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Natural convection in a closed domain STILL NEEDING help!

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Old   March 28, 2011, 07:44
Default Natural convection in a closed domain STILL NEEDING help!
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Gregory
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Hi FLUENT users, I am trying to model natural convection in a closed car cabin with radiation. Below is the summary of my solution. But the temperature and velocity distributions do not seem to make sense, and the mass flow rate between two arbitrary planes steadily increases with more iterations. Please give me your valuable advise, please!

I would be glad to answer any questions.

FLUENT
Version: 3d, dp, pbns, rngke (3d, double precision, pressure-based, RNG k-epsilon)
Release: 6.3.26
Title:

Models
------

Model Settings
-----------------------------------------------------------------
Space 3D
Time Steady
Viscous RNG k-epsilon turbulence model
Wall Treatment Standard Wall Functions
RNG Differential Viscosity Model Disabled
RNG Swirl Dominated Flow Option Disabled
Heat Transfer Enabled
Solidification and Melting Disabled
Radiation None
Species Transport Disabled
Coupled Dispersed Phase Disabled
Pollutants Disabled
Pollutants Disabled
Soot Disabled

Boundary Conditions
-------------------

Zones

name id type
--------------------------------
air 2 fluid
outlet 3 wall
bottomhalf 4 wall
tophalf 5 wall
rearwindscreen 6 wall
frontwindscreen 7 wall
default-interior 9 interior

Boundary Conditions

air

Condition Value
------------------------------------------------------------------
Material Name air
Specify source terms? no
Source Terms ()
Specify fixed values? no
Local Coordinate System for Fixed Velocities no
Fixed Values ()
Motion Type 0
X-Velocity Of Zone (m/s) 0
Y-Velocity Of Zone (m/s) 0
Z-Velocity Of Zone (m/s) 0
Rotation speed (rad/s) 0
X-Origin of Rotation-Axis (m) 0
Y-Origin of Rotation-Axis (m) 0
Z-Origin of Rotation-Axis (m) 0
X-Component of Rotation-Axis 0
Y-Component of Rotation-Axis 0
Z-Component of Rotation-Axis 1
Deactivated Thread no
Laminar zone? no
Set Turbulent Viscosity to zero within laminar zone? yes
Porous zone? no
Conical porous zone? no
X-Component of Direction-1 Vector 1
Y-Component of Direction-1 Vector 0
Z-Component of Direction-1 Vector 0
X-Component of Direction-2 Vector 0
Y-Component of Direction-2 Vector 1
Z-Component of Direction-2 Vector 0
X-Component of Cone Axis Vector 1
Y-Component of Cone Axis Vector 0
Z-Component of Cone Axis Vector 0
X-Coordinate of Point on Cone Axis (m) 1
Y-Coordinate of Point on Cone Axis (m) 0
Z-Coordinate of Point on Cone Axis (m) 0
Half Angle of Cone Relative to its Axis (deg) 0
Relative Velocity Resistance Formulation? yes
Direction-1 Viscous Resistance (1/m2) 0
Direction-2 Viscous Resistance (1/m2) 0
Direction-3 Viscous Resistance (1/m2) 0
Choose alternative formulation for inertial resistance? no
Direction-1 Inertial Resistance (1/m) 0
Direction-2 Inertial Resistance (1/m) 0
Direction-3 Inertial Resistance (1/m) 0
C0 Coefficient for Power-Law 0
C1 Coefficient for Power-Law 0
Porosity 1
Solid Material Name aluminum

