Optimization Design And Flow Control Of S-Shaped Inlet Of Subsonic UAV

S-Shaped inlet has not only good stealth performance,but also the compact structure as well as short axial distance,which plays a key role in the design of UAV powered by turbojet engine.However,the geometrical characteristic of large curvature will lead to severely flow distortion in the exit of inlet as well as the uneven of the airflow distribution in S-Shaped inlet which results in serious engine accident(e.g.engine surge).Therefore,aerodynamic optimization for S-shaped inlet has a decisive position in the field of modern aircraft design.Firstly,this paper presents the geometrical optimization of S-Shaped inlet to improve its aerodynamic characteristics.In addition,flow control technology is applied to redesign S-Shaped inlet.In consideration of some recent researches of drilling overflow apertures along exit section in UAVs,powered by turbojet engine,it can cool engine's parts.In this thesis,certain strategy developed by using flow control technology on the overflow apertures to achieve a better aerodynamic characteristics in exit section of S-shaped inlet.Detail contributions of this paper is organized as follows:(1)Firstly,this paper presents the geometrical shape of a type of s-shaped inlet to Improve aerodynamic characteristics.Specifically,this paper uses the automatic optimization design platform,which bases on NSGA-II optimization algorithm to automatically optimize the geometrical shape of this type of inlet.The simulation results show that the total pressure distortion of this type of inlet has dropped by 54% compared with the inlet before optimization,and meanwhile the total pressure recovery coefficient of this type of inlet has been improved in both designed and off-design conditions.(2)Furthermore,this thesis applied flow control technology on the overflow apertures to further improve the aerodynamic characteristics in exit section of S-Shaped inlet.This flow control technology has three parts,including the position,the layout and the displacement.The results indicate that 1)Setting the overflow apertures in the area where low energy fluid piling up has a better result for flow control.2)Setting the overflow apertures in the equivalently straight section of inlet exit can effectively improve the structure of exit's flow field,which reduces the total pressure distortion,however,it makes small improvement for total pressure recovery coefficient.3)Setting the overflow apertures in the separation zone of inlet exit can effectively improve the quality of the flow field,which can increase the total pressure recovery coefficient,however,it makes small improvement for total pressure distortion.4)There is no absolute linear relationship between the total pressure distortion and displacement.(3)Finally,the aforementioned strategy is applied to one practical S-Shaped subsonic inlet,by designing the layout for overflow apertures,and considering the effects of far field,the fuselage and the cowl lip.By using conventional layout for overflow apertures,four layouts are designed to obtain the optimal one by comparing the control effect under several working condition.Then,this optimal layout design for overflow apertures provides reasonable suggestions for this s-shaped subsonic inlet in engineering practice.