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Old   March 1, 2011, 20:19
Exclamation Domain Imbalance
  #1
HMR
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HMR
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Hi,

I am new user of CFX. I am doing transient simulation of two heat source(with same dimension) located bottom side of inside of a rectangular area.Top of the rectangular area(1mx1mx1m) is open, 4 wall is insulated and bottom is also insulated.Distance between two heat sources is 28cm.

I tried to do simulation in different way but I found that domain imbalance in P-mass is always 200%.

I also tried to do above simulation on steady state (this is not my target) but results again showed that domain imbalance P-mass 200%.

For convenience I attached the CCL

+--------------------------------------------------------------------+
| |
| CFX Command Language for Run |
| |
+--------------------------------------------------------------------+

LIBRARY:
MATERIAL: Air at 25 C
Material Description = Air at 25 C and 1 atm (dry)
Material Group = Air Data, Constant Property Gases
Option = Pure Substance
Thermodynamic State = Gas
PROPERTIES:
Option = General Material
EQUATION OF STATE:
Density = 1.185 [kg m^-3]
Molar Mass = 28.96 [kg kmol^-1]
Option = Value
END
SPECIFIC HEAT CAPACITY:
Option = Value
Specific Heat Capacity = 1.0044E+03 [J kg^-1 K^-1]
Specific Heat Type = Constant Pressure
END
REFERENCE STATE:
Option = Specified Point
Reference Pressure = 1 [atm]
Reference Specific Enthalpy = 0. [J/kg]
Reference Specific Entropy = 0. [J/kg/K]
Reference Temperature = 25 [C]
END
DYNAMIC VISCOSITY:
Dynamic Viscosity = 1.831E-05 [kg m^-1 s^-1]
Option = Value
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 2.61E-02 [W m^-1 K^-1]
END
ABSORPTION COEFFICIENT:
Absorption Coefficient = 0.01 [m^-1]
Option = Value
END
SCATTERING COEFFICIENT:
Option = Value
Scattering Coefficient = 0.0 [m^-1]
END
REFRACTIVE INDEX:
Option = Value
Refractive Index = 1.0 [m m^-1]
END
THERMAL EXPANSIVITY:
Option = Value
Thermal Expansivity = 0.003356 [K^-1]
END
END
END
MATERIAL: Air at 27 C
Material Description = Air at 27 C (dry)
Material Group = Air Data,Constant Property Gases
Option = Pure Substance
Thermodynamic State = Gas
PROPERTIES:
Option = General Material
EQUATION OF STATE:
Density = 1.1777 [kg m^-3]
Molar Mass = 28.96 [kg kmol^-1]
Option = Value
END
SPECIFIC HEAT CAPACITY:
Option = Value
Specific Heat Capacity = 1005 [J kg^-1 K^-1]
Specific Heat Type = Constant Pressure
END
REFERENCE STATE:
Option = Specified Point
Reference Pressure = 1 [atm]
Reference Specific Enthalpy = 0 [J kg^-1]
Reference Specific Entropy = 0 [J kg^-1 K^-1]
Reference Temperature = 300 [K]
END
DYNAMIC VISCOSITY:
Dynamic Viscosity = 1.983e-05 [kg m^-1 s^-1]
Option = Value
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 0.02619 [W m^-1 K^-1]
END
ABSORPTION COEFFICIENT:
Absorption Coefficient = 0.01 [m^-1]
Option = Value
END
SCATTERING COEFFICIENT:
Option = Value
Scattering Coefficient = 0. [m^-1]
END
REFRACTIVE INDEX:
Option = Value
Refractive Index = 1.0
END
THERMAL EXPANSIVITY:
Option = Value
Thermal Expansivity = 0.003356 [K^-1]
END
END
END
END
FLOW: Transient Analysis
SOLUTION UNITS:
Angle Units = [rad]
Length Units = [m]
Mass Units = [kg]
Solid Angle Units = [sr]
Temperature Units = [K]
Time Units = [s]
END
ANALYSIS TYPE:
Option = Transient
EXTERNAL SOLVER COUPLING:
Option = None
END
INITIAL TIME:
Option = Automatic with Value
Time = 0 [s]
END
TIME DURATION:
Option = Total Time
Total Time = 1000 [s]
END
TIME STEPS:
Option = Timesteps
Timesteps = 0.581899 [s]
END
END
DOMAIN: Two Heat Sources
Coord Frame = Coord 0
Domain Type = Fluid
Location = B46
BOUNDARY: Atm
Boundary Type = OUTLET
Location = F48.46
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
MASS AND MOMENTUM:
Normal Speed = 0 [m s^-1]
Option = Normal Speed
