Dynamic coupling of a near with a far field model for outfall discharges

The dynamic/online coupling of the Distributed Entrainment Sink Approach with the model CORMIX for the near field and Delft3D-FLOW for the far field of outfall discharges is analysed in terms of hydrodynamic results. Six test cases have been performed, considering a straight channel with a steady state flow with a submerged positively buoyant discharge, varying the discharge flow and the ambient velocity applying offline and dynamic coupling. Three criteria were evaluated, defining the necessity of dynamic coupling approaches: a near field stability criterion, the distributed momentum criterion, and the ambient Froude number. Results showed that different coupling methods had led to distinct results for all tests, especially in the near field region. The three criteria demonstrated that tests with large flow rates or into almost quiescent waters led to hydrodynamic changes beyond the near field and thus should use the dynamic coupling.