Wall-Mounted Finite Airfoil-Noise Production and Prediction

Abstract

This paper presents the results of an experimental investigation of the flow-induced sound produced by a smooth, wall-mounted finite length airfoil with a flat-ended tip and a tripped turbulent boundary layer. Acoustic measurements have been taken in the Stability Wind Tunnel at Virginia Polytechnic Institute and State University with a microphone array at a range of Reynolds numbers (, based on chord), angles of attack (), and for a variety of airfoil aspect ratios (airfoil length-to-chord ratio of ). Spectral data show the dominant noise sources are airfoil trailing-edge noise and tip-vortex-formation noise. Acoustic data are also used to evaluate semi-empirical prediction of wall-mounted finite airfoil trailing edge and tip noise with the so-called Brooks, Pope, and Marcolini model. The prediction method employs the Brooks, Pope, and Marcolini trailing-edge-noise model modified to incorporate spanwise variations in flow properties in combination with the Brooks, Pope, and Marcolini flat-tip-noise model. Three-dimensional trailing-edge-noise predictions agree well with measured spectra at a Strouhal number of , based on airfoil chord. The Brooks, Pope, and Marcolini tip-noise model underpredicts the peak level and frequency of tip-noise contributions at . A new empirical model of flat-tip-airfoil noise is presented that provides an accurate estimation of the wall-mounted finite airfoil dominant tip-noise contribution to within 1.7 dB.