Numerical investigations of Fenestron(tm) noise characteristics using a hybrid method
The present article gives an overview of numerical investigations performed during a research project aimed at in depth understanding of noise generation mechanisms of a shrouded helicopter tail rotor such as Airbus Helicopters Fenestron$\mathrm{TM}$TM. Both aerodynamic and aeroacoustic studies are performed based on a full scale lightweight transport helicopter configuration with detailed geometry of the Fenestron$\mathrm{TM}$TM and by neglecting of the main rotor downwash effect. Analysis is carried out by using a hybrid method, combining Unsteady Reynolds Averaged Navier Stokes (URANS) simulation with Ffowcs Williams and Hawkings (FW H) acoustic analogy. Two representative helicopter flight conditions, namely fast forward flight and hovering, are considered. Thereby, it is intended to assess the influence of cross flow in forward flight condition on the Fenestron$\mathrm{TM}$TM acoustic property. Effect of turbulence model on the accuracy of noise prediction is also investigated by comparing the Shear Stress Transport (SST) turbulence model with the Scale Adaptive Simulation (SAS) The capability of the applied hybrid methodology is estimated by means of flight test measurements. A good agreement is found between the predicted and measured sound spectra in terms of blade passing frequency (BPF) and its corresponding sidebands for both flight conditions investigated.