Numerical simulations of flow distribution structure at central WWTP Prague using CFD model

The presented study deals with the distribution of the flow into four equal parts in the circular distribution structure of the Central Wastewater Treatment Plant (WWTP) in Prague. The objective of the study is to assess the existing splitter geometry and the newly proposed geometry in terms of uniform flow distribution into four equal parts. Each variant is assessed for wet weather flow, selected variants also for dry weather flow. The hydraulic design is based on numerical CFD simulations in OpenFoam, which is complemented by a 1D calculation of the mechanical energy balance of the flow along the entire object and a simple 1:3 scaled model of the weir crest. The results show that the influence of inflow curvature and high cross-sectional velocities at the inflow affect the asymmetry of the flow field, which is manifested in the different hydraulic loading of the weir quadrants, which is than propagated in the different overflow discharges over the four indivdual weir sections. This was confirmed for all variants considered. After a number of numerical experiments, the original variant appears to be the most advantageous one, as it best accounts for the symmetrical flow conditions in the RO. The hydraulic efficiency of this variant can be significantly increased by installing a concentric bore wall, where the maximum differences are reduced from values of ± 7÷10% to values of ± 2÷3% for the maximum flow rate considered.