Comparison of the aerodynamics of bridge cables with helical fillets and a pattern-indented surface

In this paper, the aerodynamics of bridge cables with helical fillets and a pattern-indented surface are examined. To this end, an extensive wind-tunnel test campaign was undertaken to measure the static force coefficients about the critical Reynolds number region, with varying relative cable-wind angles. The tests confirmed that the pattern-indented tubing exhibits the lowest drag coefficient, reaching its supercritical flow state for Reynolds numbers lower than the other cables tested. For this cable, vortex-shedding was found to be present throughout the supercritical range. The asymmetry of the surface pattern introduce a wind-angle of attack dependency that leads to a prediction of Den Hartog galloping instability. For yawed positions, flow transition was found to be independent of the relative cable-wind angle and therefore only governed by the along-wind flow velocity. The helically filleted cable was found to have a much slower flow transition for near normal flow and relatively large lift force components for the yawed positions. Flow visualizations confirmed the existence of specific flow structures which are often associated with the presence of lower drag or large lift forces. The visualization tests confirmed the presence of an axial flow that was greatly hindered by the presence of the helical fillets.

► Force coefficients of cables with helical fillets and a pattern-indented surface.
► Pattern-indented cable has an early flow transition with continuous vortex shedding.
► The pattern-indented cable also has the lowest drag coefficient.
► Helically filleted cable has a higher drag coefficient and a slower flow transition.
► Flow visualizations showed suppressed axial flow for helically filleted cable.