Effect of Sensor Mounting and Flow History on Measured Wall Pressure Spectra

Abstract

An experimental study of wall pressure fluctuations beneath a turbulent boundary layer was carried out on a plate model with a streamwise varying pressure gradient along the plate length. The wall pressure fluctuations were measured with flush-mounted Kulite sensors, and mean velocity measurements across the boundary layer were performed by using a single-wire hot-wire anemometer. A variety of streamwise pressure distributions were imposed by changing the position and the angle of attack of a NACA 0012 airfoil installed above the plate. The effect of the upstream flow history on the wall pressure spectra in the presence of the streamwise varying pressure gradient was studied. Spectral attenuation due to the spatial averaging associated with a finite sensor size was corrected via the Corcos correction. The results show that the Corcos correction to the measured Kulite spectra leads to an overprediction of the spectral intensity at medium frequencies and an underprediction at high frequencies. Hence, a new correction is proposed based on the measured spectral attenuation. Finally, the measurements also indicate that even slight imperfections in sensor mounting and relatively weak upstream flow disturbances can have a significant influence on the measured spectra of the wall pressure fluctuations.