Research On Rotor Vibration Load Predictionusing CFD/CSD Coupling

Prediction of helicopter rotor vibration load is a key thrust area within the field of rotor aeroelastic. An accurate computation of the flow field generated by helicopter rotor requires us to consider at the same time both the aerodynamic and the structural properties of the rotor. Typical methods to solve the dynamic by computing the aerodynamic loads according to a 2D quasi-steady model based on a lifting line affects the accuracy of rotor vibration load for prediction because of lacking accurate capabilities for modeling unsteady,three-dimensional flowfields,transonic flow with shocks,dynamic stall. The paper presents a coupling method between CFD codes and CSD codes to improve upon prediction of helicopter rotor vibration load in steady forward flight.The main work includes the following aspects aiming at the CFD/CSD coupling procedure.(1)An formulation of fully coupled nonlinear dynamic of advanced geometry blades is developed based on the beam theory of medium deformation by introducing advanced geometry shape description, involving variable sweep, droop, pretwist. Then blade is discreted using the space FEM while considering the changes of element internal stiffness and mass properties as the coordinate along the radial varies in the element local coordinate system. It is finally completed that nonlinear structural dynamic model using the six point Guass numerical integral method.(2)Synthetically a research on the pitch-heave coupling as well as NACA0012 2-D airfoil dynamic stall character under the cycle alternating incoming flow circumstance is carried out. Besides the 3-D CFD model of rigid rotor blade is established and accomplished the motion simulation of heave and pitch by the dynamic mesh, and computed the pneumatic load of rotor blade airfoil in F.X.Caradonna model, validated the usefulness of using CFD method to establish the model.(3)An trimming method of rotor is developed in forward flight as well as different strategies of CFD/CSD coupling. It is executed that an aeroelastic coupling analysis for 2-D airfoil to use the CFD/CSD tight coupling.Besides, take SA349/2 as an trial,.then using the CFD/CSD loose couple iteration method to compute, finally got the different profile’s vibration load, and contrast with the flying actual measurement data,give an conclusion about the regular pattern of the blade vibration load changes as the aerodynamic load varies.