Experimental Investigation of the Flow Characteristics and Noise Generation at the Wing–Wall Junction

Abstract

This paper is concerned with the flow characteristics and noise generation at the finite wing–wall junction. To characterize junction flow noise, acoustic measurements were taken in the acoustic wind tunnel at the Brandenburg University of Technology in Cottbus, Germany, with a planar 47-microphone array at a chord-based Reynolds number (Rec) of 2.3×105. The wings used have an aspect ratio (AR) of 2 and six different section profiles with variations in camber and thickness. The results show that the junction noise dominates at the low-frequency range below 4 kHz (chord-based Strouhal number of Stc=5.6), which is particularly obvious for the symmetric wing. On the other hand, the addition of leading-edge bluntness and camber are found to have less of an influence on the junction noise spectra. Both symmetric and nonsymmetric wings near the stall angle exhibit a dramatic increase in the high-frequency junction noise content above 8 kHz (Stc=11.2), indicating the existence of a different junction noise mechanism. To provide insight into the junction flow, measurements of the mean streamwise total pressure field within the wing–wall junction were performed in the acoustic tunnel at the University of New South Wales for two wing ARs of 0.2 and 1.0 at Rec=2.6×105 and several angles of attack (AoA). The contour maps of the mean streamwise total pressure field indicate the existence of the horseshoe vortex around the wing and exhibit variations of the flow structure at different streamwise locations and AoA. Further, the AR influences the upwash and downwash near the junction due to the effect of the tip vortex. These competing effects are observed on different sides of the wing under different lifting conditions and AR. The relatively simple geometries of the test cases and the complex physics they create make this data set particularly valuable for validation of numerical simulations and models.