Following on from my recent blog post, Mixing Fluids in Houdini, I wanted to simulate a toroidal eddy effect where the incoming drip takes the form of a torus and the fluid flows around the circumference of its minor radius.
My first thought was to use a POP Axis Force, but that rotates particles around the circumference of the major radius. So, I took another approach: create lots of curves placed around a circle and use those as the geometry source for a POP Curve Force.
To create the geometry, I simply created two circles and copied the smaller one to the points of the larger one:
The PolyFrame nodes ensures the smaller circles radially align by setting the normal and tangent names:
Making the smaller circle an arc rather than a full circle and setting both circle's type to open arc, the resulting geometry looks like a fruit bowl:
I used the same technique I discussed in Mixing Fluids in Houdini to split the fluid into two groups. Over in the DOP Network, the POP Curve Force was set to use the bowl shape of curves and assigned to the drip group. This means that only the drip is affected by the curves and the body of the fluid remains static.
Here's the final render, along with some other fluid mixing experiments:
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