A study of passive compliant coatings on trailing edge noise through simulations and experiments

Abstract

Studies that involve mitigating aerodynamic noise in rotating components such as rotors of wind turbines or propellers of Unmanned Aerial Vehicles have gained immense interest in the research community over the last few years. The present study explores noise mitigation potential of passive compliant coatings through Computational Aeroacoustics Analysis (CAA) and experimentation through wind tunnel testing. CAA was performed on a flat plate for a chord-based Reynolds number of Re_c = 460,000 using the SST k-ω Improved Delayed Detached Eddy Simulation and the Ffowcs Williams and Hawkings acoustic analogy. Trailing edge (TE) noise was accurately predicted from 750 to 7000 Hz. Noise results were compared with cases where compliant coatings with different material properties are applied onto flat plate. It was observed that coating-1 (Dow Corning Silastic S-2) may increase TE noise by 10 – 15 dB/Hz throughout the frequency range of interest, with an increase in Overall Sound Pressure Level (OASPL) by 2.89 dB. Whereas coating-2 (Dow Corning Sylgard 184) shifted energy content in TE noise to a lower frequency range and reduced noise by 2 – 4 dB/Hz from 600 to 1575 Hz. Additionally, it resulted in a 1.85 dB reduction in OASPL, thus demonstrating that choice of coating material’s viscoelastic properties plays a crucial role in its ability to mitigate TE noise. Further, noise measurements recorded inside a closed loop wind tunnel revealed a farfield noise reduction of 2 – 4 dB/Hz from 253 to 1367 Hz, with a corresponding 3.23 dB reduction in OASPL. These results demonstrate the favorable effects of compliant coatings on TE noise.