[HMR]

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

[joey2007]

velocity inlet and velocity outlet is numerically not advantageous. Check your boundaries and the according chapters in the help

[ghorrocks]

Rather than "not advantageous", I would say "physically impossible". Read the CFX documentation as joey says on boundary condition selection.

[HMR]

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

[urosgrivc]

I have a question about P-mass imbalance.

I have a rotor spining ( 1/6=60° rotating domain with ciclic simetry) problem, it is a wentilated braking disk with cooling fins.

Convergence of residuals is good and my monitor points are converging to some value (torque, avgHTC...), imbalances in the domain are all wery close to 0 but the
P-mass imbalance jumps from +-100 the frequency is somewhat timescale dependant.

https://drive.google.com/open?id=0Bw...DBiTlItbjIxX1U in the figure there is all ~350 itterations. monitor points are constant at ~100 itter, all RMS residuals are under 1e-4 but max residuals are above 1e-2.

I only have an opening tipe boundary condition and the flow is induced by
rotors rotation, there is also heat transfer included and domain has properties of air ideal gas, SSTmodel with wery fine inflation layers is used for turbulence model.

Is there a problem if P-mass is jumping -+100?
Can I change something to make it beter?
I dont understand why it is jumping and how can my simulation still looks well converged.

Thank you

[ghorrocks]

If you only have a single flow boundary then you cannot generally use imbalances. That is because the smallest net flow in or out the boundary (even if just cause by numerical noise) has nothing to balance it and so shows as 100% imbalance. And the next time step when the tiny flow is in the other direction the imbalance shows up as -100%. That is why imbalances is an optional convergence criteria - for some simulations it is meaningless.