About the SPREAD_RATE setting

[abc-k]

Dear,
I want to simulate a spreading flame. So I added a SPREAD_RATE with RAMP_Q input to the SURF line.
However, when I run the simulation in this state, the behavior of the HRR no longer matches the RAMP_Q input.

When SPREAD_RATE is not specified, it is confirmed to follow the input of RAMP_Q.

When using SPREAD_RATE, why is the output of HRR different from the input of RAMP_Q?

[abc-k]

&HEAD CHID='SPREAD', TITLE='' /

&MESH IJK=40,40,20 XB=0.0,10,0.0,10,0.0,5/
&TIME T_END=60. /

&DUMP MASS_FILE=T /

&REAC ID = 'N-HEPTANE'
FUEL='N-HEPTANE'
CO_YIELD = 0.1
SOOT_YIELD = 0.1/

!SURF
&SURF ID='N-HEPTANE',
COLOR='RED',
SPEC_ID='N-HEPTANE'
HRRPUA=1000
RAMP_Q='fire'
XYZ=5,5,2,
SPREAD_RATE=0.25/
&RAMP ID='fire'T=0,F=0/
&RAMP ID='fire'T=10,F=0/
&RAMP ID='fire'T=30,F=1/
&RAMP ID='fire'T=40,F=1/
&RAMP ID='fire'T=50,F=0/
&RAMP ID='fire'T=60,F=0/

!BURN OBST
&OBST ID='BURNER' ,XB= 2,8,4,6,0,2,SURF_ID6(6)='N-HEPTANE'/
&VENT XB=0,10,0,10,5,5,SURF_ID='OPEN'/

&DEVC ID='FUEL_CENTER', XYZ=5,5,2, QUANTITY='MASS FRACTION',SPEC_ID='N-HEPTANE'/
&DEVC ID='FUEL_R' , XYZ=5,8,2, QUANTITY='MASS FRACTION',SPEC_ID='N-HEPTANE'/
&DEVC ID='FUEL_L' , XYZ=5,2,2, QUANTITY='MASS FRACTION',SPEC_ID='N-HEPTANE'/
&DEVC ID='FUEL_R_1' , XYZ=5,6.5,2,QUANTITY='MASS FRACTION',SPEC_ID='N-HEPTANE'/
&DEVC ID='FUEL_L_1' , XYZ=5,3.5,2,QUANTITY='MASS FRACTION',SPEC_ID='N-HEPTANE'/

[drjfloyd]

SPREAD_RATE determines when a specific grid cell starts emitting fuel. HRRPUA+RAMP_Q defines the rate the grid cell emitts fuel where the time used for the RAMP is the time that grid cell started to emit fuel.

[abc-k]

Thank you very much.
I understand about RAMP_Q time and SPREAD_RATE.