Application of a dynamic stall model to rotor trim and aeroelastic response.

摘要

A unified aerodynamic lift model including dynamic stall is used to describe the aerodynamic environment of a rotor blade. The model is successfully used in conjunction with an elastic blade formulation to predict the aerodynamic forces on the helicopter blade and the flap-lag-torsional response before and after stall occurs. The control settings are assumed to be initially unknown and are computed as a part of the solution by an auto-pilot controller. A solution method based on a modified Galerkin's method is used to separate the time and space variables in the differential equations. The numerical solution is obtained by a time marching method which is based on Gear-Adams predictor-corrector method for solving systems of first-order differential equations.; The structural model consists mainly of flap, lag, and torsion equations. These equations can be reduced to rigid blade equations by using a single mode for each degree of freedom. The fast rate of convergence of the elastic solution shows that the orthogonal polynomials used in this work represented a good choice for the comparison functions. The unified-aerodynamic model is an extension of the model developed by the Office National d'Etudes et de Recherches Aerospaciales and includes plunge, unsteady free stream, and large angles of attack. The model is used to predict both the unsteady nonlinear lift and pitching moment.; Dynamic response has been conducted for a variety of thrust coefficients and advance ratios with both rigid and elastic blade assumptions and at several torsional frequencies. The results show that flap has 2/rev response and inplane and torsion have 1/rev responses.; The correlation of the results with flight test data from the SA349/2 helicopter has generally resulted in a good prediction of the vehicle control settings. For flight conditions at high speed and low thrust, the section normal force is well predicted. For flight conditions at high speed and high thrust, it is shown that nonlinear unsteady aerodynamics have a major effect. The dynamic stall model predicts a more realistic value of the section normal force coefficient than does linear unsteady aerodynamics.