Design Of Solar-powered UAV For Low Altitude Application And Study Of Methods For Lift Augmentation And Drag Reduction

Development of UAV makes its applications expand to numerous fields,including aerial surveys&aerial photography,transmission line inspection,plant protection,environmental monitoring,traffic accident handling,crime monitoring,fire disaster monitoring,post-disaster rescue,LPG pipeline inspection,border patrol,drug planting monitoring,etc.However,the problem of insufficient endurance of UAVs has begun to be exposed in practical applications,which has even become a major defect to limit their role in various industries.With the development of photovoltaic technology,solar-powered UAVs get capacity to break the endurance limitation.At present,the HALE(high altitude long endurance)solar-powered UAVs have been studied deeply by governments and large companies all over the world,but the technology still have a certain gap from the aim of high-altitude long-endurance flight.However,applying the technology of solar-powered UAVs into the civilian low-altitude UAVs becomes much feasible nowadays.Beyond that,solar energy as green and sustainable energy is suitable for application and deeply promoted in the civil industry.Therefore,research of low-altitude solar-powered UAVs may be difficult,but its application will be broad.This dissertation proposes design schemes of a low-altitude solar-powered UAV and a solar-powered unmanned seaplane,which are applied for the pratical applications,like transmission line inspection,LPG pipeline inspection,and sea inspection.The manufacture and flight test of the prototype of the low-altitude solar-powered UAV was carried out.In order to expand endurance and improve flight performance,this dissertation proposes two kinds of lift augmentation and drag reduction methods for low-altitude solar-powered UAV,which are auxiliary means for further development of this kind of UAV.The main research contents and results of this paper dissertation are:(1)The design scheme of ZJU-SP-L low-altitude solar-powered UAV was proposed,and the conceptional model of the UAV layout was established.Based on the balance between the converted solar energy and consumption energy of flight,the design parameters of the ZJU-SP-L UAV were studied deeply.According to the requirements of light-weight structure in solar-powered UAV,a new structure designed for wing was proposed,applied with composite materials and polymer foam materials.Futhermore,the structure and aeroelastic analysis of the wing were carried out,which shows that the design can fully meet the flight requirements.In order to verify the feasibility of the ZJU-SP-L UAV,several prototypes were designed and manufactured.Also,the basic flight test was carried out,which fully demonstrates that the ZJU-SP-L UAV is able to be used for pratical operations.(2)According to the need of marine inspection with UAVs,this dissertation proposes the design scheme of ZJU-SP-S,a solar-powered unmanned seaplane,which was based on ZJU-SP-L UAV.ZJU-SP-S is designed to have a layout of seaplane,and its basic design parameters were determined.According to the energy balance of system and the requirements of periodic task,two flight strategies are proposed for the offshore operation.Taking somewhere of the East China Sea as an example of flight zone,a guidance for the ZJU-SP-S UAV to implement the flight strategy in a year was developed.(3)According to the characteristics of solar-powered UAVs,the flow control method of local vibration of a wing is proposed.Detailed research by numerical simulation was carried out.The influence of frequency,position of local vibration and width of vibration area to the effect of lift augmentation and drag reduction was studied.It is found that the reduction of drag coefficient was up to 23%.Futhermore,the effectiveness of this lift-augmentation drag-reduction method was verified by wind tunnel experiments.This flow control method optimizes the drag characteristics of solar-powered UAVs,thereby increases the UAV's voyage and improves its maneuverability.(4)The lift-augmentation drag-reduction method by applying a rotating cylinder on a wing is developed,and deep research by numerical simulation was carried out.The influence of the speed ratio and the protruding height ratio on the aerodynamic performance optimization of a wing was studied.It was found that the stall angle of attack was greatly improved,and the lift coefficient was increased up to 24%.Futhermore,the effectiveness of this lift-augmentation drag-reduction method was verified by wind tunnel experiments.This method will effectively improve the lift characteristics and maneuverability of solar-powered UAVs,thereby reduce the UAV's requirements for the runway and increase its climb rate.