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Documentation

Wedge Boundary Condition

The wedge boundary condition is used in computational fluid dynamics to define an axisymmetric situation, for eg. a cylinder. The model and flow must be axisymmetric along a central line such that all physical variables of the flow have the same value and distribution at a given radius for all angles.

This boundary condition is specified by two planes that must be selected on separate sides of the domain (referred to as front and back) on surfaces running along the axis. It works for 2D simulations only.

Settings

The settings panel for the Wedge boundary condition in the SimScale Workbench looks as follows:

wedge boundary condition settings panel
Figure 1: Settings panel for the wedge boundary condition

Besides the face assignment, the user doesn’t have to insert any numeric values.

Note

To simulate a two-dimensional model or flow the geometry needs to be specified as a wedge with a small angle (<5 degrees) and a single cell thickness along the curvature.

2d mesh for wedge boundary condition
Figure 2: An example mesh used for simulating subsonic flows in a de Laval nozzle. The wedge boundary condition will be applied to the front and back (unseen) faces

A Wedge boundary is different from the symmetry boundary condition in the sense that the wedge boundary condition applies the Navier-Stokes (NS) equations in cylindrical coordinates whereas the latter applies the NS equations in cartesian coordinates. One big advantage of wedge boundary is that it allows for the rotational flow around the axis and this is possible only because the fluxes and normal components are not assumed as zero.

Notes

Readers may also need to assure that the face elements of the mesh on both the selected surfaces are congruent. Such a mesh currently cannot be created in SimScale and hence needs to be locally created and uploaded to the SimScale platform.

There are also some limitations when using wedges for a finite volume fluid simulation. The size of the cells near the axis can get extremely small in volumes which can result in considerable numerical problems.

Get more insight into using the wedge boundary condition in SimScale with the help of the following compressible flow validation case:

Last updated: August 25th, 2022

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