Experimental study of porous treatments for aerodynamic and aeroacoustic purposes

This paper is concerned with the noise generation mechanism from blunt trailing-edges and the use of porous treatments for reducing the radiated noise, and stabilizing the vortex shedding and the wake region. Experiments have been carried out for a flat plate with and without porous trailing-edges. To gain a better understanding of the underlying physics of the noise generation mechanism and the effects of porous trailing-edges, velocity measurements have been carried out within the boundary layer and wake. Surface pressure fluctuation measurements have also been performed near the plate trailing-edge. Results have shown that the use of porous surfaces leads to an increase of the shear stresses in the near wall region of the boundary layer but significant reduction of the energy content of the larger turbulent structure in the outer layer. The PIV results have also shown that the porous trailing-edge can delay the vortex shedding and significantly increase the vortex formation length, resulting in a very low turbulent near wake region. The surface pressure measurement results indicate that the use of porous treatment increases the broadband energy content of the surface pressure fluctuations globally in the whole frequency ranges, but, also effectively eliminates the vortex shedding frequencies. A noticeable reduction can also be observed in the lateral coherence of the turbulent structure in the case of porous trailing edges. The results demonstrate that porous treatments can be used for stabilizing boundary layer, wake flow and noise reduction purposes.