Extensive Validation of CFD/CSD Aeroelastic Simulations for a Helicopter in Descending Flight

In this work, various CFD (Computational Fluid Dynamics)-based approaches are employed to extensively validate the airloads, trim angles, blade elastic motions, vortex positions, and structural loads of a rotor in low speed, descending flight. To this end, two different comprehensive codes, CAMRAD II and DYMORE, are coupled respectively with a CFD code, KFLOW, using a loose coupling methodology. A CFD approach using the measured blade motions is also carried out for the validation. For both clarity and consistency required in the relative comparison between different methods, an identical CFD grid system is used throughout the study. A fuselage model is incorporated in the analysis. Generally, reasonable agreements against the measured data are obtained between the different approaches. The CFD results using the measured deformation show accurate predictions in estimating the vortex positions, however, it is indicated a relatively poor correlation on BVI (Blade Vortex Interaction) airloads. The DYMORE coupling results demonstrate the most reliable predictions on trim control angles, BVI airloads, and structural loads, but less satisfactory for lag motions. It is observed that there has been a systematic discrepancy between the predictions and measurements on the aerodynamic pitch moments. This discrepancy is shown to be fixed by considering the actual pressure sensor locations used in the test. The blade-vortex miss distance at a desired instant is also evaluated for a rotor with and without a higher harmonic control (HHC) input.