Houdini 20.5 Nodes Geometry nodes

VDB Potential Flow geometry node

Computes the steady-state air flow around VDB obstacles.

Since 17.5

VDB Potential Flow computes how air will flow around obstacles by solving for the closest divergent free velocity field. While this does not create any turbulence, it is effective for allowing particle streams to anticipate collisions and avoid them.

The result is output as a vec3 VDB named flowvel. The other VDBs are passed through unchanged.

Note that this is a static solve - there is no history to the field so it may change substantially given slightly different colliders.

Parameters

Group

The first scalar VDB in this group is used as the collision to compute the flow around. If it isn’t a SDF, it’s activation will be used instead.

NOTE: Only the first VDB is used. If you have multiple colliders, sample them into a single VDB before processing.

Velocity VDB

The first vec3 VDB in this group is used as the velocity of the collision objects. It is thus only used at the collision boundary to set the solved velocities at those locations.

Mask VDB

Only perform the computation in the region specified by this mask. The mask is provided on the second input.

Domain Mask Type

How to treat the mask.

Intersection

Only process voxels within the mask.

Difference

Process all voxels except those in the mask.

Iterations

The potential flow will be computed until the specified tolerance is reached. However, some systems may never converge. This caps the number of iterations that are run before terminating the solve.

Tolerance

The potential solve is considered converged when the magnitude of the absolute error is below this value. If no tolerance is specified, 1e-20 is used.

Use World Space Units

If enabled, use world space distances to determine the bandwidth around collisions to compute the potential flow.

Dilation Voxels

Distance in voxels around the collisions to compute the potential flow. Beyond this range the air is assumed to be undisturbed, so this also controls how tightly the air flow will wrap the collider.

Dilation

Distance in world space around the collisions to compute the potential flow. Beyond this range the air is assumed to be undisturbed, so this also controls how tightly the air flow will wrap the collider.

Background Velocity

Direction and magnitude of the default background velocity field. This is applied across all voxels.

Apply Background Velocity to Flow Field

Include the background velocity in the output flowfield. If not set, the flowfield will provide the difference between the background velocity and the solved velocity.

Output Potential

Output the scalar potential field, that can be thought of as pressure. This scalar VDB is called potential.

Geometry nodes