[FLASH-BUGS] ppm/kurganov test differences

From: Sean Matt (matt@physics.mcmaster.ca)
Date: Mon May 26 2003 - 18:18:29 CDT

  • Next message: Greg Weirs: "Re: [FLASH-BUGS] ppm/kurganov test differences"

    Hello again,

            We have recently been testing and comparing the ppm and kurganov
    hydro solvers, and we've encountered an interesting problem.
    Specifically, we are running the standard sod problem in setups/sod.
    We setup with:

    setup sod -auto -maxblocks=1000

    And, we are running on Tru64 (OSF1 V5.1) using a Compaq fortran compiler
    (V5.5-1877-48BBF).

            We can run the standard run with ppm (without modifying
    "flash.par" or any other files) and get a result that is consistent with
    the true sod solution. However, when we make only one change to the
    Config file to select the kurganov solver, the computed solution is wrong
    by exactly a factor of two. The change we make to Config is to replace
    the line:

    REQUIRES hydro

    with:

    REQUIRES hydro/explicit/delta_form/kurganov

    Then, of course, we rerun the setup command and recompile. We make no
    changes to the flash.par file (except to basenm for a different file
    name). I've attached two gif's of 1-d slices in density of the solutions,
    so that you can see the error. ppm.gif is the solution from ppm and
    kurg.gif is the solution from the kurganov solver, and each are from the
    final checkpoint file at a physical time of t=0.2. As you may know, the
    true Sod problem solution looks the same at different times, but one
    simply has to rescale the x-axis proportional to time. It is quite
    interesting and baffling that the kurganov solution is off by exactly a
    factor of two. That is, if you rescale the x-axis of the kurganov
    solution by a factor of two, it would then match with the ppm. In other
    words, the kurganov solution is behaving as though everthing is moving at
    half speed.

    Have we done something wrong? It is worth noting that we have also
    compared the two solvers for the standard sedov setup, and the shock speed
    is the same for both solvers (i.e., both solvers give the "right"
    answer, in that setup).

                    -Sean


    ppm.gif
    kurg.gif

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