CFX Intro 14.5 WS04 Multi Species Postpro

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    2012 ANSYS, Inc. December 17, 2012 1 Release 14.5

    14. 5 Release

    Introduction to ANSYS

    CFX

    Workshop 04

    Multi-Species Flow andPostprocessing

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    In this workshop you will analyze the release of heat and combustion gases

    from a single car with an engine fire in a ventilated parking garage. The

    simulation will be run steady state assuming the fire has reached a stable

    developed stage.

    Simulation Physics & Boundary Conditions Mixture of N2, O2, CO2and H20

    0.1 kg/s combustion gases (H2O and CO2) at 1200 K

    80 N/m

    3

    momentum source in jets

    Introduction

    Fresh Air Inlet

    velocity_inlet_fresh_air

    Jet Fan

    fluid_jet_fan

    Heat and gas release from fire

    mass_flow_inlet_car_fire_source

    Air Outlet

    pressure_outlet_all_air

    Symmetry Plane

    symmetry

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Important Note

    NOTE:

    This workshop has been designed to be completed in one of two ways. Pleasecheck with your trainer on whether you are to take the short or long option.

    [Short Option] This workshop can be used just to demonstrate post-processing in CFD-Post. Results files are supplied. So please jump straight to

    page 26 for post-processing

    [Long Option] Follow all the instructions, which will demonstrate how to set

    up a multi-species simulation of a car fire. Once the model is set up you canchoose to wait for it to converge or replace your results with the supplied set.

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    If doing the short version (postprocessing only)

    please jump to page 26 now

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Learning Aims:

    The first part of this workshop will show how to set up a multi-species problem.The domain will contain a blend of several different gases (nitrogen, oxygen,

    carbon dioxide, water vapour)

    Other topics that will be introduced are:

    Including gravitational (buoyancy) effects

    Setting a momentum source term to account for a jet fan

    Learning Objectives:

    To understand how CFX can be used to simulate mixtures of fluids and account

    for buoyancy effects. Note that a multi-species problem like this assumes that

    the components are mixed at a molecular level (as normally happens with gases).

    The alternative is a multi-phase problem where there is an identifiable boundary

    between the components (either droplets / particles / bubbles or a free-surface).

    Multi-phase workshops include Workshop 9 (Tank Flush) and Workshop 7

    (Centrifugal Pump)

    I Objectives (Flow Simulation Part)

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Starting Workbench Open Workbench

    Start> Programs>ANSYS 14.5 > Workbench 14.5

    Drag a CFX Analysis System into the project schematic

    Rename the system to Garage(RMB on cellA1to rename the system)

    Save the project to your working directory as Car_and_Garage.wbpj (File >Save As)

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Importing the Mesh

    Right-click on Meshand select Import Mesh File

    Set the mesh filter to FLUENT Files (*.cas,*.msh) Select car_and_garage.msh(workshop_input_files\WS_04_Multi-Species andPostProcessing)and click Open

    Right-click Setupand select Editto open CFX-Pre

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Material Specification

    In the Outlinetree, right-click Materialsandselect Insert>Material

    Set the Nameto Mixtureand click OK

    Set Optionto Variable Composition Mixture

    For Materials List, click the icon to the right of thedrop-down list , and then click the Import

    Library Dataicon (as shown on the upper right)

    Under Gas Phase Combustionhold down the key as you select the following materials:

    CO2, H2O, N2, O2

    Click OKto import them and close the Importform

    Now select the same Materialsunder the Materials

    List form Click OKto close the Materials List form

    Click OKto complete specifying the Mixture

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Domain Specification

    Double-click Default Domain

    Set the Materialto Mixture

    Set the Reference Pressureto 1 [atm]

    Set Buoyancy Modelto Buoyant Set the X and Y directions to 0 [m/s^2]

    Set the Z direction to the expression: -g You need to click the Enter Expression

    icon to enter this expression

    Set the Buoyancy Ref. Density to1.1989 [kg/m^3]

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Operating Conditions

    ANSYS CFX avoids the problem of round-off error by solving for a relative pressure, i.e. a

    pressure relative to the Reference Pressure. For compressible fluids, the density is based ontheAbsolute Pressure, which is the sum of the Reference Pressure and the solved for

    relative pressure. The Reference Pressureshould be chosen such that variations in the

    relative pressure are significant compared with the values in the solution field.

