OK I am trying to define a symmetry plane in Star-CCM+ that has some negative geometry lying in it. How would I go about selecting the symmetry plane if the lines defining that plane are discontinuous due to the negative volume? Attached is a (very) simplified schematic of what I am trying to achieve here. Also note that there is a positive volume cylinder in my model that has an inlet BC. Not sure if that makes a difference, I don't think it would as the defined symmetry plane shouldn't have a problem with it.

Thanks in advance! John

http://img181.imageshack.us/img181/6650/symmetryra9.jpg

Split face by angle. Make sure angle is very low so that the internal 1/2 cylinder gets defined by split.