This summarizes Computational Fluid Dynamics (CFD) work that is included in a Research Study Project for AWWARF (American Water Works Association Research Foundation, Project #260; "Water Quality Modelling of Distribution System Storage Facilities").

Eighteen cases were modeled in detail using CFD. Variations from one case to the next includes tank shape, inlet and outlet location, inlet water temperature, and variability of flow rates. Results for these cases are displayed in the pages linked to the following outline.

Rectangular Tanks:
Square Tank. Study of Pillars (including movies).
Brentwood (Wash DC).

Cylindrical Tanks:

Ed Heck Reservoir (Azusa, Ca). Impact of a Tangential Inlet.
EBMUD (Oakland, Ca). Study of Thermal Effects and Inlet Location.

Table of Mixing Statistics for these cases This table show the mixing performance for a variety of cases. Different tank shapes, different fill and draw protocols, different thermal conditions, inlet locations and flow rates are all included. The comparison is possible by normalizing each case's mixing rate by the Okita time; this is the time it takes to mix a hypothetical cylindrical tank of the same floor area and water depth as the tank in question. "Okita" tanks have a vertical inlet at the tanks center. Okita times are dependent on the tank floor area, initial water depth, and inlet velocity and cross-section. Okita times are determined from laboratory work on Cylindrical Tanks over a large range of tank sizes, water depths and inlet momentums. One entry in our study is in fact a cylindrical tank with a central vertical inlet. It correlates to the Okita time to within 2%. The other entries can be compared to the Okita time to see if that configuration is better or worse than the analogous cylindrical tank. Most tanks we studied are well mixed after 12 hours of operation. But tank operation or the presence of baffles can cause mixing times in some tanks to be longer than 12 to 20 hours.

All the material in these Web pages are supplemented by a formal Final Report for this project. Please see that report for a summary of both the methods and results of this work. The report includes a discussion of the relative water quality performance of these storage tanks and others. It also discusses other methods of evaluating these tanks.