The flow and noise generated by a sharp trailing edge

Aeroacoustic results obtained from the study of the noise generated by turbulent flow over a trailing edge are presented. The test model used was a 5 mm flat plate with a sharp trailing edge. Models with and without side walls were studied and the results show the effects of the side wall boundary layer on farfield noise. The effect of trips and wind socks on the measured noise spectra are also presented. Mean and unsteady flow data in the very near trailing edge wake were measured and provides important information on the turbulent noise sources. Such information is needed for the future development and validation of predictive models. Introduction Lighthill [7] originally described how free turbulence is a source of noise, such as that produced by a jet. When turbulent flow passes a sharp trailing edge (as in the case of a boundary layer on an airfoil), acoustic diffraction occurs thus increasing the efficiency of noise production [4]. This type of flow induced noise is an important source of noise for aircraft, wind turbines and submarines and needs to be understood in greater detail in order to design new, quieter technology. In particular, new aeroacoustic prediction schemes are required. Most are either too computationally demanding [10, 11] or are semi-empirical in nature [1] hence are not valid for conditions used to derive them. A new computationally efficient predictive methodology is currently under development at the University of Adelaide [2]. This scheme combines steady CFD solutions with a boundary layer velocity space-time correlation statistical model to calculate noise. Early results are promising and since the methodology is applicable to any airfoil or hydrofoil shape, it is useful for the designers of wind turbines and submarines. However, datasets providing both boundary layer velocity data and farfield noise simultaneously are rare but are needed to validate any new predictive model. This paper presents some initial results for the baseline case of a flat plate. The aims of this paper are as follows: (1) to present aeroacoustic test data for a flat plate test model placed in uniform flow; (2) to illustrate the influence of extraneous noise sources on the test results and (3) to present the turbulent mean and unsteady flow information near the trailing edge.