Ctarg related issue

[Bhargav Mantravadi]

Dear Team,

My Nek5000 simulation is exiting due to a Ctarg-related issue. I am restarting the simulation with a larger time step and increasing the polynomial order to N=7. Currently, I have specified the following options in the .par file:

dt = 1E-03

variableDT = no

targetCFL = 10.0

With these settings, although the simulation runs initially with the time step I provided, it quickly exits, citing the Ctarg. Please see the output shown below. 

When I set variableDT=yes and specify a target CFL number, the simulation runs well and consistently defaults to a target CFL of 0.5. 

Could you please advise on how to modify the target CFL number? I also attempted to change parameter 26 in the .rea file, but this did not resolve the issue. 

Thank you in advance for your help.

Regards,

Bhargav

---------------------------------------------------------

Step   2424, t= 4.1893551E+01, DT= 1.0000000E-03, C=  4.431 2.2070E+03 1.2632E+00
             Solving for Hmholtz scalars
       2424  Hmholtz TEMP       5   5.0481E-09   4.4417E+00   1.0000E-07
       2424  Scalars done  4.1894E+01  4.2053E-02
             Solving for fluid
       2424  PRES gmres        36   9.2156E-07   3.9322E-02   1.0000E-06   4.5336E-01   7.3972E-01    F
       2424  Hmholtz VELX       4   8.9329E-08   1.0273E+00   1.0000E-07
       2424  Hmholtz VELY       4   5.6231E-08   1.0366E+00   1.0000E-07
       2424  Hmholtz VELZ       5   1.4949E-09   1.1577E+00   1.0000E-07
             L1/L2 DIV(V)           2.6899E-12   1.1869E-01
             L1/L2 QTL              0.0000E+00   0.0000E+00
             L1/L2 DIV(V)-QTL       2.6899E-12   1.1869E-01
             WARNING: DIV(V)-QTL too large!
       2424  Fluid done  4.1894E+01  8.8102E-01
 CFL, Ctarg!   5.1733289541872711       0.50000000000000000

     2425  4.1894E+01 Write checkpoint
       FILE:e0.7_ra1e10_pr1_f1_g399360.f00001
 min/max:  -3.3333       3.3333      -3.3333       3.3333      -3.3333       3.3333
 min/max:  -3.7073       9.1931      -8.9972       6.2730      -19.152       7.9102
 min/max:  -2.1596      0.25867
 min/max:  -105.89       31.082

     2425  4.1894E+01 done :: Write checkpoint
                              file size =     0.66    GB
                              avg data-throughput =     0.4GB/s
                              io-nodes =   512


         130  Emergency exit:        2425    time =   41.893550889144350
  Latest solution and data are dumped for post-processing.
  *** STOP ***

[Bhargav Mantravadi]

Dear Team,

Please ignore this email -- I have identified the issue. I can achieve CFL > 0.5 when using extrapolation = OIFS.

Thanks,

Bhargav