Research On Aerodynamic Optimization Design Of Low-Reynolds-Number Multi-Propeller Configuration Taking Into Account The Slipstream Effects

Nowadays,both the distributed electric proplusion(DEP)system technology and the high-altitude long-endurance(HALE)solar-powered unmanned aerial vehicles(UAVs)are research hotspots all over the world.While the HALE solar-powerd UAVs are operating at a high altitude and low speed,the low Reynolds number flow condition will lead to a need for the application of multiple distributed propellers,which will bring series of aerodynamic problems because of the additional effects.Hence,it is necessary to carry out the research work about aerodynamic simulation and integrated design of HALE low-Reynolds-number multi-propeller driven aircrafts taking into account the slipstream effects.Firstly,to solve the contradictions between the efficiency and precision of numerical simulations,both the high-efficiency and the high-precision numerical methods are developed respectively to meet the needs of different design stages.Secondly,both the aerodynamic performance and low-Reynolds-number flow characteristics of multi-propeller/wing integration are studied deeply to supply design experiences for the aerodynamic design of multi-propeller driven aircrafts.Thirdly,an optimization platform which can coordinate the efficiency and accuracy to meet the design reqiurments is constructed,and different aerodynamic design methods based on understanding of low-Reynolds-number flow mechanism are developed,validatations of both the necessarity to introduce the slipstream effects into the aerodynamic design process and the reliability of these methods are also carried out by cases studies.Finally,both the development and application of the multi-layer collaborative optimization framework for the multi-propeller driven aircrafts coupling with the slipstream effects is introduced based on a typical HALE multi-propeller driven aircraft,both the proposed design philosophies and methods are also validated by the detailed analyses of aerodynamic performance and flow characteristics of the optimized platform.This dissertation carries out several aspects of research work as follows:(1)Viewing from the point of demand,the low-Reynolds-number numerical simulation methods for the aerodynamic design of HALE solar-powered UAVs are studied in both ways of high-efficiency software and high-accuracy method to solve the contradiction between efficiency and accuracy.The high-efficiency software is conclusive of the program based on the vortex lattice method(VLM)for quasi-steady numerical simulations and the low Reynolds correction(LRC)method based on the database of aerodynamic performance of low Reynolds airfoils.The high-accuracy method is to quasi-steadily solving the the Reynolds-averaged Navier-Stokes(RANS)equations based on the multiple reference frame (MRF)methods coupling with the transition model.The high accuracy and the high efficiency to simulate the low-Reynolds-number flow around the multi-propeller/wing model are validated for both methods,and the reliability and adaptation of both numerical methods to be applied into the aerodynamic design of multi-propeller driven aircraft are also validated.(2)In order to supply the guidances and experiences for the aerodynamic design of multi-propeller driven aircrafts coupling with the slipstream effects,researches on the aerodynamic performances and the flow characteristics of the low-Reynolds-number multi-propeller/wing configurations are conducted.The variation trends of both the aerodynamic performances and the flow characteristics related to the variation of propeller parameters are analyzed in details.(3)Research on the optimization methods to solve the complex design problem with both the low Reynolds flow characteristics and the multi-propeller driven characters in practices,basd on which an optimization platform which can coordinate the efficiency and accuracy to meet the design reqiurments is constructed.Besides,both the two-dimensional(2-D)low-Reynolds-number airfoil design method and the wing planform design method are developed with not slipstream effects taken into consideration,furthermore,the flowfield redistribution method,the wing section design method,the wing planform design method,and the wing angle distribution design method are developed with slipstream effects taken into consideration.Then,both the necessarity to introduce the slipstream effects into the aerodynamic design process and the reliability of these proposed methods are validated by cases studies.(4)Research on aerodynamic design philosophies and methods of the HALE full-wing multi-propeller driven aircrafts is carried out,then,a high-efficiency multi-layer collaborative optimization framework is constructed based on the inner relationships of the previously proposed design methods.Studies about the application of the framework are conducted,analyses of the aerodynamic performance and the flow characteristics of the optimized platform are also carried out.It is worth mentioning that parts of the results have been used into the aerodynamic design of a certain type of solar-powered aircraft.