Bias factor vs expansion factor
 

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?

Expansion Factor
 

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.

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?

CFX vs Fluent Mesh
 

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.