Aerodynamic forcing characteristics of dry cable galloping at critical Reynolds numbers

This article attempts to highlight characteristics of the aerodynamic forcing on a rigid circular cylinder experiencing dry galloping vibrations. Observations from a series of wind tunnel tests are studied comparatively with the literature on rain-wind cable vibrations and on flow past inclined lifting bodies such as missiles, for drawing similarities. Unsteadiness and spatial variation of the flow, both previously undermined, are significant during the large cylinder motions recorded. Thus, they are here suspected to play a role in triggering unstable behaviour. Instabilities were restricted to specific ranges of cable-wind angles and Reynolds numbers. The transitional features identified refute the view of simple bursting separation bubbles that rhythmically produce lift and suggest that there is a multitude of paths for energetically feeding dry galloping. Finally explanations are provided and a mechanism incorporating unstable features is proposed for future modelling.