Rotor Aeroelastic Stability Analysis Using Coupled Computational Fluid Dynamics/Computational Structural Dynamics

Abstract

Computational fluid dynamics/computational structural dynamics (CFD/CSD) coupling was successfully applied to the rotor aeroelastic stability problem to calculate lead–lag regressing mode damping of a hingeless rotor in hover and forward flight. A direct time domain numerical integration of the equations in response to suitable excitation was solved using a tight CFD/CSD coupling. Two different excitation methods—swashplate cyclic pitch and blade tip lead–lag force excitations—were investigated to provide suitable blade transient responses. The free decay transient response time histories were postprocessed using the moving-block method to determine the damping as a function of the rotor operating conditions. Coupled CFD/CSD analysis results are compared with the experimentally measured stability data obtained for a 7.5-ft-diameter Mach-scale hingeless rotor model as well as stability predictions using the comprehensive analysis Rotorcraft Comprehensive Analysis System (RCAS). The coupled CFD/CSD predictions agreed more closely with the experimental lead–lag damping measurements than RCAS predictions based on conventional aerodynamic methods, better capturing key features in the damping trends.