END
END
END
BOUNDARY: Bottom
Boundary Type = WALL
Location = F47.46
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Adiabatic
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
END
END
BOUNDARY: Vent 1
Boundary Type = INLET
Location = F138.46
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
HEAT TRANSFER:
Option = Static Temperature
Static Temperature = 298.644619578 [K]
END
MASS AND MOMENTUM:
Normal Speed = 0.0841895 [m s^-1]
Option = Normal Speed
END
END
END
BOUNDARY: Vent 2
Boundary Type = INLET
Location = F137.46
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
HEAT TRANSFER:
Option = Static Temperature
Static Temperature = 298.644619578 [K]
END
MASS AND MOMENTUM:
Normal Speed = 0.0841895 [m s^-1]
Option = Normal Speed
END
END
END
BOUNDARY: Wall
Boundary Type = WALL
Location = F49.46,F50.46,F51.46,F52.46
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Adiabatic
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
END
END
DOMAIN MODELS:
BUOYANCY MODEL:
Buoyancy Reference Temperature = 300 [K]
Gravity X Component = 0 [m s^-2]
Gravity Y Component = 0 [m s^-2]
Gravity Z Component = 9.81 [m s^-2]
Option = Buoyant
BUOYANCY REFERENCE LOCATION:
Option = Automatic
END
END
DOMAIN MOTION:
Option = Stationary
END
MESH DEFORMATION:
Option = None
END
REFERENCE PRESSURE:
Reference Pressure = 1 [atm]
END
END
FLUID DEFINITION: Fluid 1
Material = Air at 25 C
Option = Material Library
MORPHOLOGY:
Option = Continuous Fluid
END
END
FLUID MODELS:
COMBUSTION MODEL:
Option = None
END
HEAT TRANSFER MODEL:
Option = Thermal Energy
END
THERMAL RADIATION MODEL:
Option = None
END
TURBULENCE MODEL:
Option = Laminar
END
END
END
INITIALISATION:
Option = Automatic
INITIAL CONDITIONS:
Velocity Type = Cartesian
CARTESIAN VELOCITY COMPONENTS:
Option = Automatic with Value
U = 0 [m s^-1]
V = 0 [m s^-1]
W = 0 [m s^-1]
END
STATIC PRESSURE:
Option = Automatic with Value
Relative Pressure = 1 [atm]
END
TEMPERATURE:
Option = Automatic with Value
Temperature = 300 [K]
END
END
END
OUTPUT CONTROL:
RESULTS:
File Compression Level = Default
Option = Standard
END
TRANSIENT RESULTS: Transient Results 1
File Compression Level = Default
Include Mesh = No
Option = Selected Variables
Output Variables List = Temperature,Velocity
OUTPUT FREQUENCY:
Option = Time Interval
Time Interval = 0.5 [s]
END
END
END
SOLVER CONTROL:
ADVECTION SCHEME:
Option = High Resolution
END
BODY FORCES:
Body Force Averaging Type = Volume-Weighted
END
CONVERGENCE CONTROL:
Maximum Number of Coefficient Loops = 5
Minimum Number of Coefficient Loops = 1
Timescale Control = Coefficient Loops
END
CONVERGENCE CRITERIA:
Residual Target = 1.E-4
Residual Type = RMS
END
TRANSIENT SCHEME:
Option = Second Order Backward Euler
TIMESTEP INITIALISATION:
Option = Automatic
END
END
END
END
COMMAND FILE:
Version = 12.1
Results Version = 12.1
END
SIMULATION CONTROL:
EXECUTION CONTROL:
EXECUTABLE SELECTION:
Double Precision = Off
END
INTERPOLATOR STEP CONTROL:
Runtime Priority = Standard
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
END
PARALLEL HOST LIBRARY:
HOST DEFINITION: fmcv42s
Host Architecture String = winnt
Installation Root = C:\Program Files\ANSYS Inc\v%v\CFX
END
END
PARTITIONER STEP CONTROL:
Multidomain Option = Independent Partitioning
Runtime Priority = Standard
EXECUTABLE SELECTION:
Use Large Problem Partitioner = Off
END
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
PARTITIONING TYPE:
MeTiS Type = k-way
Option = MeTiS
Partition Size Rule = Automatic
END
END
RUN DEFINITION:
Run Mode = Full
Solver Input File = C:\Documents and Settings\jc218370\Local \
Settings\Temp\2HS-28CM-UPDATE-1_1052_Working\dp0\CFX\CFX\Work1\Fluid \
Flow.def
END
SOLVER STEP CONTROL:
Runtime Priority = Standard
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
PARALLEL ENVIRONMENT:
Number of Processes = 1
Start Method = Serial
END
END
END
END

