Simulations For The Flowfield Of Rotor With New Tip Shape Based On High-accuracy Algorithm

As the key aerodynamic component of the helicopter, the rotor usually operates in extremely complex vortex flowfield, which brings great impacts on the aerodynamic characteristics of the helicopter. Numerical simulation for the flowfield and the aerodynamic characteristic of the rotor, especially for the generation and evolution of blade-tip vortex, is still one of the most challenging tasks for helicopter technology. Thus various advanced rotors with new tip shapes have been proposed to improve the aerodynamic performance of helicopter, which also increase the complexity of the numerical simulation. In this paper, high-accuracy algorithm has been established to analyze the aerodynamic characteristics of advanced rotor with new tip shape. And the major contents are as follows:As background of the present work, the developments of the CFD methods in rotor flowfield simulation, advanced rotors with new tip shape and the high-accuracy CFD methods are introduced firstly in Chapter one. Then the significance of the research of high-accuracy algorithm for the simulation of the flowfield and the aerodynamic characteristics of rotor with new tip shape is pointed out and the main contents of the paper are given.In Chapter two, considering the complex blade-tip shape aerodynamic shape of advanced rotor, a parametric grid generation method around rotor based on the solution of Poisson equations is established. In order to describe the complex motions of blade such as rotating, flapping and pitching, the moving-embedded grid system is also used in the simulations of unsteady flowfield of rotor in forward flight. On that basis, the novel “disturbance diffraction” method and the Inverse map method are employed to solve the problems about hole cells identification and donor cells searching among the embedded grid system respectively.In Chapter three, based on the three-dimensional compressible RANS equations and the one equation S-A turbulence model, the rotor CFD methods are established to solve the unsteady flowfield of the rotor. In order to reduce the non-physical dissipation, the ROE scheme is used to calculate the convective flux. To simulate the unsteady characteristics of the flowfield, the dual-time method is adopted and the high-efficiency implicit LU-SGS method is used for pseudo-time iteration. To further improve the computation efficiency of the CFD method, the OpenMP parallel computation technology is employed in the simulations.In Chapter four, in order to improve the accuracy and reduce the numerical dissipation of the convective flux calculation scheme, the construction of high-order WENO scheme is investigated in the paper. Based on the one-dimensional hyperbolic equation, the construction of high-order accuracy WENO scheme is derived by the choice of the stencils, the construction of interpolation polynomial, choice of the weights and calculation of the smoothness indicators. Then the WENO scheme is used to reconstruct the higher-order left and right states in the ROE scheme. It is demonstrated that WENO scheme has higher accuracy and lower dissipation in the simulations of the flowfield of the typical 2-D airfoil and 3-D wing.In Chapter five, based upon the present CFD methods, the numerical simulations of the unsteady vortex flowfield and aerodynamic characteristics of different rotors(conventional rotor and new type of tip rotors) are conducted in hovering and forward flight respectively. Compared with the experimental data and the calculated results by using low-order accuracy JST scheme and ROE-MUSCL scheme, the characters of high accuracy and low dissipation of the WENO scheme are demonstrated.In Chapter six, the UH-60 A rotor is selected as baseline rotor, the impacts of blade tip shape parameters(sweep, taper and anhedral angle) on the vortex flowfield and aerodynamic characteristics in hovering and forward flight are analyzed, as a result, the effect characteristics of different blade-tip shapes on the flowfield and aerodynamic characteristics of rotor have been obtained.