Three-Dimensional Numerical Modeling of Urban Green Stormwater Infrastructure Curb Inlets

Abstract

The current equations for curb inlet opening sizing often inaccurately estimate the capture efficiency of small urban green stormwater infrastructure (GSI) curb inlets. Most of these equations are based on studies with openings much larger than typical urban GSI curb inlets (i.e., less than 0.6 m). This study introduces a new, three-dimensional (3D) numerical approach for evaluating curb efficiency using the ANSYS Fluent computational fluid dynamics (CFD) model that can be applied to a wide range of curb inlet conditions. Simulated curb efficiency results for typical urban curb inlet openings are verified by laboratory experiments of field-scale conditions. A high prediction accuracy is obtained (Nash-Sutcliffe efficiency $\mathrm{coefficient}=0.97$ ) between the observed and the CFD model results. The CFD model also performs better than three commonly used methods for estimating curb inlet efficiency; the Hydraulic Engineering Circular No. 22, and the 2009 and 2012 Comport and Thornton equations. The high level of accuracy observed in this study makes 3D CFD modeling a more effective alternative to existing equations for evaluating GSI curb inlet efficiency. The quick simulation times realized in this study also demonstrate that CFD modeling of GSI inlets has an added benefit of quickly evaluating several design alternatives without a need for costly full-scale or on-site testing often performed to assess such inlets.