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Analysis of the Spanwise vortex of open channel flows based on the Omega-Liutex vortex identification method

Journal of Hydrodynamics 2022年第1期34卷 148-155页

作者： Bin Li Wen-jun Yang Jie Li Si-yu Jing Yue Chen Changjiang River Scientific Research Institute Wuhan430010China Fujian College of Water Conservancy and Electric Power Sanming353000China Department of Water Conservancy and Hydropower Engineering Hohai UniversityNanjing210098China

In this paper, a particle imaging velocimetry (PIV) system of high-temporal-spatial resolution is used to investigate the Spanwise vortex distribution of fully developed turbulent flows in an open channel and its relationship with the turbulence. The distributions of the time-averaged velocity, the turbulence intensity and the Reynolds stress are obtained in the longitudinal profile. The third-generation vortex identification method (based on the Omega-Liutex vector) is applied to accurately identify and analyze the vortex in the spanwise direction. The results suggest that the vortex density increases with the Reynolds number at a given aspect ratio (B / H) of the flow. The distribution trend of the Spanwise vortex density in the vertical direction remains unchanged for different discharges. Specifically, the vortex density increases along the vertical direction and reaches the peak at y / H = 0.15, then decreases and reaches the bottoms at the flow surface.

关键词： Open channel turbulent flows Spanwise vortex Reynolds number particle imaging velocimetry(PIV) aspect ratio

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Investigations of entrainment characteristics and shear-layer vortices evolution in an axisymmetric rear variable area bypass injector

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Chinese Journal of Aeronautics 2022年第4期35卷 230-244页

作者： Guoping HUANG Chao LI Chen XIA Qian LI College of Energy and Power Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016China

In this study,firstly,for the axisymmetric RVABI,the change-rule of adverse pressure gradient caused by radial velocity during the transition of internal flow mode in variable geometry is summarized,and a Bypass Ratio(BR) iterative algorithm based on the empirical correlation of non-equilibrium pressure is proposed.The algorithm can estimate the nonlinear relationship between area ratio and BR,with an error range falling below 6.5%.Then,we discuss the favorable effect of uniform mixing on the thrust augmentation of mixed exhaust under variable BR conditions.From this point of view,the characteristics of vortices evolution in different shear strength jets are compared,to clarify the effect of variable cycle parameters on jet mixing.As the results suggest,when ■ is as low as 0.22,the K-H disturbance is of high-frequency wavelet property,and it is difficult to induce large-scale spanwise vortices.The macro migrations of fluid elements in span wise vortices and the diffusion effect caused by edge tearing is weak,which is not conducive to the energy exchange between the two streams.However,the low ■ jet will also correspondingly weaken the viscous dissipation effect of vortices.It is concluded that the dissipation level is proportional to the 2.31 power of the ■.

关键词： Variable cycle engine Rear variable area bypass injector Bypass ratio adjustment Mixed exhaust Thermal mixing Spanwise vortex

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Numerical Investigation on the Influence of Nozzle Lip Thickness on the Flow Field and Performance of an Annular Jet Pump

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Journal of Harbin Institute of Technology(New Series) 2014年第3期21卷 59-67页

作者： Long-Zhou Xiao Xin-Ping Long Xue-Long Yang School of Power and Mechanical Engineering Wuhan University Key Lab of Jet Theory and New Technology of Hubei Province

The performance of an annular jet pump( AJP) is determined by its area ratio A( ratio of cross sectional area of throat and annular nozzle) and flow rate ratio q( ratio of primary and secondary flow rate,Qs/Qj),while the nozzle lip thickness is neglected in the present studies. This paper presents a study on the effect of the thickness on the flow field and performance of an AJP with A = 1. 75. With the increasing flow rate ratio and nozzle lip thickness,a small vortex forms at the nozzle lip and keeps on growing. However,as the flow rate ratio or nozzle lip thickness is extremely low,the vortex at the lip vanishes thoroughly. Moreover,the recirculation width varies conversely with the nozzle lip thickness when the flow rate ratio q ≤ 0. 13. While the deviation of the recirculation width with different nozzle lip thickness is negligible with q ≥ 0. 13. Additionally the existence of nozzle lip hinders the momentum exchange between the primary and secondary flow and leads to a mutation of velocity gradient near the nozzle exit,which shift the recirculation downstream. Finally,based on the numerical results of the streamwise and Spanwise vortex distributions in the suction chamber, the characteristics of the mixing process and the main factors accounting for the AJP performance are clarified.

关键词： annular jet pump nozzle lip recirculation streamwise vortex Spanwise vortex

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