The Remote Microphone Probe for Unsteady Surface Pressure Measurement

This study aimed to develop a remote microphone probe to measure unsteady surface pressure in order to localize and identify force-induced sound and/or vibration sources. The probe achieved a center-to-center tap distance of 0.81mm and a frequency response up to 15kHz, thereby facilitating discrete point surface measurements with high-spatial resolution and high-frequency response. The probe consisted of 3-tubes: a rigid tube connected the surface tap to a gradual inside diameter expansion, a rigid tube from the expansion to the sensing region and a non-rigid tube to act as an anechoic termination. Analytical and experimental transfer function methods in the frequency domain are provided to correct for tubing distortions resulting from viscous attenuation and acoustic impedance changes. Various lengths of tubing were tested to show the design's impact on transfer function. Measurement results from a zero-pressure-gradient turbulent boundary layer validate the method, and measurements along the trailing cylinder of a circulation control airfoil demonstrate its ability to yield measurements along complex geometries. The remote microphone probe technique can be used in many applications and optimized for specific experiments by changing the lengths and radii of the tubing. The analytical method allows for probe details to be determined in the design phase, and the experimental method allows for correction of any real world discrepancies that may be encountered.