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 Chris89 May 27, 2014 06:25

1 Attachment(s)
Hi,
I’m new in working with ANSYS CFX. I searched this forum for clarifying my issue but I did not find a real solution. So I will explain what I want to do.
I want to do a thermal analysis of a rough board in space. For the first approach I just want to irradiate this board from the sun in the distance of 1AU (sun-earth distance). The board should absorb this radiation in the solar spectrum and emit it in the infrared spectrum. I want to check this easy case of radiation modeling with the calculations I did by my own before I start with the harder simulation. The reason why I use CFX is because of directional radiation. I want to analyze the rough board later for hot spots due to reflections. That is not possible with the thermal steady-state analysis of ANSYS according to the support.
At first I want to create the surrounding area close to reality. Therefore I created a box for the vacuum (see attached picture). This domain is defined as a fluid with Air at 25 C (I switched to “false” for solving fluids). In this domain is my board, defined as a solid domain which is connected by a fluid-solid interface with the “vacuum”. My radiation flux at 1AU is about 1367 W/m^2. Therefore I defined a Radiation Source with a Directional Radiation Flux of the mentioned value at the boundary of the fluid domain. Additionally I fixed the temperature (3 K) of the walls of the fluid domain for the heat transfer and set the initial temperature of the board to 273 K. I am using Monte Carlo on both sides of the interface for thermal radiation. Solid and Fluid domain are participating medias. Do you think my definitions for the simulations are correct by now?
Here comes my real problem with CFX. As I said, I want to absorb and emit in different spectra. I have totally no idea how I can define this correctly in CFX!? I read something like the emissivity is derived by the absorption coefficient. So I tried to get this connection but I just found information about the “Einstein coefficients” which are not that easy to understand. Is there another possibility to define values like emissivity, absorptivity, transmittance and reflectivity or how should the absorption coefficient defined? I also read that for example the absorptivity is defined in CFX by “absorptivity= diffuse fraction* internal emissivity”. But the internal emissivity is not the same like you can define for the “Opaque” option. Maybe I have to work more on understanding thermal radiation or can you help me?!

So all in all my two questions are:
• Are my basic conditions correctly defined? If not, what should I change?
• Is it possible to define the mentioned values like emissivity, absorptivity and so on for my board (material: aluminum)? If yes, how :)?

Best regards,
Chris

Edit: I forgot to post a part of the data from the output-file, sorry.

