Trim And Load Estimation Of Steady Flight State Of Helicopter Based On CFD/CSD Loose Coupling

The accurate prediction of rotor load is the foundation of vibration reduction design of helicopter.Based on CFD/CSD loose coupling method,the aerodynamic loads and vibration loads of rotor are estimated in this thesis.It has important theoretical value and engineering utility value.This thesis mainly focuses on the key problems in rotor CFD/CSD loose coupling method,and the main tasks include:1)The CFD/CSD master control platform and loose coupling process are established based on the aeroelastic analysis model of rotor medium deformation beam.On this basis,the whole helicopter trim and incremental iterative analysis method of CFD/CSD loosely coupling is established.The coupling process is divided into internal and external two-layer cycle.The external cycle starts the calculation with an analytic trim method as well as obtains the initial control parameters and rotor posture.Then the internal cycle solves the steady-state periodic solution of rotor blades by space finite element and time finite element method of rotor.The rotor force obtained by the internal cycle is substituted into the equilibrium equations and Newton iteration method is used to find the new trim values.The convergent trim values and response are transmitted to CFD module for rotor flow field and aerodynamic load calculation.The back-substituted CFD aerodynamic force participates in the iteration of aero-elastic coupling and trim of rotor in the form of increment.2)The CFD solving process based on OverCFD software is established.A structured movingembedded grid system of rotor blades which can realize complex motion relation is established on the base.The mesh adaptive parameters are used to refine or roughen the rotor near-body mesh and the cartesian background mesh.In the grid drive,the rigid body motion of the blade is realized through the motion of the component and its overlapping grid.After the component and its grid motion position are updated,the mesh hole cutting and interpolation processing need to be carried out again.However,the elastic deformation of the blades drives the airfoil profile movement in the grid through the spline interpolation method,and then drives the movement of the near body grid,so as to realize the movement and deformation of the coupled circle of the blade.3)Take the helicopter SA349/2 at low speed as an example,the rotor flow field is solved and the aerodynamic load and vibration load are estimated in this thesis.The calculated results are in good agreement with the measured flight data.And the grid adaptive method is used to capture the vortex of the rotor blade tips and its interference with blades,which verifies the effectiveness of the proposed method in this thesis.