Panel flutter is a common aeroelastic phenomenon and occurs when the structures are subjected to aerodynamic force on one side. The occurrence of a panel flutter induces nonlinear large deflection vibrations within the structures and can cause fatigue damage of panels of an aircraft in supersonic airflow. Therefore, it is imperative to develop effective and sustainable panel flutter suppression methods. Most studies on the suppression of panel flutter are based on different structures, including composite materials that have gained popularity in the aerospace industry. Nevertheless, most of these studies have mainly focused on the vibration and aeroelastic behaviors of transversely functional graded (TFG) structures, and the dynamic characteristics of axially functionally graded (AFG) plates and shells, but not flutter behaviors of AFG shells.
Mode localization occurs in the panel flutter structural systems due to the variation in the aerodynamic pressure along the axial direction. Thus, the aeroelastic stability of the structure can be improved by changing the geometric sizes and material properties of the structure along the direction of the airflow. Equipped with this knowledge, a team of researchers from Harbin Engineering University: Jiucun Wei (Ph.D. Student), Professor Zhiguang Song, and Professor Fengming Li investigated the aeroelastic properties of AFG cylindrical shells. The main objective was to enhance aeroelastic stability to prevent the occurrence of panel flutter in the structural systems. Their work is currently published in the journal, Journal of Fluids and Structures.
In their approach, an axially functionally graded cylindrical shell was designed, and its aeroelastic behaviors studied in supersonic airflow. The thickness of the cylindrical shell was described based on the analysis of three different functions, while two groups of functions were considered for the material properties. Moreover, the effects of the functional parameters on the occurrence of the panel flutter were evaluated. Eventually, the feasibility of the approach was validated by comparing the flutter stability of the AFG cylindrical shell with that of the conventional transversely functionally graded shell.
The authors found out that the AFG design exhibited enhanced aeroelastic stability desirable for effective flutter suppression. Moreover, all three functions showed the ability to increase the cylindrical shell’s flutter bound but at varying extents. Due to the occurrence of local mode coalescence in some situations, the authors added a lumped mass and observed that it performed much better in eliminating the local mode coalescence. It was worth noting that under suitable parameters of the functions, the flutter bound of the structure could still be increased regardless of the decrease in the effective stiffness of the whole structure. Compared to the traditional functionally graded shell, the flutter stability of the AFG cylindrical cell was better.
In summary, the study investigated the aeroelastic behaviors of AFG cylindrical shell based on the analysis of three functions describing the thickness of the shell and two groups of functions describing the material properties. The AFG design exhibited enhanced aeroelastic stability and performance compared to conventional designs. In a statement to Advances in Engineering, Professor Zhiguang Song said their study provided a significantly improved approach for increasing the aeroelastic stability desirable to suppress panel flutter. It also provided an effective method for eliminating the local mode coalescence. Therefore, it would be of great significance in the design of aerospace vehicles.
Wei, J., Song, Z., & Li, F. (2020). Superior aeroelastic behaviors of axially functional graded cylindrical shells in supersonic airflow. Journal of Fluids and Structures, 96, 103027.