Numerical Investigation of Flow past a Circular Cylinder beneath a Free Surface with Volume of Fluid (VOF) Method

In this paper, flow through a fixed two-dimensional circular cylinder beneath of a free surface at various gap ratios at Reynolds number of 180 and Froude number of 0.2 is numerically investigated. Continuity and momentum equations is resolved with control volume method by commercial software Ansys Fluent 14.00. For the low Froude number case (i.e., gravity-dominated), the results obtained are similar to those for flow past a cylinder close to a no-slip boundary, so that similar vortex shedding mechanism can be observed. As the distance between the surface and the cylinder is reduced, the Strouhal number, as measured from the time varying lift, increases to a maximum at a gap ratio of 0.70. Further gap reduction leads to a rapid decrease in the Strouhal number, with shedding finally ceasing altogether at gap ratios below 0.16. The agreement between the results for a free surface and a no-slip boundary suggests that the mechanism behind the suppression of vortex shedding is common to an adjacent no-slip boundary. In this research, Lift coefficients and velocity contours for various gap ratios has been investigated, also the effect of free surface on flow hydrodynamic for low Froude number s is considered.