CFD and CSD Coupling Algorithms and Fluid Structure Interface for Rotorcraft Aeromechanics in Steady and Transient Flight Conditions

A Fluid Structure Interface (FSI) is used to couple a computational fluid dynamics (CFD) code and a rotorcraft computational structural dynamics (CSD) code. Loose coupling (LC) is used to couple periodic cases on a per revolution basis. Tight coupling (TC), with exchange of information every time step is used for transient maneuvers. A sensitivity study of loose coupling applied to a fast forward case for the UH-60 is used to examine convergence properties of the LC algorithm. A restart from a well converged LC solution to TC with fixed controls gives identical results within engineering accuracy. This appears to be an efficient method of initiating a transient maneuver. A TC transient maneuver with a rapid doublet disturbance to the collective pitch control for the UH-60 fast forward case shows both close similarities and significant differences with computations with the CSD model using lifting line aerodynamics. Both the LC and TC algorithms appear to be convergent, robust and well behaved. CFD/CSD coupling offer a wealth of additional insights to rotorcraft aeromechanic periodic and transient problems, at reasonable computational cost, and is expected to play an increasing role in rotorcraft analysis as computational power continues to become more affordable.