Analysis of noise generated by a wall mounted finite-length airfoil

Abstract

In order to produce aircraft, turbo-machinery and helicopters with low acoustic signatures and without annoying tones, it is essential to understand the noise generated by airfoils. A series of experiments were carried out in the ane-choic wind tunnel facility at the University of Adelaide with subsonic, low Mach number turbulent flow over a wall-mounted finite-length NACA 0012 airfoil of span 124 mm and chord 67 mm (aspect ratio of 1.851). Acoustic data were acquired using two phase-matched microphones, one mounted 560 mm above and the other 560 mm below the trailing edge of the airfoil, for flow conditions in the Reynolds number range of 2.2×104 - 1.675×105. Experiments were conducted for airfoil geometric angles of attack (α) of 0º, 5º and 10º. From the experimental measurements, it is evident that the noise spectra contained broadband noise together with tonal components of various frequencies and sound pressure levels. In this paper, the effect of the airfoil tip on its tonal noise behavior and the effects of Reynolds number and angle of attack on the far-field noise radiated from the airfoil are presented and compared with experi-mental and numerical investigations carried out by others for similar geometries and flow conditions.