outlet


Condition Value
-------------------------------------------------------------
Wall Thickness (m) 0
Heat Generation Rate (w/m3) 0
Material Name aluminum
Thermal BC Type 1
Temperature (k) 300
Heat Flux (w/m2) 0
Convective Heat Transfer Coefficient (w/m2-k) 20
Free Stream Temperature (k) 300
Enable shell conduction? no
Wall Motion 0
Shear Boundary Condition 0
Define wall motion relative to adjacent cell zone? yes
Apply a rotational velocity to this wall? no
Velocity Magnitude (m/s) 0
X-Component of Wall Translation 1
Y-Component of Wall Translation 0
Z-Component of Wall Translation 0
Define wall velocity components? no
X-Component of Wall Translation (m/s) 0
Y-Component of Wall Translation (m/s) 0
Z-Component of Wall Translation (m/s) 0
External Emissivity 1
External Radiation Temperature (k) 300
Wall Roughness Height (m) 0
Wall Roughness Constant 0.5
Rotation Speed (rad/s) 0
X-Position of Rotation-Axis Origin (m) 0
Y-Position of Rotation-Axis Origin (m) 0
Z-Position of Rotation-Axis Origin (m) 0
X-Component of Rotation-Axis Direction 0
Y-Component of Rotation-Axis Direction 0
Z-Component of Rotation-Axis Direction 1
X-component of shear stress (pascal) 0
Y-component of shear stress (pascal) 0
Z-component of shear stress (pascal) 0
Surface tension gradient (n/m-k) 0
Specularity Coefficient 0

bottomhalf


Condition Value
-------------------------------------------------------------
Wall Thickness (m) 0
Heat Generation Rate (w/m3) 0
Material Name aluminum
Thermal BC Type 2
Temperature (k) 300
Heat Flux (w/m2) 0
Convective Heat Transfer Coefficient (w/m2-k) 20
Free Stream Temperature (k) 300
Enable shell conduction? no
Wall Motion 0
Shear Boundary Condition 0
Define wall motion relative to adjacent cell zone? yes
Apply a rotational velocity to this wall? no
Velocity Magnitude (m/s) 0
X-Component of Wall Translation 1
Y-Component of Wall Translation 0
Z-Component of Wall Translation 0
Define wall velocity components? no
X-Component of Wall Translation (m/s) 0
Y-Component of Wall Translation (m/s) 0
Z-Component of Wall Translation (m/s) 0
External Emissivity 1
External Radiation Temperature (k) 300
Wall Roughness Height (m) 0
Wall Roughness Constant 0.5
Rotation Speed (rad/s) 0
X-Position of Rotation-Axis Origin (m) 0
Y-Position of Rotation-Axis Origin (m) 0
Z-Position of Rotation-Axis Origin (m) 0
X-Component of Rotation-Axis Direction 0
Y-Component of Rotation-Axis Direction 0
Z-Component of Rotation-Axis Direction 1
X-component of shear stress (pascal) 0
Y-component of shear stress (pascal) 0
Z-component of shear stress (pascal) 0
Surface tension gradient (n/m-k) 0
Specularity Coefficient 0

tophalf


Condition Value
-------------------------------------------------------------
Wall Thickness (m) 0
Heat Generation Rate (w/m3) 0
Material Name aluminum
Thermal BC Type 2
Temperature (k) 300
Heat Flux (w/m2) 0
Convective Heat Transfer Coefficient (w/m2-k) 20
Free Stream Temperature (k) 300
Enable shell conduction? no
Wall Motion 0
Shear Boundary Condition 0
Define wall motion relative to adjacent cell zone? yes
Apply a rotational velocity to this wall? no
Velocity Magnitude (m/s) 0
X-Component of Wall Translation 1
Y-Component of Wall Translation 0
Z-Component of Wall Translation 0
Define wall velocity components? no
X-Component of Wall Translation (m/s) 0
Y-Component of Wall Translation (m/s) 0
Z-Component of Wall Translation (m/s) 0
External Emissivity 1
External Radiation Temperature (k) 300
Wall Roughness Height (m) 0
Wall Roughness Constant 0.5
Rotation Speed (rad/s) 0
X-Position of Rotation-Axis Origin (m) 0
Y-Position of Rotation-Axis Origin (m) 0
Z-Position of Rotation-Axis Origin (m) 0
X-Component of Rotation-Axis Direction 0
Y-Component of Rotation-Axis Direction 0
Z-Component of Rotation-Axis Direction 1
X-component of shear stress (pascal) 0
Y-component of shear stress (pascal) 0
Z-component of shear stress (pascal) 0
Surface tension gradient (n/m-k) 0
Specularity Coefficient 0