    If buoyancy is switched on, a hydrostatic component is also included , , in whichrefis the Buoyancy Reference Densityand is the Buoyancy Reference Location. Buoyancy

    Reference Density is set so as to avoid round-off errors. For single-phase simulations the

    value should be an average value anticipated for the domain.

    Introduction part 1: long version Setup Solving Proceed to Part 2.

    )( refref rrg

    refr

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    Fluid Models On the Fluid Models tab:

    Set Heat Transfer to Total Energy

    Kinetic energy effects will be included

    In the Component Models section click on N2in theComponentbox and make sure the Optionis set to

    Constraint.

    In a multi-component mixture, one component

    must be defined as a Constraint. Other settings on the form can be left as the defaults

    The k-epsilon turbulence model is selected bydefault

    Turbulence modelling, as with all physics modelling, is a

    complex area. There are many application specific

    options. The k-epsilon model is a simple and robustmodel. The documentation provides further guidance on

    which models to use for specific applications.

    Click OKto complete the specification of the domain

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Forced convection modelling a Fan

    Right-click Default Domain and select Insert> Subdomain

    Set NametoFanand click OK

    Set Locationtofluid_jet_fan

    Click the Sourcestab Enable Sources, Momentum Source/Porous

    Loss, then General Momentum Source

    Set the Y Component to -80 [kg m^-2 s^-2]

    Set other components to 0 [kg m^-2 s^-2]

    Click OK

    We need to account for the air movement produced by the ceiling jet fan. We have done this by

    adding momentum to the subdomain which is local to the jet. The advantage of this technique (over

    using a pair of velocity boundary conditions) is that we preserve the concentrations of combustion

    gases through the fan. If we had used velocity boundary conditions, we would have needed to use

    expressions at the intake to the jet fan and apply them to the jet fan discharge.

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Boundary Conditions (Fresh Air) Select Insert> Boundary

    Set Nameto Fresh Air

    LeaveBoundary Type asInlet

    Set the Locationto velocity_inlet_fresh_air

    Click Boundary Details(more settings on the next page)

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Boundary Conditions (Fresh Air) On the Boundary Detailstab:

    Set Mass and Momentum to Normal Speed

    Set Normal Speed to 0.8 [m/s]

    Set Heat Transfer to Static Temperature

    Set Static Temperature to 20 [C]

    Note the units for temperature

    Set the following component Mass Fractions: CO2: 0.0

    H2O: 0.0

    O2: 0.23

    Click OK

    Introduction part 1: long version Setup Solving Proceed to Part 2.

    The mixture species contains 4 components (H2O, O2, CO2,and N2). You do not need to enter a mass fraction for the

    constraint species, N2; its concentration is set automatically

    such that the sum of all mass fractions is 1.0.

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    Boundary Conditions (Air Outlet) Insert> Boundary

    Set NametoAir Outlet

    Set Boundary Type to Opening

    Set Locationtopressure_outlet_all_air

    Click Boundary Details

    Set Mass and Momentum to Opening Pres. And Dirn

    Set Relative Pressure to 0 [Pa]

    Set Heat Transfer to Opening Temperature

    Set Temperatureto 20 [C] (as for previous BC)

    Set the following component Mass Fractions:

    Set O2to 0.23

    Set the other component mass fractions to 0

    Click OK

    Introduction part 1: long version Setup Solving Proceed to Part 2.

    The values for turbulence, temperature and mass fractions specified on the opening will only be

    used where there is inflow.