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: Aluminium
Material Group = CHT Solids,Particle Solids
Option = Pure Substance
Thermodynamic State = Solid
PROPERTIES:
Option = General Material
EQUATION OF STATE:
Density = 2702 [kg m^-3]
Molar Mass = 26.98 [kg kmol^-1]
Option = Value
END
SPECIFIC HEAT CAPACITY:
Option = Value
Specific Heat Capacity = 9.03E+02 [J kg^-1 K^-1]
END
REFERENCE STATE:
Option = Specified Point
Reference Specific Enthalpy = 0 [J/kg]
Reference Specific Entropy = 0 [J/kg/K]
Reference Temperature = 25 [C]
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 237 [W m^-1 K^-1]
END
ABSORPTION COEFFICIENT:
Absorption Coefficient = 0.0001 [mm^-1]
Option = Value
END
END
END
END
FLOW: Flow Analysis 1
SOLUTION UNITS:
Length Units = [m]
Mass Units = [kg]
Solid Angle Units = [sr]
Temperature Units = [K]
Time Units = [s]
END
ANALYSIS TYPE:
EXTERNAL SOLVER COUPLING:
Option = None
END
END
DOMAIN: Platte
Coord Frame = Coord 0
Domain Type = Solid
Location = B18
BOUNDARY: Default Fluid Solid Interface Side 1 1
Boundary Type = INTERFACE
Location = F19.18,F20.18,F21.18,F22.18,F23.18,F24.18
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Conservative Interface Flux
END
Diffuse Fraction = 1.
Emissivity = 1.
Option = Opaque
END
END
END
DOMAIN MODELS:
DOMAIN MOTION:
Option = Stationary
END
MESH DEFORMATION:
Option = None
END
END
INITIALISATION:
Option = Automatic
INITIAL CONDITIONS:
Option = Automatic
END
TEMPERATURE:
Option = Automatic with Value
Temperature = 273 [K]
END
END
END
SOLID DEFINITION: Solid 1
Material = Aluminium
Option = Material Library
MORPHOLOGY:
Option = Continuous Solid
END
END
SOLID MODELS:
HEAT TRANSFER MODEL:
Option = Thermal Energy
END
Number of Histories = 100000
Option = Monte Carlo
Radiation Transfer Mode = Participating Media
SCATTERING MODEL:
Option = None
END
SPECTRAL MODEL:
Option = Gray
END
END
END
END
DOMAIN: Umgebung
Coord Frame = Coord 0
Domain Type = Fluid
Location = B57
BOUNDARY: Default Fluid Solid Interface Side 1
Boundary Type = INTERFACE
Location = F64.57,F65.57,F66.57,F67.57,F68.57,F69.57
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Conservative Interface Flux
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
Diffuse Fraction = 0
Emissivity = 1.
Option = Opaque
END
END
END
BOUNDARY: Grenze
Boundary Type = WALL
Location = F58.57,F59.57,F60.57,F61.57,F62.57
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Fixed Temperature = 3 [K]
Option = Fixed Temperature
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
Diffuse Fraction = 0
Emissivity = 1.
Option = Opaque
END
END
END
BOUNDARY: Quelle
Boundary Type = WALL
Location = F63.57
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Fixed Temperature = 3 [K]
Option = Fixed Temperature
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
Diffuse Fraction = 0
Emissivity = 1.
