Passive control on the wake of a thin flat plate by drilling a hole from the surface

To control the wake of flat plate, passive control is performed by drilling a hole from the surface. The differences of the turbulence wake between a flat plate and a perforated plate are investigated using particle image velocimetry (PIV). Through power spectral density (PSD) function, proper orthogonal decomposition (POD) and the phase-averaged method combined with a conditional detection by spatial multi-scale local average function, the vortex structure and distributions of the velocity statistics are explored in the wake. Compared with the results of the wake of flat plate, it can be found that the hole can greatly reduce the turbulence intensity of the wake, and the turbulence tends to be isotropic but not homogeneous behind a distance of 35D from the perforated plate trailing edge. The perforation changes the initial boundary condition of the very near wake, and the analysis of phase average indicates that the perforation effectively breaks the large-scale vortex structures, suppresses the intensity peak of velocity statistics and weaken the alternant of vortex. The PSD and POD analysis imply that under the influence of the hole, the wake vortex shedding are suppressed, and the energy distribution is more uniform in each mode.