I am running a free surface simulation with surface tension of a bubble forming and detaching from an orifice.
If I run my case in CFX 11.0 in parallel and the bubble grows to the point where its boundaries cross parallel partition boundaries, I am seeing an unphysical increase in surface tension at the partition boundaries.

This did not happen in 10.0. What's going on?

Some changes were made in CFX 11.0, including a two-pass approach for calculating gradients (which are used to calculation surface tension curvature) to avoid zone-based synchronization bottlenecks for coupled partitioning. In the released version of CFX 11.0, the surface tension force on overlap nodes is incorrect because of this.

One workaround is to set the expert parameter 'element surface tension force' to t.

Setting this expert parameter helps because it also controls a detail of how the interface delta function is used; in particular, whether vertex or element gradients are used. If vertex gradients are used (the new default), these gradients are incomplete because of the gradient restructuring for parallel runs done in CFX 11. Setting the parameter to `t` reverts to element gradients.

This is fixed in Service Pack 1 for ANSYS CFX which will be released later in 2007. The gradients are completed properly before updating the surface tension force (which triggers the interface delta calculation).

If the Service Pack is not available, setting the expert parameter is a workaround.

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