Broadband noise from helicopter rotors is shown to be generated by the blades passing through turbulence associated with the trailing tip vortices in the rotor wake. This happens when the trailing tip vortices are ingested into the rotor and during flight regimes such as level flight or low angles of ascent. To predict the broadband noise levels generated by this mechanism the details of the turbulent flow close to trailing tip vortices must be known accurately and the location of the vortices relative to the rotor blades must be specified. This study evaluates recent wind tunnel measurements of turbulent trailing tip vortices and specifies a model for the turbulent velocity spectrum and the size of the turbulent region. The results are then combined with the calculations of the trailing vortex locations obtained from the CAMRAD.Mod1 code to give absolute noise level predictions. The predictions are compared with measurements and show that the flow modeling accurately predicts the spectral shape but tends to underpredict the overall level. However the overall level is very sensitive to the wake calculations obtained from the CAMRAD.Mod1 code and blade vortex miss distance is found to be the most important source of error in the noise calculations.
Broadband helicopter noise generated by blade wake interactions
Durch Rotorblatt-Wirbel-Interaktionen verursachte Helikopter-Breitbandgeräuschemissionen
Journal of the American Helicopter Society ; 44 , 4 ; 293-301
1999
9 Seiten, 17 Bilder, 17 Quellen
Article (Journal)
English
Broadband Helicopter Noise Generated by Blade Wake Interactions
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