The use of CFD to directly predict helicopter main rotor source noise is shown to be quite promising as an alternative means for low frequency noise evaluation. Results using existing state-of-the-art grid systems and higher-order numerical schemes demonstrated that small perturbation pressures, associated with acoustics radiation, can be extracted with some degree of fidelity. Assessment of the direct CFD method is performed via comparing predicted results to conventional acoustic analogy-based predictions and with measurements from wind tunnel and flight test data. Evaluation of in-plane noise radiation of the MD-902 main rotor at several advance ratio conditions yields the following results: -Low frequency noise content, below 6th blade-passing harmonics, are reasonably well-captured using the direct CFD method with a grid spacing on the order of the blade chord at the microphone. Results are in general agreement with wind tunnel and flight test data to within 4 dB; -Mid-to-high frequency noise content cannot be predicted by the direct CFD method due to grid spacing constraints and numerical limitations. Large discrepancies of up to 20 dB, in the mid-frequencies, are found especially at conditions dominated by impulsive noise fluctuations associated with blade-vortex interactions; -A conventional 'on-surface' acoustic analogy approach is better at predicting the overall noise at lower advance ratios where impulsive noise dominates. At higher advance ratios where thickness noise becomes more important, low frequency noise tends to be underpredicted. It is speculated that this discrepancy is due to the flow-field effects off the blade tips not accounted for in the 'on-surface' modeling.
Direct cfd predictions of low frequency sounds generated by a helicopter main rotor
Direkte CFD-gestützte Vorhersage der von einem Hubschrauberrotor abgehenden, niederfrequenten Schallwellen
AHS International Annual Forum, 66 ; 2058-2072
2010
15 Seiten, 11 Bilder, 3 Tabellen, 22 Quellen
Aufsatz (Konferenz)
Englisch
Direct CFD Predictions of Low Frequency Sounds Generated by Helicopter Main Rotors
British Library Conference Proceedings | 2010
|Generalized Helicopter Rotor Performance Predictions
NTIS | 1977
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