simulation of the stepan problem with ansys fluent
 

hello everyone,
i'm working on the stefan problem which is the melting of semi infinite PCM.
I'm simulating this with ansys fluent, but i got a différence between the numérical results and the analytical one.I did some initiatives like increasing the number of iterations per time step, decreasing the time step ...and no valuable results.The following graph illustre an exemple:https://community.ansys.com/personal/