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-   -   Combustion Convergence problems (https://www.cfd-online.com/Forums/phoenics/51375-combustion-convergence-problems.html)

 Art Stretton March 25, 2002 14:12

Combustion Convergence problems

I'm doing the following simulation and would like to hear from others who have experience doing similar work:

6 m by 2 m by 1.5 m furnace with refractory lined walls considered adiabatic

0.5 m dia. circular exhaust port in center of roof, -50 Pa pressure outlet

3 burners - 0.05 m dia. natural gas (methane) ports, 20 m/s velocity inlet

- 0.15 m dia. annulus air ports, 30 m/s velocity inlet

- locations two at one end on wall, single burner in roof for other half

load - bottom surface represents molten metal bath, 1000C const. temperature

tramp air - 0.2 by 0.7 vent where molten metal enters in real life, 2 m/s inlet

The issue is non-uniformity of the temperature distribution in the gas phase above the molten metal. The modelling is focussed on the flames and exhaust gases. The issue I'm having is that I've been having trouble converging the solution for the cold gases without combustion below 1E-03 average total residual and experiencing very slow convergence with combustion because I have to set relaxations very low to avoild crashing the simulation. Here are some details on the grid and relaxations I'm using:

largest cell dimension 0.0635 m in parts of the domain away from the flames

smallest cell dimension 0.0127 m in the vicinity of the burner ports

total cell count 144 by 94 by 55 = 744,480 cells

expected max velocity in flames about 220 m/s

solved for variables: P1, U1/V1/W1, EP/KE, H1, MIX1

models: KEMODL default for turbulence, 3_gases_mixing for combustion, buoyancy

3 gases density, old property table viscosity, 3 gases mixing temperature

library reference case: C113

relaxation strategy: clamp down on P1 to at least -1.0E-04, even to -1.0E-06

for first 1000 iterations, up by factor of 10 each 1000

clamp down on U1/V1/W1 to at least 1.0E-05, even to 1.0E-06

for first 1000 iterations, up by factor of 2 each 1000

clamp down on EP/KE to at least -1.0E-03, even to -1.0E-04

for first 1000 iterations, up to 0.1, then 0.5 thereafter

set H1/MIX1 to at least 1.0E-02, even to 1.0E-04

for first 1000 iterations, up by factor of 100 each 1000

model feedback: in first 1000 iterations (critical points at 30, 300, 600)

velocity field will degrade to random E+05 values if relaxations

for P1/U1/V1/W1 are at 2.0E-04 or above (except when I've tried

MIGAL for faster convergence on large grid and found I could

use 1.0E-03 and even higher)

non-uniformity between the three flames in size and peak velocities

variations from 15% to 50% for identical inlet conditions

The best I've done so far is to use 1E-06 for first 1000 iterations to overcome the non-uniformity issues between the three flames, only reaching E+07 on residual error and E+03 on mass balance.

The people with experience I talk to expect me to reach typical total error residuals of 1E+06 in under 500 iterations and mass balance to 1E-01 within 1000 iterations. It has been taking me on the order of 3000 iterations (20 hours on a P4 1.6 GHz with 1 GB RDRAM 3GB SCSI-UW swap file) to reach those goals.

I will attach the Q1 file in anticipation that I haven't provided enough detail. Thanks in advance for any advice that can be offered on my simulation experience.

Art Stretton

Houston, Texas

P.S. I made up three new dat files which I can e-mail on request

RIDGE8.DAT - like a staircase with 50% first step, 25% second step, 25% last step

RIDGE8R.DAT - for fitting two RIDGE8.DAT objects together in a corner

BABET4.DAT - like BABET.DAT but only a quarter domain with a 30 degree truncation

P.P.S. sorry my cut and paste of Q1 got formatted poorly, my attempts to edit combined lines didn't work

---------------------------- 8< CombE3b.q1 follows 8< -----------------------------

TALK=T;RUN( 1, 1)

************************************************** **********

Q1 created by VDI menu, Version 3.4, Date 10/08/01 CPVNAM=VDI;SPPNAM=Core ************************************************** ********** Echo DISPLAY / USE settings

DISPLAY

The case considered is the current roof mounted burner

with combustion without the burner chambers.

