Poro-Serrated trailing edge devices for airfoil self-noise reduction

Abstract

This paper represents the continuation of the works previously published in Chong et al. (“Self-Noise Produced by an Airfoil with Nonflat Plate Trailing-Edge Serrations,” AIAA Journal, Vol. 51, No. 11, 2013, pp. 2665–2677), who used several nonflat plate serrated trailing edges for the reduction of airfoil self-noise. The poro-serrated concept developed in the current work improves substantially the overall noise performance of the nonflat plate trailing-edge serration type. The use of porous metal, synthetic foams, or thin brush bundles to fill the gaps between adjacent members of the sawtooth can completely suppress the bluntness-induced vortex shedding tonal noise. Most important, up to 7 dB turbulent boundary layer–trailing-edge broadband noise reduction can simultaneously be achieved without compromising the aerodynamic performances in lift and drag. The poro-serrated trailing edges do not cause any noise increase throughout the frequency range investigated here. The reduction of the turbulent broadband noise is primarily caused by the serration effect, but under a condition that the sawtooth surface must be solid and nonporous. The primary role of the porous metal foams in a poro-serrated trailing edge is to suppress the vortex shedding tonal noise. However, an optimum selection of the porous material is also found to be able to further reduce the broadband noise level. The new serrated trailing-edge concept developed here has the potential to improve the industrial worthiness of the serration technology in achieving low noise radiation in fan and turbine blades.