# Lift-Thrust Integrated Ducted-Grid Fusion Configuration Design for a Ducted Fan Tail-Sitter UAV
###### Abstract  
A new lift enhancement scheme is designed for the cruise flight process of a tail-sitter UAV (Unmanned Aerial Vehicle), proposing a fusion configuration with embedded grid channels on the duct wall. The low pressure zone at the lip of the duct is induced to expand through the grid channels, forming a significant force component difference with the non-grid side, thereby generating significant lift effects for the propeller of the ducted fan during level flight. Taking a ducted fan system as an example, a design method for embedding grids into the ducted wall is established. By using the sliding mesh technique to simulate propeller rotation, the effects of annular distribution angle, grid channel width, circumferential and flow direction grid quantity on its aerodynamic performance are evaluated. The results indicate that the ducted fan embedded in the grid can generate a lift about 22.16% of total thrust without significantly affecting thrust and power characteristics. The increase in circumferential distribution angle increases within a reasonable range and benefits the lift of the propeller. However, the larger the grid width, the more it affects the lip and tail of the duct. Ultimately, the overall effect actually deteriorates the performance. The number of circumferential grids has a relatively small impact. As the number of flow grids increases, the aerodynamic characteristics of the entire fusion configuration significantly improves, due to its favorable induction of airflow at the lip and tail of the duct, as well as blocking the dissipation of blade-tip vortices. dynamic characteristics are one of the key factors that determine the flight performance of the vertical level flight as well as the transition process. On the one hand, the ducted fan gives full play to the high efficiency and low fuel consumption characteristics of propellers; on the other hand, it generates considerable thrusts through the propeller excitation of the ducted wall. It can also be said that for the ducted fan, the aerodynamic characteristics of the ducted propeller are the main factors determining the overall aircraft performance [7, 8]. In order to deeply explore and analyze the aerodynamic mechanism of ducted propellers, a great deal of work has been conducted by many researchers based on various methods. [PERSON] [9] presented an experiment to investigate the aerodynamic performance on a ducted fan, and through different cases with and without an annular duct, he demonstrated that although the coaxial lift did not perform as 2 times of the single rotor, the duct can effectively increase the lift of the whole system. [PERSON] [10] constructed an aerodynamic model of a ducted fan UAV. He detailedly investigated the effect of the air stream from the propellers on the duct to increase the thrust and momentum drag. [PERSON] [11] designed a test to analyze the aerodynamic control effect of the wing-electric ducted fan on the boundary layer flow separation. The new dynamic power flow control method by using the wake flow of the duct can improve the lift-to-drag ratio during a wide range of angles of attack. [PERSON] [12] investigated the three engineering parameters (twist, sweep, lean) on the aerodynamic and structural performance of the ducted fan. He found that the twist and sweep have a relatively strong influence on aerodynamic performance. [PERSON] [13] proposed a study on the aerodynamic performance of a ducted fan under the ground, in static and dynamic water surface conditions. The results showed that the rigid ground can increase the lift of the propeller and weaken the lift of the duct due to the lip vortex resorbence, and the soft water surface generated a mild change on the lift of the system due to the drainage area. [PERSON] [14] utilized an unsteady CFD method to simulate the proximity effect of a ducted fan drone. The study revealed that the ground and ceiling effect mainly affect the thrust, and the wall effect mainly changes the lateral force and pitching moment.