Measured spatial filtering characteristics of membranes and plates

Abstract

Two rectangular plates and a membrane were designed to be used as spatial filters for measuring the low‐wavenumber components of turbulent boundary layer wall pressure fluctuations. For such stuctures it is convenient to define wavenumber filter‐shape functions which are obtained from spatial transforms of the normal mode shapes. This suggests that it is possible to determine experimentally the wavenumber filter shapes by measuring the normal mode shapes. Detailed measurements of selected mode shapes were made for a membrane, a clamped plate, and a simply supported plate. The mode‐shape data was then transformed numerically to obtain typical wavenumber filter shapes for the structures. These measured wavenumber filter shapes compare favorably with theoretical predictions; however, to obtain reliable results it was necessary to attain both frequency and spatial matching of the excitation to the desired resonant mode. [Work supported by the Sensor Technology Program, ONR.]