Flutter Wind Tunnel Model Design And Ground Vibration Test Of Wing Considering Geometric Nonlinearity

In recent years,high-altitude and long-endurance UAVs have been widely used in military and civilian fields.Most of the wings of this type of UAV have the characteristics of light structure,high structural flexibility,and large aspect ratio,resulting in large deformation of the wing under aerodynamic load,and there are obvious geometric differences compared with the undeformed state.Therefore,the traditional aeroelastic analysis method based on linear assumption is no longer applicable.On the other hand,although the structural deformation is large,the internal strain is still small,and the stress-strain relationship is still linear.The characteristics of "large displacement" and "small strain" are a kind of structural geometric nonlinear problem.The effect of geometric nonlinearity on the aeroelasticity of high aspect ratio wings is a hot topic in current theoretical research.For the beam-like long straight wing,it can be assumed to be an elastic beam,and the aeroelastic analysis can be performed by coupling the nonlinear beam theory with the aerodynamic model.But for complex structure wings,this completely non-linear analysis method is difficult to apply,and it can be nonlinearly aeroelastically analyzed by linearizing the dynamics at the static equilibrium position.In addition to the study of theoretical methods,wind tunnel testing also plays a vital role in observing and studying the phenomena,mechanism and verification of nonlinear aeroelasticity under large deformations and verifying the accuracy of theoretical methods.First,using the method of dynamic linearization at the static equilibrium position,combined with the vortexlattice method and doublet lattice method of steady and unsteady aerodynamic calculations,a wing flutter analysis method considering geometric nonlinearity is established This method is used to explain the influence of the large deformation generated by the wing on the wing dynamics and flutter.Secondly,based on the method of dynamic linearization at the static equilibrium position,this paper designs a high aspect ratio flexible wing model for SHDF low-speed wind tunnel performance indicators,and establishes a large aspect ratio wing aeroelastic wind tunnel test program.The aeroelastic analysis of the design model shows that the geometric nonlinearity will significantly affect the model's natural vibration characteristics and flutter characteristics.The first-order torsional mode frequency of the model decreases significantly and has the horizontal bending motion component,and the horizontal-bending mode frequency increases Obviously and with the torsional motion component,the model's critical flutter speed and flutter frequency are significantly reduced compared to the linear case.Finally,linear and nonlinear ground vibration tests were carried out on the high aspect ratio wing model produced.Under linear conditions,the dynamic characteristics of the wing structure and the calculated values of the finite element model are in good agreement.The results of the nonlinear ground vibration test show that the fist torsional mode frequency decreases with increasing load value,the horizontal-bending mode frequency increases with increasing load value,and the coupling of the two has the motion component of the other.