Numerical Simulation Research And Conceptual Design On Small UAVs' Deep Stall Landing Procedure

Retrieval for UAV is a complicated stage which is prone to failure.A safe landing has become one of the most important indicators evaluating the performance of the UAV.Lots of research and attempts on the retrieval mode were carried out by many countries these years.Lately,the deep stall landing of small UAVs,which has been extended by the bionic concept of the perching birds,can achieve fast,accurate and nondestructive recovery.This approach has a good application prospect in UAV express delivery,relief materials transportation in distress area and UAV recycling under the background of battlefield,becoming one of the most frontier research in the field of UAV retrieval at home and abroad.This dissertation analyzes the deep stall recovery principle and its motion process,pointing out the three key aerodynamic problems of deep stall landing process,the overall research ideas and direction is explicit.Loose coupling algorithm is applied to achieve the data interaction with six degrees of freedom motion equations and the governing equations of flow,which turns out to the dynamic aerodynamic characteristics of aircraft aerodynamics / kinematics coupling calculation method.After the establishment of a dynamic aerodynamic characteristics numerical simulation method,several cases are adopted accordingly in order to verify the simulation method.The simulation results of three common turbulence models for high angles of attack flow are analyzed compared to the two dimensional airfoil wind tunnel experiment.The comparison results with Langely Research Center indicates that,these three types of Reynolds averaged turbulence models can well stimulate the lift and drag coefficient of NACA0012 varied from 0-180°,the flow pathlines around airfoil at high angles of attack can also be correctly expressed.While,the simulating accuracy of the SST k-? model is relatively high between these three.In addition,the influence of turbulence model parameters is analyzed by uniform experimental design method,and the turbulence model parameters at high angle of attack is re-calibrated.A case of airfoil pitching oscillation is used to verify the validity and accuracy of the unsteady flow numerical simulation method based on unstructured dynamic mesh.Finally,the two-dimensional storage-seperation classic examples are reproduced.Grid quality in the process is high,the centroid position,attitude,and the aerodynamic are in good accordance with the literature data,which means that this calculation method can be well applied in aerodynamics / motion coupling problem.Then,referring to the design experience of congeneric UAVs,further calculation of components' geometric parameters is implemented.Using AVL software based on vortex lattice method,the static stability analysis and the trim calculation of the preliminary designed aircraft is carried out,thus final geometric model under trim state is applied to CFD.Results shows that the the preliminary design method using vortex lattice is feasible and effective.Finally,based on the previously established UAV geometric model,calculation and analysis of the whole process is conducted using “virtual flight” technology which integrates the equation of aerodynamics and kinematics.Then the factors which may affect the deep stall recovery process are also pointed out from the perspecticve of mechanics and fluid dynamics of rigid bodies.According to the mission objectives,design requirements of the deep stall landing process is proposed.By exploring the effects of different structure and control parameters on the deep stall recovery process,the feasible region of engineering design is ultimately obtained which lays a foundation for the practical application and further research of this technology.