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February 14, 2010, 16:45 |
[CFX] How to avoid negative temperatures?
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#1 |
Senior Member
Jack
Join Date: Mar 2009
Posts: 106
Rep Power: 16 |
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! |
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February 14, 2010, 18:40 |
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#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,852
Rep Power: 144 |
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. |
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February 15, 2010, 06:50 |
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#3 | |
Senior Member
Jack
Join Date: Mar 2009
Posts: 106
Rep Power: 16 |
Is this book: Roache, P. J. Computational Fluid Dynamics. Albuquerque: Hermosa, 1972. 446 p.?
How to do that (convergence sensitivity check)? Rogerio Quote:
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February 15, 2010, 06:59 |
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#4 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,852
Rep Power: 144 |
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.
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