ENDDIS ************************************************** ********** IRUNN = 1 ;LIBREF = 0 ************************************************** ********** Group 1. Run Title TEXT(COMINCO CDF Combustion E ) ************************************************** ********** Group 2. Transience STEADY = T ************************************************** ********** Groups 3, 4, 5 Grid Information

* Overall number of cells, RSET(M,NX,NY,NZ,tolerance) RSET(M,144,94,55)

* Set overall domain extent:

* xulast yvlast zwlast

name XSI= 6.188000E+00; YSI= 2.088000E+00; ZSI= 1.380000E+00 RSET(D,CHAM ) ************************************************** ********** Group 6. Body-Fitted coordinates ************************************************** ********** Group 7. Variables: STOREd,SOLVEd,NAMEd ONEPHS = T

* Non-default variable names NAME(142) =PRPS ; NAME(143) =EPKE NAME(144) =ENUT ; NAME(145) =FUEL NAME(146) =PROD ; NAME(147) =OXID NAME(148) =RHO1 ; NAME(149) =TMP1 NAME(150) =MIXF

* Solved variables list SOLVE(P1 ,U1 ,V1 ,W1 ,H1 ,MIXF)

* Stored variables list STORE(TMP1,RHO1,OXID,PROD,FUEL,ENUT,EPKE,PRPS)

* Additional solver options SOLUTN(P1 ,Y,Y,Y,N,N,Y) TURMOD(KEMODL)

************************************************** ********** Group 8. Terms & Devices TERMS (H1 ,N,Y,Y,Y,Y,Y) NEWRH1 = T NEWENL = T ISOLX = 0 ;ISOLY = 0 ;ISOLZ = 0 DENPCO = T ************************************************** ********** Group 9. Properties SETPRPS(1, 30) RHO1 = GRND6 RHO1A = 1.604303E+01 ;RHO1B = 2.894200E+01 RHO1C = 2.918912E+01 PRESS0 = 1.013250E+05 TMP1 = GRND7 TMP1A = 1.500000E+03 ;TMP1B = 1.500000E+03 TMP1C = 1.500000E+03 TMP2A = 5.482456E-02 ;TMP2B = 4.943350E+07 TMP2C = 0.000000E+00 TEMP0 = 2.731500E+02 CP1 = GRND10 ENUL = GRND10 ENULA = 1.460000E-06 ;ENULB = 1.100000E+02 ENULC = 0.000000E+00 DRH1DP = 3.410000E-03 DVO1DT = 3.330000E-03 PRNDTL(H1 ) = -2.630000E-02 PRT (EP ) = 1.314000E+00 ************************************************** ********** Group 10.Inter-Phase Transfer Processes ************************************************** ********** Group 11.Initialise Var/Porosity Fields RESTRT(ALL)

No PATCHes used for this Group

No PATCHes used for this Group ************************************************** ********** Group 13. Boundary & Special Sources

PATCH (CHSO ,VOLUME,0,0,0,0,0,0,1,1)

PATCH (BUOYANCY,PHASEM,0,0,0,0,0,0,1,1) COVAL (BUOYANCY,U1 , FIXFLU , GRND2 ) COVAL (BUOYANCY,V1 , FIXFLU , GRND2 ) COVAL (BUOYANCY,W1 , FIXFLU , GRND2 )

