PIV study on flow around leading-edge slat of 30P30N airfoil

We acquired the flow field around a leading-edge slat using PIV and flow visualization. Simultaneously, sound measurement using a microphone was also performed. The leading-edge slat and main wing model was placed in the tunnel. The angle of attack was varied from 4 to 10 degrees, and the free stream velocity was set at 15m/s in maximum. At the slat cusp, a shear layer and vortices are formed. When the vortices convect along the shear layer towards the slat trailing edge, they split finely and then impinge on the slat inner wall. The magnitude of the correlation coefficient between the sound and the vorticity takes the maximum value near the vortex impingement region. In FFT analysis, peak frequencies in the sound spectrum were agreed well with that in the vorticity spectrum and the spectrum of the brightness in the images of the smoke visualization. The first peak frequency is agreed with the natural frequency of the model. The second and third ones are agreed with the movement of the vortices in the slat cove. By reconstruction of the vorticity fluctuation from several POD modes, the trajectory of the vortices is considered to correlate with the peak frequency in the sound spectrum.