Structural Design And Flow Field Analysis Of A Small Unmanned Helicopter For Individual Reconnaissance

The individual unmanned reconnaissance system has a very important practical application value for modern warfare,especially for special combat teams.It can provide asymmetric information advantages for combat teams,thus reducing casualties and improving operational capability of combat teams.At present,modern warfare is gradually developing into urban warfare,and the miniaturization and concealment of unmanned reconnaissance system are gradually becoming the focus of research.In this paper,the micro-unmanned helicopter used for individual reconnaissance is selected as the research object,focusing on its mechanical structure,aerodynamic components and other aspects,and optimizing the design of rotor and fuselage from the aerodynamic perspective.Aiming at the functional requirement of the miniature unmanned helicopter,unmanned helicopter structure is determined as the single rotor with tail rotor,according to the design index,takeoff gross weight,rotor disc loading and compaction degree of the micro miniature unmanned helicopter is estimated and the miniature unmanned helicopter overall layout is designed,combined with helicopter flight principle,main rotor and tail rotor system variable pitch control mechanisms is designed.For low Reynolds number of miniature unmanned helicopter working environment,based on the conventional helicopter rotor flow field numerical simulation method,master equation analysis,turbulence model,discrete method are analyzed,combination of multiple reference frame model,the structure of the C type grid and based on unstructured grid of the Mosaic technology,this paper put forward and set up a set of rotor is suitable for low Reynolds number flow field simulation of CFD method,according to this method,with two-dimensional airfoil and three-dimensional model which have full wind tunnel test data and simulation calculation,comparing their test data of literature,the CFD method that established by this paper is verified the accuracy,validity.Based on rotor theory model and the theory of airfoil aerodynamic characteristics,analysis the influence under the environment of low Reynolds number of conventional NACA4 digits airfoil aerodynamic performance factors,using the simulation calculate and determine the reasonable airfoil geometric parameters,which determine the excellent initial airfoil aerodynamic performance,and based on the third order the Bezier curve,Xfoil software and genetic algorithm,put forward and set up a kind of suitable for miniature unmanned helicopter airfoil optimization design method,optimize the selection of the initial airfoil,obtained the better aerodynamic performance of airfoil curve,finally the optimized airfoil maximum lift-todrag ratio increased by 1.5%,When the Angle of attack was 4°,6° and 8°,the lift-to-drag ratios increased by 20.47%,8.5% and 24.72%,respectively.Referring to the conventional helicopter rotor tail rotor interference research method,and based on the multi-reference system model,the interference flow field of the main rotor and tail rotor was simulated.Considering the size requirements of unmanned helicopter,the rotation direction of the tail rotor was determined as "bottom forward" rotation and the relative position layout of the tail rotor and the main rotor.Based on aerodynamics,the resistance characteristics of the fuselage of a small unmanned helicopter are analyzed,and it is concluded that the nose part is the main source of fuselage resistance,accounting for about 42.25%?47.22% of the total fuselage resistance,no matter when the fuselage Angle of attack is 0° or-5° or at low speed or high speed.According to the Bezier curve,the agent model and genetic algorithm,put forward and set up a head drag reduction optimization method based on symmetric cross section curve,specific for use of the third order the Bezier curve,parametric modeling of the nose curve by orthogonal experiment and the third order polynomial response surface between the nose parameters and airframe resistance coefficient was established agent model,and by using genetic algorithm,has carried on the drag reduction to the nose curve optimization,the optimized airframe resistance is reduced by 29.61% before optimization.Finally,the flow field simulation of the whole machine is carried out to study the flow field characteristics during the flight of the whole machine,and the small model unmanned helicopter is modified to make a test prototype.The main rotor and tail rotor designed in this paper are simply verified for flight,and the performance of the main rotor and tail rotor is proved.