BUOYA = 0.000000E+00 ; BUOYB = 0.000000E+00 BUOYC =-9.806000E+00 BUOYD = 1.184000E+00 ************************************************** ********** Group 14. Downstream Pressure For PARAB ************************************************** ********** Group 15. Terminate Sweeps LSWEEP = 1000 RESFAC = 1.000000E-03 ************************************************** ********** Group 16. Terminate Iterations LITER (U1 ) = 20 ;LITER (V1 ) = 20 LITER (W1 ) = 20 ENDIT (P1 ) = 1.000000E-01 ;ENDIT (U1 ) = 1.000000E-01 ENDIT (V1 ) = 1.000000E-01 ;ENDIT (W1 ) = 1.000000E-01 ENDIT (KE ) = 1.000000E-01 ;ENDIT (EP ) = 1.000000E-01 ENDIT (H1 ) = 1.000000E-01 ;ENDIT (PRPS) = 1.000000E-01 ENDIT (EPKE) = 1.000000E-01 ;ENDIT (ENUT) = 1.000000E-01 ENDIT (FUEL) = 1.000000E-01 ;ENDIT (PROD) = 1.000000E-01 ENDIT (OXID) = 1.000000E-01 ;ENDIT (RHO1) = 1.000000E-01 ENDIT (TMP1) = 1.000000E-01 ;ENDIT (MIXF) = 1.000000E-01 ************************************************** ********** Group 17. Relaxation RELAX(P1 ,LINRLX, 1.000000E-02) RELAX(U1 ,FALSDT, 2.000000E-05) RELAX(V1 ,FALSDT, 2.000000E-05) RELAX(W1 ,FALSDT, 2.000000E-05) RELAX(KE ,LINRLX, 1.000000E-02) RELAX(EP ,LINRLX, 1.000000E-02) RELAX(H1 ,FALSDT, 1.000000E+02) RELAX(MIXF,FALSDT, 1.000000E+02) KELIN = 3 ************************************************** ********** Group 18. Limits VARMAX(P1 ) = 1.000000E+20 ;VARMIN(P1 ) =-1.000000E+05 VARMAX(U1 ) = 1.000000E+06 ;VARMIN(U1 ) =-1.000000E+06 VARMAX(V1 ) = 1.000000E+06 ;VARMIN(V1 ) =-1.000000E+06 VARMAX(W1 ) = 1.000000E+06 ;VARMIN(W1 ) =-1.000000E+06 VARMAX(H1 ) = 1.000000E+10 ;VARMIN(H1 ) = 1.000000E-10 VARMAX(EPKE) = 1.000000E+10 ;VARMIN(EPKE) = 1.000000E-10 VARMAX(ENUT) = 1.000000E+10 ;VARMIN(ENUT) = 1.000000E-10 VARMAX(FUEL) = 1.000000E+00 ;VARMIN(FUEL) = 0.000000E+00 VARMAX(PROD) = 1.000000E+00 ;VARMIN(PROD) = 0.000000E+00 VARMAX(OXID) = 1.000000E+00 ;VARMIN(OXID) = 0.000000E+00 VARMAX(RHO1) = 5.000000E+02 ;VARMIN(RHO1) = 1.000000E-03 VARMAX(TMP1) = 1.000000E+10 ;VARMIN(TMP1) = 1.000000E-10 VARMAX(MIXF) = 1.000000E+00 ;VARMIN(MIXF) = 0.000000E+00 ************************************************** ********** Group 19. EARTH Calls To GROUND Station USEGRD = T ;USEGRX = T GENK = T ASAP = T RADIA = 0.000000E+00 ;RADIB = 0.000000E+00 EMISS = 0.000000E+00 SPEDAT(SET,MIGAL,SOLVED01,C,HYDRO) SPEDAT(SET,MIGAL,SOLVED02,C,H1) SPEDAT(SET,MIGAL,SOLVED03,C,MIXF) SPEDAT(SET,MIGAL,REFAC01,R,0.00000E+00) SPEDAT(SET,MIGAL,REFAC02,R,0.00000E+00) SPEDAT(SET,MIGAL,REFAC03,R,0.00000E+00) SPEDAT(SET,MIGAL,LITER01,I,5) SPEDAT(SET,MIGAL,LITER02,I,5) SPEDAT(SET,MIGAL,LITER03,I,5) SPEDAT(SET,MIGAL,LINRLX01,R,5.00000E-01) SPEDAT(SET,MIGAL,LINRLX02,R,1.00000E+00) SPEDAT(SET,MIGAL,LINRLX03,R,1.00000E+00)

