Effect of front inclined hole on flow structure around a wall-mounted cube

Abstract

To control the wake flow around a wall-mounted cube, passive control is performed by drilling a front inclined hole (FIH) from the front surface to the free end of the cube. To study the control features and mechanism, controlled and uncontrolled cubes are experimentally investigated. A circulation water tunnel is used to perform PIV measurements, where the Reynolds number is ReD = 11550 based on the cube side length of D = 70 mm, and the thickness of the boundary layer on the tunnel bottom is δ/D = 0.25. To study the effect of the hole position, three FIHs with inlet heights of 20, 35, or 50 mm are investigated. The time-averaged flow fields show that the velocity of the FIH jet increases with the FIH inlet height. Comparing with the flow structures around standard cube, it is found that the reverse zone and shear layer above free-end are obviously suppressed due to the FIH jet. In addition, the scale of the reverse zone and arch-type vortex in the near-wake is reduced by the FIH jets. Because the FIH jets disrupt the development of wake vortices, the Reynolds shear stress and turbulent kinetic energy in the near-wake decrease. The control effect is most apparent for the cube with an FIH at a spanwise height of 50 mm (the FIH50 cube). In this case the effect of the free-end downwash flow on the wake is weaker, and the shedding frequency of the wake vortices near the free-end increases. Proper orthogonal decomposition analysis indicates that the FIH50 suppresses the alternately arranged flow features and enhances the symmetrically arranged features.