Assessment of Nonlinear Beam Models for a Novel Rotorcraft Aeromechanics Analysis System

Helicopter blades are generally modeled as one-dimensional beams and undergo medium-to-large deformations. In this study, quantitative evaluations are conducted for the static and dynamic behavior of beams using the moderately large deformation beam (MLB) model against a geometrically exact beam (GEB) model. A rotorcraft aeromechanics analysis framework is constructed to incorporate both beam models. The framework contains various solution procedures, such as trim, blade response, loads, and vibrations, with external interfaces to computational fluid dynamics (CFD) analysis. A validation study is performed to examine the extent of the accuracy of the large deformation behavior under static and dynamic conditions. Subsequently, the Higher-Harmonic Aeroacoustic Rotor Test (HART) II rotor is applied to evaluate the prediction accuracy of the beam models. Numerical simulation results indicate that the MLB model exhibits poor correlation with the test data or fails to reach stable solutions as the level of loads or geometric twist angles increases substantially. However, in the case of the HART II rotor, the MLB-based predictions show reasonable correlations with the measured data while indicating good agreement with the GEB results. The centrifugal stiffening caused by rotor rotation suppresses large blade deformation, resulting in comparable accuracy between the two beam formulations.