Investigating the influence of compressibility on the second mode flutter instability of a clamped–free cylinder in axial flow using fluid–structure interaction simulations with the Chimera technique

Abstract

In this research a numerical framework is presented and validated to investigate the influence of compressibility on the flutter instability of a clamped–free cylinder in axial flow by means of fluid–structure interaction (FSI) simulations. The FSI simulations consist of a computational fluid dynamics (CFD) model coupled with a finite-element model. In the CFD model the large deformation of the cylinder is handled by employing a Chimera technique in which the background mesh remained fixed.The framework was first validated by performing simulations in water flow and comparing these to experimental data from literature. Afterwards, the framework was applied to air flow simulations. The inlet velocity and structural parameters were adapted to investigate the effect of compressibility at different Mach numbers. The dimensionless velocity is kept constant in order to remain in the same working point with second mode flutter.The simulations showed that for a low Mach number there is negligible influence of compressibility on the established flutter regime. At higher Mach numbers the compressibility triggers a more violent flutter regime in which the contact between the cylinder and the channel wall extends over a larger length. In the simulations the flutter motion starts out planar and, given sufficient time, usually develops into a rotational motion. It was also observed that supersonic zones and, consequently, shocks are created in the flow while the inlet is subsonic.