CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

[CFX] How to avoid negative temperatures?

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 14, 2010, 16:45
Default [CFX] How to avoid negative temperatures?
  #1
Senior Member
 
Jack
Join Date: Mar 2009
Posts: 106
Rep Power: 16
rogbrito is an unknown quantity at this point
Hi folks,

I´m having negative temperatures like -6.10352E-06 [ºC], using ANSYS CFX 12, as a lower limit, with these boundary conditions (please, see below). Is there anything wrong with my set-up in ANSYS CFX Pre 12.0? The files were stored in http://rapidshare.com/files/35064994...tures.rar.html or at http://www.4shared.com/file/22215781..._temperat.html. The initial temperatures were 0.0 [ºC] and the heat flux condition was only 1.0 [W m^-2]. The computational domain was a solid.


MATERIAL: k10
Material Group = CHT Solids,Particle Solids
Option = Pure Substance
Thermodynamic State = Solid
PROPERTIES:
Option = General Material
EQUATION OF STATE:
Density = 14900 [kg m^-3]
Molar Mass = 1.0 [kg kmol^-1]
Option = Value
END
SPECIFIC HEAT CAPACITY:
Option = Value
Specific Heat Capacity = 332.94 [J kg^-1 K^-1]
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 43.1 [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 = Transient
EXTERNAL SOLVER COUPLING:
Option = None
END
INITIAL TIME:
Option = Automatic with Value
Time = 0 [s]
END
TIME DURATION:
Option = Total Time
Total Time = 110 [s]
END
TIME STEPS:
Option = Timesteps
Timesteps = 0.22 [s]
END
END
DOMAIN: metalduro
Coord Frame = Coord 0
Domain Type = Solid
Location = METAL
BOUNDARY: conv
Boundary Type = WALL
Location = SURFACE_ INFERIOR,SURFACE_ LATERAIS,SURFACE_ SUPERIOR
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Adiabatic
END
END
END
BOUNDARY: fluxo
Boundary Type = WALL
Location = SURFACE_ FLUXO
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Heat Flux in = 1 [W m^-2]
Option = Heat Flux
END
END
END
DOMAIN MODELS:
DOMAIN MOTION:
Option = Stationary
END
MESH DEFORMATION:
Option = None
END
END
INITIALISATION:
Option = Automatic
INITIAL CONDITIONS:
TEMPERATURE:
Option = Automatic with Value
Temperature = 0 [C]
END
END
END
SOLID DEFINITION: k10
Material = k10
Option = Material Library
MORPHOLOGY:
Option = Continuous Solid
END
END
SOLID MODELS:
HEAT TRANSFER MODEL:
Option = Thermal Energy
END
THERMAL RADIATION MODEL:
Option = None
END
END
END
OUTPUT CONTROL:
MONITOR OBJECTS:
MONITOR BALANCES:
Option = Full
END
MONITOR FORCES:
Option = Full
END
MONITOR PARTICLES:
Option = Full
END
MONITOR POINT: Monitor Point 1
Cartesian Coordinates = 0 [mm], 3.95 [mm], 2.129 [mm]
Option = Cartesian Coordinates
Output Variables List = Temperature
END
MONITOR RESIDUALS:
Option = Full
END
MONITOR TOTALS:
Option = Full
END
END
RESULTS:
File Compression Level = Default
Option = Standard
END
TRANSIENT RESULTS: Transient Results 1
File Compression Level = Default
Include Mesh = On
Option = Selected Variables
Output Variables List = Temperature,Total Temperature
OUTPUT FREQUENCY:
Option = Time Interval
Time Interval = 0.22 [s]
END
END
END
SOLVER CONTROL:
ADVECTION SCHEME:
Option = High Resolution
END
CONVERGENCE CONTROL:
Maximum Number of Coefficient Loops = 100
Minimum Number of Coefficient Loops = 1
Timescale Control = Coefficient Loops
END
CONVERGENCE CRITERIA:
Residual Target = 0.000001
Residual Type = RMS
END
TRANSIENT SCHEME:
Option = Second Order Backward Euler
TIMESTEP INITIALISATION:
Option = Automatic
END
END
END
END
COMMAND FILE:
Version = 12.0.1
Results Version = 12.0
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: unifei
Host Architecture String = winnt-amd64
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
Partition Weight Factors = 0.250, 0.250, 0.250, 0.250
END
END
RUN DEFINITION:
Run Mode = Full
Solver Input File = \
C:\0_IHTC_2010_04_02_2010\05_ferramentasemrevest\0 1semrevferramenta1s\
emfuro.def
END
SOLVER STEP CONTROL:
Runtime Priority = High
EXECUTABLE SELECTION:
Double Precision = On
END
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
PARALLEL ENVIRONMENT:
Number of Processes = 4
Start Method = HP MPI Local Parallel
Parallel Host List = unifei*4
END
END
END
END

Thanks for helping me!
rogbrito is offline   Reply With Quote

Old   February 14, 2010, 18:40
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,854
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
This sounds like a normal boundedness problem. I think "Computational Fluid Dynamics" by Roache has a discussion about this.

Have you done a mesh, time step and convergence sensitivity check? If not then do it - these are the sort of problems which come up when you take short-cuts.
ghorrocks is offline   Reply With Quote

Old   February 15, 2010, 06:50
Default
  #3
Senior Member
 
Jack
Join Date: Mar 2009
Posts: 106
Rep Power: 16
rogbrito is an unknown quantity at this point
Is this book: Roache, P. J. Computational Fluid Dynamics. Albuquerque: Hermosa, 1972. 446 p.?

How to do that (convergence sensitivity check)?

Rogerio

Quote:
Originally Posted by ghorrocks View Post
This sounds like a normal boundedness problem. I think "Computational Fluid Dynamics" by Roache has a discussion about this.

Have you done a mesh, time step and convergence sensitivity check? If not then do it - these are the sort of problems which come up when you take short-cuts.
rogbrito is offline   Reply With Quote

Old   February 15, 2010, 06:59
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,854
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Yes, that's the book. It is the classic reference text for things relating to CFD accuracy. It explains the mesh sensitivity issue in great detail. But the simple version is you keep refining the mesh until the output parameter you are interested in converges to an accuracy tolerance which is acceptable for your analysis.
ghorrocks is offline   Reply With Quote

Reply


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
negative element volume (CFX-10.0) CFDworker CFX 8 September 27, 2011 19:16
[blockMesh] BlockMesh FOAM warning gaottino OpenFOAM Meshing & Mesh Conversion 7 July 19, 2010 15:11
[ICEM] Hex refinement negative quality afterwards Anorky ANSYS Meshing & Geometry 8 March 22, 2010 04:25
Contour plot with negative velocity J CFX 11 November 3, 2008 17:46
[blockMesh] Axisymmetrical mesh Rasmus Gjesing (Gjesing) OpenFOAM Meshing & Mesh Conversion 10 April 2, 2007 15:00


All times are GMT -4. The time now is 19:41.