Time-Domain Analysis of Body Freedom Flutter Based on 6DOF Equation

Abstract

The reduced weight and improved efficiency of modern aeronautical structures result in a decreasing separation of frequency ranges of rigid and elastic modes. Particularly, a high-aspect-ratio flexible flying wing is prone to body freedom flutter (BFF), which is a result of coupling of the rigid body short-period mode with 1 st wing bending mode. Accurate prediction of the BFF characteristics is helpful to reflect the attitude changes of the vehicle intuitively and design the active flutter suppression control law. Instead of using the rigid body mode, this work simulates the rigid body motion of the model by using the six-degree-of-freedom (6DOF) equation. A dynamic mesh generation strategy particularly suitable for BFF simulation of free flying aircraft is developed. An accurate Computational Fluid Dynamics/Computational Structural Dynamics/six-degree-of-freedom equation (CFD/CSD/6DOF)-based BFF prediction method is proposed. Firstly, the time-domain CFD/CSD method is used to calculate the static equilibrium state of the model. Based on this state, the CFD/CSD/6DOF equation is solved in time domain to evaluate the structural response of the model. Then combined with the variable stiffness method, the critical flutter point of the model is obtained. This method is applied to the BFF calculation of a flying wing model. The calculation results of the BFF characteristics of the model agree well with those from the modal method and Nastran software. Finally, the method is used to analyze the influence factors of BFF. The analysis results show that the flutter speed can be improved by either releasing plunge constraint or moving the center of mass forward or increasing the pitch inertia.