湍流边界层相干结构空间拓扑形态的 层析TRPIV测量

用层析TRPIV(time-resolved paticle image velocimetry)技术精细测量了水洞中平板湍流边界层三分量速度的时空序列信号,提出了空间局部平均多尺度速度结构函数的新概念描述湍流多尺度涡结构的空间拉伸、压缩、剪切变形和旋转.用空间局部平均多尺度速度结构函数对湍流脉动速度进行了空间多尺度分解.用空间局部平均多尺度速度结构函数的新概念,根据湍流多尺度涡结构在空间流向的拉伸和压缩特征,提出了新的湍流相干结构条件采样方法,检测并提取了层析TRPIV数据中相干结构的“喷射”和“扫掠”事件中的速度、涡量等物理量的空间拓扑形态.发现在喷射和扫掠事件中均存在一对反向旋转的准流向“马蹄形”涡结构.

Tomo-TRPIV measurement of coherent structure spatial topology in turbulent boundary layer

The spatial-temporal sequence of 3D-3C(three-dimensional-three-component) simultaneous velocity field in a turbulent boundary layer was finely measured by tomographic TRPIV(time-resolved particle image velocimetry) in a water channel.A new concept of spatial local averaged velocity structure function was introduced to describe the dilation,compression and shear distortion and rotation of multi-scale eddy structures in turbulent flow.The three fluctuating velocity components of TBL (turbulent boundary layer) were decomposed into multi-scale components by spatial local averaged velocity structure function.A new turbulence coherent structure conditional sampling method was proposed based on the dilation and compression features of turbulent multi-scale eddy structures and the new concept of spatial local averaged velocity structure function.The eject and sweep process due to large-scale coherent structure burst was conditionally detected and the characteristic spatial topology modes of physical quantities,such as velocity and vorticity,during coherent structure bursts,were extracted from the tomo-PIV(particle image velocimetry) experimental dataset.A pair of counter-wise quasi-longitudinal horseshoe shaped vortex was discovered during coherent structure eject and sweep process.