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Hydrology

Free-Surface Computational Fluid Dynamics Modeling of the Spillway and Tailrace

Decision Support for Operational and Structural Modification Alternatives

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Three-dimensional unsteady simulation of flow over a spillway and stilling basin. Click for a larger version.

Based on acoustic tracking and fish tagging data, the Dalles Project has been shown to have one of the highest mortality rates for juvenile salmonids on the Lower Columbia River. To assist in improving fish survival at the Dalles, PNNL has applied a three-dimensional computational fluid dynamics (CFD) model to the spillway, stilling basin, and tailrace zones downstream of the dam.

A free-surface computational fluid dynamics (CFD) numerical model has been applied to simulate the highly transient and turbulent flow conditions in this region. The model is based on the volume-of-fluid (VOF) method, and is capable of simulating sudden discontinuities in the free surface, including wave breakup. The model solves the non-hydrostatic Reynolds-averaged Navier-Stokes (RANS) equations over variable-sized hexahedral cells.

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Close up of the velocity flow field downstream of the non-spilling bays. Click for a larger version.

To verify the ability of the numerical model to simulate flows downstream of the spillway, the model was verified against data from three different physical models of the Dalles tailrace at scales of 1:36, 1:40, and 1:80. Results from these physical models allows for validation of the numerical model at various scales of motion from the small scale highly dynamic variations near the baffle blocks (1:36 and 1:40 scale) to the larger scale general circulation patterns that encompass the tailrace (1:80 scale).

Results and Benefits

CFD model results are being used together with field and physical model data to study operational and structural modifications that could improve hydraulic conditions for fish survival.

Hydrology

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