Noise and drag reduction by riblets.
The aeroacoustic emission generated by the interaction between the trailing-edge of an airfoil and the layer of fluid near the airfoil surface (boundary layer) is known as trailing-edge noise. Trailing-edge noise is among the dominant sources of noise pollution from a landing aircraft and the most significant contributor of the aeroacoustic emissions of a wind turbine. Strategies for the abatement of this source of noise were developed over the last few years, but they deteriorate the aerodynamic performance (lift over drag ratio), which hinders their implementation in engineering solutions. Riblets on the other hand have never been explored in aeroacoustics, although they lead to a drag reduction of up to 10% when applied on a flat plate. Riblets are tiny surface protrusions aligned along the flow direction. A texture analogous to riblets is found in the wing feathers of the owl, the most silent bird in the animal kingdom when flying. To investigate how riblets of different geometries impact on the aeroacoustic and aerodynamic properties of an airfoil, this project pairs a researcher with experience in experimental fluid mechanics and turbulence research with an expert in aeroacoustics and numerical methods, achieving a mutually beneficial transfer of knowledge. The Fellow will examine the effects on noise and drag reduction of a complete set of independent geometrical parameters for the riblets. This will be followed by a detailed study of the flow physics using a complementary approach involving time-resolved tomographic particle image velocimetry at high spatial resolution and high-fidelity numerical simulations with the software PowerFLOW™. The project dissemination will target scientific communities where immediate impact is envisaged, comprising aeroacoustics, aerospace and energy engineering, and turbulence. This pairing and build of project will ensure the successful completion of this ambitious research project and promote the Fellow’s career development.