COMPUTATION OF HELICOPTER ROTOR ACOUSTICS IN FORWARD FLIGHT

This paper presents a new method for computing acoustic signals from h elicopter rotors in forward flight. The aerodynamic and acoustic solut ions in the near field are computed with a finite-difference solver fo r the Euler equations. A nonrotating cylindrical Kirchhoff surface is then placed around the entire rotor system, This Kirchhoff surface mov es subsonically with the rotor in forward flight. The finite-differenc e solution is interpolated onto this cylindrical surface at each time step and a Kirchhoff integration is used to carry the acoustic signal to the far field. Computed values for highspeed impulsive noise show e xcellent agreement with model-rotor and flight-test experimental data, Results from the new method offer high accuracy with reasonable compu ter resource requirements.