Tip vortex formation noise produced by wall-mounted finite airfoils with porous and sinusoidal tip geometries

Acoustic measurements were performed in a quasi-anechoic open jet wind tunnel at the Brandenburg University of Technology. The airfoils used in this study have chord length of 70 mm, aspect ratio of 2, NACA0012 and NACA6412 profile and an interchangeable tip. For the NACA0012 airfoil, 11 sinusoidal tips and 8 porous tips were tested. The sinusoidal tips have amplitude of 3 to 10 mm and a wavelength of 7 to 23.3 mm. For the porous tips, porosities between 5.14 and 50.3% were achieved by varying the size and location of the pores on the tip surface. For the NACA6412 airfoil, 6 selected sinusoidal tips and 3 selected porous tips were tested. Acoustic data were obtained using a planar microphone array containing 47 microphones. Acoustic measurements were taken at Reynolds numbers based on chord of 2.5e4 to 2.25e5 and geometric angles of attack between -10 and 20 degrees.