SPEDAT(SET,MIGAL,COEFF01,R,1.00000E+00)

SPEDAT(SET,MIGAL,COEFF02,R,1.00000E+00)

SPEDAT(SET,MIGAL,COEFF03,R,1.00000E+00) ************************************************** ********** Group 20. Preliminary Printout ECHO = T ************************************************** ********** Group 21. Print-out of Variables OUTPUT(P1 ,Y,Y,Y,N,Y,Y) OUTPUT(TMP1,Y,Y,Y,N,Y,Y) ************************************************** ********** Group 22. Monitor Print-Out IXMON = 141 ;IYMON = 47 ;IZMON = 34 NPRMON = 1 NPRMNT = 1 TSTSWP = -1 ************************************************** ********** Group 23.Field Print-Out & Plot Control NPRINT = 100000 ISWPRF = 1 ;ISWPRL = 100000

No PATCHes used for this Group ************************************************** ********** Group 24. Dumps For Restarts NOWIPE = T

GVIEW(P,0.000000E+00,-1.000000E+00,0.000000E+00) GVIEW(UP,0.000000E+00,0.000000E+00,1.000000E+00)

> DOM, SIZE, 6.188000E+00, 2.088000E+00, 1.380000E+00
: DOM, MONIT, 6.115190E+00, 1.050350E+00, 9.595750E-01
: DOM, SCALE, 1.000000E+00, 1.000000E+00, 1.000000E+00
: DOM, SNAPSIZE, 1.000000E-02
: GRID, RSET_X_1, 4, 1.400000E+00,G
: GRID, RSET_X_2, 29,-1.300000E+00
: GRID, RSET_X_3, 4, 1.000000E+00
: GRID, RSET_X_4, 4, 1.000000E+00
: GRID, RSET_X_5, 4, 1.000000E+00
: GRID, RSET_X_6, 30, 1.300000E+00
: GRID, RSET_X_7, -8,-1.000000E+00
: GRID, RSET_X_8, 55,-1.200000E+00
: GRID, RSET_X_9, 6,-1.350000E+00
: GRID, RSET_Y_1, 4, 1.400000E+00,G
: GRID, RSET_Y_2, 8,-1.300000E+00
: GRID, RSET_Y_3, 4, 1.000000E+00
: GRID, RSET_Y_4, 4, 1.000000E+00
: GRID, RSET_Y_5, 4, 1.000000E+00
: GRID, RSET_Y_6, 5, 1.300000E+00
: GRID, RSET_Y_7, 5, 1.050000E+00
: GRID, RSET_Y_8, 6,-1.300000E+00
: GRID, RSET_Y_9, 4, 1.000000E+00
: GRID, RSET_Y_10, 4, 1.000000E+00
: GRID, RSET_Y_11, 4, 1.000000E+00
: GRID, RSET_Y_12, 6, 1.300000E+00
: GRID, RSET_Y_13, -3, 1.000000E+00
: GRID, RSET_Y_14, 8,-1.300000E+00
: GRID, RSET_Y_15, 4, 1.000000E+00
: GRID, RSET_Y_16, 4, 1.000000E+00
: GRID, RSET_Y_17, 4, 1.000000E+00
: GRID, RSET_Y_18, 8, 1.300000E+00
: GRID, RSET_Y_19, 5,-1.500000E+00,G
: GRID, RSET_Z_1, 9, 1.200000E+00
: GRID, RSET_Z_2, 19,-1.250000E+00
: GRID, RSET_Z_3, 4, 1.000000E+00
: GRID, RSET_Z_4, 4, 1.000000E+00
: GRID, RSET_Z_5, 4, 1.000000E+00
: GRID, RSET_Z_6, 7, 1.200000E+00
: GRID, RSET_Z_7, 8,-1.200000E+00
: DOM, RELAX, 5.000000E-01