Option = Opaque
END
END
BOUNDARY SOURCE:
SOURCES:
Radiation Flux = 1367 [W m^-2]
DIRECTION:
Option = Cartesian Components
Unit Vector X Component = 0
Unit Vector Y Component = 0
Unit Vector Z Component = -1
END
END
END
END
END

 Chris89 June 2, 2014 06:04

And the rest:

DOMAIN MODELS:
BUOYANCY MODEL:
Option = Non Buoyant
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
Number of Histories = 100000
Option = Monte Carlo
Radiation Transfer Mode = Participating Media
SCATTERING MODEL:
Option = None
END
SPECTRAL MODEL:
Option = Gray
END
END
TURBULENCE MODEL:
Option = Laminar
END
END
INITIALISATION:
Option = Automatic
INITIAL CONDITIONS:
Velocity Type = Cartesian
CARTESIAN VELOCITY COMPONENTS:
Option = Automatic
END
Option = Automatic
END
STATIC PRESSURE:
Option = Automatic with Value
Relative Pressure = 0 [Pa]
END
TEMPERATURE:
Option = Automatic
END
END
END
END
DOMAIN INTERFACE: Default Fluid Solid Interface
Boundary List1 = Default Fluid Solid Interface Side 1 1
Boundary List2 = Default Fluid Solid Interface Side 1
Interface Type = Fluid Solid
INTERFACE MODELS:
Option = General Connection
FRAME CHANGE:
Option = None
END
HEAT TRANSFER:
Option = Conservative Interface Flux
HEAT TRANSFER INTERFACE MODEL:
Option = None
END
END
PITCH CHANGE:
Option = None
END
Option = Side Dependent
END
END
MESH CONNECTION:
Option = Automatic
END
END
OUTPUT CONTROL:
RESULTS:
File Compression Level = Default
Option = Standard
END
END
SOLVER CONTROL:
Option = High Resolution
END
CONVERGENCE CONTROL:
Length Scale Option = Conservative
Maximum Number of Iterations = 200
Minimum Number of Iterations = 10
Solid Timescale Control = Auto Timescale
Timescale Control = Auto Timescale
Timescale Factor = 1.0
END
CONVERGENCE CRITERIA:
Conservation Target = 0.01
Residual Target = 1.E-4
Residual Type = RMS
END
DYNAMIC MODEL CONTROL:
Global Dynamic Model Control = On
END
Iteration Interval = 5
COARSENING CONTROL:
Target Coarsening Rate = 4
END
END
END
EXPERT PARAMETERS:
solve fluids = f
END
END
COMMAND FILE:
Version = 14.5
Results Version = 14.5.7
END
SIMULATION CONTROL:
EXECUTION CONTROL:
EXECUTABLE SELECTION:
Double Precision = On
END
INTERPOLATOR STEP CONTROL:
Runtime Priority = Standard
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
END
PARALLEL HOST LIBRARY:
HOST DEFINITION: ry000391
Remote Host Name = RY-000391
Host Architecture String = winnt-amd64
Installation Root = C:\Program Files\ANSYS1457\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
Partition Weight Factors = 0.50000, 0.50000
END
END
RUN DEFINITION:
Run Mode = Full
Solver Input File = Fluiddynamik CFX.def
END
SOLVER STEP CONTROL:
Runtime Priority = Standard
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
PARALLEL ENVIRONMENT:
Number of Processes = 2
Start Method = Platform MPI Local Parallel
Parallel Host List = ry000391*2
END
END
END
END

