Pressure equation cannot converge for backstep flow with zeta-f model, and temperature equation does not work properly.

[mhadziabdic]

Residuals for pressure correction do not drop as well as number of inner iterations (always stays at maximum number). Temperature equation diverged for some reason. I suspect B.C.

[Niceno]

I am not sure what was the pressure tolerance in the old version of the code, but I do remember it was "hard coded" before calling a solver.

In the new version it is specified in the control file.

So, if the value for pressure tolerance in control file is much lower than the one which was previously hard coded, you may be unable to reach convergence. I hope that is the reason behind it.

For temperature there have been some changes when specifying heat flux (wall_flux) with a keyword "t" or keyword "q". In the first implementation it was "q", but then I changed it to "t" for better consistency with user scalars (our users will have many scalars and many possible fluxes.)

But, at an earlier meeting with Egor today we proposed the following. For temperature, we use "t" for wall, "q" for wall_flux. User scalars are called c01, c02, c03 ... c48, and their fluxes q01, q02, q03 ... q48. Does everyone agrees we stick to such a scheme?

[palkinev]

Well, I have tried this Backstep_Re_28000 myself today.
I noticed high CFL there, so changed dt to:
TIME_STEP 0.00001

and other parameters:

 MAX_SIMPLE_ITERATIONS                 8
 MIN_SIMPLE_ITERATIONS                 5
 MAX_ITERATIONS_FOR_MOMENTUM_SOLVER    10
 MAX_ITERATIONS_FOR_PRESSURE_SOLVER    40
 MAX_ITERATIONS_FOR_TURBULENCE_SOLVER  10

Linear solvers
 TOLERANCE_FOR_MOMENTUM_SOLVER        1.e-7
 TOLERANCE_FOR_PRESSURE_SOLVER        1.e-2
 TOLERANCE_FOR_TURBULENCE_SOLVER      1.e-7
 TOLERANCE_FOR_ENERGY_SOLVER          1.e-6
 TOLERANCE_FOR_SIMPLE_ALGORITHM       1.e-6

After some time pressure started to converge.

  #====================+====================+====================+====================#
  #   Iteration:  5    | Mass:    1.057E-07 | PP  :  9 7.746E-03 |                    #
  # U   :  2 1.132E-09 | V   :  2 2.621E-08 | W   :  2 1.293E-08 | T   :  1 1.210E-09 #
  # KIN :  2 9.445E-09 | EPS :  2 9.996E-09 | ZETA:  2 6.784E-09 | F22 :  2 6.274E-08 #
  #--------------------+--------------------+--------------------+--------------------#
                                                                                       
  #=========================================+=========================================#
  #    Maximum Courant number: 4.144E-01    |    Maximum Peclet number: 2.681E+04     #
  #---------------------------+-------------+-------------+---------------------------#
  #    Flux x :  1.57E-01     |    Flux y : -3.98E-06     |    Flux z :  0.00E+00     #
  #    Pdrop x:  0.00E+00     |    Pdrop y:  0.00E+00     |    Pdrop z:  0.00E+00     #
  #---------------------------+---------------------------+---------------------------#

And I think this q and q01 are much more clearer for new user than special behavior in case of "wall_flux" b.c.

[Niceno]

So ... can we close this issue?

[mhadziabdic]

Yes we can. Barak Obama :)