Numerical Simulation On Aerodynamic Characteristics Of Elastic Rotors With New Tip Shape By N-S Equations

The numerical computation of flowfields and aerodynamic characteristics for helicopter elastic rotors is a highly challenging subject in the field of Helicopter Aerodynamics. The moving-embedded grid methodology with actual blade elastic deformation and a corresponding effective donor-element searching strategy, the rotor flowfield numerical simulation method, and the blade dynamic analysis approach have been investigated in this thesis. By employing the moving-embedded grid and Navier-Stokes equations, a high-accuracy numerical method and code is developed to simulate the helicopter rotor unsteady flowfield. The flowfield and aerodynamic characteristics for rigid/elastic rotors are computed and analyzed. Meanwhile, the effects of blade-tip shape on rotor aerodynamics of elastic rotor are also simulated. The major contributions of the author's research work are as follows: As the background of present work, the objectives of the research are firstly described. The research and development in the field of calculation of rotor aerodynamic characteristics, blade structural analysis, and aerodynamic calculation for elastic rotors with new tip are briefly reviewed. The difficulties in the current research are also pointed out. In addition, the methods used in the present research are briefly introduced.Aiming at the simulation of the complex rotor flowfield in which there are many blade movements, a structured moving-embedded grid method has been firstly developed in the thesis. At the same time, in order to model blade body-fitted grid movement and elastic deformation, a mesh deformation approach based on the modified spring analogy is presented, which is suitable for the flowfield numerical simulation of elastic rotors. Then, an efficient method for hole-cutting and donor searching of overset grids is given.Based on the developed moving-embedded grid system, a numerical method and solver is developed to solve the flowflied and aerodynamic characteristics of helicopter rotors in hover and forward flight. For the solution of N-S equations, both the low dissipation Roe scheme and the third-order upwind scheme (MUSCL) are employed, which can reduce the false dissipation of the rotor wake vorticity effectively. Also, the dual-time stepping method is used for simulating the unsteady phenomenon in helicopter flowfield. Meanwhile, based on the Hamilton's principle and the moderate-deformation beam theory, a finite-element analysis model for the rotor with new blade tips is established, a trim algorithm for the rotor system is also coupled into the blade structural analysis.By combining the rotor flowfield analysis with the elastic-blade structural analysis, the flowfield/structure loose coupled solving algorithm for the elastic rotor aerodynamic characteristics is presented. Base on this, the flowfield and aerodynamic characteristics of rigid and elastic rotors have been calculated on UH-60A rotor, 7A rotor and SA349/2 rotor respectively, and the capability of this method is demonstrated by comparing with available experimental data.Finally, the rotor performance and aerodynamic characteristics of elastic blades in hover and forward flight with such new blade tips as swept, tapered, anhedral and combined shapes are calculated by the method developed, and the influence of different blade-tip shapes on elastic rotor performance and aerodynamic characteristics is analysed. Some meaningful conclusions for rotor design are also drawn.