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    Insert> Boundary

    Set Nameto Exhaust. OK

    Leave Boundary Type as Inletand set

    Locationto

    mass_flow_inlet_car_fire_source

    Click Boundary Details

    Set Mass and Momentum to Mass FlowRate

    Set Mass Flow Rate to 0.1 [kg s^-1]

    Set Heat Transfer to Static Temperature

    Set Static Temperature to 1200 [K]

    Set the following component MassFractions:

    CO2: 0.568

    H2O: 0.432

    O2: 0

    Click OK

    Boundary Conditions (Exhaust)

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Boundary Conditions (Walls) Insert> Boundary

    Set Nameto Walls

    Set Boundary Type to Wall

    Set Locationto walls_outer, wall_floor andwall_ceiling

    Use the key to select multiple

    boundaries

    Click Boundary Details Set Heat Transfer to Heat Transfer Coefficient

    Set Heat Trans. Coeff to 5 [W m^-2 K^-1]

    Set Outside Temperature to 300 [K]

    This boundary condition is intended to simulate the effect

    of a solid material between the CFD domain and the air

    outside the garage, for example, a concrete wall.

    Click OK

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Boundary Conditions (Symmetry)

    Insert > Boundary

    Set Nameto Symmetry

    Set Boundary Type to Symmetry

    Set Locationto symmetry

    Click OK

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Initialization

    Right-click on Flow Analysis 1 in the Outlinetree and select Insert> Global Initialization

    Set TemperaturetoAutomatic with Value

    Set Temperatureto 300 [K]

    Under Component Details, set O2toAutomatic with Value

    Set Mass Fraction for O2to 0.23

    Leave all other settings at their defaultvalues

    The solver will calculate automatic values for

    the remaining variables

    The flow is initialized without any products ofcombustion present

    Click OK

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Monitor Quantities

    Double-click on Output Control under Solverin the Outlinetree

    On the Monitortab create a new monitor Set NametoAverage Temperature

    Set Optionto Expression

    Set Expression Value to volumeAve(T)@Default

    Domain

    Create two new monitors in the same way: Name: Heat Flow through Floor

    Expression:areaInt(Wall Heat Flux)@REGION:wall_floor

    Name: Fan Intake Mass Flow Rate Expression:

    massFlow()@REGION:Primitive 2D B

    Click OK

    The monitor points will track average

    temperature in the domain, total heat flux

    through the floor region, and mass flow throughthe simulated fan region.

    The region where mass flow is monitored was

    not tagged as a Named Selection in the mesh.

    So the mesh region of the primitive CAD surface

    that represents it has to be chosen.

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Monitor Quantities

    Notes on monitors:

    Buoyancy driven flows often show transient behavior. For this reason the

    residuals will often oscillate. Because of this convergence should also be judged

    by solution variable monitors and imbalances.

    In cases of an oscillating steady-state solution, a common approach is to

    continue the simulation in transient mode. In many cases the residuals will

    reduce significantly after a few time steps.

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Solver Control

    Double-click Solver Control

    Under Convergence Control, set Max.Iterationsto 250 (or use a smaller number,

    e.g. 50 to force the run to stop after a

    shorter time)

    Set Timescale Control to Physical Timescale

    Set a Physical Timescale of 5 [s]

    Set Residual Target to 1e-4

    Enable Conservation Target Set Valueto 0.01

    Click OK

    Introduction part 1: long version Setup Solving Proceed to Part 2.

    The conservation target sets a minimum level of imbalance information for the

    solved quantities. In this case, the solver is aiming for 1% imbalance.

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    Solution (Optional)

    Close CFX-Pre

    The solution takes 30-60 minutes tocomplete

    A results file is provided in thisworkshop if you do not wish to solve

    the case. To use the provided results

    file, go to the next page

    To solve the case manually: Right-click Solutionand select Edit

    When the CFX-Solver Manager opens clickStart Run

    Skip the next page of instructions andcontinue from the slide headed

    Monitoring the Solution

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Using Results Provided (Optional)

    To use the results file provided:

    Browse to the results file garage_001.resusing Windows Explorer

    Drag garage_001.resinto the ProjectSchematic. A new component system will

    appear.

