ansys fluent intro 12.0 1st-edition - workshops

TOC-1ANSYS, Inc. Proprietary 2009 ANSYS, Inc. All rights reserved.

April 28, 2009Inventory #002601

Workshop Supplement

Introductory FLUENT Training



Workshop SupplementTable of ContentsInventory Number: 002601

1st EditionANSYS Release: 12.0

Published Date: April 28, 2009

Registered Trademarks:ANSYS is a registered trademark of SAS IP Inc. All other product names mentioned in this manual are trademarks or registered trademarks of their respective manufacturers.

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Copyright 2009 SAS IP, Inc.

Proprietary data. Unauthorized use, distribution, or duplication is prohibited.

All Rights Reserved.



Workshop SupplementTable of Contents

Workshop 1: Fluid Flow and Heat Transfer in a Mixing TeeWorkshop 2: Transonic Flow over a NACA 0012 AirfoilWorkshop 3: Room Temperature Study (Parts 1 and 2)Workshop 4: Electronics Cooling with Natural Convection and RadiationWorkshop 5: Centrifugal PumpWorkshop 6: Modeling of Catalytic ConvertorWorkshop 7: Tank Flushing

WS1-1ANSYS, Inc. Proprietary 2009 ANSYS, Inc. All rights reserved.



Workshop 1

Fluid Flow and Heat Transfer in a Mixing Tee



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WS1: Mixing Tee

Welcome! Introductory tutorial for FLUENT

starting from existing mesh (generated in earlier tutorial) model set-up, solution and post-processing

Mixing of cold and hot water in a T-piece how well do the fluids mix? what are the pressure drops?

Its a good idea to identify the key simulation outcomes from the start. You can use these to monitor progress of solution.



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Start in Workbench If starting from a ready-made mesh file (*.meshdat),

start Workbench and import the file (see screenshot below) and save the project

Alternatively, start in the Workbench project that generated the mesh



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Start a FLUENT case Drag a FLUENT analysis into the project

Drag the existing mesh into the FLUENT analysis then Update the mesh (via Right-click) to convert the mesh format

Double-click on Setup to launch FLUENT click OK on the FLUENT Launcher screen

You can see that the mesh needs to be updated, because its status icon changes.



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FLUENT interfaceThe main commands are reached from the navigation pane

Each item in the navigation pane brings up a new task page. A typical workflow will tackle these in order

One or more graphics windows will be available (shown here with reduced size)

The console window displays text, and can accept TUI (Text User Interface) commands

Some useful commands have toolbar buttons

The Help button brings up context- sensitive help pages



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Mesh scale and check In the General task page, press Scale

select Mesh Was Created In to be in (inches) press the Scale button (once only!) and Close

Press Check and Report quality review the text output

Mesh quality is very important to getting a converged, accurate solution. The User Guide suggests that maximum cell squish and skewness should be below 0.95, which the mesh here obeys. The maximum aspect ratio is 34, which is high, but acceptable in inflation layers.If the mesh quality is unacceptable, it is best to remesh the problem before proceeding. There are other possible remedies in FLUENT, such as conversion to polyhedral cells.

The mesh check ensures that each cell is in a correct format, connected to other cells as expected. It is recommended to check every mesh immediately after reading it. Failure of any check indicates a badly-formed or corrupted mesh, which will need repairs.



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Display geometry Press Display

select Edge Type to be Feature, and press Display and then Close mesh has scaled, so press Fit to Window

Adjust the view if you like in rotation mode:

drag left-mouse-button rotates drag middle-mouse-button zooms (to zoom in, drag down and right)

(to zoom out, drag up and left) click middle-mouse-button centre on click



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Change units of temperature Click Units

select Temperature to be c (Celsius) press Close

FLUENT stores values in SI units. Most postprocessing can be converted to other units.



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Activate models Double-click (or click and press Edit...) these models:

Energy Equation: On Viscous model: k-epsilon, Realizable

Turbulence modeling is a complicated area. The choice of model depends on the application. Here, the Realizable k-epsilon model is used. This is an improvement on the well-established Standard k-epsilon model. Accept the remaining default settings.

