Abstract: To improve the accuracy in the simulation of rotor flowfield and noise in the CFD/Kirchhoff method, a combination of the third-order upwind scheme(MUSCL) and flux-difference splitting scheme, instead of the second-order center-difference scheme which may cause larger wake dissipation, is employed and a N-S solver based upon embedded grids is developed. On the basis of the flowfield solution, a harmonic expansion approach is presented for rotor far-field noise. The approach gives an analytical expression of the integral function in the Kirchhoff formula and thus improves the interpolation efficiency and accuracy. A rotor high-speed impulsive(HSI) noise is calculated and a comparison with available experimental data is made, and good agreement was demonstrated. In addition, the HSI noise of helicopter rotors at different tip Mach numbers and on different observer locations is calculated and analyzed. The calculated results indicate a highly directional nature of the rotor high-speed impulsive noise with a maximum in the plane of rotor, and the impulsive feature of the high-speed noise radiation weakened rapidly with the increase of the directivity angle below the rotor plane.

Key words: rotor noise, high speed impulsive noise, computational fluid dynamics, Kirchhoff method, helicopter