Research On Aerodynamic Compatibility And Dynamic Characteristics Of Hose-Drogue Aerial Refuling System

With the development of aerial refueling methods,there have been a growing number of researches and flight tests on the probe-and-drogue aerial refueling at home and abroad,which involves a wide range of comprehensive methods and technologies.CFD methods are used in this thesis to investigate the probe-and-drogue aerial refueling in the following aspects.In order to describe geometrical deformation,relative body movement and shape changes which may occur in the hose-drogue aerial refueling system and the coupled flowfield between the drogue and the receiver during the process of refueling,several dynamic grid techniques implemented in the flow solver are presented,including Delaunay graph mapping method,spring tension analogy,as well as local mesh coarsening and enrichment.The feasibility of those methods is validated by describing the dynamic grid deformation due to relative movements between a tanker and a receiver.Numerical methods incorporated dynamic grid techniques have been developed and applied to solve flow of probe-and-drogue refueling system.An unstructured mesh based flow solver has been developed in this study to solve Reynolds averaged Navier-Stokes equations,which combines the features of finite volume discretisation,upwind spatial schemes and the dual time-stepping with both explicit Runge-Kutta and implicit three-point backward difference schemes.Spalart-Allmaras one-equation model is adopted either as a RANS or a DES model with wall distance modification for turbulent calculations.Solver parallelisation has also been paid attention to dramatically reduce the simulation time and to improve computation efficiency,which involves a lot of efforts of seeking well-balanced mesh partitioning and inter-partition dada communication strategies.Validation is then carried out by comparing numerical calculations with experimental and theoretical data for several cases to demonstrate the robustness,accuracy and efficiency of the flow solver.The flow solver is then applied to investigate the simulation of aerodynamic compatibility between the tanker aircraft and the receiver aircraft in various computation conditions.Downwash and upwash impacts from the tanker on the receiver are analysed.Aerodynamic compatibilities in two modes of probe-and-drogue aerial refuelling,namely wing pod refuelling and central line refuelling,are simulated and analysed to explore the changes in aerodynamic characteristics of the receiver aircraft.An estimate-and-correction method is developed to calculate the shape of the hose and the position of the drogue in the complex flowfield under various flight heights,velocities as well as different hose length and paradrogue drag coefficients.An initial configuration of the hose-drogue is obtained in the estimate stage by discretizing the hose-drogue into a number of nodes which represent physical properties of the hose-drogue system;the accurate configuration is then achieved in the stage of correction by CFD methods combining dynamic grid techniques.The study of the shape variation of the probe-and-drogue in the wake of the tanker can provide a reference for appropriate refueling contact position.The dynamic behavior of the refueling drogue of a fighter at different velocities is simulated and analysed.Numerical simulation results show that when the receiver aircraft approaching the refueling drogue,the forward pressure from the receiver aircraft breaks the balance of the hose-drogue system and make it to oscillate.Different docking velocities lead to different oscillation magnitude.When docking at lower velocity,the refueling drogue moves upward with obvious cycle oscillation,making the refueling docking difficult;while it is much easier to dock and refuel at higher speed with comparatively slight cycle oscillation of the drogue.Bow wave effect of the receiver aircraft on the drogue is also investigated,which make an additional explanation for the movement of the drogue during the contact stage.The hose whip phenomenon in probe-and-drogue aerial refueling is simulated through CFD methods,and the results have reasonable agreements with previously reported flight test data.The aerodynamic forces transmission and the following response after the instant contact will cause the hose to exhibit interactive coupling phenomenon and backward transverse wave oscillation,which will lead the probe to subject to great bending moment.The dynamic response process of hose-drogue system at different paradrogue angles in aerial refueling is simulated by establishing variable damping paradrogue model,the variation rule for instantaneous position of the drogue and that for pulling force of towing point are concluded.