Research And Application Of The Overall Aerodynamic Shape Of The Diamond Joined-wing Configuration UAV

The excellent aerodynamic and structural characteristics of the diamond joined-wing configuration makes it one of the most promising candidates for the future long-endurance UAVs.The mechanism of aerodynamic characteristics change under the condition of the Frt-wing and the Aft-wing flow field strength coupling is not clear;the optimization design method for this special configuration lacks effectiveness and the problems of the low Reynolds number and propeller slipstream influence on the aerodynamic characteristics of this special configuration remain unsolved.Aiming at the above problems,the aerodynamic characteristics of the HALE diamond joined-wing configuration UAV and the low-speed long-endurance diamond joined-wing configuration UAV is studied.According to the special requirements of the Sensor Craft UAV,the optimization design of the airfoil and the wing based on phased array radar antenna installation is studied.Based on the characteristics of the low Reynolds number flow,the unique aerodynamic characteristics of the low-speed long-endurance diamond joined-wing configuration UAV and the influence of slipstream on the aerodynamic characteristics of the UAV with different propeller mounting modes are studied.Through these studies,the following innovative results have been achieved:1.The mechanism of interference between the Frt-wing and the Aft-wing of the diamond joined-wing configuration is studied.The results show that the Aft-wing of the diamond joined-wing configuration can restrain the flow separation and retardation on the Frt-wing,but its influence is relatively small in general.In addition to the downwash effect on the Aft-wing,the influence of the Frt-wing wake on the Aft-wing is related to the strength of the wake.For the HALE diamond joined-wing configuration UAV,when the wake is far away from the Aft-wing surface,the weaker wake can supplement the energy in the Aft-wing boundary layer to enhance its ability to resist the adverse pressure gradient.However,although the lift characteristics of the Aft-wing are not changed obviously,it can make the position of flow transition move backward and reduce the friction.But when the wake is close to the Aft-wing surface or directly sweeps the Aft-wing,the wake with large turbulent kinetic energy will blend with the boundary layer of the Aft-wing,destroying its flow field structure,reducing its lift characteristics and increasing the friction resistance.For the low-speed long-endurance diamond joined-wing configuration UAV,the strength of the Frt-wing wake is relatively weak.Even if the Frt-wing wake directly sweeps the Aft-wing,the lift characteristics of the Aft-wing will not decrease significantly.On the contrary,the wake will inhibit the laminar flow separation caused by the low Reynolds number effect on the Aft-wing,which will lead to a small increase in its lift characteristics.2.The design method of the HALE diamond joined-wing configuration UAV is proposed.The pitching moment characteristic curve of the HALE diamond joined-wing configuration UAV has nonlinear characteristics.It is found that the main reasons for those nonlinear regions are the change of the Aft-wing flow field structure caused by the direct sweep of the Frt-wing wake and the separation of the Aft-wing root.The coupling of the Frt-wing and Aft-wing separation characteristics lead to the phenomenon of 'pitch up' of the pitching moment characteristic curve.By changing the angle of the Frt-wing and the Aft-wing can solve this problem.When use the positive staggered layout,the angle of attack of the direct sweep of the Frt-wing wake on the Aft-wing can be moved to the negative angle of attack which is seldom used.When use the negative staggered layout,the 'rise' phenomenon caused by the Frt-wing wake direct sweep on the Aft-wing can be moved backward which can be coupled with the 'rise' phenomenon caused by the Aft-wing root separation so that the pitching moment characteristic curve non-linear region can be reduced to one,reducing the difficulty of control.But for the positive staggered layout,the Frt-wing with sweep angle serves to provide lateral static stability and the anhedral angle serves to provide lateral static instability,the rolling moment coefficient counteracts each other.The lateral stability characteristics of the Aft-wing are similar to that of the Frt-wing.The lateral stability of the positive staggered layout is poor.The sweep angle of the Frt-wing and Aft-wing will affect the lift and structural characteristics of the UAV,and its choice is related to the cruising speed in the design index.Based on the research,this paper analyzes the design idea of Boeing Sensor Craft UAV and designs the application configuration.3.The basic principle and installation method of airfoil mounted planar phased array radar is analyzed,and an optimization design idea based on planar phased array radar antenna installation constraint is proposed and optimized.The flying height of the Sensor Craft UAV is high,so the phased array radar antenna in the wing should be installed with a certain mounting angle.Determining the installation angle to meet the high and low