Does anyone know a way to test a SketchUp model’s effect on wind patterns, like putting it in a wind tunnel and seeing direction, velocity, and pressure of air movement around (and through) the building?
Better late then nevah 
There are several options, butmost are pretty costly [price estimates]:
- forma (former spacemaker) by autodesk [2k / year]
- simscale by simscale [4k / year]
- simflow by simflow [7k / year]
- google can find more
There was a sketchup extension, but unfortunately it got discontinued.
In case you know how to program and such, you could try OpenFOAM.
You may need to export your models first before you can import them into OpenFOAM, i haven’t worked with OpenFOAM directly, so it’s a gues.
If it is a one-off thing it might be cheaper to print a 3D model and run it through an actual wind tunnel.