AWWA ACE63048

Maintaining adequate water quality is a chief criterion when designing and retrofitting water storage and mixing facilities (e.g. reservoirs, mixing tanks, contact chambers, etc.). Common problems associated with a poor design include: hydraulic short-circuiting; formation of dead zones; poor circulation; and, excessive detention time. The design of such a facility requires the engineer to favorably locate and orient inlet and outlet structures (and possibly baffle systems and mixers). Until recently, the only method for reliably evaluating design alternatives was to perform a laboratory/field tracer study (i.e. physically injecting dye into the system, observing the overall dye pattern, and sampling at the outlet). Today, an alternative to the laboratory/field tracer study exists a numerical tracer test performed on a computer using a computational fluid dynamics (CFD) model. A CFD model supplies the engineer with a "virtual laboratory" for testing and optimization providing the ability to screen numerous design alternatives and converge on a favorable system design. In this study, two commercially available CFD models are used to numerically evaluate reservoir mixing characteristics. To build confidence in the numerical results, the CFD models were first applied to the following verification/validation cases: a free-jet; a 180-degree sharp bend; and, a rectangular tank with a baffle wall. As part of the validation studies, the CFD results were compared with analytical solutions, experimental data, and laboratory tracer studies. Next, the CFD models were applied to two "real world" projects where the model results were used to help evaluate design alternatives. The information presented herein will assist engineers in applying CFD models to other water storage and mixing facilities. Includes figures.