PDF model, respectively. A joint fluctuating velocity- frequency-composition PDF was used. The governing equa- tions are solved by a consistent hybrid finite volume/Monte- Carlo algorithm on triangular unstructured meshes. A non- reacting flow behind a triangular-shaped bluff body flame stabilizer in a rectilinear combustor was simulated by the present method. The results demonstrate the capability of the present method to capture the large-scale coherent struc- tures. The triple decomposition was performed, by divid- ing the coherent Favre-averaged velocity into time-averaged value and periodical coherent part, to analyze the coherent and incoherent contributions to Reynolds stresses. A sim- ple modification to the coefficients in the turbulent frequency model will help to improve the simulation results. Unsteady flow fields were depicted by streamlines and vorticity con- tours. Moreover, the association between turbulence produc- tion and vorticity saddle points is illustrated.

关键词： vortex shedding PDF method Unsteady RANS Finite volume. Bluff bodies

Influence of thermal inhibitor position and temperature on vortex-shedding-driven pressure oscillations

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Chinese Journal of Aeronautics 2013年第3期26卷 544-553页

作者： Su Wanxing Li Shipeng Zhang Qiao Li Junwei Ye Qingqing Wang Ningfei School of Aerospace Engineering Beijing Institute of Technology China Academy of Space Technology

vortex-acoustic coupling is one of the most important potential sources of combustion instability in solid rocket motors （SRMs）. Based on the Von Karman Institute for Fluid Dynamics （VKI） experimental motor, the influence of the thermal inhibitor position and temperature on vortex-shedding-driven pressure oscillations is numerically studied via the large eddy simulation （LES） method. The simulation results demonstrate that vortex shedding is a periodic process and its accurate frequency can be numerically obtained. Acoustic modes could be easily excited by vortex shedding. The vortex shedding frequency and second acoustic frequency dominate the pressure oscillation characteristics in the chamber. Thermal inhibitor position and gas temperature have little effect on vortex shedding frequency, but have great impact on pressure oscillation amplitude. Pressure amplitude is much higher when the thermal inhibitor locates at the acoustic velocity anti-nodes. The farther the thermal inhibitor is to the nozzle head, the more vortex energy would be dissipated by the turbulence. Therefore, the vortex shedding amplitude at the second acoustic velocity antinode near 3/4L （L is chamber length） is larger than those of others. Besides, the natural acoustic frequencies increase with the gas temperature. As the vortex shedding frequency departs from the natural acoustic frequency, the vortex-acoustic feedback loop is decoupled. Consequently, both the vortex shedding and acoustic amplitudes decrease rapidly.

关键词： Combustion instability Pressure oscillation Solid rocket motor vortex-acoustic coupling vortex shedding

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

Animating turbulent water by vortex shedding in PIC/FLIP

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Science China(Information Sciences) 2013年第3期56卷 16-26页

作者： ZHU Jian LIU YouQuan CHANG YuanZhang WU EnHua Computer Graphics and Multimedia Laboratory(NG04) Faculty of Science and TechnologyUniversity of Macau School of Information Engineering Chang'an University State Key Laboratory of Computer Science Institute of SoftwareChinese Academy of Sciences

In this paper,we present a hybrid method,which integrates PIC/FLIP and vortex particle methods into a unified framework,to efficiently simulate vortex shedding that happens when fluids flow around internal obstacles.To improve efficiency and reduce the numerical dissipations,we first solve the governing equations on a coarse grid using PIC/FLIP,and then interpolate the intermediate results to a finer grid to obtain the base flow.When the regular particles in PIC/FLIP enter the boundary layer,if the specified conditions are satisfied to cause vortex shedding,they are selected as vortex particles by assigning additional vorticity related attributes.The vortex particle dynamics are controlled by the vorticity form of NS equations,and several efficient methods are proposed to solve them on the finer grid.Finally,the obtained turbulence flow is added to the base flow.As a result,we are able to simulate turbulent water with rich wake details around the internal obstacles.

关键词： physically based fluid simulation turbulence vortex shedding vortex particle PIC/FLIP

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

INVESTIGATION OF DOMINANT FREQUENCIES IN TRANSITION REYNOLDS NUMBER RANGE OF FLOW AROUND A CIRCULAR CYLINDER PART I:EXPERIMENTAL STUDY OF THE RELATION BETWEEN vortex shedding AND TRANSITION FREQUENCIES

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Chinese Journal of Mechanical Engineering 2006年第2期19卷 159-167页

作者： AHMED N A School of Mechanical and Manufacturing Engineering University of New South Wales Sydney 2052 Australia

A comprehensive hot wire investigation of the flow around a circular cylinder is carried out in an 18＂ × 18＂ wind tunnel to look into the dominant frequencies at the stagnation, separation and separated shear layers in the transition Reynolds number range. The majority of the experiments are carried out at Reynolds number of 4.5×104, with additional transition frequency tests at Reynolds numbers of 2.9×104, 3.3×104 and 9.7×104 respectively. The results are analysed in terms of power spectral density. While the frequency associated with stagnation is found to be essentially due to vortex shedding, frequency doubling of vortex shedding is also evident in the separated shear layers. Two peaks associated with transition frequencies are detected and their possible implications are presented.

