Prediction of the aeromechanics for HART II rotor in descending flight using mixed variational geometrically exact beam analysis

This paper presents validation of the helicopter rotor aeromechanics in descending flight. In its structural analysis, mixed variational geometrically exact beam model was used to capture nonlinear behavior of the rotor blade precisely. The present beam model was expressed by a mixed varational formulation in terms of the displacements, rotations, inertial forces, moments, and linear/angular momenta. Then displacements, inertial forces, and momenta can be directly extracted and solved simultaneously. And the finite-state dynamic inflow aerodynamics combined with blade element theory was used to predict induced inflow. The present results are compared by the wind tunnel test data for the higher-harmonic aeroacoustics rotor test (HART) II rotor with and without higher harmonic pitch control in descending flight. In the numerical results, trim control angles, section normal force, structural deflections, and structural loads were compared with those of the measurement. Predicted trim control angles and structural deflections show a good agreement with the measurement. But predicted flap bending moments show certain discrepancy with the measurement.