Activating the Energy equation simply says that temperature changes should be simulated in the model.



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Define a new material In Materials, click Create/Edit...

press FLUENT Database... select water-liquid, press Copy, then close both windows



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Cell Zone Conditions In Cell Zone Conditions, double-click the zone called fluid

change the material it contains to water-liquid accept all other settings

Throughout the problem setup, there are many options and default settings that will not be investigated in this tutorial.

Alternatively, click once on fluid to highlight it, and then click Edit....



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Boundary Conditions In Boundary Conditions, double-click the zone called inlet-y

Velocity Magnitude 5m/s Turbulent Intensity 5% Hydraulic Diameter 0.15m Temperature 10C

Inlet flows bring turbulence with them. The quantities depend on the upstream conditions, so they are user inputs. For flow in pipes, turbulent intensity is typically 5% to 10%, and the length- scale of the turbulence can be deduced from the pipe diameter.



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Boundary Conditions Still in Boundary Conditions: Double-click the zone called inlet-z

Velocity Magnitude 3m/s Turbulent Intensity 5% Hydraulic Diameter 0.10m Temperature 90C

Double-click the zone called outlet for backflow: Turbulent Intensity 5%

Hydraulic Diameter 0.15m Temperature 30C

The simulation may predict that flow enters the model through parts of the outlet. This backflow will bring turbulence and energy back into the model, but the model cannot predict how much (because the flow is coming from outside of the model). So, it is necessary to specify backflow conditions.Ideally, the geometry should be selected such that flow enters the model only at well-defined inlets. The backflow settings then do not affect the final solution (although they may be used in intermediate iterations).



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Second-order discretization In Solution methods

Discretization Second Order for pressure Discretization Third Order MUSCL for all other quantities

Discretization schemes define how the solver calculates gradients and interpolates variables to non-stored locations. The default schemes are First Order generally more stable but less accurate than other schemes. Often, users run First Order discretization initially and switch to higher-order schemes for the final solution. This case is simple enough to use higher- order schemes from the start.



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Monitors In Monitors, press Create... for a Surface Monitor

Name p-inlet-y Plot in window 2 Area-Weighted Average Pressure inlet-y

By default, FLUENT reports values of the residuals, which are indications of the errors in the current solution. These should decrease during calculation. There are guidelines on the reductions that indicate a solution is converged.It is also recommended to observe other quantities, chosen to be important in the simulation. In the current case, we will look at pressure drops and temperature as monitors.

Accept Static pressure in the sub-category menu.



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Monitors In Monitors, press Create... for a Surface Monitor

Name p-inlet-z Plot in window 2 Area-Weighted Average Pressure inlet-z

In Monitors, press Create... for a Surface Monitor Name tmax-outlet Plot in window 3

Vertex maximum Temperature outlet

Here is an instance where FLUENT does not convert units. Click OK.

Not the default, 3 (which puts the new monitor in a new window).

Accept Static pressure and Static temperature in the sub-menu.



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Initialization In Solution Initialization

select Compute from to be inlet-y press Initialize

Initialization creates the initial solution that the solver will iteratively improve. Generally, the same converged solution is reached whatever the initialization, though convergence is easier if they are similar. Basic initialization imposes the same values in all cells. You can improve on this in various ways for example, by patching different values into different zones.Several features, including patching and post-processing, are not available until after initialization.

This computes a value for each variable, based on average conditions in the select zone. This value is used in every cell when you press Initialize.



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FMG initialization Click in the console window, then:

press RETURN to see the TUI (Text User Interface) command menu to enter the solve sub-menu, type solve and RETURN to go up a level, type q and RETURN to issue a command starting from top level, start the command with / many abbreviations are allowed (try it!)

type /solve/initialization/fmg-initialization and RETURN override the default by typing yes and RETURN

Here we use an advanced feature to improve on the basic initialization: Full Multi-Grid (FMG) initialization. This solves a very simplified set of flow equations, initially considering the geometry at a crude level and then building up detail.



