Rotor Simulation and Multi Body Systems: Coupling of Helicopter Aerodynamics with SIMPACK

Abstract

The Institute of Flight Systems of the German Aerospace Center uses and develops a high resolution comprehensive simulation tool called S4 for the computation of isolated helicopter rotors. The aerodynamic calculation is based on blade element theory and employs advanced models for the sectional air loads. S4 uses a modal synthesis approach for a one-dimensional, pre-twisted beam to calculate the blade motion. New and advanced blade designs cannot be represented by simple linear beam approaches with sufficient accuracy especially when large deformations occur. Modern multibody systems offer the potential to remedy that deficit by incorporating high-fidelity finite state models of rotor blades and provide implicit facilities to simulate moved reference frames and complex kinematics of entire rotor systems including the hub and control system. This paper describes the work to establish and verify a tight coupling between the rotor simulation S4 and the multibody system SIMPACK. The structural dynamics model of S4 is replaced by a SIMPACK model supplied with NASTRAN solutions for the flexible properties of the blade. The coupling architecture is explained in detail and differences between both approaches are discussed. The NASTRAN model and the Houbold-Brooks beam are compared in terms of eigenmodes and eigenfrequencies. Simple load cases are used during verification and the tight coupling is demonstrated with trimmed calculations for the hover case.