Houdini 19.5 Shelf tools

Sparse Billowy Smoke shelf tool

Creates thick cloud-like smoke rising from a spherical base.

On this page
Pyro simulation in the viewport. Colorspace: ACES, Voxels Size: 0.0025.
Pyro simulation rendered with Karma. Colorspace: ACES, Voxels Size: 0.0025.


This shelf tool sets up a sparse pyro simulation of a rising smoke stack, with a meter-scale base. The setup can be used as a starting point for simulating scenarios such as chimney smoke or cooling tower steam.

Understanding Sparse Billowy Smoke

The shelf tool creates a node network that consists of three components.

  1. smoke_source takes care of setting up the density and temperature sources that continuously get injected into the simulation. The start of the node chain in this subnetwork (smoke_base) defines the shape of the smoke base. You can switch out this node for another geometry object if you'd like to modify the look of the base.

  2. smoke_simulation contains the DOP network that consumes the sources and carries out the fluid simulation. The parameters on the sparse pyro solver have the greatest influence on the emergent shape of the smoke.

    To...Do this

    Change how fast the smoke starts to rise

    Modify the Buoyancy Scale. Increasing its value will make the smoke rise faster, while decreasing it will slow its ascent.

    Set how fast the rising smoke slows down

    Modify the Cooling Rate. Lower values will keep the smoke hot for longer, so that buoyancy force will continue to accelerate it.

    Control how fast the smoke disappears

    Change the Dissipation parameter. Higher values will make the smoke rapidly disappear and smaller values will force the smoke to stick around for longer.

    Change how much the smoke breaks up

    Tweak the Disturbance parameter. Higher values will break up the smoke more, while lower values will yield a more smooth-looking result.

  3. smoke_import subnetwork extracts results of the simulation into a SOP geometry. A pyro post-process node sets the proper viewport visualization settings for the smoke and creates a matching render material.

Shelf tools

Using the shelf

  • Customize the shelf

    How to change the look of the shelf, change and rearrange its contents, and create your own shelf tools.