Pond Overflow

Pond Overflow — ANSYS Fluent CFD Simulation

Description

When water spills over an ogee overflow and discharges into a pond, the way it behaves depends heavily on whether the flow runs as a free surface or under pressure. Capturing that difference is essential for designing spillways and overflow structures that handle their intended flow safely. In this project, you'll use ANSYS Fluent to simulate water flowing over an ogee overflow into a pond, comparing two distinct flow regimes side by side. Within the Hydraulic & Civil: Beginner CFD Training Package, this project moves from open channels toward hydraulic structures, introducing overflow behavior and the important distinction between free-surface and pressurized flow.

Methodology

The model is built in two dimensions in ANSYS DesignModeler as an ogee overflow leading into a pond, and two separate cases are studied. In the first, the flow is a free surface reaching the overflow at a defined height with a flow rate of 140 kg/s; in the second, the water flows under pressure with a flow rate of 420 kg/s. The geometry is configured in two variants — one that includes an upstream region before the overflow and one that omits it — and the inlet is split into separate water-flow and airflow sections. Meshing is carried out in ANSYS Meshing using a semi-structured grid, with roughly 20,100 elements for the free-flow case and 16,400 for the pressure-flow case. Because both cases involve a moving interface between air and water, a two-phase Volume of Fluid (VOF) model is used, with air defined as the primary phase and water as the secondary phase.

Analysis

From the results, you'll examine 2D contours of pressure and velocity along with the volume-fraction field that reveals the free surface and the path of the water into the pond. You'll also obtain a plot of static pressure along the flow direction for both models, allowing a direct comparison between the free-surface and pressurized regimes. By the end of this project, you'll be able to set up a two-phase free-surface flow in ANSYS Fluent using the VOF model, configure and compare multiple flow scenarios on a single hydraulic structure, and interpret the results to understand how overflow conditions change the pressure and velocity behavior.