Effect of Plate Distance on Steady and Unsteady Characteristics of Impinging Rectangular Jet

Acoustic and unsteady characteristics of a rectangular jet impinging on a flat plate were investigated. Experiments were performed at the nozzle pressure ratio of 2 for the impingement distances H/Dh=2, 4, 8, and 12. The mean and unsteady flow properties of the impinging jet were studied using the steady and unsteady pressures on the impinging surface, time-resolved schlieren images, and acoustic measurements at different directivity angles. Mean schlieren images elucidate the flow features including redirected flow, and the plate shock for the impingement distance H/Dh=2. The mean surface pressures show unidentical pressure profiles in the x-z and x-y planes. The pressure profile in the x-y plane is found to be identical to the free-jet case. Proper orthogonal decomposition performed on the time-resolved schlieren images shows that the impinging jet is dominated by the flapping instability mode for a given range of impingement distances. Flow features such as plate shock and the redirected flow were assessed using proper orthogonal decomposition and time-resolved schlieren images. Synchronized acoustic and unsteady pressure measurements reveal the coupling between the upstream acoustic waves and the unsteadiness arising from the impinging surface.