Transonic Flutter of Skin Panels Pinned at the Center

Abstract

This work is a numerical and experimental study of transonic panel flutter. Two configurations were explored: clean and pinned geometry. The former is a panel clamped on all sides, while the configuration with pin also includes an additional constraint in the middle of the panel. This case study was inspired by the skin-panel design used for Skylon, a single-stage-to-orbit concept vehicle. In Skylon, a series of discrete supports are used to stiffen thinner skin panels to maximize the payload; thus, there is a need to explore the dynamic stability of this configuration also in the transonic regime. To this end, a panel clamped on all sides and with a pin in the center was tested in the transonic wind tunnel, where time-accurate displacement measurements were performed using laser sensors. From the analysis of experiments and numerical simulations, transonic flutter appeared to be a one-way type of interaction, where the aerodynamic pressure characteristic is not affected by the structure deformation. This is due to small panel displacements, typically two orders of magnitude smaller than the panel thickness. Higher natural modes, with a frequency close to the aerodynamic fluctuating pressure, are directly excited. Generally, the additional constraint in the center does not seem to add significant benefits in terms of dynamic stability in the transonic regime. A numerical parametric study showed that for external Mach numbers ranging approximately between 0.8 and 1.2, flutter oscillation amplitude is the largest for low Mach speeds.