Assessment of Large-Capacity Stormwater Treatment Devices with 3D CFD Modelling

Manufactured stormwater treatment devices (MTDs) such as oil–grit separators are one of the primary stormwater management tools to remove floatables (such as oil), sediment and other particulate matters from runoff in space-limited urban and industrial areas. MTDs are suitable for the cold climate if installed below the frost line, and their capacities can be varied over a large range. Designs of these devices can be adapted to local conditions to serve large areas that may cost up to half a million dollars each for construction. However, their performances cannot be estimated with confidence. The project, therefore, focused on assessing large-capacity stormwater treatment units with three-dimensional (3D) computational fluid dynamics (CFD) modelling. Field surveys of four local MTD sites provided data to assess the operational conditions of the structures and to verify the models. CFD models were developed applying the Eulerian multiphase flow approach and the standard turbulence closure. The sediment transport was simulated using a Lagrangian discrete particle tracking method. Two large capacity treatment devices of different designs were modelled to simulate the complex flow patterns and eddies that facilitated understanding and predicting treatment performances for different designs. The study demonstrated the potential use of CFD as a cost-effective and robust tool for assessing large capacity treatment devices that cannot be tested in the laboratory.