> OBJ1, NAME, WEST
: OBJ1, POSITION, 0.000000E+00, 0.000000E+00, 0.000000E+00
: OBJ1, SIZE, 0.000000E+00, 2.088000E+00, 1.380000E+00
: OBJ1, CLIPART, cube
: OBJ1, ROTATION24, 1
: OBJ1, VISIBLE, -1.000000E+00
: OBJ1, TYPE, PLATE

> OBJ2, NAME, EAST
: OBJ2, POSITION, 6.188000E+00, 0.000000E+00, 0.000000E+00
: OBJ2, SIZE, 0.000000E+00, 2.088000E+00, 1.380000E+00
: OBJ2, CLIPART, cube
: OBJ2, ROTATION24, 1
: OBJ2, VISIBLE, -1.000000E+00
: OBJ2, TYPE, PLATE

> OBJ3, NAME, NORTH
: OBJ3, POSITION, 0.000000E+00, 0.000000E+00, 0.000000E+00
: OBJ3, SIZE, 6.188000E+00, 0.000000E+00, 1.380000E+00
: OBJ3, CLIPART, cube
: OBJ3, ROTATION24, 1
: OBJ3, VISIBLE, -1.000000E+00
: OBJ3, TYPE, PLATE

> OBJ4, NAME, SOUTH
: OBJ4, POSITION, 0.000000E+00, 2.088000E+00, 0.000000E+00
: OBJ4, SIZE, 6.188000E+00, 0.000000E+00, 1.380000E+00
: OBJ4, CLIPART, cube
: OBJ4, ROTATION24, 1
: OBJ4, VISIBLE, -1.000000E+00
: OBJ4, TYPE, PLATE

> OBJ5, NAME, BATH
: OBJ5, POSITION, 0.000000E+00, 0.000000E+00, 0.000000E+00
: OBJ5, SIZE, 6.188000E+00, 2.088000E+00, 0.000000E+00
: OBJ5, CLIPART, cube
: OBJ5, ROTATION24, 1
: OBJ5, VISIBLE, -1.000000E+00
: OBJ5, TYPE, PLATE
: OBJ5, SURF_TEMP, 0.000000E+00, 1.000000E+03

> OBJ6, NAME, EXHAUST
: OBJ6, POSITION, 2.909000E+00, 8.190000E-01, 1.380000E+00
: OBJ6, SIZE, 4.500000E-01, 4.500000E-01, 0.000000E+00
: OBJ6, CLIPART, cylinder
: OBJ6, ROTATION24, 1
: OBJ6, TYPE, OUTLET
: OBJ6, PRESSURE, -4.786300E+01
: OBJ6, TEMPERATURE, 2.500000E+01
: OBJ6, COEFFICIENT, 1.000000E+03
: OBJ6, VELOCITY, -1.026000E+04,-1.026000E+04,-1.026000E+04
: OBJ6, TURBULENCE, -1.026000E+04,-1.026000E+04

> OBJ7, NAME, VENT3
: OBJ7, POSITION, 1.000000E-03, 6.500000E-01, 1.200000E+00
: OBJ7, SIZE, 0.000000E+00, 7.000000E-01, 1.800000E-01
: OBJ7, CLIPART, cube
: OBJ7, ROTATION24, 2
: OBJ7, TYPE, INLET
: OBJ7, DENSITY, 1.183778E+00
: OBJ7, VELOCITY, -2.292000E+00, 0.000000E+00, 0.000000E+00
: OBJ7, TEMPERATURE, 2.500000E+01
: OBJ7, TURB-INTENS, 5.000000E+00

> OBJ8, NAME, WRIDGE
: OBJ8, POSITION, 0.000000E+00, 1.500000E-01, 0.000000E+00
: OBJ8, SIZE, 1.500000E-01, 1.788000E+00, 3.000000E-01
: OBJ8, CLIPART, ridge8
: OBJ8, ROTATION24, 5
: OBJ8, TYPE, BLOCKAGE
: OBJ8, MATERIAL, 117
: OBJ8, INI_TEMP, 2.000000E+01

