Effect of Surface Roughness on Boundary Layer Transition and Far Field Noise

摘要: Surface roughness elements are often used to force laminar turbulent transition during aerodynamic and aeroacoustic experiments in wind tunnels. The statistical features frequency content of the forced boundary layer can influence far-field trailing edge noise. To study this dependence, induced by randomly distributed a zigzag strip same height over NACA 0012 airfoil is investigated experimentally. effects type on near-field flow topology, location, noise addressed. At fixed height, less effective forcing than trip at low freestream velocity (u∞ l 20 m/s). As u∞ increases, front for moves close reaching or even further upstream location compared with strip. intensity depends location. For m/s, higher level measured respect Whereas, l20m/s, earlier onset leads lower data confirms that an adequate characterization state necessary when measuring tunnel experiments.