Comparison of finlet rails and fences for trailing edge noise reduction in NACA0012 aerofoil

In this paper, two surface treatments have been investigated experimentally for reducing trailing edge noise generated by an aerofoil. The aerofoil surface treatments include a Finlet rail supported by rods (called canopies) and walls (called Finlet fences). The surface treatments were applied near the trailing edge of the NACA0012 aerofoil. Far-field noise, near-field velocity, and surface pressure measurements were made for both the designs and compared with the untreated aerofoil. The far-field noise results show that both the surface treatments provide moderate noise level reductions in different frequency ranges, though huge reductions are seen in the surface pressure measurements. The finlet fences control the mid-and high-frequency noise reductions, while the canopies control the low-frequency noise reductions. Also, the noise reduction provided by the aerofoil with the combined surface design of Finlet fence and canopies treatments didn’t improve further reductions in the noise. Furthermore, the mechanism of pressure shielding hypothesised with the canopy treatment is a local phenomenon and very sensitive to the location of the canopy itself. The results for finlet fences indicate that the top edge of the fence generate localised flow separation which are responsible for the increase in Urms and Vrms at z/h = 1 (top edge), rather than lifting the turbulence structures from the trailing edge of an aerofoil. The work presented in this paper will be further extended in the future, which will include a more detailed parametric study.