 Chris89 June 12, 2014 08:52

Update:

I changed the boundary conditions of the vacuum to "openings" and set the opening pressure to 0 Pa and the opening temperature to 3 K. If I choose opaque for the domain interface with an emissivity of 1 I get the correct value for the temperature after adjusting the absorption coefficient. My problem regarding the absorptivity and emissivity is still present. For the first approach I know my ratio from the absorptivity to the emissivity. Therefore if I can set the emissivity to 1 I can multiply my incoming radiation flux with the ratio. That's ok for testing but because of the defined option opaque, the aluminum plate would not be considered. So I have to define also the reflectivity and transmissivity because I want to analyze a specimen with wrinkles. I already read the theory behind radiation modeling from ANSYS CFX but I have still no clue how CFX derives my desired values with the help of the absorption coefficient, scattering coefficient, the refractive index and the radiative transfer equation.

Some radiation experts or non-radiation experts :) out there who can help me?

Best regards,
Chris

P.S. Ordered "Thermal Radiation Heat Transfer" from Siegel and Howell. If I get the solution, I let you know. But if someone has an idea for the solution please post it :).

 Opaque June 13, 2014 21:38

Below is sample CFX command language code on how to implement a spectral property for a thermal radiation model

You can use 1D interpolation functions, or write your own expression with step functions (or logical CEL if you like as well).

The main points are
- Decide how many spectral intervals you need
- Create either expressions, or 1D-interp functions
- Activate the multiband spectral model
- Create as many spectral intervals you decided for this simulation
- Use the expressions or function on the appropriate sections: emissivity at boundaries, absorption coefficients for materials, or even radiation fluxes at boundary sources (check with ANSYS support here for care on setting up spectral sources)

