The flow past a circular cylinder moving through a fluid at different heights above a plane no-
slip boundary is investigated numerically for Reynolds numbers≤ 200. The gap height is
varied from large values, effectively corresponding to the freestream case (G/D=∞), down to
a small value where the cylinder is just above the wall (G/D= 0.005). The initial transition
from steady two-dimensional flow can occur through either a Hopf bifurcation to unsteady
flow or through a regular bifurcation to steady three-dimensional flow. The critical Reynolds …