Flow-field and Noise Characterization of a Controlled-Diffusion Airfoil under stall

The present experimental investigation focuses on a flow-field and noise characterization of a CD airfoil experiencing large flow separation and stall. Measurements are performed to investigate the effect of Reynolds number stalling noise signature of the CD airfoil. This study includes investigation of the potential interaction of wind tunnel shear layers with the separating shear layer of the airfoil, in an effort to validate previous experimental studies performed on a similar jet width using Planar-PIV. While a mean flow separation is observed near the leading-edge of the CD airfoil at angles of attack of 15 degrees, the mean reattaches before the trailing-edge region for the case of 15 degrees. In contrast for 22 degrees case the mean flow becomes completely separated and airfoil experiences a deep stall. For the latter, the Sound Pressure Levels are reduced and it is possibly linked to a decrease in overall velocity disturbances and attenuation of modulations in SPL linked to diffraction. More importantly, the velocity disturbances do not scale with overall extent of the separated shear layer or the boundary layer. As such, a one to one correspondence does not exist between SPL and boundary layer thickness.