MAIN ROTOR AND TAIL ROTOR BLADE VORTEX INTERACTION NOISE UNDER THE INFLUENCE OF THE FUSELAGE

This paper addresses the effects of the fuselage on the mutual interference between main rotor (MR) and tail rotor (TR), their shed wakes as well as noise characteristics. For this purpose, a BO105 MR/TR/Fuselage configuration is chosen in the numerical simulations. An unsteady free wake 3-D panel method (UPM) is used to account non-linear effects associated with the mutual interference between MR/TR/Fuselage as well as development of MR/TR shed wakes. Free wake and rotor noise computations were performed to study the effect of MR/TR/Fuselage mutual interaction on rotor wake development, blade loads and noise radiation. The sound propagation into the far field is calculated with DLR FW-H code APSIM by using UPM unsteady blade pressure as input. The effect of the fuselage, tail boom and stabilizers on MR/TR aerodynamic (unsteady blade loads, wake development) will be discussed and compared with HELINOVI wind tunnel measured data. In addition, tip vortex core radius development model derived from experiment has been calibrated. The numerical results indicate that in 6° descent flight where MR is major source of noise, inclusion of the fuselage in the simulation has in general improved clearly the correlation against the measured data and caused a reduction of MR BVI at advancing side and therefore improves comparison of maximum BVI noise level with experiment, while in low speed climb and high speed level flight where TR is major source of noise, the effect of the fuselage increases slightly TR BVI at advancing side when TR blade passes over the vertical stabilizer and therefore causes increasing TR BVI noise. The study on change TR rotational direction indicated aerodynamic interaction between the main and tail rotors is sensitive to the tail rotor rotational direction. The reduction of TR BVI amplitude and number of TR BVIs on the advancing TR blade side in TR rotating in Advancing Side Up (ASU) is the cause of a significant aerodynamically-induced loading noise reduction. The comparison between the experimental results and the numerical ones highlighted once more the extreme complexity of the aerodynamic phenomena involved in a complete helicopter configuration operating at different flight conditions