Bias factor vs expansion factor

tahtawy · May 25, 2020, 02:56

I am validating an old paper which says ( expansion factor of 1.27) but I didn't find sth called expansion factor in ansys meshing and all I can find is bias factor instead

1) what is definition of each ?
2) how to convert from one another?

vinerm · May 25, 2020, 13:17

Expansion factor is not a user-specified parameter rather determined using the generated mesh. It is important, but usually used in CFX simulations and CFX calculates it and reports it, while Fluent does not. It signifies the variation in expansion of a cell as compared to its adjacent cell. So, it is not a cell property but a mesh property and changes from location to location.

tahtawy · May 26, 2020, 03:44

So there is no way to generate the same exact mesh of this CFX in fluent ? In other words can't I turn this expansion factor into bias factor?

vinerm · May 26, 2020, 12:26

Mesh is not handled same way in CFX and Fluent. So, you don't even need to worry about the expansion factor. As long as skewness and orthogonal quality are good, the mesh is fine. Maintain growth rate lesser than 1.2.

Bias factor is a ratio between sizes of largest and smallest cell, not the adjacent cells while expansion factor is related to adjacent cells' volumes.

May 25, 2020, 02:56	Bias factor vs expansion factor	#1
tahtawy Member Ahmed Join Date: Sep 2019 Posts: 34 Rep Power: 7	I am validating an old paper which says ( expansion factor of 1.27) but I didn't find sth called expansion factor in ansys meshing and all I can find is bias factor instead 1) what is definition of each ? 2) how to convert from one another?

May 25, 2020, 13:17	Expansion Factor	#2
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36	Expansion factor is not a user-specified parameter rather determined using the generated mesh. It is important, but usually used in CFX simulations and CFX calculates it and reports it, while Fluent does not. It signifies the variation in expansion of a cell as compared to its adjacent cell. So, it is not a cell property but a mesh property and changes from location to location. tahtawy likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

May 26, 2020, 12:26	CFX vs Fluent Mesh	#4
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36	Mesh is not handled same way in CFX and Fluent. So, you don't even need to worry about the expansion factor. As long as skewness and orthogonal quality are good, the mesh is fine. Maintain growth rate lesser than 1.2. Bias factor is a ratio between sizes of largest and smallest cell, not the adjacent cells while expansion factor is related to adjacent cells' volumes. tahtawy likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

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May 26, 2020, 03:44		#3
tahtawy Member Ahmed Join Date: Sep 2019 Posts: 34 Rep Power: 7	So there is no way to generate the same exact mesh of this CFX in fluent ? In other words can't I turn this expansion factor into bias factor?