Numerical Simulation For The Flowfield Of New-Tip Rotors With Effect Of Blade Elasticity

Elastic rotor flowfield numerical simulation is a challenging subject in the field of Helicopter Aerodynamics. The dynamic grid deforming approach and overset grid system for elastic rotors, the blade structural finite-element analyzing modeling, and the rotor flowfield simulation are investigated in this thesis. A solving method and the corresponding code for rotor flowfield are developed based on the RANS equations and the grid system, and based on the method, the elastic rotor flowfield of helicopters is computed and analyzed. Meanwhile, the elastic rotor flowfield with new blade tips is also simulated. The major contributions of the author's research work are as follows:As the background of present work, the research and development in the field of the rotor Computational Fluid Dynamics, blade structural analysis, flowfield simulation for elastic-blade rotors as well as flowfield simulation for new blade-tip rotors are briefly reviewed. The difficulties in the current research are pointed out, and the significance of modeling elastic rotor flowfield, including new blade-tip rotor flowfield is then described. In addition, the methodology used in the present research is briefly introduced.In order to model blade elastic movement, on the basis of modified spring simulation approach, the thesis establishes a method of blade body-fitted grid dynamic deformation wich is suitable for the flowfield solution of elastic rotor. According to the characteristics of rotor transient flowfield and the blade-tip vortex movement, a dynamic overset grid system, which is composed of a body-fitted grid used for simulating the blade aerodynamic circumstance in the near field and a background grid for capturing the movement of tip vortice, is constructed. Also, an efficient method for grid information search is given to reduce the searching cost. Based on the Hamilton's principle and the beam theory of small strain and moderate deformation, a finite-element analysis model for rotor blade dynamics is established. In this model, the partial differential gorverning equation on blade movement is derived, and the equation is discretized and then solved by applying the improved implicit Newmark-beta method. Furthermore, a trim algorithm for the rotor system is coupled into the blade structural analysis for impoving the solution of blade structural response.Based on the overset grid, a CFD analyzing method for rotor flowfield is developed with the application of RANS equations. In this method, the high-order upwind scheme is combined with the flux-difference splitting scheme to discretize the rotor flowfield spatially. Then, the equation is integrated in the time domain with the matrix-free LU-SGS implicit scheme of Krylov subspace iteration, so as to improve the computational efficiency of rotor CFD simulation. With the help of'Partitioned'method, the coupled solving strategy for the elastic rotor flowfield is also provided, by combining the elastic blade structural analysis. On this basis, the elastic rotor flowfield simulation is further carried out. Afterwards, the present rigid and elastic rotor flowfield simulation methods are validated by comparing with available reference results for different rotor cases.To study new blade-tip rotors, the author expands the above work to simulate flowfield of the elastic rotor with linear-changed blade tips, and a corresponding method is developed. The computations on the elastic rotor flowfield in hover with sweep, tapered, anhedral and combined shapes are performed by the use of the method, and the influence of elasticity on the rotor flowfield with new blade tips is analysed. From the analyses, the conclusions about how the tip shape parameters affect the blade surface airloading are drawn.