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hello,everyone! I guess I have left something out in my questions : Darcy's law relates 'v' and 'P' has neat expressions, thus it can be directed into mass and energy equations for gas phase combined with ideal gas state equations, so that 'rho' and 'v' are eliminated in the governing equations and 'P'as well as 'T' become the variables to solve, this is the standard method appeared in references; for my part, I want to try a different process as in my last message, however,the calculation is not very stable unless very small time step is adopted, I don't know how to overcome the flaw, would you please enlight me on the solution? Thanks, young.