Numerical simulations of helicopter aerodynamics and acoustics

This paper demonstrates several new methods for computing acoustic signals from helicopter rotors in hover and forward flight. Aerodynamic and acoustic solutions in the near field are computed with two different finite-volume flow solvers for the Euler equations. A solution-adaptive unstructured-grid Euler solver models a rotor in hover while a more conventional structured-grid solver is used for forward flight calculations. A nonrotating cylindrical surface is then placed around the entire rotor system. This surface moves subsonically with the rotor hub in forward flight. The finite-volume solution is interpolated onto this cylindrical surface at every time step and a Kirchhoff integration propagates the acoustic signal to the far field. Computed values for high-speed impulsive noise in hover and forward flight show excellent agreement with experimental data. Results from the combined finite-volume/Kirchhoff method offer high accuracy with reasonable computer resource requirements.