Abstract: A numerical method of 3 D unsteady transonic flows about rotary wings is proposed. The small disturbed potential equation is solved by using the finite difference method. The non reflecting boundary conditions in far boundaries are derived and successfully applied in the numerical calculation. They reduce the size of physical solution domain. Body fitted and non uniform meshes are constructed to obtain high accuracy. In this way, 3 D unsteady subsonic and transonic flows for non lifting rotors are calculated with fewer grids, and the numerical results are in good agreement with the experimental data.

Key words: rotary-wing, unsteady flow, potential flow, boundary conditions