Rotor Vibratory Load Prediction Based on Generalized Forces

Abstract

Three rigid-body motion DOFs are introduced for the motion of the flap, lag hinge and pitch bearing. The rotor blade is discretized using a five-nodes, 15 DOFs beam finite element. The dynamic coupling effect between the rigid motion of the blade and the nonlinear elastic deflections is taken into account. Utilizing the constitutive law of the curvilinear coordinate system, the typical moderate deflection beam theory is reformulated. In addition, the Leishman and Beddoes unsteady and dynamic stall model is incorporated and the inflow is evaluated with the free wake analysis. The derived nonlinear ordinary differential equations with time-dependent coefficients of the rotor blade are given in the sense of the generalized forces. The sectional loads of the blade and the equations of motion are solved simultaneously in the physical space. The blade vibratory loads predicted by present analysis show generally fair agreement with the flight test data of the SA349/2 Gazelle helicopter.