Jerry Ken Walks Through Creating a Custom Velocity Forces for Simulations in Houdini.

Houdini Artist Jerry Ken posts a tutorial that shows how you can create custom forces for any simulations in Side Effects Houdini. His examples share a look at how to make a custom velocity force for Pyro simulations within the DOP.

Houdini is quite extensible in this way. A previous tutorial from Ben Watts also had a look at creating a custom force inside Houdini, working with the VFX of a tornado scene.

Artist Stefan Sietzen also showed off some experimentations with custom force fields in Pyro simulations. His system uses a geometry-based vector field to contain a pyro simulation of smoke.