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

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 Rec=9.2×104–1.6×105Rec=9.2×104–1.6×105, based on chord, and for a variety of airfoil aspect ratios (length to chord ratio of L/C=0.2–2L/C=0.2–2, corresponding to length to thickness ratio of L/T=1.7–16.7L/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>8.3L/T>8.3. Despite the incoming boundary layer height at the junction being 1.30≤δ/T≤1.461.30≤δ/T≤1.46, junction and tip flow suppresses tonal noise production for airfoil׳s up to L/T=8.3L/T=8.3 at Rec=9.2×104–1.2×105Rec=9.2×104–1.2×105. 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.