Computational and Physical Modelling of the Flow and Sediment Transport in a New Vortex-type Stormwater Retention Pond
Given the current water quality requirements for a stormwater retention pond, the civil and environmental engineering community requires accurate and efficient methods to explore the sediment removal of retention ponds. This research studied the use of Computational Fluid Dynamics (CFD) for modeling sediment retention ponds with comparison of the fluid flow results to in-house experimental data. This study provided insight on the pond design using single- and two-phase modeling approaches. This research highlighted the potential of using an Eulerian-Eulerian two-fluid model (TFM) approach, without the empirical ad hoc relations often used to determine the sediment concentration profile, for modeling flow and sediment in a new vortex-type pond design. This manuscript-based thesis documented four different studies. The first study summarized the fundamental concepts involved in the overall design of stormwater retention ponds. A comprehensive and in-depth description of different computational methods used in the literature for modeling stormwater retention ponds was given. Previous applications of CFD to modeling stormwater retention ponds was critically reviewed. The present position of multiphase modeling in the simulation of storage ponds was addressed, and possible directions for future development were outlined. The second study explored the potential of single-phase CFD modeling in a new vortex-type stormwater retention pond. The flow pattern in a 1:13.3 scale model of the vortex-type retention pond was characterized and some problematic recirculation zones were identified. The mean and fluctuating velocity fields in the pond were explored using computational and experimental methods. For the CFD modeling, the 3D Reynolds averaged Navier-Stokes (RANS) equations together with a k-ε turbulence model were solved using ANSYS Fluent 19.2. In general, the predictions and measurements were in good agreement. In the third study, an Eulerian-Eulerian TFM using constitutive equations based on granular kinetic theory, coupled with a low-Reynolds-number turbulence model, was used to predict the liquid and sediment transport in an equilibrium channel for fully-developed, steady, dilute flow. The particle-wall boundary condition was also investigated. The model predictions of the liquid and sediment velocity profiles, sediment concentration, turbulence statistics and fluctuating particle velocity field were documented against experimental data from the literature. In the last study, the TFM was implemented to assess pond performance and to provide insight on the sediment transport in the vortex-type stormwater retention pond for the case of steady, dilute flow with no sediment deposition. The model predictions of the liquid and sediment velocity profiles, and sediment concentration were documented. The study demonstrated the spatial distribution of sediment in the pond: the recirculation zones documented in the single-phase CFD study were characterized by relatively high concentrations of sediment. Overall, the current study demonstrated the application of single-phase CFD in detecting problematic regions such as low velocity zones and stagnation regions in a new pond design by providing a map of the flow patterns. This study also showed the application of two-phase CFD in the simulation of fluid and dilute sediment transport in the same pond as a step towards more comprehensive simulations, which in turn supports the goal of achieving higher water quality. No sediment deposition was included, which is the next step in applying the TFM formulation to retention pond studies.
Computational Fluid dynamics, Stormwater retention pond, Flow pattern, Sediment transport, Two-Fluid model.
Doctor of Philosophy (Ph.D.)
Civil and Geological Engineering