    In the new system, right-click Solutionandselect Display Monitors The CFX-Solver Managerwindow will open to

    show the diagnostic info associated with the

    supplied results file

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Monitoring the Solution

    Click the User Pointstab

    The development of a fairly regular pattern inthe variation of the monitor, Heat Flow

    Through Floor, indicates that there are some

    transient characteristics in the flow. This

    workshop has assumed that the flow can be

    treated as steady state but for a higher

    fidelity solution a transient study would be

    necessary.

    View the ResidualsOscillations in the RMS residuals help to

    affirm possible transient solution behaviour.

    The solution in this case terminated because

    the maximum number of iterations, 250, was

    reached and not because the solution

    converged to the required level.

    Introduction part 1: long version Setup Solving Proceed to Part 2.

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    Create a new monitor to see how closely

    the target imbalance of 1% was met

    Click on the New Monitor icon and accept

    the default Name andType

    Select the Plot Lines tab of the Monitor

    Properties window

    ExpandIMBALANCE>Default Domain andswitch on imbalances for all equations

    Select Range Settings, check Set Manual

    Scale (Linear) and set the Lower Bound to

    -1 and the Upper Bound to 1

    The imbalances are all within the 1% target

    Monitoring the Solution

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    Post-processing in CFD-POST

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    Learning Aims:

    This workshop is designed to teach a range of skills in post-processing results files using

    CFD-Post. Topics to be covered include:

    Creating surface groups - Creating line graphs

    Creating isosurfaces - Creating expressions (CEL)

    Creating portable (.cvf) images - Performing integrals

    Creating automatic reports - Volume rendering

    Learning Objectives:

    To understand the ways in which CFD Post can be used both for high quality images, as well

    as producing quantitative data from volume/surface integrals, and writing custom

    functions.

    I Objectives (Postprocessing)

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    Results Preparation

    If you have set up the problem manually, the

    results file will already be available. If you are only performing Post-processing in

    this workshop

    Browse to the results file garage_001.resusing

    Windows Explorer

    Drag garage_001.resinto the Project Schematic. Anew component system will appear

    Right-click Resultsand select Edit

    CFD-Postwill open and the results will be

    automatically loaded

    Depending on the path chosen, you will be loading resultsfrom a complete analysis system (top right) or a

    component system (bottom right). To ensure Resultsare

    valid, check to see that Solutionhas a green tick

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

    OR

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    Post-processingWall Temperature

    Add a Location representing a group of surfaces(Surface Group)

    This lets you group a selection of entities (in this case walls) and apply the same post-processingtreatment to all items in the group.

    Select Locations > Surface Groupand enter the name Grouped Walls

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    PostprocessingWall Temperature

    Define Location details

    The details of the new location will be displayed

    in the bottom left pane

    Select Locations, and click on

    Expand the Regionslist and select everything

    beginning wallEXCEPT wall_car(CTRL click to

    multiple select).

    Click OK in the Location Selector

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    PostprocessingWall Temperature

    Click the Colortab Set Modeto Variable

    Set Variableto Temperature

    Set Rangeto Local

    ClickApply

    Modify the Legend

    Double-click Default LegendView 1in the Outline tree

    On theAppearancetab:

    Set Precisionto 1

    Change Scientificto Fixed

    ClickApply

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

    This option has allowed us to produce a temperature contour plot

    of identical colour range on a group of surfaces.

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    PostprocessingGenerating a Figure

    Click the Figureicon Enter the name Figure 1 Wall

    Temperature

    OK

    Remember where this option is as you

    will be asked to use it several times on

    subsequent slides.

    Later on we will demonstrate how to use

    these figures to automate report-writing.

