Three-dimentional surface treatments for trailing edge noise reduction

The present study is concerned with the experimental investigation of a novel passive trailing edge noise control technique. The technique is based on upstream manipulation of large coherent turbulent structures using two and three dimensional blade-shaped surface treatments. To investigate the effects of the new trailing edge noise control technique on point spectra of surface pressure fluctuations and the spanwise length scale in the trailing edge region, a long flat-plate model, equipped with a non-uniformly spaced L-shaped array of surface pressure microphones has been designed and built. The measurements of the surface pressure fluctuations have been carried out at low to moderate Reynolds numbers for 2D surface treatments, with various lengths and chord-wise positions. Furthermore, to improve surface treatment performance, various 3D combinations of fences has been proposed. Results have shown that the efficiency of the 2D surface treatments in reducing both the surface pressure point spectra and spanwise length scales improves as they are positioned closer to the flat plate trailing edge. Moreover, it has been observed that the use of fences with small length is enough to significantly reduce surface pressure power spectral density and spanwise length scale over a wide range of frequencies, implying that the large coherent turbulent structures have been successfully removed from the boundary layer. It has also been shown that the 3D surface treatments composed of proper combination of fences with different spacing exhibit better performance than the straight 2D fences.