Aerodynamic noise contributions in a ducted tail-rotor configuration using high-fidelity simulation

The characteristics of the flow in a shrouded tail rotor configuration are investigated using explicit Large Eddy Simulations (LES). Some turbulence statistics in the boundary layer of the blade are analyzed and a laminar separation bubble is observed in the pressure coefficient plots at some span locations on the blade. A coherent tip leakage vortex (TLV) that originates in the vicinity of the blade tip is observed and the most dominant flow features are analyzed using a Dynamic Mode Decomposition (DMD) method in a plane intersecting the TLV. The dominant mode highlights the helical oscillation and breakdown of the TLV. On the blade, DMD modes highlight a coupling between the root and the tip of the blade. The noise sources contained in the unsteady flow are propagated in the far field using Ffowcs Williams and Hawkings (FW-H) analogy for noise predictions. The acoustic power spectra showed good agreement with experimental results in terms of tonal components and broadband shape despite an over prediction of 5–10 dB of noise levels.