Free Surface Flow Past a Piercing Circular Cylinder at High Froude Numbers

摘要

Flows past a free surface piercing cylinder are studied numerically by large eddy simulation (LES) at Froude numbers up to FrD=2.0 and Reynolds numbers up to ReD=1.10^5. A two-phase FCT-VOF method is employed to simulate the air-water interface. The effects of the free surface on vortex structure and Reynolds stress in the near wake are investigated. The loadings on the cylinder at various Reynolds and Froude numbers are also studied. Computation results show the free surface inhibits the vortex generation in the near wake, and this effect is stronger at higher Froude numbers. At a relatively lower Froude number, FrD=0.8, a vortex street characterized by a dominant mode of StD~0.23 is observed in the area away from the free surface, whereas no regular vortex shedding is found throughout the wake at a higher Froude number (FrD=2.0). It is also shown that the strong three dimensionality in the near wake at higher Froude numbers affects the force distribution dramatically along the cylinder, whereas variation in the Reynolds number has no significant effect. At FrD=2.0, in the region well below the free surface, there is a huge increase of both the mean drag and rms lift.