Using symmetry to create a heat sink

Hi guys,

I am looking to design a heat sink with pin fins however I'm finding that if I make a full design it takes ages to compute. How can I use some form of symmetry so that the software only has to compute a small part of the array, rather than the whole thing? I have a small heat source in the centre of my sink (the sink sits on a chip that dissipates heat). Would that change anything?

Thank you very much