cfx intro 14.5 ws04 multi species postpro
TRANSCRIPT
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
1/57
2012 ANSYS, Inc. December 17, 2012 1 Release 14.5
14. 5 Release
Introduction to ANSYS
CFX
Workshop 04
Multi-Species Flow andPostprocessing
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
2/57
2012 ANSYS, Inc. December 17, 2012 2 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
3/57
2012 ANSYS, Inc. December 17, 2012 3 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
4/57
2012 ANSYS, Inc. December 17, 2012 4 Release 14.5
If doing the short version (postprocessing only)
please jump to page 26 now
Introduction part 1: long version Setup Solving Proceed to Part 2.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
5/57
2012 ANSYS, Inc. December 17, 2012 5 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
6/57
2012 ANSYS, Inc. December 17, 2012 6 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
7/57 2012 ANSYS, Inc. December 17, 2012 7 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
8/57 2012 ANSYS, Inc. December 17, 2012 8 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
9/57 2012 ANSYS, Inc. December 17, 2012 9 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
10/57 2012 ANSYS, Inc. December 17, 2012 10 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
11/57
2012 ANSYS, Inc. December 17, 2012 11 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
12/57
2012 ANSYS, Inc. December 17, 2012 12 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
13/57
2012 ANSYS, Inc. December 17, 2012 13 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
14/57
2012 ANSYS, Inc. December 17, 2012 14 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
15/57
2012 ANSYS, Inc. December 17, 2012 15 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
16/57
2012 ANSYS, Inc. December 17, 2012 16 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
17/57
2012 ANSYS, Inc. December 17, 2012 17 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
18/57
2012 ANSYS, Inc. December 17, 2012 18 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
19/57
2012 ANSYS, Inc. December 17, 2012 19 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
20/57
2012 ANSYS, Inc. December 17, 2012 20 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
21/57
2012 ANSYS, Inc. December 17, 2012 21 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
22/57
2012 ANSYS, Inc. December 17, 2012 22 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
23/57
2012 ANSYS, Inc. December 17, 2012 23 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
24/57
2012 ANSYS, Inc. December 17, 2012 24 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
25/57
2012 ANSYS, Inc. December 17, 2012 25 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
26/57
2012 ANSYS, Inc. December 17, 2012 26 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
27/57
2012 ANSYS, Inc. December 17, 2012 27 Release 14.5
Post-processing in CFD-POST
Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
28/57
2012 ANSYS, Inc. December 17, 2012 28 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
29/57
2012 ANSYS, Inc. December 17, 2012 29 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
30/57
2012 ANSYS, Inc. December 17, 2012 30 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
31/57
2012 ANSYS, Inc. December 17, 2012 31 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
32/57
2012 ANSYS, Inc. December 17, 2012 32 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
33/57
2012 ANSYS, Inc. December 17, 2012 33 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
34/57
2012 ANSYS, Inc. December 17, 2012 34 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
35/57
2012 ANSYS, Inc. December 17, 2012 35 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
36/57
2012 ANSYS, Inc. December 17, 2012 36 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
37/57
2012 ANSYS, Inc. December 17, 2012 37 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
38/57
2012 ANSYS, Inc. December 17, 2012 38 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
39/57
2012 ANSYS, Inc. December 17, 2012 39 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
40/57
2012 ANSYS, Inc. December 17, 2012 40 Release 14.5
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/ -
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
41/57
2012 ANSYS, Inc. December 17, 2012 41 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
42/57
2012 ANSYS, Inc. December 17, 2012 42 Release 14.5
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.
Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
43/57
2012 ANSYS, Inc. December 17, 2012 43 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
44/57
2012 ANSYS, Inc. December 17, 2012 44 Release 14.5
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.
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
45/57
2012 ANSYS, Inc. December 17, 2012 45 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
46/57
2012 ANSYS, Inc. December 17, 2012 46 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
47/57
2012 ANSYS, Inc. December 17, 2012 47 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
48/57
2012 ANSYS, Inc. December 17, 2012 48 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
49/57
2012 ANSYS, Inc. December 17, 2012 49 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
50/57
2012 ANSYS, Inc. December 17, 2012 50 Release 14.5
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!
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
51/57
2012 ANSYS, Inc. December 17, 2012 51 Release 14.5
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
Part 2: Postprocessing Colour Images Line Graphs Expressions and Integrals Reports Summary
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
52/57
2012 ANSYS, Inc. December 17, 2012 52 Release 14.5
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
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
53/57
2012 ANSYS, Inc. December 17, 2012 53 Release 14.5
The new variable can be used, for example, to colour the location xzplane
Post-processingVariables
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
54/57
2012 ANSYS, Inc. December 17, 2012 54 Release 14.5
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
Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
55/57
2012 ANSYS, Inc. December 17, 2012 55 Release 14.5
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.
Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
56/57
2012 ANSYS, Inc. December 17, 2012 56 Release 14.5
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.
Part 2: Postprocessing Color Images Line Graphs Expressions and Integrals Reports Summary
-
8/13/2019 CFX Intro 14.5 WS04 Multi Species Postpro
57/57
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