rearwindscreen


Condition Value
-------------------------------------------------------------
Wall Thickness (m) 0
Heat Generation Rate (w/m3) 0
Material Name aluminum
Thermal BC Type 4
Temperature (k) 300
Heat Flux (w/m2) 0
Convective Heat Transfer Coefficient (w/m2-k) 0
Free Stream Temperature (k) 300
Enable shell conduction? no
Wall Motion 0
Shear Boundary Condition 0
Define wall motion relative to adjacent cell zone? yes
Apply a rotational velocity to this wall? no
Velocity Magnitude (m/s) 0
X-Component of Wall Translation 1
Y-Component of Wall Translation 0
Z-Component of Wall Translation 0
Define wall velocity components? no
X-Component of Wall Translation (m/s) 0
Y-Component of Wall Translation (m/s) 0
Z-Component of Wall Translation (m/s) 0
External Emissivity 1
External Radiation Temperature (k) 340
Wall Roughness Height (m) 0
Wall Roughness Constant 0.5
Rotation Speed (rad/s) 0
X-Position of Rotation-Axis Origin (m) 0
Y-Position of Rotation-Axis Origin (m) 0
Z-Position of Rotation-Axis Origin (m) 0
X-Component of Rotation-Axis Direction 0
Y-Component of Rotation-Axis Direction 0
Z-Component of Rotation-Axis Direction 1
X-component of shear stress (pascal) 0
Y-component of shear stress (pascal) 0
Z-component of shear stress (pascal) 0
Surface tension gradient (n/m-k) 0
Specularity Coefficient 0
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Old   March 28, 2011, 07:44
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Gregory
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frontwindscreen


Condition Value
-------------------------------------------------------------
Wall Thickness (m) 0
Heat Generation Rate (w/m3) 0
Material Name aluminum
Thermal BC Type 4
Temperature (k) 300
Heat Flux (w/m2) 0
Convective Heat Transfer Coefficient (w/m2-k) 0
Free Stream Temperature (k) 300
Enable shell conduction? no
Wall Motion 0
Shear Boundary Condition 0
Define wall motion relative to adjacent cell zone? yes
Apply a rotational velocity to this wall? no
Velocity Magnitude (m/s) 0
X-Component of Wall Translation 1
Y-Component of Wall Translation 0
Z-Component of Wall Translation 0
Define wall velocity components? no
X-Component of Wall Translation (m/s) 0
Y-Component of Wall Translation (m/s) 0
Z-Component of Wall Translation (m/s) 0
External Emissivity 1
External Radiation Temperature (k) 340
Wall Roughness Height (m) 0
Wall Roughness Constant 0.5
Rotation Speed (rad/s) 0
X-Position of Rotation-Axis Origin (m) 0
Y-Position of Rotation-Axis Origin (m) 0
Z-Position of Rotation-Axis Origin (m) 0
X-Component of Rotation-Axis Direction 0
Y-Component of Rotation-Axis Direction 0
Z-Component of Rotation-Axis Direction 1
X-component of shear stress (pascal) 0
Y-component of shear stress (pascal) 0
Z-component of shear stress (pascal) 0
Surface tension gradient (n/m-k) 0
Specularity Coefficient 0

default-interior


Condition Value
-----------------

Solver Controls
---------------

Equations

Equation Solved
-------------------
Flow yes
Turbulence yes
Energy yes

Numerics

Numeric Enabled
---------------------------------------
Absolute Velocity Formulation yes

Relaxation

Variable Relaxation Factor
----------------------------------------------
Pressure 0.3
Density 1
Body Forces 1
Momentum 0.5
Turbulent Kinetic Energy 0.8
Turbulent Dissipation Rate 0.8
Turbulent Viscosity 1
Energy 0.8

