Numerical Modeling of Downstream Scour in Circular Culverts: Impact of Inlet Blockages and Variable Flow Conditions

Abstract Accurate estimation of scour depth downstream of culvert outlets is essential for culvert design integrity. Inadequate designs can result in structural failures, leading to increased costs for maintenance and rehabilitation. This research evaluates the efficacy of numerical models in predicting scour depth and its location downstream of circular culverts under variable flow conditions. Two hydrographs were created for unsteady flow, featuring nine different flow discharges, while steady flow conditions were analysed at flow rates of 14 l/s and 22 l/s. The study investigated circular culverts with inlet blockages of 0%, 15%, and 30%, comparing outcomes with predictions from the Flow-3D software by using renormalization group (RNG) turbulence model. Extensive experimental data on circular culverts were utilized, with simulations performed using commercial software. This involved analysing the scour’s downstream profile, its maximum depth, and location, and comparing these metrics with actual observed data. Results showed that numerical model predictions closely matched the experimental data, although the simulated scour was generally less than what was observed for both steady and unsteady flows. While blockage rates notably impacted the scour patterns in unsteady flow scenarios, escalating blockage percentages did not uniformly translate into proportional increases in scour depth within steady flow environments.