Evolution and control of multiscale vortical structures in a wall-mounted cube wake

Abstract

In this study, multiscale flow features in a wall-mounted cube wake are investigated experimentally based on two-dimensional time-resolved particle image velocimetry measurements and wavelet transform. Moreover, the control mechanism of the horizontal control hole (HCH) on the cube wake is studied. The width of the cube model is D = 50 mm, and the corresponding Reynolds number is ReD=7800. The flow control cases include nine kinds of HCHs with three different diameters and three different heights. The results show that the shear layer contains a continuous merging process of multiscale vortices, which leads to the momentum deficit. Particularly, the evolution of large-scale vortices causes exponential growth of momentum deficit. In the xy-plane, the large spanwise vortices cause fluctuations in the near wake (x/D ≲ 3), which are stronger than those in the shear layer but are not present in the xz-plane. The downstream wake is anisotropic due to its strong downwash flows and weak inward flow. The HCH issuing flow weakens the intermediate- and large-scale vortices in the shear layer and hinders the interacting shear flows in the wake, thus reducing the momentum deficit in the near wake. In the downstream wake, the effect of HCH is also anisotropic: in xz-plane, the momentum recovery is slow due to the decrease in the downwash flow by HCH; in the xy-plane, the momentum recovery is fast due to the increase in the range of the inward flow by HCH.