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Iteration output

  • What are those iteration records?
  • Let us take a closer look at e.g. time 0.49 s:


    Time = 0.49
  • Time means physical time in seconds


    Courant Number mean: 0.222158 max: 0.852134
  • Courant Number mean/max are mean/maximal CFL number for convergence condition. Roughly speaking, it can be ralated to the well known formula:


    $\displaystyle CFL = \frac{\vert U\vert \Delta t}{\Delta x}$(3.2)


  • Particularly, OpenFOAM uses the following formula:


    $\displaystyle CFL = \frac{\Delta t}{2 V} \sum_{i\in\text{Cell Faces}}\vert\phi_i\vert\,,$(3.3)


    where $ V$ is a cell volume, $ \phi_i$ is face volumteric flux and summation goes over each cell face
    smoothSolver:  Solving for Ux, Initial residual = 2.59115e-07, Final residual = 2.59115e-07, No Iterations 0
  • smoothSolver is linear system solver for U with smoother.
  • Linear system solver set-up is in file fvSolution
  • Solver decomposes velocity vector into components and solves them separately
  • Initial residual is a measure of stability of solution with respect to previous iteration.
  • Final residual is a residual when linear system solver has finished.
  • No Iterations is number of iterations of linear system solver


    DICPCG:  Solving for p, Initial residual = 8.63844e-07, Final residual = 8.63844e-07, No Iterations 0

  • DICPCG is linear system solver used for pressure (Diagonal Incomplete Cholesky Preconditioned Conjugate Gradient)
  • In PISO algorithm the pressure computation is repeated according to number of correctors nCorrectors


    time step continuity errors : sum local = 6.11228e-09, global = 1.51821e-18, cumulative = 1.09644e-17
  • time step continuity errors is continuity equation error, basically it is a sum of fluxes over all mesh faces and ideally should be zero


    ExecutionTime = 0.19 s  ClockTime = 1 s
  • ExecutionTime is the time elapsed since start of the computation.
  • ClockTime is the time spent on processor(s).

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TCFD\textregistered – Configuration File Options

The TCFD file produced by TCFDSource has mostly the *.tcfd extension. It is a human-readable plain text file where every line falls into one of the following categories:
  • Empty line.
  • Comment, introduced by a hash sign (`#’).
  • Keyword-values pair.
The keywords are strings uninterrupted by a whitespace character. They contain only alphanumerical characters, numbers, dashes and underscores. Every keyword can be generally set to an arbitrary number of values. A value is a string uninterrupted by a whitespace character. Some keywords have a special structure “N$ \_$something”, where “N” is a positive number. These are used to assign properties to individual components, speedlines, working points, post-processing modes etc. This nest to deeper levels, resulting in keywords like “X$ \_$keywd1-Y$ \_$keywd2-Z$ \_$keywd3”. A complete list of recognized keywords, together with some sample values and explanation, is presented in the table at the end of this chapter. Both the UNIX-like (LF) and Windows (CR+LF) line endings are supported on both UNIX-like and Windows operating systems. Some numerical values in the TCFD file can bear a user-selectable physical unit. This is always indicated in the keyword table as “Selectable unit”. Table [*] summarizes the available units. The unit is appended to the numerical value using an underscore. So, for instance, one millimeter is denoted as 1$ \_$mm or 0.1$ \_$cm or 0.001$ \_$m. While the temperature quantities allow the use of the degree symbol, e.g. 100$ \_^\circ$C, it is recognized in UTF-8 encoding only (degree symbol is not part of ASCII). This is natural in modern Unix-like operating systems, but we recommend sticking to 1$ \_$C in Windows. When a number is used without unit suffix, it is assumed that it is in SI (i.e. the metric system).
Table: Physical units recognized by CFD Processor.
Quantity Symbol Known units Suffixes
time $ t$ seconds (SI) $ \_$s, $ \_$sec, $ \_$seconds
minutes $ \_$m, $ \_$min, $ \_$minutes
hours $ \_$h, $ \_$hrs, $ \_$hours
revolutions $ \_$revolutions
length $ l$ metres (SI) $ \_$m
decimetres $ \_$dm
centimetres $ \_$cm
millimetres $ \_$mm
inches $ \_$in
feet $ \_$ft
temperature $ T$ Kelvin (SI) $ \_$K, $ \_$Kelvin
degrees of Celsius $ \_^\circ$C, $ \_$C, $ \_$Celsius
degrees of Fahrenheit $ \_^\circ$F, $ \_$F, $ \_$Fahrenheit
pressure $ p$ Pascal (SI) $ \_$Pa, $ \_$Pascal
bar $ \_$bar
millibar $ \_$mbar, $ \_$millibar
atm $ \_$atm
Torr $ \_$torr, $ \_$Torr, $ \_$mmHg
pounds per square inch $ \_$psi
density $ \rho$ kg per cubic metre (SI) $ \_$kg/mˆ3
g per cubic centimetre $ \_$g/cmˆ3
heat capacity $ c$ SI $ \_$J/(kg.K)
Btu/(lb$ \cdot$F$ ^\circ$) $ \_$Btu/(lb.F)
angular velocity $ \omega$ radian per second (SI) $ \_$rad/s, $ \_$sˆ-1
revolutions per minute $ \_$RPM
mass flow rate $ \dot{m}$,$ \phi$ kg per second (SI) $ \_$kg/s
g per second $ \_$g/s
volumetric flow rate $ \phi$ $ \mathrm{m^3}$ per second (SI) $ \_$mˆ3/s
$ \mathrm{m^3}$ per hour $ \_$mˆ3/h
litres per second $ \_$l/s
dynamic viscosity $ \mu$ poiseouille (SI) $ \_$Pa.s, $ \_$Pl
poise img81P
centipoise $ \_$cP

