Comparison of Results Using the Fine Resolution Environmental HydroDynamic Model with Laboratory PIV Analysis of Vortex Dynamics for Shallow Tidal Inlets

Abstract

Tidal flows through inlets with vortex formation have long been of great environmental importance. The transport mechanisms between the bay and the ocean must be well understood to correctly predict the transport of sediment, pollutants, or living organisms. The results from the 3D Fine Resolution Environmental Hydrodynamic (FREHD) model with a hydrostatic pressure assumption and a one equation turbulence model are compared with experimental measurements of surface velocities. The one equation turbulence model was proven to be essential to the model performance. A constant viscosity turbulence model gave poor results in comparison to the experimental data. The FREHD model is able to predict the characteristics of the primary starting-jet vortices with relative accuracy including the trajectory and size of the vortex. The model has limitations on grid resolution which does not allow the high swirl strength in the center of the vortex or any secondary vortices formed by boundary layer separation from the inlet boundary to be predicted by the model. In the experimental data, secondary vortices form and eventually contribute to the total circulation within the primary vortex. Vortices with low circulation also decay faster than observed. The model is able, however, to predict the total circulation well during parts of the tidal cycle when the experimental data does not show secondary vortex formation. A third order upwind advection scheme improved the results of the FREHD model and allowed for higher swirl strength values which increased the amount of total circulation within the primary vortices.