Self-Noise Produced by an Airfoil with Nonflat Plate Trailing-Edge Serrations

Abstract

This paper represents the results of an experimental study aimed at reducing the airfoil self-noise by the trailing-edge serration of four different sawtooth geometries (defined in the serration angle and length). These serrations have a common feature: all of the sawtooth patterns are cut directly into the trailing edge of a realistic airfoil. This configuration offers better structural strength and integrity. For the sawtooth trailing edges investigated here, the radiation of the extraneous vortex shedding noise in a narrowband frequency due to the partial bluntness at the serration roots is unavoidable. However, this narrowband component tends to be less significant provided that the serration angle is large and the serration length is moderate. Sound power was measured, and some of the sawtooth geometries have been shown to afford significant boundary-layer instability tonal noise and moderate turbulent broadband noise reductions across a fairly large velocity range. This paper demonstrates that a nonflat plate serrated trailing edge can also be effective in the self-noise reduction. Some experimental results are also presented in order to explain the self-noise mechanisms.