Shock wave generation by transonic vortex-profile interaction

Two impulse noise generation mechanisms, parallel interaction between a vortex and an airfoil in two-dimensional airflow, are investigated experimentally. The first one originates from the area of the stagnation point of the airfoil. When the vortex rotates toward the airfoil, the pressure and the density increase at the stagnation point while the vortex is passing. The pressure then decreases with the emission of a sound wave propagating upstream, called a compressibility wave. The second observed source of impulse noise is the shock generated by the decay of a local supersonic flow regime. This unsteady supersonic flow regime is induced by the vortex flow near the leading edge of the airfoil. After the vortex has passed the leading edge, the shock at the end of the supersonic flow regime propagates upstream. This kind of shock generation, called transonic wave generation, is determined by the vortex-induced Mach number.