Measurement and analysis of moment of inertia using torsional pendulum method with air damping consideration

MA Weiping; ZHAO He; SONG Yuzhou; LI Tenglong

doi:10.16579/j.issn.1001.9669.2025.08.015

Abstract：To address the issue of accuracy degradation caused by aerodynamic damping when measuring the moment of inertia of irregular specimens with large airfoil surfaces using the torsional pendulum method,a compensation approach based on drag simulation results was proposed.Initially,the mechanism of aerodynamic damping in torsional oscillations was analyzed,and a measurement model incorporating compensation through calculation of aerodynamic damping torque was established.Subsequently,the reduced frequency parameter was introduced to characterize the unsteady aerodynamic nature of the aerodynamic damping torque.By employing a quasi-steady assumption combined with equivalent linearization techniques,the unsteady time-varying aerodynamic damping torque was equivalently represented as viscous damping.Furthermore,computational fluid dynamics(CFD)simulations were conducted to obtain drag coefficients during specimen motion,from which a compensation formula based on drag coefficients was derived.Finally,validation test were designed and performed to verify the proposed method.The findings indicate that under low reduced frequency conditions(reduced frequency less than 0.01),the relative error between the equivalent aerodynamic damping ratio calculated via quasi-steady assumption and test separation values is approximately 7%.After compensating using the proposed equivalent aerodynamic damping ratio,the error between measured and theoretical moments of inertia is approximately 0.2%,demonstrating that the proposed method effectively enhances measurement accuracy for moments of inertia of irregular specimens with large airfoil surfaces.