Lagwise Resonance Crossing Analysis of a Variable Speed Rotor

摘要

An aeroelastic simulation of a stiff in-plane rotor in forward fight is conducted to investigate the dynamic characteristics of a variable speed rotor during resonance crossing. A finite element analysis based on a moderate defection beam model is employed to capture the coupled flap, lag and torsion deflections of rotor blade. The nonlinear quasi-steady blade element theory with table look-up of airfoil aerodynamics is utilized to calculate the blade aerodynamic loads. By using Hamilton's principle, system equations of motion are derived based on the generalized force formulation. An implicit Newmark integration scheme is used to calculate the steady and transient rotor responses. Transient aeroelastic responses of a four-blade stiff in-plane rotor are calculated to analyze the blade lagwise root bending moment and rotor torque. Rotor systems with identical and dissimilar blades are investigated. During 2/rev resonance, for identical rotors, the transient lagwise root bending moment is amplified significantly and can exceed more than 3.8 times the steady state level. The variation of rotor torque is substantially small. For dissimilar rotors, 5% reduction of one blade flap, lag or torsional stiffness at 0.6-0.7R has substantially small influence on the transient rotor torque. 5% reduction of one blade mass at 0.6-0.7R can cause a sharp rise of 2/rev rotor torque, and the transient peak-peak rotor torque increases to more than 10 times that of identical rotor. The transient rotor torque increases significantly when the mass dissimilarity occurs far from the blade root. Increasing blade damping can significantly reduce the transient loads during resonance crossing. During 4/rev resonance crossing, for identical or dissimilar rotors, the 4/rev lagwise root bending moment is transferred to the rotor shaft.