Optimal Design And Analysis On Advanced Aerodynamic Shape Of Rotor Based On A Viscous Adjoint Method

Rotor is the key aerodynamic component of the helicopter, since it provides the lift, control force and propulsion of the helicopter, and its aerodynamic characteristics has close relationship with the aerodynamic shape of rotor blade. For the advanced helicopter, execellent Figure of Merit and equivalent lift/drag ratio of rotor for forward flight are usually needed. This is a typical multiobjective and multi-constraint optimization problem, and many contradictions and difficulties still exist during the design, thus bringing a big challenge for the aerodynamic shape design of advanced rotor. To overcome this challenge, a highly-accurate and highly-efficient numerical method is established to predict the unsteady flowfield of rotor. On these bases, the viscous adjoint-based design method is adopted for optimal design of advanced rotor airfoil under multi-objective and multiconstraint conditions, and the surrogate model method is then employed to design the aerodynamic shape of the rotor with higher Figure of Merit, thus it provides the methodology and the technical basis for the aerodynamic shape design of advanced rotor. The major contents are as follows:In Chapter one, the research background and significance of the research of advanced rotor aerodynamic shape optimal design is briefly introduced. Both domestic and abroad research status and technical issues of numerical simulation of rotor flowfield, advanced rotor blade aerodynamic shape and the adjoint-based aerodynamic optimal design are respectively analyzed, and the main research content of this article is also given.In Chapter two, a set of rotor moving-embedded grid strategy has been established, which is suitable for the optimal design of rotor blade. The shape of rotor blade is firstly parameterized by the airfoil distribution, chord distribution, aerodynamic line distribution and twist distribution. Then the O-C-O type orthogonal and body-fitted grid around rotor blade is generated by using Poisson equations, grid interpolation and folding approach. On these bases, the “Disturbance Diffraction Method”(DDM) and parallel “Inverse Map” method are employed in the identification of hole cells and searching the hole boundary donor cells respectively, thus to solve the bottleneck problem of the moving-embedded grid technique.In Chapter three, a highly-accurate and highly-efficient CFD method is developed to predict the unsteady flowfield of rotor, which is suitable for optimization. In the method, the unsteady RANS equations are used as the governing equations, and the finite volume method is adopted to solve the governing equations. The modified Jameson central scheme is used for spatial discretisation of convective fluxes, and a dual-time based implicit scheme of LU-SGS is adopted for temporal discretisation, and the S-A turbulence model is utilized to calculate the turbulent viscocity, and the x data sharing Open MP parallel strategy is employed to accelerate the calculation as well. Finally, the flowfield and aerodynamic characteristics of the several rotor airfoils, hovering rotors and forward flight rotors have been simulated by the present method. By comparisons of numerical results with experiment data, it demonstrates that the present rotor moving-embedded grid system is effective, and that the present CFD method has the high-efficiency and high-accuracy characters on the simulation of the rotor unsteady flowfield.In Chapter four, the investigations on aerodynamic shape optimal design of the rotor airfoil by using the viscous adjoint method have been carried out. According to different rotor airfoil objective functions(inverse design, lift optimization, drag optimization and moment optimization), its corresponding adjoint equations, wall boundary conditions and gradient expressions are newly derived, and the numerical method for solving the adjoint equations is also introduced. Therefore, the theoretical research principle of highly-efficient optimization design method has been set up.In Chapter five, the comprehensive optimal design on aerodynamic shape of the rotor airfoil with multi-objective and multi-constraint is carried out. Aiming at the design features of the rotor airfoil, the corresponding objective function and constraint conditions of several states(hover, forward flight and maneuver flight) are given, and several typical rotor airfoils are chosen for comprehensive aerodynamic shape optimization under single-objective and multi-constrait characteristics or multiobjective and multi-constraint characteristics based on the highly-efficient viscous adjoint method. As a result, the rotor airfoils with better comprehensive aerodynamic performance are obtained.In Chapter six, a combination method of the viscous adjoint-based and surrogate model is set up for aerodynamic shape optimal design of rotorwith high aerodynamic performance. For the sample rotor, the impacts of blade shape design parameters(airfoil, blade twist, blade planform shape) on the Figure of Merit are firstly analyzed, and then the combinationmethod is continually employed to comprehensive aerodynamic shape design of rotor. As a result, somemeaningful results and design experience on the aerodynamic shapedesign of advanced rotor are obtained.