Wall pressure spectra on a DU96-W-180 profile from low to pre-stall angles of attack

Abstract

In an effort to characterize noise induced by separated turbulent boundary layers, surface pressure fluctuations on a DU96-W-180 airfoil were measured using miniature pressure sensors. Because of limitation in amplifier channels and available sensors, a rearrangeable configuration of sensors was applied. Chordwise distributions of the surface pressure were obtained for aerodynamic angles of attack of $-0.8^\circ\leq\alpha\leq10.3^\circ$ and at three Reynolds numbers $(0.8, 1.0, and 1.2) \times 10^6$. The boundary layer profile at 1%c behind the trailing edge was measured using constant temperature anemometry. The boundary layer thickness compares well with that simulated using XFOIL for $alpha\leq7.8^\circ�$. Within the limits of the simulation, other relevant boundary layer properties from XFOIL were used to calculate the surface pressure spectrum predicted from published empirical models for zero and non-zero pressure gradient turbulent boundary layers. Finally, a modified Blake-TNO semi-empirical model was used to predict the surface pressure spectrum near the trailing edge for separated flow. The modification is introduced to the so called `moving axis spectrum' and the chord-normal correlation length scale. It is found that in the low frequency range, the modified semi-empirical model �fits well with the measured surface pressure spectrum of a separated turbulent boundary layer.