NUMERICAL-SOLUTION OF 2-LAYER, 2-DIMENSIONAL TIDAL FLOW IN A BOUNDARY-FITTED ORTHOGONAL CURVILINEAR COORDINATE SYSTEM

A new two-layer, two-dimensional mathematical model employing a finite difference method based on numerically generated boundary-fitted orth ogonal co-ordinates and a grid 'block' technique for unsteady boundary problems is developed which can be used to simulate flows with densit y stratification in a natural water-body with complicated topography. In the model the turbulent exchange across the interface is treated em pirically and a time-splitting finite difference method with two fract ional steps is employed to solve the governing equations. The model is calibrated and verified by comparing the computational results with d ata measured in Tolo Harbour, Hong Kong. The simulation results mimic the field measurements very closely. The computation shows that the mo del reproduces the two-layer, two-dimensional tidal flow with density stratification in Tolo Harbour very well. The computed velocity hodogr aphs show that the tidal circulations at various positions in each lay er have different patterns and that the features of the patterns are i ndependent of the tidal type except for their scales. The computed Lag rangian pathlines show that the tidal excursion is dependent on the ti dal type, especially in the inner harbour and side-coves.