Abstract：The problems, such as too high energy consumption for oxidation ditch operation and how to decide submerged propellers installation position, exist in sewage treatment plants currently, thus the flow in an oxidation ditch was simulated based on the Navier-Stokes equations, standardturbulence model and SIMPLE algorithm. The threedimensional submerged propeller model was built by the existing blade pattern drawing, and the fluid domains were meshed with unstructured tetrahedral cells. The shaft power of submerged propeller and the velocity distribution in various crosssections of the oxidation ditch were estimated under different working conditions; meanwhile, the flow field driven by the propeller was investigated as well. The results indicate that on the premise of the submerged propeller installation parameters unchanged, altering the installation position of submerged propeller can avoid the back mixing phenomenon caused from a too strong driving force. Besides, the sludge deposition problem, which is caused from too low flow velocity resulted by too much attenuation of the driving power in the bends, also can be solved. By properly adjusting the number of submerged propellers, a minimum power density can be determined to meet the driving force needed for mixing. Thus not only the velocity in the oxidation ditch has met the requirement, but also the minimum energy consumption has been achieved. The study can provide a theoretical guidance for determining the installation position and number of submerged propellers.
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