Research On Aerodynamic Properties And Trim Characteristics For Low Speed UAV In Full Configuration

The whole aircraft aerodynamic analysis is a critical element of UAV conceptual design and precondition of grasping general performance and optimization design.Small UAVs have some unique features,such as small size,low speed,low Reynolds number and so on,the known aerodynamic parameters can provide important reference for flight test.Propeller slipstream can severely influence aerodynamic performance and trim characteristics,so it is essential to take slipstream into consideration in the procedure of analysis to better simulate realistic flight surrounding.In addition,it is advisable to introduce transition model to obtain more accurate aerodynamic parameters and flowfield feature.So,for UAVs that impel by propeller at low Reynolds number,analysis on whole aircraft aerodynamic characteristics is very significant in engineering.The RANS(Reynolds Averaged Navier-Stokes)solver coupled with ?-Re?t transition model are adopted to analyze a low speed UAV,which flies at 0.1 Mach and 5.0×105 Reynolds number.Unstructured hybrid grid is generated to adapt to complex configuration and MRF(Multiple Reference Frames)is used to compute propeller slipstream.Control equation discretization scheme selects finite volume approach and second-order upwind MUSCL scheme in spatial discretization and temporal discretization is provided.Preconditioning is used to handle incompressible flow.Firstly,SD7032 airfoil at low Reynolds number is computed by different turbulent models by contrast,it turns out to SA and SST k-? model have more accurate numerical values.Then preconditioning technique based on ?-Re?t model is put forward and verified reasonably by plats transition analysis.Furthermore,the method that Michel transition criterion couples with ?-Re?t model is developed to compute flow at low Reynolds number,E387 airfoil and FX 63-137 wing are calculated and compared with experiment values,results show that the method is feasible.The discrepancy between with propeller and without propeller is revealed by whole aircraft aerodynamic characteristics analysis.Then results show that propeller slipstream has little effect on wing and an evident effect on horizontal stabilator.While propeller slipstream is neglected,?-Re?t transition model can gain less 11% drag than SA model and the difference focus on wing,computed lift coefficient appears consistency.When propeller slipstream is considered,?-Re?t model gain approximate values compared with SA model.The lift coefficient increases 2% with propeller than without propeller,the reason is that propeller rotation produces a lower pressure area on upper of fuselage bottom,meanwhile the whole drag coefficient also increases.Propeller slipstream changes flowfield around horizontal stabilator and decreases negative lift on it,so additional pitching moment is produced.The trim conditions of different altitudes(0km,3km,6km)are analyzed by contrast and it finds that trim keeps nearly unchanged with altitude changing.Effects of different rotation speeds on trim are also investigated,which demonstrates that the faster rotation speed is,the more serious the discrepancy is.Furthermore,differences caused by propeller diameter are discussed to find out more appropriate propeller size for the aircraft,results display that propeller rotation speed would change obviously with different size,consequently,trim condition is altered.Based on previous results,performance about whole aircraft is evaluated.The aircraft has an excellent static stability that is about 25% and 50% elevator efficiency.At last,cruise range and duration are estimated based on computed propeller efficiency.Therefore,the all-round performance is known comprehensively by analysis in this paper.