Spillway Analysis Techniques Using 3-D Computational Fluid Dynamics Modeling

Spillway design and analysis has historically been performed mostly using: 1) equations from Bureau of Reclamation, Army Corps of Engineers, American Society of Civil Engineers, and other publications or 2) one-dimensional (1D) flow modeling (programs such as HEC-RAS). For complex or non-standard spillway chute designs, traditional 1D modeling and hand calculations may be inadequate for determining water surface profiles and flow regimes, including considerations for factors such as bulking from air entrainment and cross-waves.
Historically physical model studies have been conducted for complex or non-standard spillway designs to simulate the water surface profile, pressure, and general flow regime. Computational fluid dynamics (CFD) modeling has been used in the recent years to analyze flow in spillways as a stand-alone analysis tool and in many cases in conjunction with physical modeling.
The comparison of flow simulations in spillways by physical hydraulic and CFD modeling has been encouraging. CFD modeling has been able to simulate the free surface flow in spillways including pressure on spillway surface, jet trajectory, potential for cavitation, and flow pattern in the catch chute and tailrace. CFD modeling provides an alternative to the more expensive and time-consuming physical model studies. A CFD model leads to more reliable results than charts and semi-empirical equations or 1D modeling using previously. This may be especially valuable early in design to provide better cost estimates and compare various spillway alternatives or configurations even where physical modeling is still required.
This paper presents a CFD model of the Platte Canyon Dam Spillway and compares the computed flow characteristics with those estimated by the historical approach. The spillway includes a labyrinth weir crest, curved spillway chute, and baffled chute (Figure 1), was designed using traditional techniques including hand calculations, HEC-RAS modeling, and the Bureau of Reclamation publication “Engineering Monograph No. 25 - Hydraulic Design of Stilling Basin and Energy Dissipators”. 14 pp, 8 references.