Study On Aerodynamic-structural-flight Dynamics Coupling Problems Of Near Space Solar Powered Aircraft

In recent years,the near space has become another strategic high ground.For its special flight altitude,long-term residence,low cost,and fast response characteristics,in the regional communications,environmental monitoring,high-resolution earth observation and other fields have shown a wide range of application prospects.Solar powered aircrafts take advantage of the stable atmospheric environment,the use of inexhaustible solar energy as the power to achieve long-term stay at high altitude,which has become an international research hotspot.Due to high altitude and low density conditions,the realization of long-term,safe and stable flight across the day and night is the key technology in this field.Under the closed-loop energy constraints,the aircraft must have the typical features of low wing load,large size and light weight.The aerodynamic-structural-flight dynamics of the aircraft are strongly coupled when suffering the aerodynamic perturbations.The aircraft safety is seriously dangerous.Based on complex the flight environment and technical constraints of the aircraft,this paper analyzes the general characteristics of the solar powered aircraft,explicates the necessity and urgency of the research on the aerodynamic-structural-aerodynamic coupling research.Furthermore,the aerodynamic-structural-aerodynamic coupling characteristics of the flexible aircraft are analyzed based on the coupled analysis model of the aircraft dynamics and the unsteady aerodynamics.Finally,the stability of the aircraft is analyzed based on the coupling characteristics,the design guidances are provided to guarantee the safe flight.The main research contents include:The general characteristics of near space solar powered aircraft are studied.Based on the detailed investigation of the near space solar-powered aircraft development,starting with the design constraints of the aircraft and taking the energy as the core,the closed-loop energy realization of the aircraft is considered.Taking the wing area and weight as the main design variables,gerenal design and discussion are applied.Furthermore,aiming at the long high-altitude aircraft,the gerenal design of the closed-loop system is given in detail.The numerical method is used to analyze the influences of different design parameters on the gerenal design.Finally,the characteristics aircraft are discussed.The results show that in order to meet the energy requirements of long flight,the aircraft must have the characteristics of large size,light weight and low wing load.The aerodynamic-structural-aerodynamic coupling problem of the aircraft is crucial,and the aircraft safety is severely challenged.Rigid-flexible coupled dynamic model with a large range of motion and structural deformation is established.Firstly,the rigid-flexible coupling characteristics are researched,and the floating coordinate system is used to separate the deformation from the large-scale motion.Based on the Lagrange equation,the rigid-flexible coupling governing equations are deduced.Then,the coupling model is analyzed and discussed,and the necessity of unsteady aerodynamic analysis is illustrated.Finally,the response analysis under special conditions is carried out,which provides the foundation for further research.The results show that the mass distribution has a prominent impact on the structural deformation.In addition,the variation of the non-uniform force along the span is the fundamental reason for the large deformation of the structure.The aerodynamic characteristics of the deformed aircraft under arbitrary motion conditions are studied.The aerodynamic characteristics involved in this study are firstly analyzed.Then the potential flow theory is used to simulate the aerodynamic characteristics.The panel method is used to solve discretely;further,according to the theoretical derivation and numerical method,the programming and numerical solution are carried out.Finally,the computational fluid dynamics method is used to validate the aerodynamic calculation results.The results show that the unsteady aerodynamic estimation based on the panel method can obtain the aerodynamic results accurately and meet the requirements for the research,providing the aerodynamic foundation for the aerodynamic-structural-flight dynamics coupling of the aircraft.The coupling of aerodynamic-structural-flight dynamics is studied.Based on the above models and the coupling process,the aerodynamic-structural-aerodynamic coupling research of flexible-flexible aircraft is carried out.Then,under the condition of pitch angle constrites,the position and structure deformation of the aircraft are studied,which will provide reference for further coupling research.Then,the coupling of aerodynamic-structural-flight dynamics is studied by combining the rigid-flexible coupling with unsteady aerodynamic forces.Finally,the influences of different parameters on the response are analyzed.During flight,the influences of the structure damping ratio caused by the air are very obvious,mostly larger than 1,so the structure likely convergent to the balance rather than oscillate repeatly.The deficiency of stiffness of the high-aspect-ratio aircraft would cause the high deformation and keep for long period because the air damping.Simulation results show that the divergence of the aircraft has long-period divergence characteristics and the uneven lift distribution leads to structural deformation and significant changes in pitch inertia and static stability.The instability of long-period and the divergence of pitch angular velocity caused the further change of aerodynamic distribution and the deformation increased.The stability analysis and design guidance of the near space solar powered aircraft are carried out.Based on the analysis of the coupling characteristics,the structure of the aircraft and the stability of the flight dynamics are analyzed by simplifying the model and the influences of different factors are studied.Then,combining with the analysis of the influences of different design parameters on the divergent ring,the design of the aircraft is carried out to provide a theoretical basis and technical support for the design of the aircraft.According to the results of simulation and analysis,the divergent circle is provided:The distribution of lift changes when the aircraft suffers gust perturbance,deformation would be extremely high to change the charater of the aircraft significantly,then the plungh period diverges,which causes the lift distribution changes more crucial,the divergent circle would be lasted.Besides,the results show that the mass distribution of the aircraft affects the static stability and the pitch inertia after the deformation of the aircraft.The flight speed and altitude of the aircraft mainly affect the system damping.The structural rigidity affects the deformation of the structure.The increasing of control ability ensures the safety of the aircraft.Lastly,the research prepose several approaches to improve the safety for the aircraft form the aspects of gerenal design,deformation controlling,the thoosing of velocity.Based on current research,this paper expands the understanding of the characteristics of the solar powered aircraft.The aerodynamic-structural-flight coupling analysis model is established,the characteristics and influencing factors are analyzed.The design guidances are provided for the safe flight of the aircraft and technical support for the development of solar aircraft in the near space.