Study On The Microstructure And Scattering Characteristics Of Aircraft Wake Vortices

Aircraft wake vortices are the particular hydrodynamics properties when it flying. It have intensity, stabilization, standing a long time and space scale large properties. Wake vortices have significant impact on aviation flight safety, especialy when aircraft landing or taking-off. The wake vortices are the important factor that restrict the capacity of aviation. Compare with the atmosphere, wake vortices have stronger radar detection properties. Study on the wake vortices radar scattering properties and detection technology have significant application value. From aviation safety aspect, we study on the wake vortices real time detection and forecast technology not only can improve the capacity of aviation, in urgent condition, it have significant meaning for air force, navy aviation arms, carrier plane when fast landing and taking-off. More, as the steal technology growing up, anti-steal technology based on wake vortices detection will exceed detection steal aircraft itself.Taking aircraft wake vortices real-time detection as the background, this thesis systemically studies the aircraft wake vortices micro-structure characteristics of the spatial distribution and evolution characteristics, the aircraft wake vortices electromagnetic scattering model, the aircraft wake vortices RCS properties, the crosswind influence on the aircraft wake vortices micro-structure and RCS properties, the aircraft wake vortices Doppler echo characteristics and so on. The specific research includes the following aspects:Firstly, the micro-structure of aircraft wake vortices properties have been studied. Based on the evolution rules of the aircraft wake vortices movement, the fluid N-S equations is simplfied to the convection-diffusion equation for the simulation the evolution properties of passive conservative value, such as water vapor mixing rate, potential temperature, and so on. Combining with wake vortices aerodynamic characteristics, we use local fine mesh generation technology, periodic boundary conditions and finite difference method to finish the wake vortices distribution characteristics simulation. A wake vortex simulation system software (WVSS) is developed. A wake vortices micro-structure rapid modeling method which is based on passive conservative value simulation is modified. By this method, the accuracy of micro-structure simulation condition is ensured and the calculation efficiency is enhanced. It is pointed out that the diffuse index has little influence on wake vortices distribution properties.Secondly, the aircraft wake vortices electromagnetic scattering mechanism and radar cross section characteristics is researched. The advantages and disadvantages of different methods is summrized; Based on Maxwell equations and the single scattering theory, a formula for calculating wake vortices RCS is provide under Fraunhoffer and Born approximation conditions. Comparing with other formulas, its physical meaning is more explicite and its calculation result is more accuracy. Based on the micro-structure distribution properties, such as water vapor mixing and potential temperature, we bring out a refractive index fluctuations model. The dielectric constant distribution and evolution properties are obtained. At the same time, the RCS frequency characteristics and direction maps are obtained. Based on this condition, we bring out an optimal strategy for radar to detect aircraft wake vortices.Thirdly, the influence of crowwind speed on wake vortices movement and RCS properties are studied. Using the FDTD method, the spatial distribution and evolution characteristics of middle wake vortices micro-structure at different wind speed condition are simulated. And we obtained the wake vortices microstructure distribution properties at different time. The results perfectly agree with the statistical data. At the same time, the influence of crosswind speed on wake vortices RCS properites is studied. The results show that the corsswind speed has little influence on wake vortices RCS at 90 degree observation angle but has large influence on at 0 degree observation angle. At zero degree observation angle, the wake vortices RCS is smaller when the corsswind speed is larger.Finally, The time-varying Doppler characteristics of aircraft wake vortices are studied. Based on wake vortices distribution properties, we deeply studied the Doppler properties with or without crosswind. Without corsswind, the Dopper speed is the same as wake vortices descend speed at vortical direction, the Dopper speed is zero at the horizontal direction, and at the other dirtections the Dopper speed satisfied the wake vortices descend vector decomposed value. With the affection of the crosswind, the Dopper speed equals to the crosswind speed at horizontal dirtection. The result reflect a very good laminar flow movement characteristic of aircraft wake vortices, and provides a theoretical basis for radar signal processing technology and wake vortices fluid feature extraction.The results in this paper have great significance for anti-stealth, aviation safety and airport scheduling to detection aircraft wake vortices. It is used in the weapon equipment explore and study project"XXX based on aircraft wake vortices detection".