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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:

 (3.2)

• Particularly, OpenFOAM uses the following formula:

 (3.3)

where  is a cell volume,  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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## Three Dimensional

All the models are solved in three dimensions, even 2D-like or 1D-like models are treated as 3D using special boundary conditions. See e.g. [13].

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#### TCFD – 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 “Nsomething”, 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 “Xkeywd1-Ykeywd2-Zkeywd3”. 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 1mm or 0.1cm or 0.001m. While the temperature quantities allow the use of the degree symbol, e.g. 100C, 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 1C 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 seconds (SI) s, sec, seconds minutes m, min, minutes hours h, hrs, hours revolutions revolutions length metres (SI) m decimetres dm centimetres cm millimetres mm inches in feet ft temperature Kelvin (SI) K, Kelvin degrees of Celsius C, C, Celsius degrees of Fahrenheit F, F, Fahrenheit pressure Pascal (SI) Pa, Pascal bar bar millibar mbar, millibar atm atm Torr torr, Torr, mmHg pounds per square inch psi density kg per cubic metre (SI) kg/mˆ3 g per cubic centimetre g/cmˆ3 heat capacity SI J/(kg.K) Btu/(lbF) Btu/(lb.F) angular velocity radian per second (SI) rad/s, sˆ-1 revolutions per minute RPM mass flow rate , kg per second (SI) kg/s g per second g/s volumetric flow rate per second (SI) mˆ3/s per hour mˆ3/h litres per second l/s dynamic viscosity poiseouille (SI) Pa.s, Pl poise P 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_rotatingRegion                        true

# 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
`