First iteration problem with fds

[Cesar Becerril]

Dear all,

I have a very simple configuration where an obstacle is placed in the middle of a square channel. The setup is initiated with an already existing velocity field coming from another simulation. The problem: The initialisation is OK, but at the first “solution dumped” all the velocity field, mass flow rates values are doubled and I cannot understand why. Could you please help me to understand??

 

Hereafter a part of the code and enclosed two images of the velocity field (z component):

&HEAD CHID='circular_burner_ignit', TITLE='Test cold flow' /

 

&MESH IJK=100,100,250, XB=-0.1,0.1,-0.1,0.1,0.0,0.5 / 

 

&INIT SPEC_ID(1)='METHANE', MASS_FRACTION(1)=0.0547340195132 /               

 

&TIME T_END=2. /

 

&MISC NOISE=.FALSE., NOISE_VELOCITY=0.0, SIMULATION_MODE="LES", CFL_MIN = 0.7 /

&RADI RADIATION=.FALSE. /

&CSVF UVWFILE='circular_burner_velo_field_uvw_001.csv' /

 

&REAC FUEL='METHANE', AUTO_IGNITION_TEMPERATURE=500./

 

&SURF ID='BURNER', MASS_FLUX(1) = 0.0184569608572  , SPEC_ID(1)='METHANE', TAU_MF(1)=0.0

                                 MASS_FLUX(2) = 0.3187549052065  , SPEC_ID(2)='AIR'           , TAU_MF(2)=0.0

                                 TRANSPARENCY = 0.3/

                                               

&VENT MB='ZMIN', SURF_ID='BURNER' /

&VENT MB='ZMAX', SURF_ID='OPEN'   /

 

&SURF ID='WALL', ADIABATIC=.TRUE., FREE_SLIP=.TRUE., TRANSPARENCY = 0.3 /

&VENT MB='XMIN', SURF_ID='WALL'/

&VENT MB='XMAX', SURF_ID='WALL'/

&VENT MB='YMIN', SURF_ID='WALL'/

&VENT MB='YMAX', SURF_ID='WALL'/

 

&SURF ID='IGNIT', ADIABATIC=.TRUE., FREE_SLIP=.TRUE., AUTO_IGNITION_TEMPERATURE=-273./

&OBST XB= -0.02,0.02,-0.02, 0.02,0.25,0.27, COLOR='RED', TRANSPARENCY = 0.3, SURF_ID="IGNIT"/

 

&SLCF PBY=0.0  , QUANTITY='VELOCITY', VECTOR=T/

 

&DEVC ID='Inlet mass flow'          , XB=-0.1,0.1,-0.1,0.1,0.001,0.001,            QUANTITY='MASS FLOW'/

&DEVC ID='Inlet Fuel mass flux'   , XB=-0.1,0.1,-0.1,0.1,0.001,0.001, IOR=3, QUANTITY='MASS FLUX WALL', SPEC_ID="METHANE"/

&DEVC ID='Inlet Air mass flux'     , XB=-0.1,0.1,-0.1,0.1,0.001,0.001, IOR=3, QUANTITY='MASS FLUX WALL', SPEC_ID="AIR"/

 

&TAIL /

Finally, the a part of the *devc.csv:

s	kg/s	kg/s/m2	kg/s/m2
Time	Inlet mass flow	Inlet Fuel mass flux	Inlet Air mass flux
0.00E+00	1.35E-02	1.85E-02	3.19E-01
2.67E-03	2.70E-02	3.69E-02	6.38E-01
4.00E-03	2.70E-02	3.69E-02	6.38E-01
6.67E-03	2.70E-02	3.69E-02	6.38E-01

[fde]

So the question is, why at time=0, flux is 1.85E-02 and time=0.00267s flux is doubled? I would guess; because the DEVC are averaged over DT_DEVC, and simulation starts with 0, the average of 0 and target value is smaller than the target. 

[Cesar Becerril]

Assuming that results coming from DEVC are affected by a factor 2, even so my DT_DEVC is set to the default value (dt/1000) and are very constant. That does not explain why my velocity field in the slice is also affected by a coefficient 2.

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[Randy McDermott]

There is a time ramp on inflow conditions (unless otherwise stated) for stability purposes.

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[Cesar Becerril]

Using the ramp I have the same problem but later 

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[Randy McDermott]

Simplify you case.  Blow one thing into a box.  No INIT, nothing else.  If this does not work, then send an Issue.  If it does, then starting adding complexity back until you find the culprit.

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