Structural and acoustic noise produced by turbulent flow over an elastic trailing edge

Abstract

An analysis is made of the sound and vibration produced by turbulent flow at low Mach number over the trailing edge of an elastic plate. The trailing edges of airfoils and other flow control surfaces are known to be important sources of high frequency sound. When the surface is compliant the turbulent edge-flow also excites structural modes of vibration. In conditions of heavy fluid loading, which typically occurs in underwater applications, the energy imparted to the structural motions can be large, and the subsequent scattering of ‘surface waves’ at mechanical discontinuities is frequently an important secondary source of sound. In this paper general formulae are developed for the structural and acoustic edge-noise when the control surface is modelled by a semi-infinite, thin elastic plate which can support bending waves. Numerical results are given for steel plates in air and in water. In the latter case it is shown that, when the frequency is smaller than the coincidence frequency the bending wave power exceeds the total sound power generated at the edge by 20–40 dB, independently of the mean flow velocity, so that sound generated by secondary scattering may then be the dominant source of acoustic radiation.