Wave scour around a large vertical circular cylinder

This paper presents the results of an experimental study on the steady-streaming flow and the resulting scour process around a large vertical circular cylinder exposed to a progressive wave. The flow is in the unseparated flow regime [the Keulegan-Carpenter number at the bed being KC < O(1)]. The diffraction effect is existent.

Two kinds of experiments were made: (1) rigid bed; and (2) actual scour. Detailed velocity measurements were made near the bed in the vicinity of a cylinder (1 m in diameter) in the rigid-bed experiments. These measurements show a strong presence of a 3D steady streaming induced by the waves. No such streaming exists in the absence of the cylinder.

The rigid-bed experiments together with the actual scour tests indicate that the waves stir up the sediment and bring it in suspension, and the steady streaming carries the sediment away from the cylinder, leading to scour. The scour is found to depend mainly on KC and the diffraction parameter, the cylinder-diameter-to-the-wave length ratio.

The scour depth generally increases with these parameters.