================================================== ====================
Boundary Flow and Total Source Term Summary
================================================== ====================

+--------------------------------------------------------------------+
| U-Mom |
+--------------------------------------------------------------------+
Boundary : Atm 1.6471E-06
Boundary : Bottom -1.3208E-06
Boundary : Vent 1 1.0866E-08
Boundary : Vent 2 -2.0033E-08
Boundary : Wall -4.7055E-06
Neg Accumulation : Two Heat Sources -5.1746E-09
-----------
Domain Imbalance : -4.3935E-06

Domain Imbalance, in %: -0.0177 %

+--------------------------------------------------------------------+
| V-Mom |
+--------------------------------------------------------------------+
Boundary : Atm 3.5500E-07
Boundary : Bottom -3.6152E-07
Boundary : Vent 1 2.6344E-09
Boundary : Vent 2 7.1901E-09
Boundary : Wall -4.2817E-06
Neg Accumulation : Two Heat Sources -3.1277E-07
-----------
Domain Imbalance : -4.5911E-06

Domain Imbalance, in %: -0.0185 %

+--------------------------------------------------------------------+
| W-Mom |
+--------------------------------------------------------------------+
Boundary : Atm -5.9300E-05
Boundary : Bottom -2.4246E-02
Boundary : Vent 1 -2.6491E-04
Boundary : Vent 2 -2.6527E-04
Boundary : Wall 1.2362E-06
Domain Src (Pos) : Two Heat Sources 2.4839E-02
Neg Accumulation : Two Heat Sources -2.6798E-07
-----------
Domain Imbalance : 4.8673E-06

Domain Imbalance, in %: 0.0196 %

+--------------------------------------------------------------------+
| P-Mass |
+--------------------------------------------------------------------+
Boundary : Vent 1 8.0007E-04
Boundary : Vent 2 8.0007E-04
-----------
Domain Imbalance : 1.6001E-03

Domain Imbalance, in %: 200.0000 %

+--------------------------------------------------------------------+
| H-Energy |
+--------------------------------------------------------------------+
Boundary : Vent 1 3.9746E-01
Boundary : Vent 2 3.9746E-01
Neg Accumulation : Two Heat Sources -7.9492E-01
-----------
Domain Imbalance : 1.0729E-06

Domain Imbalance, in %: 0.0001 %


I run this test 1000s and time step is 0.58s. Now I am confused whether my simulation is ok or not.If not how can i improve my simulation results.What is the error in my simulation?

In addition I want added that CFX manager screen showed that the results was converged successfully.

I need anybodys good comment on my querry

Thanks in advance.

HMR
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Old   March 3, 2011, 14:47
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velocity inlet and velocity outlet is numerically not advantageous. Check your boundaries and the according chapters in the help
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Thousands of issues can cause a division by zero. Please do not capture a thread, with the argument: "I have the same issue ...."
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Old   March 3, 2011, 18:49
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Rather than "not advantageous", I would say "physically impossible". Read the CFX documentation as joey says on boundary condition selection.
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Old   March 6, 2011, 21:10
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HMR
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Thanks JOEY2007 and GLENN for your good comments, I have checked that some thing need to adjust in boundary conditions to get good result.

Regards

HMR
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