Prediction of HART II Rotor BVI Loading and Wake System Using CFD/CSD Loose Coupling

Correlations using a loosely coupled trim methodology of the CFD (OVERFLOW-2) and CSD (CAMRAD-II) codes are presented in order to calculate the helicopter rotor bladevortex interaction (BVI) airloads and wake system for the HART II rotor at an advance ratio of 0.15. Five different grid models are studied in order to quantify the effects of grid refinement on rotor wake resolution. The fine grid model (fine near-body/fine off-body) has a total of 113 million grid points and it gives very good airloads predictions for the HART II baseline, minimum noise and minimum vibration cases. The rotor wake positions are also very well predicted by this fine grid model. The computed vorticity field for a young vortex using the fine grid model is compared with the measured PIV data and the results are surprisingly good. The fine grid model underpredicts the experimental value for maximum vorticity by only 29%. In addition, the predicted vortex core radius is 15% chord for the fine grid calculation while the measured data shows about 5% chord length. The predicted swirl velocity is, however, higher than the measured data for this vortex. The results in this paper provide the first quantitative comparisons of a measured flow field and CFD/CSD computed solutions for a helicopter rotor-wake system.

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