Code:

``` LIBRARY:   CEL : # #  Example interpolation function for spectral property as a function of #  frequency #      FUNCTION: MatSpectralAbsorption       Argument Units = [s^-1]       Option = Interpolation       Result Units = [m^-1]       INTERPOLATION DATA:         Data Pairs = \           3e+013  , 0.98, \           4.25e+013, 0.98, \           4.26e+013, 0.7, \           4.99e+013, 0.7, \           5e+013  , 0.29,\           5.99e+013, 0.29, \           6e+013  , 0.08, \           3e+014  , 0.08         Extend Max = On         Extend Min = On         Option = One Dimensional       END     END # #  Example using expressions with step function #        EXPRESSIONS : #    #  Limit for the wavelength intervals of interest #       WavlLow  = 1.E-02 [micron]       Wavl1    = 4.E-01 [micron]       Wavl2    = 7.E-01 [micron]       Wavl3    = 1.E+02 [micron]       WavlHigh = 1.E+10 [micron] #    #  Dimensionless wavelength variables, including CEL wavelo #       wavlLow  = WavlLow * 1[m^-1]       wavl1    = Wavl1 * 1[m^-1]       wavl2    = Wavl2 * 1[m^-1]       wavl3    = Wavl3 * 1[m^-1]       wavl4    = Wavl4 * 1[m^-1]       wavl5    = Wavl5 * 1[m^-1]       wavlHigh = WavlHigh * 1[m^-1]       wavldim  = wavelo * 1[m^-1] # #  Interpolation weights to describe spectral property as a function of #  wavelegth #       int1 =  step(wavl1  -wavldim)       int2 = (step(wavl2  -wavldim)-step(wavl1-wavldim))       int3 = (step(wavl3  -wavldim)-step(wavl2-wavldim))       int4 = (step(wavlHigh-wavldim)-step(wavl3-wavldim)) # #  Values of spectral property on each interval #       prop1 = ...       prop2 = ...          prop3 = ...       prop4 = ... #       SpectralProp = (prop1 * int1 + prop2 * int2 + \                       prop3 * int3 + prop3 * int4)     END   END   THERMAL RADIATION MODEL:     ...      SPECTRAL MODEL:       Option = Multiband       SPECTRAL BAND: UV         Option = Wavelength in Vacuum         Wavelength Lower Limit = WavlLow         Wavelength Upper Limit = Wavl1       END       SPECTRAL BAND: Visible         Option = Wavelength in Vacuum         Wavelength Lower Limit = Wavl1         Wavelength Upper Limit = Wavl2       END       SPECTRAL BAND: Thermal         Option = Wavelength in Vacuum         Wavelength Lower Limit = Wavl2         Wavelength Upper Limit = Wavl3       END       SPECTRAL BAND: Microwave         Option = Wavelength in Vacuum         Wavelength Lower Limit = Wavl3         Wavelength Upper Limit = WavlHigh       END     END     ...   END #  #  Usage for emissivity  #   THERMAL RADIATION:     Option = Opaque     Emissivity = SpectralProp     Diffuse Fraction = ...   END #  #  Usage for absorption coefficient of material # MATERIAL: ...   PROPERTIES:     ABSORPTION COEFFICIENT:       Absorption Coefficient = MatSpectralAbsorption(freq)       Option = Value     END   END  END```
Hope the above helps,

 Chris89 June 14, 2014 10:39

Hi Opaque,

Thank you very much for the response. I will implement the code and adjust it to my purposes.
I think this definition will work for the different spectra in absorption and emission.
But unfortunately I am still confused regarding the relation between the absorption coefficient with the absorptivity, reflectivity and transmissivity :confused:.
But I will work on this problem until I got it or one of you can explain this correlation :).

Regards,
Chris

 Opaque June 14, 2014 11:58

Another good book to read is Radiative Heat Transfer by Michael Modest. I think the 3rd edition is the most recent.

The vocabulary used in the radiation literature varies greatly between areas of application, and groups. Many times you must understand the meaning from the context.

Overall, you can assume all media absorb, emit and scatter radiative energy. Some media absorbs so much in a very short length that there is no point to model the volumetric effects, and they can be reduced to surface effects. One you are modeling them as surfaces, the interaction at surfaces are split into 2 types: self, and external. Self is emission, external is what happens to the incoming energy: reflected, absorbed, or transmitted. The last 3 must add up to the total incoming amount; therefore, their relative contribution can be represented as fractions: absortptiv-ity(tance or alpha), reflect-ivity(ance or rho), and transmit-ivity(ance or tau). They are not independent, and usually you only need to 1 of them:

- Opaque : tau = 0, rho = 1 - alpha
- Semi-transparent: alpha = 0, rho = 1 - tau
- Mirror: tau = 1, rho = alpha = 0
- Black : alpha = 1, rho = 0, tau = 0

For practical applications, the surface "properties" (no such a thing since they depend on surface quality as well as material) can be found on handbook, technical literature, or material providers.

The relation between the 3 above, and emissivity is only simple for the monochromatic (or spectral) case, where by Kirchoff law emissivity = absorptivity. Once the spectral approximations (such a gray) are used, their relationship is not straightforward, but for rough estimates you can just assume Kirchoff law always applies, and refine your approximation if needed.

When talking about non-gray (or spectral) modeling, there has been the tendency to use the word emittance for volumetric effects (which definitely depends on the absorption coefficient and other thermodynamic variables), but it is not the same as emissivity at a surface.

Hope the above helps,

 Chris89 June 15, 2014 11:30

Ok, so in my case I think the definition of an opaque boundary should fit because the transmissivity is negligible. But because this simulaion is for a space application with an absorptivity in the solar spectrum and an emissivity in the infrared spectrum it is unfortunately not possible for me to assume Kirchhoff's law of thermal radiation is valid.
I assume for the transfer mode "surface to surface" CFX calculates the solution with absorptivity=emissivity without any other specifications in the settings!? Therefore I think I have to work on the spectral approximation.

Thank you for the recommendation of the book. If the ordered book, which hopefully will be delivered next week, does not solve the problem I will order Radiative Heat Transfer :).

Best regards

 Chris89 June 19, 2014 12:15

Now I solved the problem with the help of your advices Opaque. Special thanks to you!!

Here the important informations of the output file for those who want to do the same.

Code:

