Rotor Structural Loads Analysis Using Coupled Computational Fluid Dynamics/Computational Structural Dynamics

Coupled computational fluid dynamics/computational structural dynamics (RCAS/HELIOS and CAMRAD II/HELIOS) analyses are performed, and the calculated rotor structural loads are compared with the flight-test data obtained from the NASA/Army UH-60A Airloads Program. Three challenging level-flight conditions are investigated: 1) high speed with advancing blade negative lift, 2) low speed with blade/wake interaction, and 3) high thrust with dynamic stall. The predicted flap bending and torsion moments, pitch link, and lag damper loads, in general, show reasonably good correlation with the test data. A nonlinear lag damper model is essential for the accurate prediction of root chord bending moment and lag damper load. Both analyses, however, significantly underpredict the chord bending moments, especially the harmonic amplitude. Parametric study shows that blade stiffness variations have only a small influence on the load calculations. However, modal damping in the first flap mode has a significant influence on the flap bending moments.