Study On The Radar Scattering Characteristics Of Aircraft Wake Vortex In Clear Air And Moist Air

Aircraft wake vortices are a pair of oppositely rotating turbulence that forms behind an aircraft as it passes through the air.With the characteristics of large spatial scale,long duration time and strong intensity,etc.,it's an important factor that influences the aviation safety.The rapidly developing aviation industry and the requirement of fast takeoff and landing in emergency situations increase the demand for real-time monitoring and early warning of aircraft wake vortex.Around the demand of aircraft wake vortex radar detection,this dissertation studies the radar scattering characteristics of wake vortex in the conditions of clear air,clouds and rainfall.The main research of this dissertation includes:First,in the perspective of methodology,the metrics of wake vortex radar scattering is studied.On the basis of study of three existing metrics(metric of volume scattering rate,metric of line scattering rate,metric of direct RCS),the basic physical concepts,technical route,the advantages and limitations of the three measurement methods are analyzed in depth.Then the mutual conversion between the three metrics and their internal relations are studied.On the basis of a comprehensive comparison of various proposals,the applicable occasion for each metric is given.Second,the radar scattering properties of wake vortex in the condition of clear air are studied.Based on the discussion of aircraft mechanics model in clear air,the evolution of wake vortex is simulated through numerical solution of convection-diffusion equation.Combining the Born approximation and numerical integral methods,the line scattering rate of wake vortex is calculated.During this process,a new variable grid method is proposed.This method has corrected the problem of overestimating the wave vortex's scattering in the previous researches where distinguishing the grids for dynamics computation and those for electromagnetic computation were not distinguished.Third,the radar scattering properties of wake vortex in the condition of clouds are studied.On the basis of aerodynamic characteristics modeling for the cloud particles in aircraft wake turbulence,the "weak inertia" motion feature of the cloud droplets in aircraft wake turbulence is revealed and the distribution of the cloud droplets in aircraft wake turbulence is obtained.Furthermore,with the electromagnetic scattering characteristics of the clouds droplets,the detectability of aircraft wakes in the condition of clouds is studied and the wake velocity spectral characteristics with typical radar resolution and observation angle are given.For airport security applications,a circulation retrieval algorithm of wake vortex in the clouds with vertical incidence is presented.The radar position,the resolution affect unit,velocity model and other factors are discussed and evaluated.The simulations show that the algorithm is robust and effective.Finally,the radar scattering properties of wake vortex in the condition of rainfall are studied.In steady rain region when the wake vortex velocity field is instantaneously loaded,the model of mechanical property evolution of wake vortex is proposed and it reveals the "gathering" and "thinning" effect of raindrops in the wake velocity field.Further,the Doppler spectra and the RHI graph with radar scanning are given,which are compared with United States FFA RHI radar detection experiments for verification.For airport security applications,a circulation retrieval algorithm of wake vortex in the rain with vertical incidence is presented.The research of this dissertation closely grasps the application demands of aircraft wake vortex monitoring.The achievements have important theoretical significances and application value for ensuring the aircraft flight safety,improving the capacity and efficiency of the airport and enhancing the quick takeoff ability of military aircrafts in the condition of warring emergency.