Another use for FLOW-3D is in the analysis of flows whose return interval is large. In the context of dam safety, these problems can involve the determination of spillway performance and dam stability during infrequent and extreme flooding events.
Determining Probable Maximum Flood Conditions
FLOW-3D can be used to analyze load conditions at any flow rate including probable maximum flood (PMF). In order to do this the rating curve needs to be accurately captured and all flow effects included such as the Tailwater flows with stilling basins and hydraulics jumps. FLOW-3D can simulate all aspects to be sure the spillway and stilling basin can handle the flows without the problems associated like uplift, cavitation and abrasion.
The advantages to CFD simulation are that it takes less time than physical modeling and avoids the scaling effects of friction, turbulence, air entrainment and release, fluid structure interaction and local scour below energy dissipaters because everything can be modeled at full scale.
Image courtesy of Alden
The images at left are from a case where FLOW-3D was used by Alden Research Laboratory, on behalf of a large American utility company, to assess spillway performance of the utility’s US dam project near Roanoke, Virginia, in operations under upwardly-revised probable maximum flood (PMF) conditions.
Reducing Physical Modeling Needs
Traditionally, a physical model of the dam and spillway systems would be constructed and used in the analysis. In this case, however, because detailed data were available from the original design, and since constructing a new model would be expensive and time-consuming, a numerical model of the system was developed, validated against the historical data and then used to confirm the ability of the structure to withstand PMF conditions that had been increased by over 230%. And the analysis was completed at a fraction of the cost and time that would have been required with physical modeling.