Three-dimensional shock fitting for transonic rotor acoustics

A rotor blade operating above the 'delocalization' tip Mach number produces a large-amplitude, high-frequency, impulsive noise. A dominant feature of the flow field created by such a rotor blade is the radiating shock wave which extends off the blade tip and propagates to the far field. Predicting the acoustic signature of this rotor requires a detailed knowledge of the flow properties (velocity, density, pressure) in the vicinity of the radiated shock wave both on the blade itself and in the near field. Current numerical techniques tend to smear the shock wave, particularly the portions off the blade surface, resulting in an inaccurate flow field description. The paper describes a method of applying a shock-fitting algorithm to a three-dimensional, full potential rotor code. This approach maintains the flow physics by directly invoking conservation laws as internal boundary conditions at the shock surface. Results show that the shock discontinuity is maintained using the shock-fitting technique. Comparisons with other methods show improvement in the characterization of the shock as a discontinuity.