CFD Analysis of Mixing in Large Aerated Lagoons

Abstract

A general CFD model is developed to characterize the flow fields in large aerated lagoons. The power number and flow number of a propeller used in aerated lagoons are validated against lab experiments. Numerical tests in a small lagoon with 8 propellers indicate that the pumping action of propeller can be represented by momentum source effectively. CFD simulations of a large lagoon with the existing 33 propellers and with 16 propellers for a proposed redesign are carried out by substituting one momentum source for each propeller. A local RTD model is developed to predict resident time in both designs based on the converged flow fields. Furthermore, a biological oxygen demand (BOD) model is incorporated to simulate BOD removal in the lagoon. Simulated results show that the proposed design should be more efficient than the existing design in terms of BOD removal per unit power consumption.