When describing the coupling procedure it is important to differentiate between the spatial and temporal aspects for coupling the disciplinary computational programmes. The spatial coupling enables the conservative transfer of forces and deformation between models of different discretisations. In doing so, the same work is carried out on the computing grid for both the aerodynamics and structure and there is no artificial energy input. Temporal aspects for the data exchange between the involved computational programmes must be taken into account when dealing with unsteady processes. For this, the coupling methods developed and validated by the Institute in the area of fixed wing aircraft can be referred to.
Common coupling methods for rotor craft differentiate between weak and strong coupling to calculate the aeromechanical rotor movement, which comprises the fixed movement parts of the blade joint and the elastic parts of the blade deformation. By assuming time periodic properties, the aerodynamic forces and the corresponding rotor movement for an entire rotor revolution are exchanged in cases of weak coupling, whereby the description of the exchanged quantities is carried out through a harmonic approach with Fourier coefficients. In contrast, in the case of strong coupling, the loads and movements for each physical time step is transmitted between the computational programmes. This enables testing taking into account all non-linear contributions from the aerodynamics and rotor dynamics.
Both procedures are used at the Institute and refer to the multi-body system (Mehrkörpersystem - MKS) for the improved description of rotor dynamics. In the case of weak coupling, the MKS SIMPACK in connection with HOST, the Comprehensive Code from Airbus Helicopters, is used and in the case of strong coupling the MKS SIMPACK is used together with CFD TAU.