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In this tutorial we learn about creating a more visually interesting smoke simulation by combining a volume gradient with advection.

We start with a basic smoke simulation created with a Pyro Solver. Then we go over converting the smoke simulation into a VDB, which is a volume data format used in Houdini.

Next, we dive into the concept of volume gradient. A volume gradient is a mathematical operation that computes a vector field based on a scalar field. In simpler terms, it calculates the direction of the most significant change in a particular property.

We use the density of the smoke simulation as the scalar field. The volume gradient will then calculate a new vector field that shows the direction of the highest density.

Particles are then introduced. These particles are initially advected by the smoke velocity, which means they are carried along by the flow of the smoke.

The crux of the effect comes from combining the smoke’s velocity with the newly created volume gradient velocity. This makes the particles not only move along the smoke flow but also get squeezed inwards towards the center of the smoke tendrils.

The result is a more visually interesting and dynamic smoke simulation with the flames appearing to squeeze and bunch together as time progresses.