Numerical Simulation Of Rotor Aeroelastic Using CFD/CSD Coupling

Numerical simulation of rotor aeroelastic using CFD/CSD coupling is one of the important and difficult issues in helicopter aerodynamics. Efficient CFD method and rotor blade structural dynamic model are developed for numerical simulation of helicopter rotor flowfield. Vehicle trim and rotor elastic response are calculated as one coupled solutions. General calculation code are developed using these methods.An efficient, unified numerical simulation method is developed for steady/unsteady viscous flowfield at all speed. A hybrid/unstructured finite volume method solver is developed; fluxes are computed on faces delimiting Median-Dual Cell-Vertex scheme. For second-order spatial accuracy, convective ?uxes are computed using JST scheme, Roe Riemann solver or HLLC Riemann solver. For turbulent flows, both the one-equation model of Spalart-Allmaras and the two-equation Menter's SST model are available with DES and wall function options. A LU-SGS operator is applied to time integrate, with 2rd order time-accuracy dual-time stepping method for temporal discretization. Convergence is accelerated by low speed precondition method. Mesh deformation is achieved through a fast new dynamic grid method called Delaunay graph map method for rotary wing or fixed wing unsteady flow simulation, which added moveable aid points using spring analogy. It has the characteristic of efficient and better mesh quality. Sliding mesh method based on Cell-Vertex scheme is implemented for rotor forward flight flowfield. Parallel environment, hybrid/unstructured domain decomposition technique, sub-domain boundary implement and implicit parallel method are performed. An efficient parallel computation method is developed using implicit hybrid LU-SGS. Several test cases are studied by using these methods and code. Accuracy, convergency, implicit LU-SGS convergence efficiency, parallel speedup, parallel efficiency, fluxes scheme, turbulent models, low speed preconditioning, dynamic grid and sliding mesh are validated.CFD method is coupled with structural mode equations for aeroelastic numerical simulation. Accurate interpolation techniques to transfer surface load and displacement are studied in CFD/CSD coupling method, including thin plate spline, infinite plate spline and constant volume tetrahedron. Loose coupling, tight coupling and modified loose coupling CFD/CSD coupling strategies are discussed for flutter boundary prediction. AGARD wing 445.6 static aeroelastic and flutter boundary prediction test case are computed. The computation results indicate that flutter boundary index predestined by RANS is better than Euler, especially at transonic speed and supersonic speed.The blade is treated as nonlinear moderate deflection-type elastic beams undergoing flap bending, lag bending, elastic twist and axial deflections. In deriving a nonlinear system of equations, nondimensional system and ordering scheme are introduced. The governing partial differential equations are solved using finite element method in space and time based on Hamilton's principle for blade response.Free flight trim equations are derived from the force equilibrium of a helicopter in steady ?ight, which solve method is presented. A CFD/CSD loose coupling method is developed for rotor aeroelastic. In the loose coupling method, airloads data from the CFD solver and blade motion data from the CFD solver are exchanged on per revolution or once per blade passage, periodic basis. Trimmed rotor steady solution is achieved by several coupling cycles. The coupling code is validated by rotor's hover and forward flight test case. The results indicate that elastic blade response is needed for accurate unsteady flow predictions.