AERODYNAMIC NOISE GENERATION BY A STATIONARY BODY IN A TURBULENT AIR STREAM

Abstract

When a vortex street formed at the trailing edge of an upstream plate is arranged to impinge upon the leading edge of a small downstream block of similar thickness, a very powerful aerodynamic noise source of tonal quality is formed. Such an arrangement in which the down stream block is suspended on taut wires has been used to investigate Curle's prediction of the relation between the fluctuating lift force exerted by the block on the stream and the radiated sound power in the frequency domain for flow speeds ranging from 70 m/s to 190 m/s.The possible effect of additional stiff constraint to the motion of the clock in the direction of the fluctuating lift force on the radiated noise has also been investigated. The apparent effect of the additional constraint was to increase the magnitude of the fluctuating force on the radiating block but in either the case of constrained or unconstrained block the measured sound power data tends to agree with Curle's prediction at flow speeds above 140 m/s but gradually to diverge upward at lower flow speeds toward a prediction based upon a small vibrating sphere. In all cases the measured sound power levels tend to be bounded by Curle's prediction below and 9·5 dB above by a prediction based upon a small vibrating sphere.