Setting up Internal flows with Cart3D: 

 

1. geometry setup

 Lets assume that we're talking about something that looks like a model in a wind tunnel.

Notice that the flow comes in aligned with the tunnel, and the angle of attack is specified by rotating the model with respect to the tunnel.

   

1.1 Normal Vectors:

 Cubes usually meshes a geometry using the normals pointing "into-the-flow", However, for internal flows, cubes' "-internal" flag automatically reverses the sence of the normal vectors, this means that the geometry should have its normal vectors pointing "Away-from-the-flow" and when you run cubes, be sure to use the "-internal" flag.


1.2. Laying out the Cartesian Grid:

Carteisan cells that cut solid geometry automatically get a slip boundary condition (inviscid wall) applied to the cut-faces. If a Cartesian cell does not cut geometry, you can apply either a far-field, or inviscid wall - remember, a symmetry plane is the same as a planar inviscid wall. (Actually, if your "wind tunnel" was a rectangular box, you could do this simply by setting the Ymin, Ymax and Zmin, Zmax boundaries to "symmetry/Inviscid wall" and Xmin&Xmax to "far field" -- without ever using a *tri file to specify the tunnel geometry and just let the boundary of the cartesian grid be the "tunnel walls". But anyway... lets assume that you have geometry for your tunnel. The following sketch shows how to lay it out.

2. An Example

Here is an example, showing a cutaway internal flow run at supersonic speeds, since the flow is supersonic, you can see the shock reflections off the tunnel walls.

Here is a picture of the cut-cells in the gridcut-cells for wind-tunnel example