Large Eddy Simulation of a Flow Past a Free Surface Piercing Circular Cylinder

Abstract

Interactions between surface waves and underlying viscous wake are investigated for a turbulent flow past a free surface piercing circular cylinder at Reynolds number Re=2.7×104 using large eddy simulation (LES). The computations have been performed for three Froude numbers Fr=0.2, 0.5 and 0.8 in order to examine the influence of the Froude number. A second-order finite volume method coupled with a fractional step method is used for solving the grid-filtered incompressible Navier-Stokes equations. The computational results are found to be in good agreement with the available experimental data. At low Froude numbers Fr=0.2 and 0.5, the amplitude of generated surface wave is small and the influence on the wake is not evident. On the other hand, strong wave-wake interactions are present at Fr=0.8, when the generated free surface wave is very steep. It is shown that structures of the underlying vortical flow correlate closely with the configuration of the free surface. Computational results show presence of a recirculation zone starting at the point where the surface slope changes discontinuously. Above this zone the surface elevation fluctuates intensively. The computed intensity of the surface fluctuation is in good agreement with the measurements. It is also shown that the periodic vortex shedding is attenuated near the free surface at a high Froude number. The region in which the periodic vortex shedding is hampered extends to about one diameter from the mean water level. It is qualitatively shown that the separated shear layers are inclined outward near the free surface due to the generation of the surface waves. This change in the relation between two shear layers is suggested to be responsible for the attenuation of the periodic vortex shedding.

CFD simulations and experimental measurements of flow past free-surface piercing, finite length cylinders with varying aspect ratios

“…However, near the free surface the drag coefficient decreases rapidly, a trend that is consistent with previous studies found in the literature, e.g. Chaplin and Teigen (2003), Kawamura et al (2002), Yu et al (2008), Suh et al (2011). Additionally, an increase in the drag coefficient can be seen at the bottom of the cylinder where the flow is altered due to the tip vortices from the free end.…”

“…Numerical work on the drag coefficients of surface-piercing cylinders has been carried out by Kawamura et al (2002), Yu et al (2008) and Suh et al (2011). In each of the papers, the drag coefficient for the cylinder in the presence of a free surface was found to be smaller than the subcritical constant value of 1.2 at Reynolds numbers below 1.4 × 10 5 for a fully submerged cylinder.…”

CFD simulation of two‐ and three‐dimensional free‐surface flow

“…Reference [17]). More recently, LES calculations by Reference [18] investigated the e ect of free-surface motions on ow about a surface-penetrating cylinder, concluding that wave motions attenuate the periodic vortex shedding near the free surface to a depth of order one diameter for large (but subcritical) Froude numbers. However, their simulations used a uniform approach ow with symmetry condition on the lower boundary, so eliminating any junction vortex.…”

Unsteady free-surface wave-induced boundary-layer separation for a surface-piercing NACA 0024 foil: Towing tank experiments

“…Kawamura et al (2002) perform large-eddy simulations (LES) with tracking freesurface modelling for Fr ¼ 0:2, 0.5, and 0.8 and Re ¼ 2:7 Â 10 4 , including comparisons with available experimental data. Results show fairly good agreement with data for mean and root-mean-square (r.m.s.)…”