Abstract: The impulsive sound due to blade-vortex interaction of the helicopter rotor is dis-cussed.First of all, the mechanism of such blade-vortex interaction is presented Then,a theo-retical model for the blade transient force and the radiated sound is given. The unsteady lift on the blade is calculated using the response function of a finite aspect ratio wing to an oblique gust obtained by linear unsteady aerodynamics. The sound harmonic formulation developed by Low-son is used for radiated sound due to the transient lift fluctuation,Finally,some numerical results are given to analyse the characteristics of helicopter noise due to blade-vortex interaction.The estimated transient sound pressure signal results show their reasonable agreement with the experimental data.

Key words: noiseCsound), rotary wings, blade-vortex interaction