Application of CFD/CSD to Rotor Aeroelastic Stability in Forward Flight

CFD/CSD coupling was successfully applied to the rotor aeroelastic stability problem to calculate lead-lag regressingmode damping of a hingeless rotor in forward flight. A direct time domain numerical integration of the equations in response to suitable excitation was solved using a tight CFD/CSD coupling. Three different excitationmethods– lateral cyclic, rotating pitch, and blade tip lead-lag force excitations– were investigated to provide suitable blade transient responses. The free decay transient response time histories are postprocessed using the moving-block method to determine the damping as a function of the rotor operating conditions. A number of CFD/CSD implementation issues were addressed to achieve practical aeroelastic stability results with limited computational run-time. Coupled CFD/CSD analysis results are compared with the experimentally measured stability data obtained for a 7.5-ft dia Mach-scale hingeless rotor model as well as stability predictions using traditional rotor aerodynamic modeling representations available in comprehensive analysis (RCAS). The coupled RCAS/OVERFLOWpredictions agreed more closely with the experimental lead-lag damping measurements than RCAS predictions based on conventional aerodynamic methods.