Hex versus Tet

Jade M · March 11, 2010, 16:26

I am running a CFX problem with laminar flow through a duct. The fluid flows through some fins in the middle of the duct.

When I mesh with tet, for the same number of nodes, the run times for the tet are significantly greater than those for the hex. It seems that it takes much longer for the tet mesh's solution to converge (a lot more iterations). Why? I am assuming that the matrix size is the same as it is proportional to the number of nodes, correct?

Also, for a hex mesh, the number of nodes and number of elements are about the same. For a tet mesh, the number of elements is much larger than the number of nodes. Why?

Thanks so much for some greatly needed explanations!

ghorrocks · March 11, 2010, 23:41

The node/element counts is explained in the documentation, in the section which describes the control volumes.

How big an effect hex vs tet makes is problem dependent. If you are doing a simple incompressible flow it won't make much difference. If you are doing complex stuff like free surfaces, shock waves, etc etc the improved mesh quality in a hex mesh can make a huge difference.

March 11, 2010, 16:26	Hex versus Tet	#1
Jade M Senior Member Join Date: Feb 2010 Posts: 148 Rep Power: 17	I am running a CFX problem with laminar flow through a duct. The fluid flows through some fins in the middle of the duct. When I mesh with tet, for the same number of nodes, the run times for the tet are significantly greater than those for the hex. It seems that it takes much longer for the tet mesh's solution to converge (a lot more iterations). Why? I am assuming that the matrix size is the same as it is proportional to the number of nodes, correct? Also, for a hex mesh, the number of nodes and number of elements are about the same. For a tet mesh, the number of elements is much larger than the number of nodes. Why? Thanks so much for some greatly needed explanations!

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March 11, 2010, 23:41		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	The node/element counts is explained in the documentation, in the section which describes the control volumes. How big an effect hex vs tet makes is problem dependent. If you are doing a simple incompressible flow it won't make much difference. If you are doing complex stuff like free surfaces, shock waves, etc etc the improved mesh quality in a hex mesh can make a huge difference.