Case Study: 2D and 3D/CFD Modeling along Stepped-Chute Spillways with Stilling Basin and Tailwater Weir

ABSTRACT ONLY - Computational Fluid Dynamics (CFD) 3D modeling has become an increasingly valuable tool in the evaluation and design of open channel spillway systems. However, the significant computational demand and its complexity is prohibitive in the CFD model development. The purpose of this study is to test the application limits of 2D hydraulic modeling along open channel spillway systems, which typically include turbulent and rapidly-varying flow conditions, as a supplemental tool for the optimization of CFD models. 2D modeling of flow in these areas may violate several simplifications made to the root Navier-Stokes fluid motion equations to create the Shallow Water Equations (SWEs) used in the 2D solutions (e.g., negligible vertical velocities, hydrostatic, negligible effect of air entrainment on roughness, and uniform density). Furthermore, as turbulence intensifies, the Reynolds-averaging in the SWEs to account for turbulent motion by approximating eddy viscosities, increases uncertainties in the results. The case study used to support this study involves a 2D computer model of a 38:1 scaled physical model for a spillway system at a large dam with a variety of components, including a labyrinth weir, irregular approach to the weir, steep concrete chute, flip bucket energy dissipator, downstream topography, and a downstream highway bridge (with piers). Measured parameters from the physical model were compared to output from the 2D model to inform conclusions regarding the applicability and limits of 2D modeling under similar hydraulic conditions.