Stability Analysis And Flow Control Of A Ducted Fan UAV

For the special aerodynamic characteristics and control method, the miniature ducted fan unmanned aircraft vehicle has attract more and more people’s attentions. Ducted fan UAVs for variety of application areas have become a hot field on the research and development of aviation recently. A ducted fan UAV has compact structure, light weight and various flight modes. Howener, primarily designed to be autonomous aerial robots, ducted fan UAVs need to be capable of flight in a wide range of atmospheric conditions, especially gusty winds. Maintaining vehicle attitude and position control despite wind gusts is a key issue facing the designers of these aircraft.The research presented here is focused on improved understanding of ducted fan aerodynamics in forward flight, and new control methods have been introduced in order to solve control problems. Therefore, this paper carries out the flowing research work:A comprehensive dynamic model with six degree of freedom was established firstly. According to the flight dynamics principles, the aerodynamic forces and moments of the vehicle were analyzed during the whole flight conditions. The dynamic model and the mathematical model established in this paper will be used for the vehicle’s constructional design and control system design.The aerodynamic characteristics were analyzed in this paper through Computation Fluid Dynamics(CFD) modeling of the ducted fan based on dynamic analysis. In-depth research about the aerodynamic forces and moments for different flight conditions was accomplished in this paper for the constructional design and control system design. The flow characteristics of the flow around the duct lip were also analyzed through the CFD model in order to further research of the flow control.The passive flow control method using the layout optimization of structure and the duct lip spoiler was induced in this paper for solving the stability problems of thevehicle. The lip spoiler was used to cause a flow separation around the lip, which can be used to for the vehicle’s controlling. The moment caused by the lip spoiler can be used as a auxiliary moment although it was not enough to offset the whole moment caused by the gusty wind.The active flow control concept based on a fluid jet was induced here for the flow control, and the method was explored. In the active flow control concept, a steady or synthetic jet was applied against the existing flow over the duct lip, resulting in separation. Introducing flow separation can decrease the pitching moment experienced during windscreen gusts and could reduce the amount of flight control actuator usage to maintaining stable flight.For the duct trailing edge flow control, the traditional duct trailing edge was replaced by a Coanda surface geometry and a rearward-facing step. When the fluid jet emanating from the step was turned on, it causes the flow to stay attached to the Coanda surface, thereby causing the primary flow out of the duct to turn. This results in a moment to decrease the pitching moment of the vehicle in forward flight.Analysis of the ground/wall effects of the vehicle during the flight was accomplished finally. Detailed CFD simulations were performed in CFX for different conditions of the vehicle’s flight. The aerodynamic forces and moments changed when the vehicle was closed to the ground/wall which may have negative influence on the aerodynamic characteristics of the vehicle. The data analyzed in this paper will be used for further research of the aerodynamic characteristics of the ducted fan UAVs.