SENSITIVITY OF ACOUSTIC PREDICTIONS TO VARIATION OF INPUT PARAMETERS

Rotor noise prediction codes predict the thickness and loading noise p roduced by a helicopter rotor, given the blade motion, rotor operating conditions, and fluctuating force distribution over the blade surface . However, the criticality of these various inputs, and their respecti ve effects on the predicted acoustic field, have never been fully addr essed, This paper examines the importance of these inputs, and the sen sitivity of the acoustic predictions to a variation of each parameter The effects of collective and cyclic pitch, as well as coning and cycl ic flapping, are presented, Blade loading inputs are examined to deter mine the necessary spatial and temporal resolution, as well as the imp ortance of the chordwise distribution, The acoustic predictions show r egions in the acoustic field where significant errors occur when simpl ified blade motions or blade loadings are used, An assessment of the v ariation in the predicted acoustic field is balanced by a consideratio n of CPU time necessary for the various approximations,