Evaluation Of Rotor Broadband Noise Predictions

An evaluation of several existing rotor broadband noise models is presented with the help of a high quality experimental data of a MD500E helicopter. A brief overview of the ground tests and flight tests of the helicopter is given. The prediction schemes evaluated consisted of both compact and noncampact low frequency broadband noise (LFBN) and high frequency broadband noise (HFBN) prediction models. The LFBN models considered address only turbulent inflow ingestion noise source while the HFBN models considered include trailing edge noise (TEN), tip vortex formation noise (TVN) and trailing edge bluntness noise (TEBN) sources. A brief description of these models is presented. Experimentally obtained inflow turbulence properties were used in LFBN predictions for hover, while empirically cibtained values were used in LFBN predictions for forward flight conditions. Both compact and noncampact LFBN . models are shown to signif icantly underpredict the experimental data for the main rotor in ground tests, while the correlations between the predicted LFBN values and the experimental data is shown to be fair for forward flight conditions. In the case of high frequency broadband noise, the correlations between the predicted values and experimental data are shown to range fram fair to good depending on the frequency range for both hover and forward flight conditions. Effects of using different turbulent boundary layer characteristics on trailing edge noise are also presented. In general it is concluded that the existing rotor broadband noise prediction models are fair at best and plainly inadequate at worst.