Three-dimensional wake structures controlled by the flow issuing from a horizontal hole in a wall-mounted short cylinder

This paper examines the three-dimensional (3D) wake flow structures induced by a wall-mounted short circular cylinder. The structures are controlled by the flow issuing from a horizontal hole (HH) drilled from the front to the rear of the cylinder. The 3D velocity fields are instantaneously measured at a Reynolds number of 10,720 using high-resolution tomographic particle image velocimetry (Tomo-PIV) in a water tunnel. The 3D vorticity fields, Q criterion, and characteristics of arch-type and tip vortices are compared between the HH cylinders and a standard cylinder based on the measured instantaneous 3D velocity fields. A 3D W-type arch vortex appears behind the short HH cylinders. Compared with the standard cylinder, the 3D W-type arch vortex and large-scale vortices break down more rapidly in the wake of the HH cylinders. The flow from the HH may reduce the rear recirculation region to 15%, effectively controlling the wake structures of short cylinders. A 3D wavelet multiresolution analysis is used to decompose the 3D velocity fields given by the Tomo-PIV data. The large-scale streamwise vortices in the HH cylinder wakes are smaller than those in the standard cylinder wake, and this becomes more evident as the hole height increases. The intermediate-scale vortices are also controlled by the flow issuing from the hole.