Rotor Blade Modeling in a Helicopter Multi Body Simulation Based on the Floating Frame of Reference Formulation

Abstract

The Floating Frame of Reference formulation was chosen to include the Beam Advanced Model in DLR’s Versatile Aeromechanics Simulation Tool. During the development and concurrent testing of the model in the field of helicopter rotor dynamics, some particular shortcomings have become apparent. These mainly – but not exclusively – concern inertial loads affecting the flexible motion of beams. This paper treats the related physical phenomena, and proposes enhancements to the model which remedy the deficiencies of the baseline method. Particular attention is given to the introduction of rotational shape functions to account e.g. for the propeller moment and the consideration of an accelerated Floating Frame of Reference to address the blade attachment’s radial offset from the rotor center in the centrifugal field. Furthermore, the application of external loads (e.g. airloads) away from the beam’s nodes or off the beam axis is addressed as a prerequisite for independent structural and aerodynamic discretization. Finally, the modal reduction under centrifugal loading is considered. The individual model upgrades are verified based on analytical reference results of appropriate rotor dynamics test cases. The enhancements are necessary for simulating flexible helicopter rotor blades within a Multi Body System – a feature required for sophisticated simulation scenarios in which the limitations of conventional rotor models (e.g. constant rotational hub speed) are exceeded.