Optimal Design And Verification Of Constrained Layer Damping Wind Tunnel Sting

In transonic wind tunnel force test,the frequency of pulsating flow is close to the first-order natural frequency of the model support system.The pulsating airflow is prone to induce the first-order resonance problem of the model support system.The first-order resonance of the model support system brings potential security risks,limits wind tunnel test envelope,and makes test data inaccurate.To reduce the first-order resonance response of the model support system,constrained layer damping(CLD)treatment is conducted on the model support sting.This method can increase system damping,and has high reliability as well as wide applicability.A CLD sting can be obtained by bonding the damping layer(made of viscoelastic material with high shear loss factor)to the substrate layer and then bonding the constraining layer(made of material with high Young's modulus)to the damping layer.During vibration,the constraining layer limits the tensile and compressive deformations of the damping layer.The damping layer is subjected to alternating shear forces.Vibrational energy is converted into heat and dissipated by the internal friction of the viscoelastic material.Firstly,the influence of CLD treatment on the resonance of model support system is studied.The relationship between the modal parameters and the resonance response amplitude of the model support system is analyzed.The optimal design objective of the CLD sting is to maximize the product of structural loss factor and stiffness.The structural loss factor model of the CLD sting system is established by energy method based on the shear energy dissipation mechanism.The effects of material parameters and geometric parameters on the modal parameters of the CLD sting system are studied.Secondly,the optimal design of the CLD sting is carried out.The shear loss factors and shear storage moduli of three viscoelastic damping materials at 25? from 1Hz to 50Hz are tested by dynamic mechanical analyzer.Polyurethane rubber with high shear loss factor and low shear storage modulus is selected as the damping layer material.The expressions of its shear loss factor and shear storage modulus with frequency are obtained by fitting.The Young's moduli of three commonly used constraining layer materials are compared.The 30CrMnSiA alloy structural steel with high Young's modulus,high strength,and good machinability is selected as the constraining layer material.The modal parameters of the CLD sting system vary with the outer diameters of the substrate layer and the damping layer.The optimal geometric dimensions to maximize the product of the structural loss factor and stiffness are determined.Thirdly,the finite element simulation analysis is carried out.The restraint and load are applied to the model support system based on the actual situation of the wind tunnel test.The maximum stress position is analyzed and the strength.of the CLD sting is checked with von Mises criterion.The stiffness and natural frequency of the CLD sting system are compared with that of the 30CrMnSiA sting system with the same geometric dimensions.The frequency response curves of the CLD sting system and the 30CrMnSiA sting system are obtained by harmonic response analysis.Lastly,the CLD sting and the 30CrMnSiA sting samples are manufactured.The ground test is carried out by using an exciter.The frequency response curves of the CLD sting system and the 30CrMnSiA sting system are obtained by sinusoidal sweep method.The half power point method is used to obtain the damping ratios of the CLD sting system and the 30CrMnSiA sting system from frequency response curves.The amplitude of the first-order resonance response of the CLD sting system is 64%lower than that of the 30CrMnSiA sting system.The damping ratio of the CLD sting system is 2.5 times that of the 30CrMnSiA sting system.The time-domain response curves of the CLD sting system and the 30CrMnSiA sting system are obtained by using the exciter to simulate the wind tunnel load.The root mean square of the vibration response of the CLD sting system is 43%less than that of the 30CrMnSiA sting system.Although the stiffness of the CLD sting system is smaller than that of the 30CrMnSiA sting system,the damping ratio of the CLD sting system is higher.The damping performance of the CLD sting is better than that of the 30CrMnSiA sting.