> OBJ9, NAME, SRIDGE
: OBJ9, POSITION, 1.500000E-01, 0.000000E+00, 0.000000E+00
: OBJ9, SIZE, 5.888000E+00, 1.500000E-01, 3.000000E-01
: OBJ9, CLIPART, ridge8
: OBJ9, ROTATION24, 10
: OBJ9, VISIBLE, -1.000000E+00
: OBJ9, TYPE, BLOCKAGE
: OBJ9, MATERIAL, 117
: OBJ9, INI_TEMP, 2.000000E+01

> OBJ10, NAME, ERIDGE
: OBJ10, POSITION, 6.038000E+00, 1.500000E-01, 0.000000E+00
: OBJ10, SIZE, 1.500000E-01, 1.788000E+00, 3.000000E-01
: OBJ10, CLIPART, ridge8
: OBJ10, ROTATION24, 19
: OBJ10, TYPE, BLOCKAGE
: OBJ10, MATERIAL, 117
: OBJ10, INI_TEMP, 2.000000E+01

> OBJ11, NAME, NRIDGE
: OBJ11, POSITION, 1.500000E-01, 1.938000E+00, 0.000000E+00
: OBJ11, SIZE, 5.888000E+00, 1.500000E-01, 3.000000E-01
: OBJ11, CLIPART, ridge8
: OBJ11, ROTATION24, 22
: OBJ11, TYPE, BLOCKAGE
: OBJ11, MATERIAL, 117
: OBJ11, INI_TEMP, 2.000000E+01

> OBJ12, NAME, ROOF
: OBJ12, POSITION, 0.000000E+00, 8.190000E-01, 1.380000E+00
: OBJ12, SIZE, 6.188000E+00, 4.500000E-01, 0.000000E+00
: OBJ12, CLIPART, cube
: OBJ12, ROTATION24, 1
: OBJ12, VISIBLE, -1.000000E+00
: OBJ12, TYPE, PLATE

> OBJ13, NAME, NARC
: OBJ13, POSITION, 0.000000E+00, 1.269000E+00, 1.043150E+00
: OBJ13, SIZE, 6.188000E+00, 8.190000E-01, 3.368500E-01
: OBJ13, CLIPART, babet4
: OBJ13, ROTATION24, 9
: OBJ13, VISIBLE, -1.000000E+00
: OBJ13, TYPE, BLOCKAGE
: OBJ13, MATERIAL, 117

> OBJ14, NAME, SARC
: OBJ14, POSITION, 0.000000E+00, 0.000000E+00, 1.043150E+00
: OBJ14, SIZE, 6.188000E+00, 8.190000E-01, 3.368500E-01
: OBJ14, CLIPART, babet4
: OBJ14, ROTATION24, 23
: OBJ14, VISIBLE, -1.000000E+00
: OBJ14, TYPE, BLOCKAGE
: OBJ14, MATERIAL, 117

> OBJ15, NAME, BNR1GAS
: OBJ15, POSITION, 1.521600E+00, 1.018600E+00, 1.380000E+00
: OBJ15, SIZE, 5.080000E-02, 5.080000E-02, 0.000000E+00
: OBJ15, CLIPART, cylinder
: OBJ15, ROTATION24, 1
: OBJ15, TYPE, INLET
: OBJ15, DENSITY, 6.560000E-01
: OBJ15, VELOCITY, 0.000000E+00, 0.000000E+00,-2.267900E+01
: OBJ15, TEMPERATURE, 2.500000E+01
: OBJ15, INLET_MIXF, 1.000000E+00
: OBJ15, TURB-INTENS, 5.000000E+01

> OBJ16, NAME, BNR1AIR
: OBJ16, POSITION, 1.470800E+00, 9.678000E-01, 1.380000E+00
: OBJ16, SIZE, 1.524000E-01, 1.524000E-01, 0.000000E+00
: OBJ16, CLIPART, pip2colo
: OBJ16, ROTATION24, 1
: OBJ16, TYPE, INLET
: OBJ16, DENSITY, 1.059000E+00
: OBJ16, VELOCITY, 0.000000E+00, 0.000000E+00,-3.104400E+01
: OBJ16, TEMPERATURE, 6.000000E+01
: OBJ16, TURB-INTENS, 5.000000E+01

