An Experimental Study of Turbulent Noise Reduction through Coupling Owl-like Features

In order to suppress noise associated with high-speed vehicles, owl-wing features that promote silent flight – leading-edge serrations, trailing edge serrations, and the velvet downy feathers – are being explored. The literature indicates very little work done on the coupled effects of these owl-wing features. Thus, the goal of this research is to characterize such experimentally. This is achieved by conducting particle image velocimetry measurements of flow over a plate with serrations at the leading edge, and porous surface conditions (to mimic downy owl wings). The model is tested in a flume at a chord Reynolds number of 65000. The effects are distinguished by comparing with velocities obtained using three other models at similar flow conditions, namely a blunt edge (or the plain) model, a serrated leading-edge model, and a porous surface model. Results indicate the presence of a serrated edge increases momentum thicknesses by over 70%, relative to the plain model. However, by combining the porous surface with the serrated edge, the momentum thickness is enhanced. For the wake flow, vorticity is least in the combined serration-porous surface model, yet with similar turbulence statistics as the plain model. These show that vorticity modification is key to noise reduction.