TUFLOW 2D Hydraulic Structures: Difference between revisions
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== Can I model bridge piers explicitly in 2D using very small cells? ==
It isn't recommended to explicitly model bridge piers by blocking out the pier faces in TUFLOW, or in any hydraulic modelling software based on solving Shallow Water Equations(SWE). Due to the 3-dimentiality of the flow and turbulence around a pier, computational fluid dynamics (CFD) approach is often required to simulate the flow around piers explicitly. The wake turbulence behind a simple-shape pier can be resolved to some extent using extremely fine mesh in TUFLOW (see calibration example to a flume experiment in the [https://www.tuflow.com/library/webinars/#structures webinar on Energy Losses at Structures]), however the predictions for head losses show notable sensitivities to the mesh size, the mesh design, and the choice of turbulence model. The extremely fine mesh resolution also results in significantly higher computational costs.
Therefore, the safest and strongly recommended approach with regard to establishing head losses and consequently flood levels, is to model the effects of such obstructions with form loss coefficients (applied to selected mesh cells) that have been derived from physical testing. This approach has been shown to provide the most consistent results across various mesh resolutions. It also has the added benefit that, by avoiding small cells in the mesh, it will provide much more efficient run times for flow solvers.▼
[[File:Flow round a cylinder.png]]
''The point of flow separation around an object has a major bearing on the drag coefficient and is not reliably reproduced by 2D or 3D software.''
▲Therefore, the safest and strongly recommended approach with regard to establishing head losses and consequently flood levels, is to model the effects of such obstructions with form loss coefficients (applied to selected mesh cells) that have been derived from physical testing. This approach has been shown to provide the most consistent results across various mesh resolutions. It also has the added benefit that, by avoiding small cells in the mesh, it will provide much more efficient run times for flow solvers.
<!-- SG commented out, too much CFD info
Small scale obstructions to the flow, such as trees, poles, piers, etc. cause additional head losses along a flow path due to their drag characteristics. Historically, form loss (or drag) coefficients for various profile shapes have been determined as a function of Reynold’s number through experimental testing. <br>
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