利用层析PIV(Tomo-PIV)对圆柱尾迹影响下的湍流三维相干结构的研究
The wake of a circular cylinder at Re = 2700 is investigated by means of Tomographic PIV(Tomo-PIV), a recently developed three-dimensional velocimetry technique. The paper presents theprinciples of Tomo-PIV and discusses in details the implementation of the technique to the experimentalconditions. With a measurement volume of approximately 40x40x10 mm2 two configurations are chosen inorder to describe both the 2D wake features and the span wise organization of secondary rollers dominatingthe 3D flow organization. The present data allow to directly evaluate the measurement error imposing massconservation inside the volume (viz. solenoidal velocity field). The visualization of the wake instantaneousstructure is obtained by means of vorticity vector magnitude iso-surfaces, or decomposing the vorticity in thespan wise and stream-wise(normal)/bi-normal component, which return the separate contribution of theKármán rollers and the interconnecting structures between them respectively. The properties of thesecondary rollers are given in terms of span wise wavelength, peak vorticity, vorticity stretching and theirsize and shape. A value of the span wise wavelength λz/D = 1.2 is recurring and the rollers organization intopairs is found to be similar to the instability Mode B occurring in lower Reynolds number wakes investigatedwith previous studies.