Experimental and analytical acoustic technique to measure wall shear

A technique that considers aeroacoustic technology that measures fluctuating pressure in turbulent boundary layers is proposed as a means of determining wall shear characteristics on smooth and rough surfaces. The methodology considers the classic work of Lilley (1964) where the normalized power magnitude with wall shear for a smooth wall, incompressible flow is between 1.7 and 3. The methodology considers a transformation function for extending boundary layer properties from the incompressible plane to the compressible plane. As such, the equations reduce compressible data into the incompressible plane where direct comparison can be made to the classic works of Bull et al. The methodology so developed allows for a technique to predict wall shear (drag) using measured fluctuating pressure for smooth and rough surface. An experimental program was conducted in the Wright Patterson Air Force Base, AFWAL/FIMG Mach 3 facility to validate the concept for smooth wall attached turbulent boundary layer flow. Data consisted of sound pressure level, power, and power spectra as well as wall shear measurements (Preston tube). Wall temperature and pressure were also recorded in the Reynolds number range of 4 x 10 to the 7th to 1.2 x 10 to the 10th together with boundary layer profiles using conventional pitot and LDV measurements.