Uniform Suction for the Reduction of the Trailing-Edge Noise

Abstract

Uniform inclined suction from a spanwise slot is applied upstream of a trailing edge on a zero pressure gradient flat plate with the aim of reducing trailing edge noise. The effects of the flow treatment on the turbulence statistics are experimentally investigated downstream of the flow control section using hot-wire anemometry. Surface pressure measurements from flush-mounted microphones are used to estimate the far-field trailing edge noise. The area of the flow control is kept constant, while the flow suction velocity and the angle of suction are varied. We examine four angles of flow suction velocity, namely α = 30 • , 50 • , 70 • and 90 • alongside a wide range of flow control severities. It is found that flow suction changes the overall structure of the flow. Both the boundary layer thickness and the momentum thickness increases as a result of flow suction. The mean velocity profiles nondimensionalized by the inner units show that flow suction increases the extent of the viscous region, while the logarithmic region progressively reduces its size with increasing the flow suction severity. At sufficiently high suction rates, the logarithmic region disappears, which is an evidence of flow laminarisation. Flow suction efficiently reduces the flow energy content within the entire span of the boundary layer. The estimated far-field trailing edge noise is reduced in the range of frequencies between 200 Hz and 1-2 kHz, with the highest levels of estimated noise reduction obtained at an angle of flow suction of α = 70 • , at a suction rate high enough to achieve laminarisation.

A Review on Generation and Mitigation of Airfoil Self-Induced Noise

“…Increasing flow control severity would increase the viscous region while decreasing the logarithmic region. The logarithmic region disappears when flow control severity is greater than 6 [63]. The highest noise reduction of about 5dB is achieved at a flow control severity of 6 and the suction angle of 70°.…”