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

    Generate a figure for use later in a report

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    Post-processingSection Plane

    First de-select the checkbox next toGrouped Wallsin the Outlinetree to turn off

    visibility for the object

    Add a location representing a section plane

    Select Location> Plane

    Set Nameto xzplaneand click OK On the Geometrytab set MethodtoZX Plane

    Y= 9 [m]

    ClickApply

    Continued on next slide..

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    PostprocessingSection Plane

    On the Colortab set Modeto Variable

    Set the VariabletoTemperature

    Under RenderdisableLighting

    ClickApplyto display

    Generate a new Figureandname it Figure 2

    Temperature Slice

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    PostprocessingQuick Animation

    Click theAnimationbutton in the top toolbar

    Select Quick Animation

    Highlightxzplane

    Press the Play button , and watch the display.

    When finished, use the stop button then Close.

    If required, this animation could be saved to disk in MPEG /

    AVI formats.

    The alternative to Quick Animationis Keyframe Animation. To use this you set a series of key

    animation frames. These might have different objects visible, be different points in a transient

    simulation, or use different viewing angles. The animation will progress smoothly between these

    states.

    The slice through the model gives us a useful indication of what is

    happening in the middle of the domain. A Quick Animationwill

    traverse this slice through the model so that we can see what ishappening elsewhere.

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    Post-processing3D Isosurface

    First change the look of the display: Hide the planexzplaney un-checking it in the

    Outlinetree

    Expand Mesh Regionsin the treethe top ofthe model tree

    Double-click on wall_car

    Ensure that the details box shows wall_car For Colorselect Constantand pick yellow () ClickApply

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    Post-processing3D Isosurface

    Add a 3D Isosurface representing gases

    Select Location> Isosurface Keep the default name Isosurface 1

    Set the Variable to CO2.Mass.Fractionand the value to0.001

    Set Colorto be Constant(use the default grey colour),then clickApply

    Generate a new figure calledFigure 3 CO2 Isosurface

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    Post-processingStreamlines

    Add 3D Streamlines to visualize flow

    Hide the Isosurface created in the previous step (un-check in model tree) Click the Streamline button and keep default name (Streamline 1)

    On the Geometrytab

    Start From: Fresh Air

    # of Points: 100

    Under Colorset Mode: Use Plot Variable

    Range: Local

    ClickApply

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    Post-processingPortable CVF Files

    Not only can CFD-Postexport regular image formats (jpg / png), but in addition 3D images can be saved.

    These images have the file extension .cvf.

    They can be viewed using a free CFD viewer that can be downloaded from the ANSYS website. (Go to

    www.ansys.com, and search for ANSYS CFD Viewer)

    No license is required to use the viewer. So you can install this on any computer (e.g. laptop used for

    presentations or ask your client/customer to download and install a copy).

    The 3D image can be viewed using rotate / pan / zoom functionality just as in CFD-Post, and can also be

    embedded in MS-Powerpoint. However the user cannot modify the image. They cannot add/remove

    objects from the image or alter colour ranges.

    This is a really powerful tool for when you come to present your project work. In many cases a 2D jpegimage cannot explain 3D flow features. However, rotating the model live in front of your audience will

    help convey your findings.

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

    http://www.ansys.com/http://www.ansys.com/
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    Post-processingPortable CVF Files

    In CFD-Postclick the camera icon For Formatselect CFD-Viewer State (3D)

    Click the folder icon to the right of the filename. Pick the directory you are working in (remember this!)

    Save as filename car-streamlines.cvf Click Savein both windows

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    Post-processingPortable CVF Files

    Minimise CFD Post, and use Windows Explorer to browse to thefolder used on the last slide.

    Note how this file (car-streamlines.cvf) is quite small (in this caseabout 170kB (but it will vary depending on zoom level), and

    therefore easy to email to your client or manager).