关键词： vortex shedding Transition Separated flow Power spectral density

FURTHER STUDY ON vortex shedding FLOW BY A CIRCULAR CYLINDER

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Acta Mechanica Sinica 1988年第3期4卷 211-222页

作者： Ling Guocan Institute of Mechanics,Chinese Academy of Sciences Institute of Mechanics Chinese Academy of Sciences China

In the present paper the mechanism involved in vortex shedding flows is investigated in detail.In the early stage of the unsteady separated flow the interaction between secondary vortices and primaryvortices is quite strong. In the later stage of the flow, corresponding to the vortex shedding the recirculatingflow region on each side of the aft body goes through such a cycle: growth-contraction-growth, the secondaryseparation occurs periodically rather than continuously. The reduction of circulation is taken into account inthree cases with different decay factors to study its influence on the prediction of main flow characteristics.Results show that to simulate vortex shedding flow it is necessary to include the reduction of circulation tobring the calculated results into good agreement with experiments. An improved discrete vortex model issuggested in which both the secondary separation and the reduction are incorporated. The processes of vortexshedding, the forces prediction and other flow characteristics are given and some discussions are made.@Chinese Academy$In the present paper the mechanism involved in vortex shedding flows is investigated in detail.In the early stage of the unsteady separated flow the interaction between secondary vortices and primaryvortices is quite strong. In the later stage of the flow, corresponding to the vortex shedding the recirculatingflow region on each side of the aft body goes through such a cycle: growth-contraction-growth, the secondaryseparation occurs periodically rather than continuously. The reduction of circulation is taken into account inthree cases with different decay factors to study its influence on the prediction of main flow characteristics.Results show that to simulate vortex shedding flow it is necessary to include the reduction of circulation tobring the calculated results into good agreement with experiments. An improved discrete vortex model issuggested in which both the secondary separation and the reduction are incorporated. The processes of vortexshedding

关键词： circular cylinder vortex shedding secondary separation reduction of circulation discrete vortex model

NUMERICAL STUDY OF vortex shedding FROM A SQUARE CYLINDER AND ITS EFFECTS ON HEAT TRANSFER OF MIXED CONVECTION

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Journal of Hydrodynamics 2003年第3期15卷 103-111页

作者： Zhang Ning, Li Guang-zheng, Huang Jian-chun College of Civil Engineering and Mechanics, Huazhong University of Science and Technology, Wuhan 430074, China, College of Civil Engineering and Mechanics Huazhong University of Science and Technology Wuhan 430074 China

The influence of buoyancy on vortex shedding from a heated square cylinderand its effects on the heat transfer of mixed convection were simulated. The flow equations, basedon the velocity and the pressure, were solved along with the energy equation by a modified SIMPLERalgorithm - the Quick Scheme and small Control Volume (QSCV) algorithm developed by the authors ofthe present paper. A set of optimized computational domain and artificial lateral boundaryconditions were used along with the QSCV algorithm. Several cases were simulated for the Grashofnumbers up to 1. 8 X 10~5, the Reynolds numbers up to 500, and a range of angles between free streamvelocity and gravity from 0 to 1.5π. In opposing flow, the results distinguish two different flowpatterns: periodic flow for Gr Gr_c, anda precise correlation between Gr_c and Re expressed as Gr_c = 0. 00166(Re)^(2.97795) for Re up to500 was firstly obtained. In cross flow, it could be seen that the Ri = Gr/Re^2 plays a great rolein the wake vortex patterns and the temperature fields. In aiding flow, it is found that the mainflow currents cause a large expansion of the streamlines and isotherms in the direction normal tothe free stream velocity. These changes in the wake vortex patterns and the temperature fieldsgreatly modify the heat flux along the surface of the square cylinder and consequently, the heattransfer rate is strongly dependent upon the Reynolds numbers, the Grashof numbers, and the gravitydirection.

关键词： buoyancy mixed convection vortex shedding numerical simulation

Control of vortex shedding behind a Circular Cylinder in an Electrically Low-Conducting Fluid-Revised

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Control of Vortex Shedding behind a Circular Cylinder in an ...