Flowfield and Sound from a Blunt Trailing Edge with Varied Thickness

摘要

The flowfield and sound generated by turbulent flow passing over the trailing edge of an airfoil was studied experimentally. The airfoil geometries considered were thin, flat models that provided canonical, zero-pressure-gradient, turbulent boundary layers upstream of the trailing edge. The Reynolds number based on the chord was 2×10~6. A trailing edge with a symmetric, tapered, sharp edge was studied first This allowed the use of a simple scattering theory to predict the radiated sound based on boundary-layer surface pressure. Second, a series of blunt, asymmetric, trailing-edge models were studied. The lower surface of the edge was flat, while the upper surface was rounded with a 45 deg trailing-edge angle. Three models were considered, which provided a variation in the ratio of model thickness to thickness of the approach boundary layer. Particle image velocimetry measurements were obtained to provide insight into the local flowfield dynamics that generated the sound. Acoustic measurements from the blunt edges indicated that the high-frequency sound primarily resulted from scattering from the lower surface. At lower frequency, the radiated sound was found to have significantly higher amplitude compared to the sharp-edged case. This was caused by the large-scale motions in the wake resulting from the separated flow at the trailing edge. In the case of where the boundary layers were thin compared to the trailing edge, discrete vortex shedding and tonal sound were observed. When the boundary layers were thicker, the elevated sound levels were broadband.