Integrated Optimization Design And Application On Aerodynamic/radar Stealth Characteristics Of Helicopter

At present,the integrated optimization design and application about aerodynamic/radar stealth characteristics of helicopter is a challenging subject in the field of helicopter multidiscipline optimization and integrated design.Considering the complicated aerodynamics and electromagnetic scattering characteristics,numerical methods for predicting Radar Cross Section(RCS),the flowfield of rotor in hower and rotor/fuselage interactions with momentum source model are developed,respectively.On these bases,the radar target scattering characteristics of rotor,fuselage and whole helicopter are numerically investigated.Then,the optimal method based on the surrogate model method is employed to evaluate the effects of the helicopter layout on comprehensive performance of the aerodynamic and stealth.The major contents are as follows:As the background of the current work,the research and development in the field of radar stealth characteristics,aerodynamic characteristics,and integrated optimization design of aerodynamic/stealth characteristics of helicopter are introduced briefly.The existing of the insufficiency and difficulties in the current research are also summarized.Then,the importance of optimization design platform considering aerodynamic/stealth performances of helicopter is pointed out.In addition,the methods used in the present research are briefly brought forward.In Chapter two,in order to accurately obtain the electromagnetic scattering details of the blade,taking the conservative form of Maxwell's integral equations as governing equations,a numerical methodology for simulating the RCS of helicopter rotor based on Finite Volume Time Domain(FVTD)method has been developed.Aiming at the complex influences of pitching and flapping motion of rotor,a comprehensive analysis method suitable for helicopter scattering characteristics considering the effects of rotor dynamic characteristics by combining the physical optics method,the equivalent currents method and the quasi-stationary method has been developed.The feasibility of the method is verified by comparing the numerical results with the analytical solutions or the experimental data.In Chapter three,based on embedded grids methodlogy,a highly-accurate CFD method is developed to predict the flowfield of rotor in hover.In the method,the N-S equations are used as the governing equations.The low dispersion Roe-MUSCL scheme is employed for spatial discretisation of convective fluxes,and a dual-time method based implicit scheme of LU-SGS is adopted for temporal discretisation,and the S-A turbulence model is utilized to calculate the turbulent viscosity.On the other hand,based upon the momentum source model which is used to simulate the effects of helicopter rotor on its flowfield,a numerical method suitable for solving the rotor/fuselage interactions flowfield has been developed.By comparisons of numerical results with experiment data,it is demonstrated that the present CFD method is effective to simulate the flowfield of the rotor.In Chapter four,the investigations on radar target characteristics and parameter effects of the rotor are explored.Firstly,based on the high precision FVTD method,the mechanism analyses of the rotor scattering characteristics and the effects of the airfoil geometry shape on RCS are conducted respectively.Secondly,considering the micro-Doppler effects of rotor,based on the time-frequency domain method,comprehensive analyses about the RCS mechanism and multiple responses of new blade tip shape are given.Finally,the rotor scattering echo of time domain,frequency domain and time-frequency domain gray spectrum distributions about the conventional and unconventional configuration are obtained.Simultaneously,times of rotor RCS flash zone are discovered and extracted from time-frequency domain information grayscale.On these bases,the control technologies about radar signal of the rotor are explored.In Chapter five,the investigations on radar target characteristics and parameter effects of the fuselage are conducted.Based on the scattering characteristics of the fuselage,the RCS change regulation of the fuselage with different structural parameters and the expanding trend of the strong scattering centers are analyzed,and then the scattering mechanism of the component has been revealed.Furthermore,comparisons of RCS multi responses,strong scattering distributions and radar exposure probabilities under the conditions of different wave bands between the original and modified fuselage have been conducted,as a result,the shape design method of fuselage which can improve its stealth performances are summarized.In Chapter six,the investigations on radar target scattering characteristics of the helicopter configuration are performed.The blade pitching and flapping motions are included by tilting disk plane,and the effects of dynamic rotor on the scattering characteristics of the whole helicopter are simulated.According to the relationship between scattering intensity distribution and detecting distance of radar,the four stage warning mechanism and grade of helicopter are proposed.Meanwhile,the flight schemes that can delay radar acquisition time are discussed.In Chapter seven,the optimization design and application about aerodynamic/radar stealth characteristics of helicopter are given.Firstly,Based on the high precision CEM/CFD coupling method,the integrated analysis and design about the aerodynamic/stealth of the rotor airfoil is carried out.Secondly,based on the surrogate methodology,the comprehensive optimization design about aerodynamic/stealth characteristics of rotor with different swept-tip and twist combinations has been performed,and then the structure parameter combinations which can improve aerodynamic performance and reduce RCS are given.Finally,the investigations about the distributions of the pressure coefficient,downstream load in hover and forward flight of conventional layout design and stealth design of fuselage about lift drag characteristics are analyzed.As a result,comprehensive performance of helicopter aerodynamic/stealth is analyzed by evaluating function method,some meaningful results and design experiences on the helicopter layout design with high aerodynamic efficiency / low detection performance are summarized.