Research On The Overall Design And Aerodynamic Characteristics Of A Ducted Coaxial Rotor UAV

The ducted coaxial rotor UAV generally combines the coaxial rotor system with the duct,that is,the upper and lower rotors rotating in opposite directions on the same axis are enclosed in a duct.Therefore,the ducted coaxial rotor UAV has its own unique advantages,such as vertical take-off and landing,flexibility,low noise and good safety.Due to counteracting the reaction torque,it also has a more compact structure,good hovering performance and high aerodynamic efficiency,which bring about a wide application prospect.The main power device of this UAV is ducted coaxial twin rotor system.When it works,there is serious aerodynamic interference between the upper and lower rotors and between the rotors and duct.Especially in forward flight,the aerodynamic environment of the whole system is more complex on account of the compound flow field.Consequently,it is necessary to analyze the aerodynamic characteristics of ducted rotor system.Based on the overall layout design,the aerodynamic characteristics of ducted rotor system are comprehensively and deeply studied in this paper by the theoretical modeling analysis,CFD numerical simulation and aerodynamic performance test.And the main contents of this paper refer to the following aspects:(1)We come up with a design scheme of the ducted coaxial rotor UAV.First of all,the aerodynamic layout of this UAV is determined,and its operating principle is expounded,including the attitude control mode and typical flight states.Then,according to the design indexes,the overall parameters of the UAV are analyzed and preliminarily determined including the corresponding parameters of rotor,duct and rudders.Finally,the main structures of the aircraft are designed in detail,which refer to the duct fuselage and coaxial rotor system,control system,landing gear and load,etc.And the three-dimensional assembly model of the ducted coaxial rotor UAV is also completed.What's more,the whole weight of the aircraft has been calculated and the strength check of the ducted fuselage structure were also preliminarily carried out.(2)Based on the blade element-momentum theory,the radial induced inflow distribution of the rotor blade is deeply analyzed.And then,the aerodynamic models of ducted single rotor and ducted coaxial rotor systems are presented respectively by introducing the concept of thrust distribution factor for the duct.The effects of the thrust ratio of the duct and geometric parameters of the rotor blade on the induced velocity and the thrust coefficient in the system are studied.In addition,the CFD numerical simulation is also a popular method,which is used to study the aerodynamic characteristics of ducted single rotor and ducted coaxial rotor systems in hover and forward flight so that the respective flow field distribution can be intuitively understand in this paper.And,the influences resulted from the existence of the duct in system and the advantages of ducted rotor layout are clearly defined.Besides,the results of the numerical simulation are compared with the theoretical values and verified with each other.(3)The emphasis of this paper is to carry out a series of experimental researches on the aerodynamic characteristics of four related configurations,namely,the isolated single rotor,coaxial rotor,ducted single rotor and ducted coaxial rotor respectively by the aerodynamic performance test platform.It's aimed at gradually deepening the understanding of the influence of different configurations and aerodynamic parameters on its aerodynamic performance.And,the best layout scheme of ducted coaxial rotor UAV is determined due to the optimal aerodynamic performance.In this paper,the overall design and aerodynamic characteristics of a ducted coaxial rotor UAV are studied.And,some instructive conclusions are finally obtained,which can be used to provide some technical support for the development and layout optimization of the related UAVs in the future.