HEAD-ON PARALLEL BLADE-VORTEX INTERACTION

An experimental and computational study was carried out to investigate the parallel head-on blade-vortex interaction (BVI) and its noise gen eration mechanism. A shock tube, with an enlarged test section, was us ed to generate a compressible starting vortex which interacted with a target airfoil. The dual-pulsed holographic interferometry (DPHI) tech nique and airfoil surface pressure measurements were employed to obtai n quantitative flowfield data during the BVI. A thin-layer Navier-Stok es code (BVI2D), with a high-order upwind-biased scheme and a multizon al grid, was also used to simulate numerically the phenomena occurring in the head-on BVI. The detailed structure of a convecting vortex was studied through independent measurements of density and pressure dist ributions across the vortex center. Results indicate that, in a strong head-on BVI, the opposite pressure peaks are generated on both sides of the leading edge as the vortex approaches. Then, as soon as the vor tex passes by the leading edge, the high-pressure peak suddenly moves toward the low-pressure peak-reducing in magnitude as it moves-simulta neously giving rise to the initial sound wave. In both experiment and computation, it is shown that the viscous effect plays a significant r ole in head-on BVIs.