Vortex drop structures are often used in storm and sewer systems to convey flows through large elevation changes. For this study, a vortex drop structure was proposed in both the storm and sewer lines to convey maximum flows of approximately 200 cubic feet per second down a 70-foot drop. FLOW-3D HYDRO, a Computational Fluid Dynamics (CFD) model, was used to simulate the hydrodynamics through the designed sewer system. The two-phase flow module was activated, so the flow rates of both air and water though the system and the interaction of the air-water interface could be evaluated. The goals of the CFD model were to validate that the proposed designs could pass the required maximum estimated water flows, calculate the forces on different component of the vortex drop structure, and determine the flow rate of air through the vortex drop vent for odor control purposes. Challenges of a two-phase flow model as compared to a one-phase model include computational time as well as additional assumptions or data collection required to determine the boundary conditions of the air flows that are not required when only considering water.
