Modern Computational Fluid Dynamics/Structural Dynamics Simulation for a Helicopter in Descent

Abstract

In this work, several computational-fluid-dynamics-based approaches are employed to 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 with a computational fluid dynamics code, KFLOW, using a loose coupling methodology. A computational fluid dynamics 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 computational fluid dynamics grid system is used for the study. A fuselage effect is considered in the analysis. The predicted results are correlated against the measured data. CAMRAD II coupling shows good prediction for low-frequency loadings, elastic motions, and structural lag bending and torsion moments. DYMORE coupling demonstrates good matches on trim control angles, blade vortex interaction airloads, and structural flap bending but less satisfactory for lag motions. Initial results indicate poor correlation on aeropitching moments. This discrepancy is seen to be fixed when considering the actual pressure sensor locations used in the test. The blade–vortex miss distance at a desired instant is also evaluated. About 25% larger miss distance is obtained with a higher harmonic control input.