Bonneville Project: CFD of the Spillway Tailrace

Abstract

Although 400 cubic yards of rocks were removed from the stilling basin, there are still large volumes of rock downstream of the apron that could, under certain flow conditions, move upstream into the stilling basin. CENWP is investigating operational changes that could be implemented to minimize future movement of rock into the stilling basin. A key analysis tool to develop these operational changes is a computational fluid dynamics (CFD) model of the spillway.A free-surface CFD model of the Bonneville spillway tailrace was developed and applied for four discharge scenarios. These scenarios looked at the impact of discharge volume and distribution on tailrace hydraulics. The simulation results showed that areas of upstream flow existed near the river bed downstream of the apron, on the apron, and within the stilling basin for all discharges. For spill discharges of 300 kcfs, the cross-stream and downstream extent of the recirculation zones along Cascade and Bradford islands was very dependent on the spill pattern. The center-loaded pattern had much larger recirculation zones than the flat or bi-modal pattern. The lower discharge (200 kcfs) with a flat pattern had a very large recirculation zone that extended halfway across the channel near the river bed.A single scenario (300 kcfs of discharge in a relatively flat spill pattern) was further interrogated using Lagrangian particle tracking. The tracked particles (with size and mass) showed the upstream movement of sediments onto the concrete apron and against the vertical wall between the apron and the stilling basin from seed locations downstream of the apron and on the apron.iii