3D simulations of the Galloping of Square Cylinders in Cross-Flow at Low Reynolds Numbers: Influence of the Aspect Ratio

Transverse galloping of square cylinders is investigated by means of a fully coupled fluid-structure interaction numerical model. For low values of the reduced mass, it has been shown in a previous communication that VIV have a strong influence on the amplitude of transverse galloping for 2D simulations. This paper is about the influence of two parameters: the aspect ratio and the presence of a gap or not. The aspect ratio is varied from 2 to infinity. The former corresponds to a square cylinder with a height of 1 diameter and with a symmetry boundary condition on the upper surface, the latter is an infinite square cylinder in cross-flow. For an infinite aspect ratio, stronger vortex shedding occurs which weakens galloping. At intermediate aspect ratios (L/D = 4 and 6), galloping amplitude does not seem to decrease sufficiently fast toward the amplitude of the limiting case of infinite L/D. For all these cases there was a gap between the bottom of the cylinder and the fluid domain bottom boundary. It is believed that the gap mitigates vortex-shedding and consequently leaves more room for transverse galloping occurrence. The aspect ratio could then be a less important factor than the gap.