> OBJ17, NAME, BNR2GAS
: OBJ17, POSITION, 6.188000E+00, 1.618600E+00, 9.403000E-01
: OBJ17, SIZE, 0.000000E+00, 5.080000E-02, 5.140000E-02
: OBJ17, CLIPART, cylinder
: OBJ17, ROTATION24, 9
: OBJ17, TYPE, INLET
: OBJ17, DENSITY, 6.560000E-01
: OBJ17, VELOCITY, -2.240000E+01, 0.000000E+00,-3.548000E+00
: OBJ17, TEMPERATURE, 2.500000E+01
: OBJ17, INLET_MIXF, 1.000000E+00
: OBJ17, TURB-INTENS, 5.000000E+01

> OBJ18, NAME, BNR2AIR
: OBJ18, POSITION, 6.188000E+00, 1.567800E+00, 8.888500E-01
: OBJ18, SIZE, 0.000000E+00, 1.524000E-01, 1.543000E-01
: OBJ18, CLIPART, pip2colo
: OBJ18, ROTATION24, 9
: OBJ18, TYPE, INLET
: OBJ18, DENSITY, 1.059000E+00
: OBJ18, VELOCITY, -3.066200E+01, 0.000000E+00,-4.856000E+00
: OBJ18, TEMPERATURE, 6.000000E+01
: OBJ18, TURB-INTENS, 5.000000E+01

> OBJ19, NAME, BNR3GAS
: OBJ19, POSITION, 6.188000E+00, 4.186000E-01, 9.403000E-01
: OBJ19, SIZE, 0.000000E+00, 5.080000E-02, 5.140000E-02
: OBJ19, CLIPART, cylinder
: OBJ19, ROTATION24, 9
: OBJ19, TYPE, INLET
: OBJ19, DENSITY, 6.560000E-01
: OBJ19, VELOCITY, -2.240000E+01, 0.000000E+00,-3.548000E+00
: OBJ19, TEMPERATURE, 2.500000E+01
: OBJ19, INLET_MIXF, 1.000000E+00
: OBJ19, TURB-INTENS, 5.000000E+01

> OBJ20, NAME, BNR3AIR
: OBJ20, POSITION, 6.188000E+00, 3.678000E-01, 8.888500E-01
: OBJ20, SIZE, 0.000000E+00, 1.524000E-01, 1.543000E-01
: OBJ20, CLIPART, pip2colo
: OBJ20, ROTATION24, 9
: OBJ20, TYPE, INLET
: OBJ20, DENSITY, 1.059000E+00
: OBJ20, VELOCITY, -3.066200E+01, 0.000000E+00,-4.856000E+00
: OBJ20, TEMPERATURE, 6.000000E+01
: OBJ20, TURB-INTENS, 5.000000E+01

> OBJ21, NAME, SWRIDGE
: OBJ21, POSITION, 0.000000E+00, 0.000000E+00, 0.000000E+00
: OBJ21, SIZE, 1.500000E-01, 1.500000E-01, 3.000000E-01
: OBJ21, CLIPART, ridge8
: OBJ21, ROTATION24, 1
: OBJ21, TYPE, BLOCKAGE
: OBJ21, MATERIAL, 117
: OBJ21, INI_TEMP, 2.000000E+01

> OBJ22, NAME, SERIDGE
: OBJ22, POSITION, 6.038000E+00, 0.000000E+00, 0.000000E+00
: OBJ22, SIZE, 1.500000E-01, 1.500000E-01, 3.000000E-01
: OBJ22, CLIPART, ridge8r
: OBJ22, ROTATION24, 10
: OBJ22, TYPE, BLOCKAGE
: OBJ22, MATERIAL, 117
: OBJ22, INI_TEMP, 2.000000E+01

