Non linear model of rotational galloping of square, rectangular and bundle cylinder in cross-flow

摘要

The occurrence of rotational galloping for several geometries is assessed through two-dimensional flow simulations and fluid-structure interaction simulations. A finite element formulation specifically devised for fluid-structure interactions simulations has been used. Non-linear models aimed at predicting rotational galloping are determined based on cross-flow simulations around fixed cylinders for various angles of attack. The added torsional fluid damping coefficient is modelled based on the results of forced rotational oscillation simulations. The reliability of the models is assessed by confrontation with the results of free rotation simulations, where reduced velocity and maximum amplitude of galloping have been chosen as comparison criteria, when they can be measured. The quasi-steady model is shown to have strong limitations on streamlined bodies. An extended quasi-steady model is introduced. This model does not consider history effects and considers damping up to second order. Contrarily to the previous model, this improved model can precisely predict unstable zones for a variety of section shapes. The torsional galloping of square, rectangular and bundle shape cross sections have been studied.