Hybrid Shallow Water/3D Flow

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.

Model Highlights

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

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.

Hybrid shallow water 3D flow model

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.

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.

Hybrid shallow water model

A snapshot of the combined shallow water and 3D solutions. The 3D mesh block, outlined in red, contains the three vertical peers and is nested within a larger shallow water mesh block. Color denotes velocity magnitude.

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.