In this case the baseline geometry has been modified by placing three 16 ft gaps in the baffle wall. The goal is to see if the gaps help or hinder the mixing process within the tank. Furthermore we wish to get insight for what other changes may be indicted based on the changes seen in this case.

This set of simulations were done using the same inflow and outflow rates measured in the field from 9pm, July 21 to 9pm July 23, 1997 for the baseline baffle wall geometry. During this period, the typical flow rate was 24 MGD (18,000 gpm), though rates from 12 to 48 MGD were measured over periods of ~1 hour.

It is clear that the mixing in this tank is much faster and thorough than for the baseline baffle wall configuration. This also agrees with scale model work done on this tank.

Below results from the Modified Baffle Wall Geometry with Boundary Conditions that match the Baseline Case are shown.

Geometry and Mesh for Tank with Modified Baffle Wall (1100x850 GIF 40K).

This image shows the tank geometry and mesh. The Baffle Wall has three 16 ft gaps. One of these gaps is shown in detail. This mesh has ~64,000 cells.

Tank Geometry near Inlet and Outlet pipe (1100x850 GIF 18K).

This image shows the details of the tank geometry near the inlet and outlet pipe. Both inlet and outlet pipes are below the elevation of the floor of the tank.

Typical Velocity Field during Fill Mode (1100x850 GIF 31K).

This image shows the velocity field at 1:40am, ~4.5 hour after the start of the fill cycle. The display plane is 2 feet below the water's surface. This field requires ~ 3 hours to develope, and varies somewhat during the fill cylcle as the inflow rate changes.

Fluoride Concentration during Fill Mode (1100x850 GIF 30K).

This image shows the distribution of a tracer fed to the tank during the filling cycle. This is the distibution after ~4.5 hours 2 feet below the water's surface. The interaction of the inlet jet with the nearest pillar creates a pair of jets. A third jet is created by the nearest gap.

Typical Velocity Field during Draw Mode (1100x850 GIF 31K).

This image shows the velocity field at 9:50am, ~4.5 hour after the start of the draw cycle. The display plane is 2 feet below the water's surface. This field looks somewhat similar to the fill cycle on the outlet side of the Baffle wall, but there are significant differences at the baffle wall due to different flow through the gaps. The velocity field on the inlet side is very quiet.

Fluoride Concentration during Draw Mode (1100x850 GIF 30K).

This image shows the distribution of a tracer during the draw cycle. Mixing is nearly complete throughout the tank. outlet side.

Fluoride Concentration History during Draw Mode (1100x850 GIF 20K).

This image shows the fluoride tracer history at 7 taps in the tank. Comparison of these with the histories from the Baseline case shows quicker and more thorough mixing on the outlet side of the tank.

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