Hybrid Shallow Water/3D Flow Model

Model Highlights:

Combines shallow water and full 3D flow models in one simulation using the multi-block approach, enabling users to capture key flow details and model large domains efficiently
Applies the shallow water model to simulate large scale flows where the vertical flow component has low significance
Uses a full three-dimensional model to capture flow details where vertical pressure gradient and velocity are important

The hybrid shallow water/3D flow model in FLOW-3D is designed to model flow around 3D structures within a ‘shallow water’ environment, such as bridges, drilling rigs at sea and dams in large reservoirs. The model uses multi-block meshing, where a mesh block is designated as shallow water or 3D. The standard shallow water or 3D equations are solved within each such block, based on the user selection, and the respective solutions are coupled at the block boundaries.

Flooding of a Large Area

This example describes flooding of a large area, with flow originating at a weir. The weir, which can be recognized as an example simulation provided with the FLOW-3D installation, is modeled with a full 3D model, while the flooded area downstream, containing several simple structures, is described with the shallow water equations. The two mesh blocks are adjacent to each other, i.e., they are linked.

Figure 2. Flooding of a large area with flow originating at a weir. The weir is modeled in a 3D mesh
block linked to a shallow water block that contains the flood area downstream.
Click the image to see a flooding animation.

3D Structure in a River Bed

This example demonstrates the use of a 3D nested block to resolve a fine structure consisting of four vertical posts placed in the middle of a dry river bed. The flow along the river is modeled with a larger containing mesh block that is a shallow water type.

Figure 5. A snapshot of the combined shallow water and 3D solutions. The 3D mesh block (right) is separated from the shallow water one (left), and the depth of the fluid in the shallow water solution is exaggerated for display purposes. Color denotes velocity magnitude.

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The purpose of this analysis, modeled using the hybrid shallow water model, is to simulate
road drainage passage. The shallow water model is used to model the flow on the road
and is coupled with two 3D blocks to model the drainage and the flow in the culvert boxes.