CFD Analysis On Aerodynamic Characteristics Of Helicopter Ducted Tail Rotor Based On Body-fitted And Overset Grids

Tail rotor is a very important aerodynamic assembly of conventional configuration helicopter,and its aerodynamic characteristics could have a significant impact on performance, flying qualitiesand noise characteristics of helicopter. For this reason the analysis of the tail rotor has been one of theresearch priorities in the field of helicopter technology. In this thesis, a body-fitted grid technologyand an overset grid method are presented based upon grid generation methodology by solving Poissonequations. And a CFD method is established to solve the flowfield and aerodynamic characteristics ofthe ducted tail rotor under different flight conditions by solving compressible Reynolds Average N-Sequations. Additionally, the multigrid method is employed to improve the computational efficiency.The ducted tail rotor of RAH-66helicopter has been taken as a numerical example, and its flowfieldand aerodynamic characteristics in hover, sideward flight and forward flight are investigatedemphatically, some instructive conclusions are obtained. The major research contents in this thesis areas follows:In Chapter1, the domestic and overseas research results on the aerodynamic characteristics ofducted tail rotors and the purpose of the research in this thesis have been introduced briefly. It ispointed out the necessity and importance of introducing the body-fitted grid technology and oversetgrid method with N-S equations to research the aerodynamic characteristics of ducted tail rotor. Themajor research work in the thesis was introduced at the end of this chapter.In Chapter2, considering the characteristics of the special configuration about ducted tail rotorand its flowfield, a structured mesh generation method by solving Poisson equations has beenestablished, and the mesh generation quality is improved by employing source term correctionapproach. Then, the moving-embedded grid generation method is established to analyze theaerodynamic characteristics of the ducted tail rotor while the grid around the ducted wall is taken asthe background gird. At last, the computation grid and corresponding donor element searching methodin embedded grid system have been presented.In Chapter3, a numerical method suitable to solve the flowfield and aerodynamic characteristicsof helicopter ducted tail rotor under different flight conditions is established by solving thethree-dimensional compressible turbulence N-S equations. The Jameson finite volume method isadopted in the spatial discretization, the dual-time step method is used in the temporal discretization,and Baldwin-Lomax model is selected as the turbulence model. To improve the computationalefficiency, a agglomeration multigrid method based on Full Approximation Storage (FAS) scheme and V-cycle are introduced to analyze the aerodynamic characteristics of helicopter rotor and Tail rotor.In Chapter4, the accuracy and effectiveness of the program of solving the turbulence N-Sequations are verified by comparisons of calculated results on the flowfield characteristics of theNACA0012airfoil, the ONERA M6wing and the CARADONNA-TUNG rotor with availableexperimental data. The multi-grid method is introduced to calculate the flowfield characteristics ofNACA0012airfoil, which demonstrates the acceleration effect.In Chapter5, the flowfield and aerodynamic characteristics of the FANTAIL ducted tail rotor inhovering flight, sideward flight and forward flight are calculated and compared to the experimentaldata. At the same time, the flowfield and aerodynamic characteristics of the helicopter ducted tailrotor under different flight conditions have been investigated respectively. Finally, some valuableconclusions for aerodynamic design about ducted tail rotor are obtained.