Here is a sample of a TCFD file:


# Machine type                          AF-nq105
type                                    fan

# Speedlines and initial conditions
numberOfSpeedlines                      1
angularVelocity                         -471.238898038469
1_numberOfPoints                        16
1_iterations                            500 500 500 500 500
1_initialPressure                       101325
1_initialVelocity                       0 0 9.74014381911833
1_initialTurbulentEnergy                0.001
1_initialTurbulentDissipation           100

# Simulation controls
processors                              6
UMax                                    1000
pMin                                    -50000
pMax                                    50000

# Inlet boundary conditions
numberOfInletBoundaryConditions                     1
1_inletBoundaryCondition-type                       volumetricFlowRate
1_inletBoundaryCondition-volumetricFlowRate         5 4.75 4.5 4.25 4
1_inletBoundaryCondition-turbulentEnergyIntensity   0.05
1_inletBoundaryCondition-turbulentDissipation       100

# Outlet boundary conditions
numberOfOutletBoundaryConditions                    1
1_outletBoundaryCondition-type                      fixedPressure
1_outletBoundaryCondition-fixedPressure             0 0 0 0 0

# Physical settings & Fluid properties
fluidName                               air
compressibility                         incompressible
referenceDensity                        1.2
dynamicViscosity                        1.842E-5
gravitationalAcceleration               0 0 0
referencePressure                       101325
referenceTemperature                    293.15

# Geometrical information
scaleFactor                             0.001
origin                                  0 0 0
axis                                    0 0 1
numberOfRegions                         2

# Information of region 0: Impeller
1_componentName                         impeller
1_wheelDiameter                         340
1_filePath                              ./STL
1_internalPoint                         11.5 -161 28.4
1_backgroundMeshSize                    30 30 30
1_inlet                                 impeller-inflow
1_2_outletInterface                     impeller-outflow
1_2_outletInterface-mixingPlanes        10
1_shroud                                impeller-shroud
1_hub                                   impeller-hub
1_blade                                 impeller-blades
1_blade-refinementSurfaces              2 4
1_rotatingRegion                        true
1_rotatingPatches                       impeller-shroud impeller-hub impeller-blades 

# Information of region 1: Vaned stator
2_componentName                         stator 
2_wheelDiameter                         0
2_filePath                              ./STL
2_internalPoint                         155 -11.5 85.1
2_backgroundMeshSize                    20 20 20
2_1_inletInterface                      vanedGate-inflow
2_1_inletInterface-mixingPlanes         10
2_outlet                                vanedGate-outflow
2_outlet-refinementSurfaces             2 4
2_shroud                                vanedGate-shroud
2_hub                                   vanedGate-hub
2_blade                                 vanedGate-blades
2_blade-refinementSurfaces              3 4 
2_rotatingRegion                        false

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