``` LIBRARY:   CEL:     EXPRESSIONS:       SpectralProp = (prop1 * int1 + prop2 * int2 + prop3 * int3 + prop3 * \         int4)       Wavl1 = 4.E-01 [micron]       Wavl2 = 7.E-01 [micron]       Wavl3 = 1.E+02 [micron]       WavlHigh = 1.E+10 [micron]       WavlLow = 1.E-02 [micron]       flux3 = (rad1*int1+rad2*int2+rad3*int3+rad4*int4)       int1 = step(wavl1 -wavldim)       int2 = (step(wavl2 -wavldim)-step(wavl1-wavldim))       int3 = (step(wavl3 -wavldim)-step(wavl2-wavldim))       int4 = (step(wavlHigh-wavldim)-step(wavl3-wavldim))       prop1 = 0       prop2 = 0.093       prop3 = 0.015       rad1 = 0 [W/m^2]       rad2 = 1367 [W/m^2]       rad3 = 350 [W/m^2]       rad4 = 0 [W/m^2]       wavl1 = Wavl1*1[m^-1]       wavl2 = Wavl2*1[m^-1]       wavl3 = Wavl3*1[m^-1]       wavlHigh = WavlHigh*1[m^-1]       wavlLow = WavlLow*1[m^-1]       wavldim = wavelo*1[m^-1]     END   END   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: Aluminium     Material Group = CHT Solids,Particle Solids     Option = Pure Substance     Thermodynamic State = Solid     PROPERTIES:       Option = General Material       EQUATION OF STATE:         Density = 2702 [kg m^-3]         Molar Mass = 26.98 [kg kmol^-1]         Option = Value       END       SPECIFIC HEAT CAPACITY:         Option = Value         Specific Heat Capacity = 9.03E+02 [J kg^-1 K^-1]       END       REFERENCE STATE:         Option = Specified Point         Reference Specific Enthalpy = 0 [J/kg]         Reference Specific Entropy = 0 [J/kg/K]         Reference Temperature = 25 [C]       END       THERMAL CONDUCTIVITY:         Option = Value         Thermal Conductivity = 237 [W m^-1 K^-1]       END     END   END   MATERIAL: Polyimide     Material Group = User     Option = Pure Substance     Thermodynamic State = Solid     PROPERTIES:       Option = General Material       EQUATION OF STATE:         Density = 1.42 [g cm^-3]         Molar Mass = 34000 [g mol^-1]         Option = Value       END       SPECIFIC HEAT CAPACITY:         Option = Value         Specific Heat Capacity = 1090 [J kg^-1 K^-1]       END       THERMAL CONDUCTIVITY:         Option = Value         Thermal Conductivity = 225 [W m^-1 K^-1]       END     END   END  END  FLOW: Flow Analysis 1   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 = Steady State     EXTERNAL SOLVER COUPLING:       Option = None     END   END   DOMAIN: Platte     Coord Frame = Coord 0     Domain Type = Solid     Location = B276     BOUNDARY: Bestrahlte_Flaeche_Vakuum Side 2       Boundary Type = INTERFACE       Location = F279.276,F280.276,F281.276,F282.276,F283.276,F284.276       BOUNDARY CONDITIONS:         HEAT TRANSFER:           Option = Conservative Interface Flux         END       END     END     DOMAIN MODELS:       DOMAIN MOTION:         Option = Stationary       END       MESH DEFORMATION:         Option = None       END     END     SOLID DEFINITION: Solid 1       Material = Polyimide       Option = Material Library       MORPHOLOGY:         Option = Continuous Solid       END     END     SOLID MODELS:       HEAT TRANSFER MODEL:         Option = Thermal Energy       END       THERMAL RADIATION MODEL:         Number of Histories = 10000         Option = Monte Carlo         Radiation Transfer Mode = Surface to Surface         SCATTERING MODEL:           Option = None         END         SPECTRAL MODEL:           Option = Multiband           SPECTRAL BAND: Microwave             Option = Wavelength in Vacuum             Wavelength Lower Limit = Wavl3             Wavelength Upper Limit = WavlHigh           END           SPECTRAL BAND: Thermal             Option = Wavelength in Vacuum             Wavelength Lower Limit = Wavl2             Wavelength Upper Limit = Wavl3           END           SPECTRAL BAND: UV             Option = Wavelength in Vacuum             Wavelength Lower Limit = WavlLow             Wavelength Upper Limit = Wavl1           END           SPECTRAL BAND: Visible             Option = Wavelength in Vacuum             Wavelength Lower Limit = Wavl1             Wavelength Upper Limit = Wavl2           END         END       END     END   END   DOMAIN: Umgebung     Coord Frame = Coord 0     Domain Type = Fluid     Location = B103     BOUNDARY: Bestrahlte_Flaeche_Vakuum Side 1       Boundary Type = INTERFACE       Location = F218.103,F219.103,F220.103,F221.103,F222.103,F223.103       BOUNDARY CONDITIONS:         HEAT TRANSFER:           Option = Conservative Interface Flux         END         MASS AND MOMENTUM:           Option = No Slip Wall         END       END     END     BOUNDARY: Grenze       Boundary Type = OPENING       Location = F106.103,F107.103,F108.103,F109.103,F231.103       BOUNDARY CONDITIONS:         FLOW REGIME:           Option = Subsonic         END         HEAT TRANSFER:           Opening Temperature = 3 [K]           Option = Opening Temperature         END         MASS AND MOMENTUM:           Option = Entrainment           Relative Pressure = 0 [Pa]           PRESSURE OPTION:             Option = Opening Pressure           END         END         THERMAL RADIATION:           Option = Local