altitude coverage requires a cyclic iterative process to obtain the maximum detection range.In order to meet the requirement of radar antenna installation,the optimized Frt-wing airfoil has obvious thickness increase,the maximum thickness position moves forward,the radius of curvature of the leading edge of the airfoil increases,the negative pressure of the leading edge increases significantly,and a negative pressure platform appears.The upper surface of the airfoil is relatively flat,eliminating the shock wave on the upper surface of the airfoil,and exhibiting the pressure distribution characteristics of the typical laminar airfoil.The middle and rear region of the airfoil's thickness of the optimized Aft-wing airfoil is obviously increased,and the relative position of the maximum thickness is moved backward;The central region of the upper surface of the airfoil is relatively flat,and there is an obvious process of increasing negative pressure gradient on the upper surface,and exhibiting the pressure distribution characteristics of the typical natural laminar airfoil.4.Based on a detailed study of the aerodynamic characteristics of the HALE diamond joined-wing configuration UAV,a high-efficiency three-dimensional optimization method suitable for the diamond joined-wing configuration has been developed.The design idea is to eliminate the effect of downwash of the Frt-wing by changing the airfoil shape and installation angle of the Aft-wing.The optimization design is carried out with the aim of maximizing the lift-drag ratio of the aircraft and satisfying the constraints of the installation of planar phased array radar antenna and ensuring the lift characteristics.The optimization results show that there is an obvious wave-like change trend in the installation angles of the control sections of the Aft-wing.The main reason for this phenomenon is that the downwash effect of the Frt-wing on the Aft-wing is caused by the interaction between the lift distribution of the Frt-wing and the distance between the Frt-wing and the Aft-wing.By analyzing the pressure distribution of the optimized configuration,it can be seen that the change is mainly concentrated on the leading edge;Through optimization,the pressure distribution in most areas of the Aft-wing is more consistent with the optimized pressure distribution of the Aft-wing airfoil,which effectively improves the aerodynamic efficiency of the Aft-wing.5.The unique aerodynamic characteristics of the low-speed long-endurance diamond joined-wing configuration UAV under the influence of the low Reynolds number effect are studied.The Inner-wing section of the Frt-wing is stalled first and the stall characteristics of the Frt-wing Outer-wing section is better than the Inner-wing section due to the spanwise flow along the Frt-wing is obstructed by the conformal region of the Frt-wing and Aft-wing joint section.The effective angle of attack of the Aft-wing is reduced by the effect of the downwash and the stall characteristics of the Aft-wing are significantly better than the Frt-wing.The low-speed long-endurance diamond joined-wing configuration UAV has good stall characteristics.The pitching moment characteristics change greatly with the sideslip angle changes.The factors that appear this phenomenon are quite complicated,but the change of the flow and separation characteristics of the Left-wing Aft-wing and the Right-wing Frt-wing Inner-wing section caused by the sideslip are the main reasons of this phenomenon.When using the flaps at a high angle of attack,attention should be paid to the problem that the lift of the Aft-wing and the elevator increases with the increase of the wake strength,which in turn causes a nonlinear characteristic of the pitching moment characteristic curve.6.The influence of propeller slipstream on aerodynamic characteristics of the low-speed long-endurance diamond joined-wing configuration UAV is studied.The results show that the slipstream of the pull-in fuselage propeller has a strong influence on the roots of the Frt-wing and the Aft-wing,the location of these areas is far from the focus,the pitching moment characteristics are sensitive to the influence of the lift characteristics change of these areas of the Frt-wing and Aft-wings.The longitudinal static stability margin of the UAV will increase sharply and there may be periodic oscillation.The low-speed long-endurance diamond joined-wing configuration UAV is not suitable for installing the pull-in fuselage propeller.When the propeller is installed in the middle of the Frt-wing,the vortices near the Aft-wing are difficult to predict due to factors such as flight state,propeller shape,rotational speed and the Frt-wing characteristics.The propeller is installed nearby the Frt-wing and the Aft-wing joint section may be more conducive to the design of the aircraft;Since the Frt-wing and the Aft-wing of low-speed long-endurance diamond joined-wing configuration UAV have large sweep angle,the distance between the upwash flow and downwash flow formed by the propeller slipstream and the leading edge of the wing is different.When choosing the rotation direction of the propeller,the upwash flow should be closer to the leading edge of the wing to make better use of the slipstream.