Improvement of DLR rotor aeroacoustic code (APSIM) and its validation with analytical solution

DLR's APSIM code was developed for prediction of rotor or propeller noise radiated in the free far-field. APSIM is the abbreviation for "Aeroacoustic Prediction System based on Integral Method". A new formulation based on airloads as input was derived and implemented in APSIM. The number of revolutions used in the input airloads can now be specified. This characteristic is very important for the tail rotor noise computation as the airloads on the tail rotor may not repeat after one revolution due to main and tail rotor interaction. The aeroacoustic results for the 40% scale BO105 main rotor and tail rotor configuration are calculated using both pressure distribution and airloads from DLR's UPM-Mantic code. The results using different aerodynamic inputs are compared. The implementation of the FW-H formulation based on penetrable surface into DLR's APSIM code is discussed. The aeroacoustic benchmark problems based on a point monopole source in various motions were used to validate the implementation. The comparisons were also made with Kirchhoff formulation. Finally, the effect of an open integral surface on the radiated sound field is discussed and suggestions on the future works are then presented.