In this paper, the starting flow and steady flow past a circular cylinder placed near a planar boundary are investigated both experimentally and numerically. Two cylinders, of diameter D=38 mm and D=25 mm, are used at distances G = 0, 2, 4, 6, 10, 20 mm from a planar boundary. The flow is accelerated with a constant acceleration a until it reaches an ultimate speed U and then remains steady. We explore the following various combinations of acceleration and ultimate speed: a=5.5 cm/s2, U=3.8 cm/s; a=7.2 cm/s2, U=5.4 cm/s; a=12.0 cm/s2, U=7.5 cm/s. The flow field is visualized using a hydrogen bubble technique. Time sequential photographs are taken during both the acceleration stage and the steady stage of the flow which show the vortical flow features in corresponding stages. In our numerical simulations, the Navier-Stokes equations for unsteady incompressible viscous flow combined with a k- w turbulence model are solved via finite volume method with the SIMPLEC algorithm. Using cut cells on a Cartesian background mesh, our model can deal with the complex geometries between the cylinder and the plane boundary. The same cylinder and flow parameters as those featured in the experiments are adopted in numerical tests. The results of the experiments and numerical tests reveal that vortex shedding takes place at the starting flow stage but is suppressed when the gap ratio G/D becomes smaller than 0.3. The numerically predicted flow field agrees reasonably well with the experimental results.
Flow around a circular cylinder near a planar boundary may be an ideal simplification of many practical problems such as the hydrodynamics of marine pipeline and cables. Although the geometry is simple it is characterized by complicated hydrodynamics and has attracted the attention of many researchers during the past few decades.
