Aeroelastic Researches For Flying Wing Unmanned Aerial Vehicle With High Aspect Ratios

Flying wing Unmanned Aerial Vehicle(UAV)had been identified as important research fields with potential characteristics,lower structure weight factor and highest aerodynamic efficiency.The high-aspect-ratios flying wing Unmanned Aerial Vehicle which had the wing-body fusion and beam surface wing configuration faced flow separation during the flight,made the coupling between the structural responses and aerodynamic forces became more and more serious,which could result serious aeroelastic problems.As the CFD solver and CFD solver developed,it was necessary to develop a CFD/CSD coupling aeroelastic numerical method.Based on the researches backgrounds,the research works in the paper included the flying wing UAV CFD/CSD coupled aeroelastic calculation and the doublet lattice method flutter suppression and robust flutter researches.The main researches and innovative works in the paper included as follows:The aeroelastic calculation method and aerodynamic structural coupling techniques were first introduced,and then the flow control equations,the finite volume method,the space discrete form,the time advance method and the turbulence model in the computational fluid dynamic were also introduced.Based on the aerodynamic structure interacting surface interpolation technique,a CFD/CSD aeroelastic calculation methods were developed,and also based on the CFD user defined functions and dynamic grid capacity,the CSD finite element analysis results which used in the UDF form could be used in the aerodynamic structural two-way coupling loads transferring.The NACA 0012 airfoil,NACA 0006 airfoil and M6 wing harmonic vibration unsteady aerodynamic force were calculated and compared with the experimental dates.The AGARD 445.6 wing flutter and the cropped delta wing limit cycle oscillation behaviors were investigated by the developed CFD/CSD coupling method,and then the results were compared with experiments dates.The finite element methods and RANS N-S equation,based on the flying wing UAV structural and aerodynamic model,were established.The interfaces between the structural and aerodynamic model were built with an exact match surface where load transferring was performed based on the 3D interpolations.The LU-SGS iteration and HLLEW space discrete methods based on the SST turbulence model were used to calculate the aerodynamic force.Firstly the static aeroelastic responsesof flying wing UAV based on the aerodynamic structural coupling method.The rigid and elastic aerodynamic characteristics were also given.And then the effect of height,Mach numbers,sideslip angle on the aeroelastic were also given.The single rudder and combination rudders deflection and nonlinear static aeroelastic were given.The effects of rudder crack initiation angles and different rudders control efficiency at different Mach numbers were calculated.The results shown that the rudder control efficiency was same with the combination rudder control efficiency,and the combination rudders had higher control efficiency compared with single rudder.Based on the detailed flying wing UAV structural model and aerodynamic model,the lower-upper symmetric-Gauss-Seidel iterations and Harten-Lax-van Leer-Einfeldt-Wada space discrete methods were used to calculate aerodynamic force,the structural dynamic equation and flow control equation coupling method were used to solve the flying wing UAV aeroelastic responses induced by the rudder motion,and the effects of rudder parameters on UAV vibration were also studied.The results shown that different from other parameters,the rotating angular frequency had great effect on the response frequency induced by the rudder motion;and the responses frequency increased with the rotating angular frequencies increased,and the height parameters only affected the responses displacement amplitudes.Based on the Reynolds averaged Navier-Stokes equations and the shear stress transport turbulence models,the rigid flying wing UAV buffeting onset angle at low speed high attack angle conditions could be estimated according to the lift coefficient,pitching moment coefficient and surface limit flow criterion.Based on the structural model and aerodynamic model,the flow control equation and structural dynamic equations coupling solving technology were build,the buffeting loads near the buffeting onset angle were calculated by the structural aerodynamic coupling methods,and then buffeting load responses near buffeting onset angle were calculated Based on the RANS equation and the CFD/CSD coupling method.The research result shown the buffeting onset angle based on the lift coefficient criterion and the pitching moments coefficient criterion was conservative compared with the surface limit flow criterion;and the lift coefficient criterion and the pitching moments coefficient criterion could only give the buffet onset angle,but not shown the flow separation specific reasons;and the surface limit flow criterion could give the wing surface flow separation specific reasons.The doublet lattice method and the modal analysis results,combined with infinite plate spline interpolation techniques to realize the structural aerodynamic data transferring.The generalized aerodynamic force matrix of Laplace transform was transformed by using the minimum state approximation method.By introducing the revelant state variables,the aeroservoelastic models could be built by considering the actuator model and the sensor output model.Reduction aeroelastic models could be built by reduction of the high order models,and the loop systems and closed systems responses could be simulated.The open and closed loop systems stability characteristics of the single input single output systems and multiple input multiple output systems were respectively studied by the classical SISO method and LQG method.Wing section with leading edge control surfaces and trailing edge control surface models,which considered the unsteady aerodynamic forces perturbation,nonlinear structure stiffness perturbation and nonlinear structure damping perturbation using the linear fractional transformation forms could be established;and the structure singular value was introduced to analyze the robust stability based on the ? method.The robust system robust stabilities were discussed for the nominal and robust system under the parameters perturbations condition.Based on the flying wing UAV open and closed loop state space aeroelastic equations in previous chapter,the flying wing UAV robust aeroelastic model were established considering the dynamic pressure,the stiffness and the damp perturbation.The nominal and robust systems were respectively studied by the state space method and the ? method.