| The stealth performance of armed helicopter is an essential protection for its survivability in thebattlefield. The stealth design of rotorcraft, which has been emphasized more and more besides theconcept of aerodynamic configuration design in recent years, is gradually becoming a hotinvestigation field of rotorcraft design. A high accuracy and efficiency method to estimate RadarCross Section (RCS) plays a key role in stealth design. In this thesis, a ComputationalElectromagnetics method named Finite-Volume Time-Domain (FVTD) was investigated, andprograms were established to simulate electromagnetic scattering characteristics of helicopter. Firstly,problems of electromagnetic wave propagation were simulated by the present one-dimensional FVTDmethod. Secondly, radar scattering characteristics of different rotor airfoils and helicopter fuselagewere analyzed. The major research contents in this thesis are as follows:As the background and premise, domestic and overseas researches on radar stealth technologywere summarized in the first chapter. Advantages and disadvantages of the existing research methodswere summed up. It is pointed out that FVTD method is necessary and important for the research onradar stealth of helicopter. The major research work in the thesis was introduced at the end of thischapter.In Chapter2, basic principles of FVTD method were introduced. Spatial discretization methodby combination of MUSCL scheme and Steger-Warming flux-vector splitting algorithm andfour-stage Runge-Kutta temporal discretization were derived to solve Maxwell equations inconservative form. In addition, the conductor boundary and the outer boundary approach were given.Additionally, technologies of transforming data in time domain to frequency domain and near field tofar field have been given also. Finally, the formula of calculating RCS was presented.In Chapter3, one-dimensional FVTD method and program were established to simulateelectromagnetic wave propagation in free space and multilayer media according to principlesintroduced previously. Its effectiveness was validated by comparing numerical results with theoreticalvalues. The effects of grid size, the interpolation scheme and CFL number on the calculated resultswere also investigated. As a result, some significant conclusions were obtained.In Chapter4, based on the present one-dimensional FVTD method and algebraic grid generationmethod employed in CFD, two-dimensional FVTD method was developed to simulate scatteringproblem of the infinite perfectly conducting cylinder. The calculated results were compared withtheoretical values to demonstrate the validation of this method. Several rotor airfoils were selected toanalyze their electromagnetic field distribution and bistatic radar cross section. Some conclusionsabout design parameters on stealth of rotor airfoil have been obtained.In Chapter5, based on the present numerical methods, three-dimensional FVTD method andprogram were developed to estimate radar scattering characteristics of sphere in free space. Radar cross section of helicopter blade and fuselage were simulated preliminarily. Some valuableconclusions about the effects of design parameters of helicopter on its RCS were obtained finally. |
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