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Calculate In Run Calculation

press Check Case... see No recommendations to make at this time

set Number of Iterations to 200 press Calculate

OK to Continue after replacing settings file

Problem setup has changed the mesh for example, the coordinates changed by scaling. There are many other changes that FLUENT can make for example, adapting the mesh to increase the number of cells where the solution requires it.

The link from Mesh to FLUENT in Workbench needs care are you starting a new Problem Setup with a new mesh, or are you finding a new Solution on the old mesh?



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Calculating While calculating, review residuals and monitors

change graphic windows using the drop-down box

An alternative way to stop calculation is to press CTRL-C.

In this case, 200 iterations (or fewer) are enough to reach low residuals and stable values of monitors. Most cases require many more.



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Preliminary post-processing In Graphics and Animations, select Contours, press Set Up...

select Filled contours of Turbulence...Wall Yplus on wall-fluid press Display note almost all values are between 30 and 200

The plot appears in the last active graphics window if you dont see it, check the list.

Yplus is a measure of whether mesh near the walls captures the turbulent effects. This range is acceptable.



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Check mass and heat balance In Reports, select Fluxes and press Set Up...

compute Mass Flow Rate and Total Heat Transfer Rate for inlets and outlets check that Net Results are small

Checking that mass and energy are conserved (to acceptable accuracy) is simple and important.



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WS1: Mixing Tee

Exit FLUENT Exit FLUENT

accept the default, Continue without saving In Workbench, double-click Results to launch CFD-Post

in the FLUENT session, we have completed Setup and Solution

To adjust conditions in FLUENT, double-click

on Solution.If you re-open Setup, the

link with the old, unscaled mesh is loaded back in a window will

warn you of this.



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CFD-Post The results are loaded CFD-Post displays the outline (wireframe) of the model

viewer toolbar buttons allow you to manipulate the view



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Temperature contour plot Press the contour button

accept the default name Contour 1 select Location to be wall fluid, and Variable to be Temperature press Apply

Try changing the view by rotate, zoom and pan tools.



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Create a plane Hide the contour plot by unchecking it in the tree view In the Location menu, select Plane

accept the default name Plane 1 select Method to be

YZ Plane, accept X as 0.0, and press Apply



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Velocity vector plot Hide the plane by unchecking it in the tree view Press the Vector button

select Locations to be Plane 1, and press Apply

The plane is used only as a location for the vector plot.



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Predefined Camera views and shortcuts Since the vector plot is on a YZ-plane, select a normal view

click with the right mouse-button in the view window select Predefined Camera then View Towards +X

Alternatively, press x. Keyboard shortcuts are listed by pressing here.



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Streamline plot Hide the vector plot by unchecking it in the tree view Press the Streamline button

select Start from to be inlet y and inlet z in the Symbol tab, select Stream Type to be Ribbon

To select multiple locations, press the Location editor button, and press CTRL while clicking.

Ribbons give a 3-D representation of the

flow direction.In the current plot, the colour depends on the flow velocity.



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Velocity isosurface Hide the streamline plot by unchecking it in the tree view In the Location menu, select Isosurface

in the Geometry tab, select Variable to be Velocity and Value to be 7.7 [m s^-1]

The velocity magnitude is greater than 7.7m/s inside the isosurface , and less than that outside it.

This is just one example you can try other values.



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Velocity isosurface By default, the isosurface is colored by velocity magnitude In the Colour tab

select Mode to be Variable, Variable to be Temperature, Range to be Local, and press Apply

This is the end of the tutorial. To be able to revisit this problem, quit CFD-Post and save changes to the project in Workbench.



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Further work There are many ways the simulation in this tutorial could be extended

Better inlet profiles current boundary conditions (velocity inlets) assume uniform profiles specify profiles (of velocity, turbulence, etc), or extend the geometry so that inlets and outlets are further from junction

Mesh independence check that results do not depend on mesh re-run simulations with finer mesh(es)

generated in Meshing application, or from adaptive meshing in FLUENT

Temperature-dependent physical properties density

differences could lead to buoyant forces (with gravity turned on) quite small effects in this case

viscosity, etc

Actually, the current mesh is probably not fine enough one indication of this is that low-order discretization gives different answers.

