120 対称翼から発生する後流放出渦と離散周波数騒音について

Abstract

The mechanism of the discrete frequency noise generation from the symmetric airfoils was investigated in transition Reynolds numbers. The following results are obtained. At the transition Reynolds numbers the boundary layer separate from the airfoil surface upstream of the trailing edge and the wake vortices form just at the trailing edge with inducing the shear flow fluctuation when the discrete frequency noise(DFN) generates. But the boundary layer flow attached up to the trailing edge and the wake vortices form at a downstream of the trailing edge. Then the shear flow do not fluctuate at the trailing edge and the discrete frequency noise little generate. that is, the formation of wake vortices does not always generate the DFN and the location of the wake vortices formation is closely relating to the discrete frequency noise at transition Reynolds numbers.