Linear Solver


Solver Termination Residual Reduction
Variable Type Criterion Tolerance
------------------------------------------------------------------------
Pressure V-Cycle 0.1
X-Momentum Flexible 0.1 0.7
Y-Momentum Flexible 0.1 0.7
Z-Momentum Flexible 0.1 0.7
Turbulent Kinetic Energy Flexible 0.1 0.7
Turbulent Dissipation Rate Flexible 0.1 0.7
Energy Flexible 0.1 0.7

Pressure-Velocity Coupling

Parameter Value
------------------
Type SIMPLE

Discretization Scheme

Variable Scheme
-----------------------------------------------
Pressure PRESTO!
Momentum First Order Upwind
Turbulent Kinetic Energy First Order Upwind
Turbulent Dissipation Rate First Order Upwind
Energy First Order Upwind

Solution Limits

Quantity Limit
---------------------------------------
Minimum Absolute Pressure 1
Maximum Absolute Pressure 5e+10
Minimum Temperature 1
Maximum Temperature 5000
Minimum Turb. Kinetic Energy 1e-14
Minimum Turb. Dissipation Rate 1e-20
Maximum Turb. Viscosity Ratio 100000

Material Properties
-------------------


Material: air (fluid)

Property Units Method Value(s)
-----------------------------------------------------------------------------------
Density kg/m3 incompressible-ideal-gas #f
Cp (Specific Heat) j/kg-k constant 1006.43
Thermal Conductivity w/m-k constant 0.0242
Viscosity kg/m-s constant 1.7894001e-05
Molecular Weight kg/kgmol constant 28.966
L-J Characteristic Length angstrom constant 3.711
L-J Energy Parameter k constant 78.6
Thermal Expansion Coefficient 1/k constant 0
Degrees of Freedom constant 0
Speed of Sound m/s none #f

Material: aluminum (solid)

Property Units Method Value(s)
---------------------------------------------------
Density kg/m3 constant 2719
Cp (Specific Heat) j/kg-k constant 871
Thermal Conductivity w/m-k constant 202.4

FLUENT
Version: 3d, dp, pbns, rngke (3d, double precision, pressure-based, RNG k-epsilon)
Release: 6.3.26
Title:

Models
------

Model Settings
-----------------------------------------------------------------
Space 3D
Time Steady
Viscous RNG k-epsilon turbulence model
Wall Treatment Standard Wall Functions
RNG Differential Viscosity Model Disabled
RNG Swirl Dominated Flow Option Disabled
Heat Transfer Enabled
Solidification and Melting Disabled
Radiation None
Species Transport Disabled
Coupled Dispersed Phase Disabled
Pollutants Disabled
Pollutants Disabled
Soot Disabled

Boundary Conditions
-------------------

Zones

name id type
--------------------------------
air 2 fluid
outlet 3 wall
bottomhalf 4 wall
tophalf 5 wall
rearwindscreen 6 wall
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Old   February 6, 2012, 13:23
Default modeling ventilation of a room (only cosidering buoyancy forces due to temp grad)
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arunbollavarapu
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hi , iam modeling ventilation of a room , having two windows located on oposite walls, room is square of 3.5m , temp of air in room is 303k , ambient temp is 293k , iam considering 2 domains one is for room another is for atmosphere, boundary conditions taken are interior for windows , pressure inlet for atmospher boundaries , remaning are walls, are these B.C's are sufficient for modeling natural convection taking place because of buoyancy forces ? shall i consider boussinesq approximation ? shall i specify operating density in operating conditions? what should be the density in material panel ? constant,incompressible ideal gas , piecewiseliner,piecewise polynomial,which one shall i take? fluent user guide specified that bossinesq approximation should not be used for my case , if any have idea about specifying density as function of temp . pleeeeeeeeeese help me
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Old   June 12, 2013, 02:12
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Refer literature. Boussinesq is valid for a max temp difference of 20 deg celsius.
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