    Double-click to open this file (it will take a few moments tolaunch the viewer application)

    If you have ANSYS R14.5 installed on your machine, your computer will already

    have the viewer and will recognize this file extension. You only need to do a

    separate installation of ANSYS CFD Viewer (from the ANSYS website) on machines

    that do not have Workbenchinstalled.

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    Post-processingPortable CVF Files

    ANSYS CFD Viewerwill look just

    like the graphical window ofCFD-Post

    Use left mouse button to rotate

    Middle mouse button (or wheel)to zoom

    Right mouse button to translate

    Type question mark ?for a list ofhotkeys

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    PostprocessingVolume Rendering

    Close the standalone viewer and return to CFD-Post

    Hide the streamlines plot by un-checking in model view Select Insert>Volume Renderingand set Nameto Gas Cloud

    On the Geometrytab

    set Variableto CO2.Mass Fraction

    keep Rangeas Global and clickApply

    To make it easier to see the imagechange the screen background colour to

    white:

    Edit> Options> CFD-Post> Viewer

    Set Color Typeto Solid

    Set Colorto white

    Click OK

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

    Volume Renderingapplies a variable colour and transparency to

    each grid cell depending on the plot variable. For applications

    involving smoke movement it makes it easy to assess where the

    cloud is concentrated.

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    Post-processing - Quantitative

    Create a Line through the model Hide the Gas Cloudvolume rendering object

    Location> Line and keep default name Line 1

    Set Methodto Two Points

    from X=18 Y=3 Z=2

    to X=18 Y=18 Z=2

    Set Samplesto 40

    ClickApply

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

    Until now we have used CFD-Postto create colour images to help interpret the CFD results.

    Next we will look at some quantitative techniques for extracting numerical data (volume integrals)

    and producing charts.It is also possible to write your own arithmetic expressions for custom post-processing.

    This has created a horizontal line through the model, passing

    above the front of the car

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    Post-processingChart

    Select the Chart Icon from the top toolbar

    Keep the default name, Chart 1and click OK Under Generalset the Display Titleto

    Temperature Profile

    Under Data Seriesset LocationtoLine 1

    UnderX Axisset Variableto Y

    Under Y Axisset Variableto Temperature

    ClickApply

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    Post-processingChart

    Notes on the graph:

    Notice that the peak temperature is located not above the middle of the car (y=9m) but moved

    some distance to the left (circa y=7m). This is a direct effect of the air movement from the jet fan

    To view the plot in Celsius rather than Kelvin, edit the details of Temperatureon the Variablesform

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    Post-processingVolume Integrals

    Select Calculatorstab

    Select Function Calculator

    Function: volumeInt (for Volume Integral) Location: Default Domain

    Variable: CO2.Mass.Fraction

    Click Calculate

    The result is about 1.15 m^3 of CO2

    The only source of carbon dioxide (CO2) in the model is from the car

    fire (the inlet just comprises oxygen and nitrogen). We will perform

    a volume integral to find out how much CO2 is present in the model.

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

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    Post-processingExpressions

    Select the Expressionstab

    Right click in the window and select New

    Enter name PressureDropthen click OK

    Enter the following expression, then click Apply ave(Pressure)@Fresh Air

    Note: right-click menu usage shown below

    The answer is approximately 31Pa.

    It is possible to write your own arithmetic functions for post-processing, making use of the data

    exported by the solver. The resulting expression may either return a single value (first example,

    below), or produce a quantity that varies spatially for use in a contour plot / line graph

    Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary

    1

    2

    3

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    Post-processingExpressions

    Part 2: Postprocessing Colour Images Line Graphs Expressions and Integrals Reports Summary

    Note how Pressureappears in

    italics as soon as you type it.

    It is important to make the first

    letter a capital P.

    For a full list of availablevariables right-click in this

    window and select Variables

    areaAve returns the area-

    weighted average at the location

    specified by the @

    For a list of functions available

    right-click in the window and

    select Functions> CFD-Post

    This is the name of the boundary that you are performingthe averaging function on.

