Flow-induced noise of a wall-mounted finite airfoil at low-to-moderate Reynolds number

Abstract This paper presents an experimental investigation of the flow-induced noise created by a wall-mounted finite airfoil at low-to-moderate Reynolds number and zero angle of attack. Far-field noise measurements have been taken at a single observer location and with two perpendicular microphone arrays in an anechoic wind tunnel at Reynolds numbers of Re c = 9.2 × 10 4 – 1.6 × 10 5 , based on chord, and for a variety of airfoil aspect ratios (length to chord ratio of L / C = 0.2 – 2 , corresponding to length to thickness ratio of L / T = 1.7 – 16.7 ). Additionally, surface oil-film visualisation images and unsteady velocity measurements taken in the near trailing edge wake are related to far-field noise measurements to determine the flow mechanisms responsible for noise generation. The results show that the wall-mounted finite airfoil radiates noise similar to a two-dimensional airfoil when L / T > 8.3 . Despite the incoming boundary layer height at the junction being 1.30 ≤ δ / T ≤ 1.46 , junction and tip flow suppresses tonal noise production for airfoil׳s up to L / T = 8.3 at Re c = 9.2 × 10 4 – 1.2 × 10 5 . Trailing edge noise is found to be the dominant airfoil noise generation mechanism at frequencies above 1 kHz with the position of the noise source along the trailing edge determined by the proportion of the airfoil span influenced by flow at the airfoil–wall junction.