Convergence Difficulty
 

Hello,

I am simulating diffusion of chlorine dioxide in a room (as steady state) using CFX 4.4 by solving mass fraction equation. Problem does not converge when the effects of buoyancy are included, but it converges well when the buyoncy effects are diregarded. Any light on this !! . I also tried using QUICK differencing scheme for MASS FRACTION1 but with no success.

I am attaching my command file with this post with buoyancy effects commented out.

Thanks ,

Sankalp

__________________________________________________ ___
:>CFX4
:>SET LIMITS

TOTAL CHARACTER WORK SPACE 5000000

MAXIMUM NUMBER OF PATCHES 20

END
:>OPTIONS

THREE DIMENSIONS

TURBULENT FLOW

RECTANGULAR GRID

MASS FRACTION EQUATIONS 1

STEADY STATE

COMPRESSIBLE FLOW /* BUOYANT FLOW*/

END
:>MODEL DATA
:>TITLE

PROBLEM TITLE 'AIRFLOW IN APARTMENT'

END
:>PHYSICAL PROPERTIES

>>STANDARD FLUID

FLUID 'AIR'

STANDARD FLUID REFERENCE TEMPERATURE 293.15

END

>>COMPRESSIBILITY PARAMETERS

UNIVERSAL GAS CONSTANT 8314.0

FLUID MOLECULAR WEIGHT 28.79

END /* >>BUOYANCY PARAMETERS

GRAVITY VECTOR 0.0 -9.8 0.0

END */

>>MASS TRANSFER PARAMETERS

>>MOLECULAR WEIGHTS

MASS FRACTION1 71.5

END

>>DIFFUSIVITIES

MASS FRACTION1 1.0E-5

END
:>SOLVER DATA
:>PROGRAM CONTROL

MAXIMUM NUMBER OF ITERATIONS 1000

PRESSURE REFERENCE POINT 1 1 1

OUTPUT MONITOR POSITION 1.25 1.25 0.5

MASS SOURCE TOLERANCE 1.0000E-06

END
:>MODEL BOUNDARY CONDITIONS
:>INLET BOUNDARIES

PATCH NAME 'SUPPLY'

U VELOCITY 0.1026

K 0.5

EPSILON 3.5

END
:>INLET BOUNDARIES

PATCH NAME 'DISINFECTANT'

V VELOCITY -0.06

K 0.5

EPSILON 3.5

MASS FRACTION1 0.01

END
:>STOP