基于层析PIV的湍流边界层展向涡研究

层析PIV是一种现代激光测速技术,能实现三分量空间体内三分量(3D3C)速度场的测量。应用层析PIV测量Reτ=1768的平板湍流边界层,得到150个瞬时速度场,测量体的大小为80mm×16mm×45mm。旋涡强度λci 准则用来进行涡识别,而旋涡强度在展向的投影λzci 被用来识别展向涡。根据λzci 的连通域得到展向涡位置后,统计了展向涡沿法向的变化规律,并给出了在流向-法向平面内高低速区域和正负展向涡空间位置的关系。统计结果表明:随着法向高度的增加,展向涡的强度逐渐降低;负展向涡的流向平均速度高于正展向涡,且流向速度与法向速度有很强的依赖性;在小尺度范围内,流向-法向平面内的高低速流动区域与正负展向涡的空间位置密切相关。

Study of spanwise vortices in turbulent boundary layer flow based on tomographic PIV

Tomographic particle image velocimetry (Tomo-PIV )is a novel laser technique that can be applied to measure a three-dimensional three-component (3D3C)velocity field.In the current work,Tomo-PIV was utilized to measure a plate turbulent boundary layer (TBL)at Reτ= 1768,and 150 velocity fields with each size of 80mm×16mm×45mm were obtained.The swirl strengthλci was used to identify the local vortex,while its proj ection on the spanwise directionλzci was used to identify the spanwise vortex.The spatial coherent structures of spanwise vortices and their population trends along the wall-normal direction were studied through swirling strengthλzci .The statistic results suggest that the strength of the spanwise vortices reduces with the in-crease of the wall-normal distance y+ .The streamwise velocity of retrograde spanwise vortices is higher than that of the prograde vortices and there is a strong dependence between the streamwise velocity and the wall-normal velocity.High or low momentum regions of small scale in the stre-amwise and wall-normal plane are highly correlated with the spatial arrangement of spanwise vor-tices.Some 3D plots of instantaneous flow structures in TBL are presented and discussed at the end of the paper.