> OBJ23, NAME, NERIDGE
: OBJ23, POSITION, 6.038000E+00, 1.938000E+00, 0.000000E+00
: OBJ23, SIZE, 1.500000E-01, 1.500000E-01, 3.000000E-01
: OBJ23, CLIPART, ridge8r
: OBJ23, ROTATION24, 19
: OBJ23, TYPE, BLOCKAGE
: OBJ23, MATERIAL, 117
: OBJ23, INI_TEMP, 2.000000E+01

> OBJ24, NAME, NWRIDGE
: OBJ24, POSITION, 0.000000E+00, 1.938000E+00, 0.000000E+00
: OBJ24, SIZE, 1.500000E-01, 1.500000E-01, 3.000000E-01
: OBJ24, CLIPART, ridge8r
: OBJ24, ROTATION24, 22
: OBJ24, TYPE, BLOCKAGE
: OBJ24, MATERIAL, 117
: OBJ24, INI_TEMP, 2.000000E+01 STOP

 Art Stretton March 25, 2002 14:15

Re: Combustion Convergence problems

There's one more object file I made up that is mentioned in the Q1 file:

PIP2COLO.DAT - like PIPECOLO.DAT but with 3:1 ratio instead of 2:1

Art Stretton

 PattiMichelle March 26, 2002 16:58

Re: Combustion Convergence problems

I have been using the CHEMKIN subsystem to model combustion in a simpler, laminar case, so I don't think my experience would benefit what you are doing very much. The only thing I can think of is the size of your grids. It may not affect your simulation, but I have noticed convergence to be sensitive to the grid, at least witht the CHEMKIN subsystem. You might try coarsening your grid substantially and see how that affects convergence. Just a thought. - PattiMichelle

 Art Stretton March 26, 2002 23:33

Re: Combustion Convergence problems

I started off with about 200,000 nodes and couldn't get the convergence errors below E+05, more than doubled it to 450,000 nodes to get to E+03, and hoped to get below E+01 with 750,000 nodes. The gradients from the fire plumes are so steep that about 30% of the volume needs to be pretty finely divided. I was also concerned about the aspect ratio of the cells when the finely divided grid intersects with coarse grid sections (kept it at 4:1 or below). But with the increased grid size and increase model features, runs for 1000 iterations have increased from 1/2 hour to 8 hours. Unfortunately, there has also been a decrease in rate of convergence so it seems to be taking more iterations as well to exponentially increase the total time of execution needed.

What I will probably do is increase my tolerance for aspect ratio to 8:1 or even 10:1 to probably lop at least half of the node count off. Maybe Phoenics is more tolerant of cell aspect ratio than other CFD codes that I've been exposed to.

Thanks for your input, PattiMichelle. I looked through all the relevant posts I could find before posting myself, and your name was pretty prominent:^) Here's hoping the combustion experts at CHAM volunteer chime in to give me some guidance with Phoenics issues.

 leon March 27, 2002 21:16

Re: Combustion Convergence problems

Art,

Have you adjusted your relaxtation parameters. In combustion modeling I have found that in the past the convegence was sensative to the convergance of the density of the gas. Maybe it will converge faster if you play with this relaxation parameter.

Hope this helps.

Leon

 michael malin April 2, 2002 05:59

Re: Combustion Convergence problems

If you need linear relaxation on p1 as low as 1e-4 then something is very wrong, either with the set-up, phoenics itself or the convergence parameters. The pressure relaxation should be no lower than 0.3 and more likely around 0.5 to 1.0.

As already suggested the density should be stored and relaxed, say 0.3 linear. If very strong linear relaxation (say 1.e-3) is applied to the density, then convergence should be achieved but this should not be necessary. If this fails, then I would simplify the whole problem by using as coarse a mesh as possible even if this means simplifying the geometry somewhat. The motivation is to get something that converges.

The velocity relexation also appears to be somewhat heavy. From what I can make out in your Q1 file the velocity false time step should be roughly around 1.e-3 to 1.e-2 s. Linear relaxation of 0.3 to 0.5 should be used on k and e. The enthalpy needs to be relaxed, probably using a false time step around 1 sec. The mixture fraction shouldd employ little or no relexation, which is what you are effectively doing.

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