Temperature         END       END     END     BOUNDARY: Strahlung       Boundary Type = OPENING       Location = F230.103       BOUNDARY CONDITIONS:         FLOW REGIME:           Option = Subsonic         END         HEAT TRANSFER:           Opening Temperature = 3 [K]           Option = Opening Temperature         END         MASS AND MOMENTUM:           Option = Entrainment           Relative Pressure = 0 [Pa]           PRESSURE OPTION:             Option = Opening Pressure           END         END         THERMAL RADIATION:           Option = Local Temperature         END       END       BOUNDARY SOURCE:         SOURCES:           RADIATION SOURCE: Radiation Source 1             Option = Directional Radiation Flux             Radiation Flux = flux3             DIRECTION:               Option = Cartesian Components               Unit Vector X Component = 0               Unit Vector Y Component = 0               Unit Vector Z Component = 1             END           END         END       END     END     DOMAIN MODELS:       BUOYANCY MODEL:         Option = Non Buoyant       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:         Number of Histories = 10000         Option = Monte Carlo         Radiation Transfer Mode = Surface to Surface         SCATTERING MODEL:           Option = None         END         SPECTRAL MODEL:           Option = Multiband           SPECTRAL BAND: Microwave             Option = Wavelength in Vacuum             Wavelength Lower Limit = Wavl3             Wavelength Upper Limit = WavlHigh           END           SPECTRAL BAND: Thermal             Option = Wavelength in Vacuum             Wavelength Lower Limit = Wavl2             Wavelength Upper Limit = Wavl3           END           SPECTRAL BAND: UV             Option = Wavelength in Vacuum             Wavelength Lower Limit = WavlLow             Wavelength Upper Limit = Wavl1           END           SPECTRAL BAND: Visible             Option = Wavelength in Vacuum             Wavelength Lower Limit = Wavl1             Wavelength Upper Limit = Wavl2           END         END       END       TURBULENCE MODEL:         Option = Laminar       END     END   END   DOMAIN INTERFACE: Bestrahlte_Flaeche_Vakuum     Boundary List1 = Bestrahlte_Flaeche_Vakuum Side 1     Boundary List2 = Bestrahlte_Flaeche_Vakuum Side 2     Interface Type = Fluid Solid     INTERFACE MODELS:       Option = General Connection       FRAME CHANGE:         Option = None       END       HEAT TRANSFER:         Option = Conservative Interface Flux         HEAT TRANSFER INTERFACE MODEL:           Option = None         END       END       PITCH CHANGE:         Option = None       END       THERMAL RADIATION:         Diffuse Fraction = 0         Emissivity = SpectralProp         Option = Opaque       END     END     MESH CONNECTION:       Option = GGI     END   END   OUTPUT CONTROL:     RESULTS:       File Compression Level = Default       Option = Standard     END   END   SOLVER CONTROL:     ADVECTION SCHEME:       Option = High Resolution     END     CONVERGENCE CONTROL:       Length Scale Option = Aggressive       Maximum Number of Iterations = 2000       Minimum Number of Iterations = 10       Solid Timescale Control = Auto Timescale       Solid Timescale Factor = 2       Timescale Control = Auto Timescale       Timescale Factor = 1.5     END     CONVERGENCE CRITERIA:       Conservation Target = 0.01       Residual Target = 1.E-4       Residual Type = RMS     END     DYNAMIC MODEL CONTROL:       Global Dynamic Model Control = On     END     EQUATION CLASS: energy       CONVERGENCE CONTROL:         Length Scale Option = Aggressive         Timescale Control = Auto Timescale         Timescale Factor = 1.5       END       CONVERGENCE CRITERIA:         Conservation Target = 0.01         Residual Target = 1.0E-4         Residual Type = RMS       END     END     THERMAL RADIATION CONTROL:       Iteration Interval = 5       COARSENING CONTROL:         Target Coarsening Rate = 4       END     END   END   EXPERT PARAMETERS:     solve fluids = f     solve radiation = t   END  END  COMMAND FILE:   Version = 14.5   Results Version = 14.5.7  END  SIMULATION CONTROL:   EXECUTION CONTROL:     EXECUTABLE SELECTION:       Double Precision = On     END     INTERPOLATOR STEP CONTROL:       Runtime Priority = Standard       MEMORY CONTROL:         Memory Allocation Factor = 1.0       END     END     PARALLEL HOST LIBRARY:       HOST DEFINITION: ry000391         Remote Host Name = RY-000391         Host Architecture String = winnt-amd64         Installation Root = C:\Program Files\ANSYS1457\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         Partition Weight Factors = 0.50000, 0.50000       END     END     RUN DEFINITION:       Run Mode = Full       Solver Input File = Fluiddynamik CFX.def     END     SOLVER STEP CONTROL:       Runtime Priority = Standard       MEMORY CONTROL:         Memory Allocation Factor = 1.0       END       PARALLEL ENVIRONMENT:         Number of Processes = 2         Start Method = Platform MPI Local Parallel         Parallel Host List = ry000391*2       END     END   END  END```

