High Precision Numerical Approaches Of Rotor Blade-Tip-Vortex Simulation And Flow Control Analysis

As the important component of the helicopter,helicopter rotor's performance has great influence on a helicopter's security,economy and comfort.The aerodynamics of helicopter is also a focus of research in aviation field.The rotor aerodynamics is the important content of Helicopter Aerodynamics Research.As the rapid development of computer hardware and numerical calculation method,CFD technology,which plays an important role in the process of helicopter aerodynamic design,has become an important method for the analysis of rotor aerodynamics.The blade tip vortex plays an important role in the rotor's wake.The simulation of a rotor's blade tip vortex,which is a difficult problem,is the focus point in the research of rotor aerodynamics.The strong,concentrated tip vortices generated by a helicopter rotor blade can also be a source of adverse aerodynamic problems,such as blade vortex interactions(BVI)and vortex–airframe interactions.The slotted tip technology,which can efficient dissipate the tip vortex,is a flow control technology full of potential.In this dissertation,a procedure of RANS method and RANS/LES hybrid method based on the fifth order Roe-WENO scheme is developed for analyzing the tip vortex of the rotor blade.The accurate numerical simulation of the rotor blade tip vortex is represented.Then the investigation of the slotted tip technology is analyzed.The main research content of this dissertation is described below:1? A procedure based on the Unsteady Reynolds averaged Navier-Stokes(RANS)is developed,while structured dynamic patched grid technology,third order Roe-MUSCL scheme,dual time approach and k-w SST turbulence model are used.Different rotor examples are analyzed to verify the procedure.2? To fix the problem of the dissipation of rotor tip vortex during the calculation causing by the large implicit numerical dissipation of the traditional spatial discretization schemes.A fifth order Roe-WENO scheme is used to modify the procedure.The calculation of the flowfiled of the Caradonna-Tung rotor shows that the fifth order Roe-WENO scheme is more accurate in details of capturing tip vortex and blade wake.Then the influence of Mach number based on the length of the blade tip chord and the pitch angle of the rotor blade on the rotor tip vortex is also discussed.The results show that the Mach number based on the blade tip chord length has a great influence on the vorticity magnitude of rotor blade tip vortex.The larger the Mach number is,the greater the vorticity magnitude of blade tip vortex is.The pitch angle of the rotor blade has a great influence on the development of rotor tip vortex.The bigger the pitch angle is,the greater of the downstream development and the degree of inward contraction of tip vortex is.This has important meaning for the research of the BVI and vortex airframe interaction.3? The numerical approach based on RANS equations is used to investigate flowfield of the rotor in forward flight(without pitch motion and flap motion).The result shows that the calculation captured the blade vortex interactions and the wake of the two sides of the rotor is different,the wake on the blade forward moving side is a concentrate strong vortices.4? As the RANS method inadequate to the simulation of the complex turbulence flow,a procedure using DDES and IDDES hybrid method based on fifth order Roe-WENO scheme and SST turbulence model is developed.Numerical simulation on Serial double cylindrical standard examples is conducted by using DDES and IDDES method.The ability of DDES and IDDES method in simulating complex turbulent flow is verified.The results of DDES method show that there is a long shear layers on the front cylinder,this is because the IDDES has lower turbulent viscosity than DDES method in the separating region so the prediction of shear layers on the front cylinder is more close to the experiment data.5? The numerical simulation of the Caradonna-Tung rotor blade tip vortex is studied.The tip vortex structures which are calculated by RANS,DDES and IDDES under the same grid were compared.The results show that,the details simulated by the DDES method and IDDES method in the focus region is better than the RANS method.The rotor tip vortex structure calculated by DDES hybrid method and IDDES hybrid method are more abundant than RANS method.The IDDES can capture the small turbulent worm vortex structure around the tip vortex and the vortex paring phenomena.It has important significance for the aerodynamic analysis and accurate prediction of the rotor noise analysis.6? The investigation of the slotted blade tip flow control technology is carried out by using the procedure.The flow field of the baseline tip rotor and the slotted tip rotor is compared.The flow control mechanism and study on parameter of the slot are also presented.The results show that the slotted blade tip can efficiently dissipate the vorticity magnitude of tip vortex.The number of the slots and the diameter of the slot have great influence on the control ability.The parameters of the slot have to be optimized according to the geometry and the flight condition of the rotor when using the slotted tip control flow technology.The research of this dissertation can provide theoretical basis and technical reference for the study of the slotted tip control flow technology and its engineering application.