Optimization of the poro-serrated trailing edges for broadband noise reduction

Abstract

Copyright © 2016 Author(s). This paper reports an aeroacoustic investigation of a NACA0012 airfoil with a number of Poro-Serrated trailing edge devices that contain porous materials of various air flow resistances at the gaps between adjacent members of the serrated-sawtooth trailing edge. The main objective of this work is to determine whether multiple-mechanisms on the broadband noise reduction can co-exist on a poro-serrated trailing edge. When the sawtooth gaps are filled with porous material of low-flow resistivity, the vortex shedding tone at low- frequency could not be completely suppressed, but a reasonably good broadband noise reduction can be achieved at high-frequency. When the sawtooth gaps are filled with porous material of very high-flow resistivity, no vortex shedding tone is present, but the mechanism to reduce the broadband noise reduction is undermined by the diminishing serration effect. An optimal choice of the flow resistivity for a poro-serrated configuration has been identified, where it can achieve in broadband noise reduction of 1.5 dB higher than the conventional serrated trailing edge whilst completely suppress the vortex shedding tone. A weakened turbulent boundary layer noise scattering at the poro-serrated trailing edge is reflected by the larger spanwise extent of the low-turbulence intensity measured in the near wake centreline.