I have just one more question :). I would like to visualize the rays which will be reflected. Is that possible in CFD-Post? Particle tracking is possible and maybe also ray tracking? I have to use Monte Carlo, so ray tracing with the DTM would not be possible.

Best regards,
Chris

 Opaque June 19, 2014 14:12

Unfortunately, the rays used for the radiation modeling cannot be visualized at all. You can visualize rays for a radiometer though by setting the Diagnostic Output level to a value larger than 0. A .csv file will be written for every radiometer with diagnostic output level greater than 0. Such file contain the rays leaving a radiometer including their reflections (so you can track the original source of the ray).

To visualize the rays, you create a polyline in CFD-Post, select the option From File, and apply.

If I recall correctly, a diagnostic output of 1 gives a single .csv file. For value of 2, you can get a .csv per time step. For non-deforming meshes or non-conditional domain interfaces, those .csv files will be the same. so you can just 1.

Hope the above helps,

 hrsq June 19, 2014 18:06

Could you please tell me how I can model pure radiation without convection or conduction in the domain? I want to model radiation in vacuum.

 ghorrocks June 19, 2014 19:49

Use the expert parameters to turn the flow solver and any other solvers you do not want off.

 hrsq June 19, 2014 20:05

In my problem, I have different solids and fluid domains and I have to solve energy and fluid equation in them except one of them which I want to solve only radiation heat transfer. Therefore, if I turn off the flow and energy equations from expert parameters, the energy and flow will not solve in other domains.

 ghorrocks June 21, 2014 06:54

Then I would make your vacuum a solid domain, and use a solid with a very low (but not zero) conductivity.

 hrsq June 21, 2014 15:46

Thank you very much ghorrocks.

 Chris89 August 13, 2014 08:17

Hello again :),
I have a further question regarding the radiation modeling. I want to analyze a surface with a wrinkle in vacuum. Nearly the same conditions and properties as for the last simulation (surface to surface, Monte Carlo method, different spectra for absorption and emission, interface between the surface and the vacuum). Since the incoming directional radiation flux reflects, hot spots should occur. The problem is the definition of the vacuum and therefore the convergence. If the fluid solver will be turned off, the surface of the vacuum for the interface has still the properties of the fluid and therefore the conductivity, which leads to wrong results. For these settings, the solver converges. If I create another material for the vacuum with low conductivity, low density and high viscosity as ghorrocks recommended in another thread regarding the vacuum definition, the results after 300 iterations (about 3 hours) seem to be correct but the solver does not converges. Is there a possibility to adjust the convergence criteria for the low conductivity or is there another possibility for the definition of a vacuum in CFX? Is CFX generally suitable for such radiation problems with a vacuum?

Best regards,
Chris

 ghorrocks August 13, 2014 19:44

No, my recommendation for your vacuum material is to make it a solid domain. Then you do not need to worry about any fluid properties. Also low conductivity is required, but high density might be more numerically stable.

 Chris89 August 14, 2014 05:42

I tried this option for the vacuum definition, too. The problem is the definition of the surfaces of the vacuum domain. I have to set an emissivity and either the surfaces absorb and emit the irradiation from the wrinkle surface for a value of "1" or they reflect the incoming energy, which comes from the wrinkle surface. This leads unfortunately also to wrong results for the temperature distribution due to the radiation from the surrounding "surfaces" of the vacuum.

 ghorrocks August 14, 2014 07:39

I have no idea what you are talking about. I am not an expert on radiation modelling but my understanding is that the same options are available for a solid domain as for a fluid domain. So whatever radiation boundary conditions you defined for the fluid domain can be set for the solid domain.

So whatever settings you have put on the fluid domain you can put them on the solid domain as well.

 Chris89 August 14, 2014 08:01

If I define the vacuum as a solid domain, I can either choose wall or symmetry for the boundaries. For a wall, I have to set an emissivity which leads to the mentioned problems. If I define the vacuum as a fluid domain, I can define the boundaries as openings and therefore no radiation will be absorbed, reflected or emitted, only transmitted. That is what I want but it is not possible for a solid domain. Or is there any possibility to define a transmissivity of 100% for a surface of a solid domain?

 ghorrocks August 14, 2014 08:33

Can you use a solid domain with wall boundaries where the temperature of the wall is set to almost absolute zero (like 1 [K])? Then the wall will absorb radiation but not radiate or reflect.

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