Array Measurements of the Unsteady Surface Pressure in a Sharp-Edged Impinging Jet

Abstract

Studied herein are the space-time characteristics of the surface-pressure fluctuations resulting from the impingement of an axisymmetric jet (at Reynolds number based on diameter of approximately 13500) on a flat wall. Unlike the bulk of existing literature, where the focus has been on jets emerging from a contoured nozzle or at the end of turbulent pipe flow, the present study examines a jet emerging from a sharp-edged circular opening. Pressure measurements are conducted using an array of thirty electret microphones embedded in the impingement plate. Data are acquired under normal- and oblique- impingement conditions. The results are compared to an earlier counterpart study of a jet exiting from a contoured nozzle. The comparison shows that significant fundamental differences in the observed pressure fluctuations and their spectral characteristics exist for the different jet exit conditions. Furthermore, it is found that alteration of the observed wall- pressure-field characteristics with change in the impingement angle may be explained through a hypothesis based on published work regarding the distortion of an isolated vortex ring impinging on an inclined wall. Future simultaneous measurements of the flow and wall- pressure fields are required to validate this hypothesis.