Aeroacoustic effect of boundary layer separation control by rod vortex generators on the DU96-W-180 airfoil

An experimental campaign to study the impact of a distinct type of vortex generator - rod type (RVG), on the flow characteristics and the acoustic far -field pressure of a wind turbine airfoil, is conducted. Airfoils exhibit decreased aerodynamic performance at high inflow angles due to turbulent boundary layer flow separation. RVGs are applied to mitigate the flow separation. However, this benefit is accompanied by an acoustic penalty. An assessment of the impact of RVGs on the far -field noise emission is conducted for the DU96-W-180 airfoil. The evolution of the boundary layer impacted by the rods is analyzed through Particle Image Velocimetry (PIV) measurements. The resulting reduction in the separation zone is observed through oil flow visualization. Analysis of the sound spectrum for airfoils with/without RVGs is conducted for a range of frequencies (300 Hz to 4000 Hz). Results show a reduction of the noise level at relatively low frequencies, at the expense of an increased noise level in the mid -high frequency ranges. While the former is caused by the reduction of the flow separation, the latter is determined by the combined contribution of the noise scattered by the RVG and by the change in boundary layer characteristics at the airfoil trailing edge.