    For a full list of locations, right-click and select Locations

    Note that to compute the pressure drop we did not need to

    add the outlet boundary ...- areaAve(Pressure)@Air Outlet

    The outlet boundary was set to be a pressure outlet in CFX

    with a pressure of 0 Pa. This term would return a zero

    valuetry it if you like!

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    Post-processingVariables

    As a simple example, lets convert the concentration of CO2 into a percentage byvolume

    Expressions> New

    Set Nameto CO2percent

    Enter this expression:

    100*CO2.Mass Concentration*R*Temperature/(Absolute Pressure*44.01 [kg /kmol])

    ClickApply

    Expressions can be used to define new variables

    Note:

    The concentration is calculated by dividing the concentration of CO2 on a mass per unit volume

    basis by its density according to the ideal gas equation. The molecular weight, 44.01 kg/kmol, can

    be found in the details of the Materialcalled CO2

    R, the universal gas constant, is available in CEL

    TheAbsolute Pressurerather than the relative pressure is used in the calculation of density

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    Post-processingVariables

    Click the Variablestab

    Right-click anywhere in the white space and select New Enter a name CO2VolPercent

    From the pull-down list, select the expressionTemperatureConversioncreated on the last slide

    ClickApply

    Expressions cannot be plotted directly: they need to be

    assigned to a Variable

    Part 2: Postprocessing Colour Images Line Graphs Expressions and Integrals Reports Summary

    Alternatively, the expression could be entereddirectly into the box on the Variables form

    without using the Expression Editor

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    The new variable can be used, for example, to colour the location xzplane

    Post-processingVariables

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    Post-processingReports

    Below the graphic window and selectthe Report Viewertab

    Select Refresh

    Review what is shown in the reportwindow. You can see:

    Name of the results file

    Mesh summary List of boundary conditions

    All the figures and charts producedduring this workshop

    Save the project

    If you select Publishthe report will, by default,

    be written out in html format, along with

    copies of all the results images

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    State files and Optional Extra work

    Outside Workbench: File > Save State As... to save state files as required

    Inside Workbench: A single state file is automatically saved with the projectThe state file stores all the post-processing settings and objects you have created.

    If you have done the long version of this workshop, you will recall that we ran for a fixed number

    of iterations and wanted to examine the results to help us determine if the model had converged

    or not. (The residuals were stuck and further iterations would not lower the residuals). It might

    be necessary to revisit the model set-up, e.g. by moving to a transient scheme. A usefulassessment of convergence is to see if the results of interest remain unchanged as the solver

    settings are enhanced.

    The big advantage of having this state file is that if you choose to modify the solver settings and

    re-run this model, you can quickly reproduce the equivalent post-processing images. Simply load

    the new results file and then load this state file.

    Likewise, it is common in project work to have run a series of models to test the different

    operating conditions. This technique will let you generate equivalent images so as to produce a

    good like-for-like comparison in your presentation / report.

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    State files and Optional Extra work

    The Reports feature just demonstrated lets you customise theformat of your report.

    If you have finished this exercise ahead of the rest of the class,try experimenting with the Report options in the left-hand

    toolbar.

    You can choose which objects are visible, add your own company

    logo, or add lines of text to explain the content of the report.

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    Wrap up

    CFD-Postis a very powerful post-processing tool, and capable ofproducing high quality images quickly and easily.

    In this workshop we have shown how to produce contour plots,streamlines, and isosurfaces (as seen in some other workshops

    for this course)

    In addition you have used CFD-Postto perform volume integrals,

    create line graphs, and to create your own arithmetic expressionsfor post-processing.

    3D images can be saved to disk, and viewed in a freeware viewer.This adds much impact to presentations, and can be run on any

    computer (no license needed).

    CFD-Postcan also automate the report generation process.

    Post-processing is best learned by practice. If you have timenow, try exploring the other buttons in the interface.

    Part 2: Postprocessing Colour Images Line Graphs Expressions and Integrals Reports Summary