Kelly, M.E. and Brown, R.E. (2009) The effect of blade aerodynamic modelling on the prediction of the blade airloads and the acoustic signature of the HART II rotor. In: 35th European Rotorcraft Forum, 2009-09-22 - 2009-09-25, Hamburg, Gemany.
As a rotorcraft descends or manoeuvres, the interactions which occur between the rotor blades and vortical structures within the rotor wake produce highly impulsive loads on the blades and with these a highly intrusive external noise. Brown's Vorticity Transport Model has been used to investigate the influence of the fidelity of the local blade aerodynamic model on the quality of the prediction of the high-frequency airloads associated with blade-vortex interactions and thus on the accuracy with which the acoustic signature of the aircraft can be predicted. The Vorticity Transport Model can resolve very accurately the structure of the wake, and allows significant flexibility in the way that the blade loading can be represented. The predictions of two models for the local blade aerodynamics are compared for all three of the HART II flight cases. The first model is a simple lifting-line model and the second is a somewhat more sophisticated lifting-chord model based on unsteady thin aerofoil theory. A marked improvement in accuracy of the predicted high-frequency airloads and acoustic signature of the HART II rotor is obtained when the lifting-chord model for the blade aerodynamics is used instead of the lifting-line type approach. Errors in the amplitude and phase of the loading peaks are reduced and the quality of the prediction is affected to a lesser extent by the computational resolution of the wake. Predictions of the acoustic signature of the rotor are similarly affected, with the lifting-chord model at the highest resolution producing the best representation of the distribution of sound pressure on the ground plane below the rotor.
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