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September 6, 2009, 06:37 |
natural convection
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#1 |
Member
mohsen
Join Date: Mar 2009
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hi
how can simulate natural convection of air in closed room that its floor has heated at constant temprature? |
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September 6, 2009, 07:56 |
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#2 |
Super Moderator
Glenn Horrocks
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Have a look in the tutorial manuals for examples of how to model natural convection.
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September 6, 2009, 09:18 |
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#3 |
Senior Member
Jack
Join Date: Mar 2009
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Please take a look on Tutorial 17.
http://www.4shared.com/file/72198900...tionpart1.html http://www.4shared.com/file/72199871...tionpart2.html Or these files (to download): http://www.4shared.com/file/52194930...rogeriow1.html http://www.4shared.com/file/52205921...rogeriow2.html http://www.4shared.com/file/52185334...rogeriow3.html with kind regards, Rogerio. |
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September 7, 2009, 08:42 |
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#4 | |
Member
mohsen
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Quote:
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September 12, 2009, 05:08 |
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#5 |
Member
mohsen
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why temperature contour is this?
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September 12, 2009, 08:37 |
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#6 |
Super Moderator
Glenn Horrocks
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Without a description of what you are doing there is no way anybody can help you. Steady or transient? Is it converged? (almost certainly it is not converged) Have you checked the physics, eg that gravity and buoyancy is correctly set?
The variations you are seeing are 0.1K, which are pretty small. What is the driving temperatures? |
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February 23, 2011, 09:56 |
Natural Convection Convergence Problem
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#7 |
Senior Member
Attesz
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Location: Munich
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Hi CFX users,
I'm simulating a heat convection in a room. There is a stove in the middle, which recirculates and heats the air. My solution after some checks does not converge fully. Of course, I'm using Buoyancy Model, the directions of gravity is set right. I've defned an inlet on the stove with a boundary energy source of 4kW, and a massflow of 0.06 kg/s. I'v defined at the bottom of the stove an outlet with average static pressure of 0 Pa (relative to 1 atm reference pressure). I'm using SST k-w model, Total Energy/ Thermal Energy heat transfer models. Both Automatic Timescale and Physical Timescal don't have a significant effect for the convergence. temp.jpg imbalances.jpg domain.jpg Thanks in advance for any suggestions! I post the out file: +--------------------------------------------------------------------+ 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 = 28.96 [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 = 1.831E-05 [kg m^-1 s^-1] Option = Value END THERMAL CONDUCTIVITY: Option = Value Thermal Conductivity = 2.61E-2 [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 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: Legter Coord Frame = Coord 0 Domain Type = Fluid Location = LEGTER BOUNDARY: Furdo_falak Boundary Type = WALL Location = FURDO BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Adiabatic END MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END BOUNDARY: Inlet Boundary Type = INLET Location = INLET BOUNDARY CONDITIONS: FLOW DIRECTION: Option = Normal to Boundary Condition END FLOW REGIME: Option = Subsonic END HEAT TRANSFER: Option = Total Temperature Total Temperature = volumeAve(Total Temperature )@Legter END MASS AND MOMENTUM: Mass Flow Rate = 0.06 [kg s^-1] Option = Mass Flow Rate END TURBULENCE: Option = Medium Intensity and Eddy Viscosity Ratio END END BOUNDARY SOURCE: SOURCES: EQUATION SOURCE: energy Option = Total Source Total Source = 4000 [kg m^2 s^-3] END END END END BOUNDARY: Kazan_falak Boundary Type = WALL Location = KAZAN_FALAK BOUNDARY CONDITIONS: HEAT TRANSFER: Option = Adiabatic END MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END BOUNDARY: Oldalfalak Boundary Type = WALL Location = FALAK BOUNDARY CONDITIONS: HEAT TRANSFER: Heat Transfer Coefficient = 2 [W m^-2 K^-1] Option = Heat Transfer Coefficient Outside Temperature = -10 [C] END MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END BOUNDARY: Outlet Boundary Type = OUTLET Location = OUTLET BOUNDARY CONDITIONS: FLOW REGIME: Option = Subsonic END MASS AND MOMENTUM: Option = Average Static Pressure Pressure Profile Blend = 0.05 Relative Pressure = 0 [Pa] END PRESSURE AVERAGING: Option = Average Over Whole Outlet END END END BOUNDARY: Padlo Boundary Type = WALL Location = PADLO BOUNDARY CONDITIONS: HEAT TRANSFER: Heat Transfer Coefficient = 1 [W m^-2 K^-1] Option = Heat Transfer Coefficient Outside Temperature = 10 [C] END MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END BOUNDARY: Plafon Boundary Type = WALL Location = PLAFON BOUNDARY CONDITIONS: HEAT TRANSFER: Heat Transfer Coefficient = 2 [W m^-2 K^-1] Option = Heat Transfer Coefficient Outside Temperature = 10 [C] END MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END DOMAIN MODELS: BUOYANCY MODEL: Buoyancy Reference Density = 1.2 [kg m^-3] Gravity X Component = 0 [m s^-2] Gravity Y Component = 0 [m s^-2] Gravity Z Component = -9.8182 [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 = Production and Dissipation END END TURBULENT WALL FUNCTIONS: 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 = 0 [Pa] END TEMPERATURE: Option = Automatic with Value Temperature = 19 [C] END TURBULENCE INITIAL CONDITIONS: Option = Low Intensity and Eddy Viscosity Ratio END END END END OUTPUT CONTROL: MONITOR OBJECTS: MONITOR BALANCES: Option = Full END MONITOR FORCES: Option = Full END MONITOR PARTICLES: Option = Full END MONITOR POINT: Homerseklet Cartesian Coordinates = 2.5 [m], 5 [m], 1.5 [m] Domain Name = Legter 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 END SOLVER CONTROL: Turbulence Numerics = High Resolution ADVECTION SCHEME: Option = High Resolution END CONVERGENCE CONTROL: Maximum Number of Iterations = 1000 Minimum Number of Iterations = 1 Physical Timescale = 1 [s] Timescale Control = Physical Timescale END CONVERGENCE CRITERIA: Residual Target = 1e-04 Residual Type = MAX END DYNAMIC MODEL CONTROL: Global Dynamic Model Control = Yes END END END COMMAND FILE: Version = 12.1 Results Version = 12.1 END SIMULATION CONTROL: EXECUTION CONTROL: EXECUTABLE SELECTION: Double Precision = Off END INTERPOLATOR STEP CONTROL: Runtime Priority = Standard MEMORY CONTROL: Memory Allocation Factor = 2 END END PARALLEL HOST LIBRARY: HOST DEFINITION: *********** Host Architecture String = linux-amd64 Installation Root = ****************** 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 = 2 END PARTITIONING TYPE: MeTiS Type = k-way Option = MeTiS Partition Size Rule = Automatic Partition Weight Factors = 0.12500, 0.12500, 0.12500, 0.12500, \ 0.12500, 0.12500, 0.12500, 0.12500 END END RUN DEFINITION: Run Mode = Full Solver Input File = \ /************************m0_06_4kW_totalenergy.def INITIAL VALUES SPECIFICATION: INITIAL VALUES CONTROL: Continue History From = Initial Values 1 Use Mesh From = Initial Values END INITIAL VALUES: Initial Values 1 File Name = \ ****************************szt_m0_06_4kW_001.res Option = Results File END END END SOLVER STEP CONTROL: Runtime Priority = Standard MEMORY CONTROL: Memory Allocation Factor = 2 END PARALLEL ENVIRONMENT: Number of Processes = 8 Start Method = HP MPI Local Parallel Parallel Host List = ******** END END END END Last edited by Attesz; February 23, 2011 at 10:13. |
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February 23, 2011, 16:52 |
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#8 |
Super Moderator
Glenn Horrocks
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I do not think your plan of using an inlet and an outlet with a heat source is numerically stable. Especially as you are just using the average temperature of the whole domain. I would either use a periodic pair with a heat source or join the inlet and outlet up and use a heat and momentum source.
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February 24, 2011, 05:10 |
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#9 | |||
Senior Member
Attesz
Join Date: Mar 2009
Location: Munich
Posts: 368
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Quote:
Quote:
Quote:
Momentum source can be defined only in subdomains. I've planned to do this but I have to model a little domain in the stove for the inlet and an other for the outlet or am I wrong? In this case I have to define the opposite value of the kinetic energy on the inlet/outlet sides, or what do you mean to join the inlet and outlet up? On that boundaries, only heat source can be defined. Or should I define Continuity Source with temperatures velocities etc? Thanks for wasting your time for this Best Regards, Attila |
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February 24, 2011, 19:13 |
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#10 | |
Super Moderator
Glenn Horrocks
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Quote:
A periodic pair is a type of interface condition. Look under interfaces. You have the wrong idea on sources. A source is simply where you add some momentum or heat to a region. You can use this to drive flow or heat it up. You do not define inlets and outlets. I think for what you are trying to do the periodic pair is a god approach. Try that one first before a momentum source. |
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February 25, 2011, 05:25 |
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#11 |
Senior Member
Attesz
Join Date: Mar 2009
Location: Munich
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Okay I know Periodic Interface types. The heater has a fan at the inlet, so I've defined energy source and continuity source with 0 mass flow and specified velocity at the periodic side corresponding to the inlet. Am I correct doing this?
Thanks in advance! cont.jpg Last edited by Attesz; February 25, 2011 at 09:32. |
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