Multiphase numerical modelling of hydraulic structures with rapidly rotating flows: Stormwater vortex hydrodynamic separator

Hydraulic structures exhibiting strongly rotating flows are widely applied in the field of urban and wastewater hydraulics. Given demographic, urban development and climate change challenge, such infrastructure will require significant design innovation. Computational fluid dynamics (CFD) is increasingly an effective and widely used tool to evaluate and optimise new designs and determine performance efficiency for such structures. In this study, a full-scale prototype of a hydrodynamic vortex grit interceptor for stormwater conveyance systems (the BMS Stormbreaker Defender) was investigated using experimental and numerical methods. The prototype was evaluated physically in a full-scale test rig permitting flows of up to 30 l/s. Three-dimensional velocity distributions were obtained along radial profiles using acoustic Doppler velocimetry (ADV). The three-dimensional flow field in the chamber was also modelled using the ANSYS CFX software with a multiphase homogeneous Eulerian-Eulerian approach. In particular, the effectiveness of two-phase flow modelling using the shear stress transport (SST) model with curvature correction was analysed. Good qualitative and quantitative agreements were found between the numerical solutions and the experimental data sets for the four flow scenarios investigated. The results of the CFD evaluation/validation, the practicality of obtained data, and the implications for the design of such a structure are discussed.