Flow Around and Fluid Forces on a Cross-Shaped Tube

Flow visualization tests and fluid force measurements were conducted in a water tunnel to investigate flow around and fluid forces on a cross-shaped tube (CST) in a cross-flow. The following results were obtained. Flow around a CST is classified into two patterns. One is perfect-separation flow for small incidence angle and the other is reattached flow for large incidence angle. The critical incidence angle where the flow pattern changes from the former to the latter is about 7.5°∼15°. At the critical angle, the mean drag and lift coefficients reach their minimum while the Strouhal number attains to the maximum. The amplitude of the fluctuating lift decreases as the incidence angle increases. These features of flow around and fluid forces on a CST are quite similar to those of a square prism. These results imply that one-degree-of-freedom galloping and vortex-induced vibration possibly occur for small incidence angle while ILEV (impingement of leading edge vortices) vibration might be caused for large incidence angle when a CST is elastically supported in a cross-flow.