Three-Dimensional Flow around a Bottom-Mounted Short Cylinder

摘要

The flow characteristics around short, bottom-mounted cylinders were examined with a three-dimensional nonhydrostatic model for Reynolds numbers of 300-3,900 and different obstacle geometries. Simulations using a large-eddy simulation closure scheme reproduce the vortex shedding in the wake, with reasonable Strouhal number comparisons to available laboratory data. The length of the recirculation region is also in good agreement with the data. The sensitivity of the flow to obstacle cross section and length is investigated for a Reynolds number of 500 with square and circular cylinder geometries for nondimensional lengths of 1-15. Model predicted upstream separation was found to be most sensitive to cross section. The predicted downstream recirculation lengths reproduced the nondimensional length dependency of available observations. To highlight the processes relevant to scour, the time-dependent bed shear was evaluated with the mean and peak Shields parameters. Significant wake variability was found which would not be described by the mean alone, indicating that sediment transport models assuming a mean shear will underpredict the transport in the wake.