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Experimental study on dynamic mechanism of vortex evolution in a turbulent boundary layer of low Reynolds number

Journal of Hydrodynamics 2020年第5期32卷 807-819页

作者： Yan-ang Guo Xiang-rui Dong Xiao-shu Cai Wu Zhou School of Energy and Power Engineering University of Shanghai for Science and TechnologyShanghai 200093China Key Laboratory of Multiphase Flow and Heat Transfer in Shanghai Power Engineering Shanghai 200093China

The dynamic mechanism of the vortex generation and evolution process in a fully developed turbulent boundary layer with Reθ=97-194 is experimentally *** this study,a moving single-frame and long-exposure(MSFLE)imaging method and a moving particle image velocimetry/particle tracing velocimetry(M-PIV/PTV)are designed and implemented for measuring the temporal and spatial evolution of vortex cores in both qualitative and quantitative ways,*** the other hand,the Liutex vector,which is a new mathematical definition and identification of the vortex core proposed by Liu’s group,is first applied in the experiment for the structural visualization and quantitative analysis of the local fluid *** results show that an intuitional process of vortex evolution can be clearly observed by tracking the vortex using MSFLE and verify that the roll-up of the shear layer induced by shear instability is the origin of vortex formation in ***,a quantitative investigation in terms of the critical vortex core boundary(size)and its accurate rotation strength is carried out based on the Liutex vector field analysis by M-PIV/*** to statistics of the relation between vortex core size and the rotation strength during the whole process,the physical mechanism of vortex generation and evolution in a turbulent boundary layer of low Reynolds number can be summarized as a four-dominant-state course consisting of the“synchronous linear segment(SL)-absolute enhancement segment(AE)-absolute diffusion segment(AD)-skewing dissipation segment(SD)”.

关键词： Turbulent boundary layer high-and low-speed fluid vortex generation moving single-frame and long-exposure moving particle image velocimetry/particle tracing velocimetry Liutex vector

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Achieving an optimal shock-wave mitigation inside open channels with cavities for weak shock waves:A computational study

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Theoretical & Applied Mechanics Letters 2020年第5期10卷 354-365页

作者： N.Brahmi A.Hadjadj Normandie University Institut National des Sciences Appliquées of RouenCNRSCORIA76000 RouenFrance

This paper deals with a numerical study of weak shock-waves propagation and their attenuation in channel flow having different heights and exhibiting a hollow circular cavities with different depths and diffraction angles *** effect of initial diffraction angle and cavity depth on the shock mitigation is investigated.A better shock attenuation is achieved with diffraction angle by a factor of approximately 17%in terms of shock-Mach number and 38%in terms of total *** obtained results show also,in addition to the initial diffraction angle and cavity depth,the importance of reducing the channel heights as well as the position of the reduced section in achieving an optimal shock-wave *** presence of a cavity inside the channel helps to attenuate faster the shock *** underlying physics relies on the shock diffraction phenomenon that generates large amount of vortical structures capable of dissipating part of the shock energy by inducing a pressure loss behind it.A subtle arrangement of channel position/height and a cavity location leads to an efficient pressure attenuation by approximately a factor of 57%forMs=1.6 and 16%for Ms=1.1..

关键词： Shock diffraction Shock reflection Shock attenuation vortex generation

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A COMPARISON OF FOUR RECENT NUMERICAL SCHEMES GIViNG HIGH RESOLUTION OF SHOCK WAVE AND CONCENTRATED vortex

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Applied Mathematics and Mechanics(English Edition) 1994年第9期15卷 797-804页

作者：黄敦杨淳 1. Depart. of Math. Peking University Beijing 2. Depart. of Math. Peking Normal University Beijing

In recent ten years high resolution difference schenies for the computation of thefull unsteady Eulerian system of equations for invisid compressible gas finds celebratedprogress. This paper tests furtherly, by a complex two-dimensional unsteady problem,four recent schemes. to them attentions are paid. The test problem is the initial stageof a two-dimensional diffraction and reflection of a plane shock wave, impinging on arectangular obstacle. At whose top side there are two sharp corners, near which *** finds severe variation. There is occurrence of expansion fan with a centerand also concentrated vortices. To simulate them well, the schemes should have goodadaptivity. The special shock Mach number M,=2.068 is so chosen, that at this M,the partical velocity behind impinging shock in fixed coordinate system is just equal tothe speed of sound there, this condition also occurs along a curve in the region ofexpansion fan with a center at the corner. This can clarify the computational featureof different schemes in case,when one of the eigenvalues is just zero. Zero eigenvaluemay spoil some schemes locally. Graphical visualization of the computational resultsmay, show features of the tested schemes about the shock wave resolution, schemeviscosity, expansion wave and the ability. to simulate the process of the generation ofunsteadv concentrated vortex.

关键词： high resolution schemes shock wave reflection diffraction sharpcorner vortex generation

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