Closed Domain Buoyancy Flow Problem
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I am modelling the cooling of Nitrogen gas by a cryocooler. The cryocooler body has not been modelled separately. Its been considered as a part of outer Stainless Steel vessel. The fluid domain is closed and the flow occurs only due to the density variation of the fluid. The gas is contained in a Stainless Steel vessel. I have made half geometry and given symmetry condition to reduce the computation time. The cold end of the cryocooler is at 150 K temperature. The outer walls are exposed to atmosphere at 300 K temperature. The geometry is 3D and the cut section is shown in attachment. Meshing was done in ICEM CFD. (Delaunay mesh with 3 prism layers).
I have the experimental data with me regarding the temperature at certain points and I need to verify the same using the simulations. But the problem is that I dont seem to observe any temperature field development in the fluid domain after running the simulation. The residuals also dont go below 1E4. I am attaching the images of geometry, mesh, results, residuals and also CCL. Kindly help me. LIBRARY: MATERIAL: Air Ideal Gas Material Description = Air Ideal Gas (constant Cp) Material Group = Air Data,Calorically Perfect Ideal Gases Option = Pure Substance Thermodynamic State = Gas PROPERTIES: Option = General Material EQUATION OF STATE: Molar Mass = 28 [kg kmol^1] Option = Ideal Gas 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 = 1.831E05 [kg m^1 s^1] Option = Value END THERMAL CONDUCTIVITY: Option = Value Thermal Conductivity = 2.61E2 [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 END END MATERIAL: Steel Material Group = CHT Solids, Particle Solids Option = Pure Substance Thermodynamic State = Solid PROPERTIES: Option = General Material EQUATION OF STATE: Density = 7854 [kg m^3] Molar Mass = 55.85 [kg kmol^1] Option = Value END SPECIFIC HEAT CAPACITY: Option = Value Specific Heat Capacity = 4.34E+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 = 60.5 [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: Fluid Coord Frame = Coord 0 Domain Type = Fluid Location = FLUID BOUNDARY: Cold End Fluid Boundary Type = WALL Location = COLD_END_1 BOUNDARY CONDITIONS: HEAT TRANSFER: Fixed Temperature = 151.47 [K] Option = Fixed Temperature END MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END BOUNDARY: Default Fluid Solid Interface Side 1 Boundary Type = INTERFACE Location = CRYO_WALLS_1,FLUID_BOTTOM_2,FLUID_WALL_2,Primitive \ 2D,Primitive 2D B BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Conservative Interface Flux END MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END BOUNDARY: Fluid Symmetry Boundary Type = SYMMETRY Location = FLUID_SYMMETRY END DOMAIN MODELS: BUOYANCY MODEL: Buoyancy Reference Density = 1.69335 [kg m^3] Gravity X Component = 0 [m s^2] Gravity Y Component = 9.81 [m s^2] Gravity Z Component = 0 [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 Ideal Gas Option = Material Library MORPHOLOGY: Option = Continuous Fluid END END FLUID MODELS: COMBUSTION MODEL: Option = None END HEAT TRANSFER MODEL: Option = Total Energy END THERMAL RADIATION MODEL: Option = None END TURBULENCE MODEL: Option = SST BUOYANCY TURBULENCE: Option = None END END TURBULENT WALL FUNCTIONS: High Speed Model = Off Option = Automatic 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 [bar] END TEMPERATURE: Option = Automatic with Value Temperature = 300 [K] END TURBULENCE INITIAL CONDITIONS: Option = Medium Intensity and Eddy Viscosity Ratio END END END END DOMAIN: Metal Coord Frame = Coord 0 Domain Type = Solid Location = STEEL BOUNDARY: Cold End Metal Boundary Type = WALL Location = COLD_END_2 BOUNDARY CONDITIONS: HEAT TRANSFER: Fixed Temperature = 151.47 [K] Option = Fixed Temperature END END END BOUNDARY: Default Fluid Solid Interface Side 2 Boundary Type = INTERFACE Location = CRYO_WALLS_2,FLUID_BOTTOM_1,FLUID_WALL_1,Primitive 2D \ A,Primitive 2D C BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Conservative Interface Flux END END END BOUNDARY: Metal Symmetry Boundary Type = SYMMETRY Location = METAL_SYMMETRY END BOUNDARY: Outer Walls Boundary Type = WALL Location = OUTER_WALLS BOUNDARY CONDITIONS: HEAT TRANSFER: Fixed Temperature = 300 [K] Option = Fixed Temperature 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 = 300 [K] END END END SOLID DEFINITION: Solid 1 Material = Steel 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 DOMAIN INTERFACE: Default Fluid Solid Interface Boundary List1 = Default Fluid Solid Interface Side 1 Boundary List2 = Default Fluid Solid Interface 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 END MESH CONNECTION: Option = Automatic END END OUTPUT CONTROL: RESULTS: File Compression Level = Default Option = Standard END END SOLVER CONTROL: Turbulence Numerics = First Order ADVECTION SCHEME: Option = Upwind END CONVERGENCE CONTROL: Length Scale Option = Conservative Maximum Number of Iterations = 5000 Minimum Number of Iterations = 1 Solid Timescale Control = Auto Timescale Timescale Control = Auto Timescale Timescale Factor = 1.0 END CONVERGENCE CRITERIA: Residual Target = 1.E4 Residual Type = RMS END DYNAMIC MODEL CONTROL: Global Dynamic Model Control = Yes END END END COMMAND FILE: Version = 15.0 Results Version = 15.0 END SIMULATION CONTROL: EXECUTION CONTROL: EXECUTABLE SELECTION: Double Precision = Off END INTERPOLATOR STEP CONTROL: Runtime Priority = Standard DOMAIN SEARCH CONTROL: Bounding Box Tolerance = 0.01 END INTERPOLATION MODEL CONTROL: Enforce Strict Name Mapping for Phases = Off Mesh Deformation Option = Automatic Particle Relocalisation Tolerance = 0.01 END MEMORY CONTROL: Memory Allocation Factor = 1.0 END END PARALLEL HOST LIBRARY: HOST DEFINITION: profmdatreypc Remote Host Name = PROFMDATREYPC Host Architecture String = winntamd64 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 = kway Option = MeTiS Partition Size Rule = Automatic END END RUN DEFINITION: Run Mode = Full Solver Input File = E:\Prathamesh\Cavity\Simulation 94.2.def INITIAL VALUES SPECIFICATION: INITIAL VALUES CONTROL: Continue History From = Initial Values 1 Use Mesh From = Solver Input File END INITIAL VALUES: Initial Values 1 File Name = E:\Prathamesh\Cavity\Simulation 94.2_002.res Option = Results File END END 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 
FAQ: http://www.cfdonline.com/Wiki/Ansys...gence_criteria
Also, I suspect you need to run this model for longer physical time to get the temperature field to develop. 
Thanks ghorrocks! I will try to implement your suggestions and will report back which works.:)

I was doing a pretty stupid mistake. The mesh was not scaled properly. It was created in millimetres but imported as metres. Thats why the temperature field was not developing.

4 Attachment(s)
Now that the temperature field is developing. There is one more problem. The geometry and boundary conditions are axis symmetric. I have converged the solutions till 1e5. But the temperature field developed is not axis symmetric. It should be symmetric . I dont know what is causing this. I tried different mesh size to check whether it was mesh size issue. I also switched from delaunay mesh to octree mesh to check whether that affects. The developed temperature profile shifts randomly to left or right as shown in attached pictures. Kindly help me how do I get it to be close to symmetric.

Quote:
The images you show are the flow field I would expect in this configuration. It means that the flow is 3D transient, and not 2D axisymmetric steady state as the geometry might suggest. 
Thanks Glen for your quick reply!:) Maybe my expectations for the field to be symmetrical are wrong. I have modelled the problem as 3D steady case. Now I will go for 3D Transient and see what happens to the field with respect to time. I will reply back what happens if it helps others.

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