Modeling Two-Dimensional Circulating Flow

Theoretical analysis and numerical experiments are presented to demonstrate some of the difficulties in modeling two-dimensional circulating flow. It is shown that in cases of practical interest the lateral mixing of momentum, which is essential to support the circulation, can arise in computational models from wholly spurious numerical dispersion effects. Laboratory flume measurements of the flow in the wake of a plane obstruction are presented. It is shown that the horizontal velocity profiles across the eddy indicate that the turbulent lateral mixing rate is appropriate to a shear layer mixing rather than to bed-generated turbulence. Criteria for the conditions under which shear layer turbulence dominates are presented. The practical implications for numerical and physical models are reviewed.