Note that, by default, there is no gravity in the model this is a setting in the General task page.




Workshop 2

Transonic Flow over a NACA 0012 Airfoil



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WS2: Transonic Flow Over a NACA 0012 Airfoil

Goals The purpose of this tutorial is to introduce the user to good

techniques for modelling flow in high speed external aerodynamic applications.

Transonic flow will be modelled over a NACA 0012 airfoil for which experimental data has been published, so that a comparison can be made.

The flow to be considered is compressible and turbulent.

The solver used is the density based implicit solver, which gives good results for high speed compressible flows.

The tutorial is carried out using FLUENT and CFD Post from within Workbench, but it could also be completed in standalone mode.



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Start a workbench project Launch Workbench and save the new project as naca0012 in your

working directory. Double-click or drag a FLUENT module from the component systems. Add a results module

double click or drag.

Drag the mouse from cell A3 (Solution) to B2 (Results) to couple

the modules.



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Import a mesh that was generated in Gambit Import the FLUENT mesh file (naca0012.msh).

Right click on cell A2 (setup) and select import FLUENT case file Change the Files of type

to FLUENT mesh file

Select the mesh file naca0012.msh The FLUENT launcher will start.

Keep the default options. Note that 2D

has automatically been selected



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Mesh FLUENT will launch in a new window. The mesh will read in and display, and the zones will be written

out

for the Workbench project.



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Mesh The mesh needs scaling, since it was created with lengths in mm. Select General > Scale and observe the current domain extents.

Select Mesh was created in mm. Press Scale Check that the domain extents are as expected. Close the scale panel and select General > Check

Review the text window and check there are no errors. Finally use Report Quality

to print out cell quality statistics.



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Mesh Zoom in and examine the mesh.

The maximum aspect ratio in this mesh is quite high (around 7000) This is acceptable because these cells are close to the airfoil wall

surfaces. This is needed for the turbulence model being used, since it ensures the

first grid point is in the viscous sublayer.



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Solver Select the steady-state density-based solver:

From General

in the tree select Type: Density-Based Check time is steady

Turn on the energy equation. This is needed because the flow is compressible and we will be using the

ideal gas equation. From Models

in the tree, select Energy

> Edit > and check box

Select the turbulence model to be used: From Models

in the tree, select Viscous

and Edit

Choose the one-equation Spalart-Allmaras model. Select strain/vorticity based production, then OK This is a relatively simple turbulence model that has been shown

to give

good results for boundary layers subjected to adverse pressure

gradients, particularly where there is no or only mild separation.



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Materials The properties to be used for the material air

need to be set.

Select Materials

from the model tree Highlight Air

then Create/Edit

For Density, select Ideal Gas For Viscosity, select Sutherland, and accept the default settings for the

3 Coefficient method. The Sutherland law for viscosity is well suited for high-speed compressible

flow. For simplicity, we will leave Cp and Thermal Conductivity as constants. Ideally, in high speed compressible flow modeling, these should be temperature dependent as well.

Select Change/Create

Assign the material air

to the grid cells: Select Cell Zone Conditions Highlight fluid

then Edit

Observe air

is already selected.



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Operating Conditions Set the Operating Pressure to Zero:

Absolute pressure is the gauge pressure plus the operating pressure. Setting zero operating pressure means that all pressures set in FLUENT

will be absolute. This is the most common practice for compressible flows.

Select Cell Zone Conditions > Operating Conditions Set the Operating Pressure to Zero, then OK



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Boundary Conditions Set the upstream boundary conditions:

Select Boundary Conditions

> pressure-far-field-1 > edit The pressure-far-field boundary type is applicable only when the density is

calculated using the ideal-gas law. It is important to place the far-field boundary far enough from the object of interest. For example, in lifting airfoil calculations, it is not uncommon for the far-field boundary to be a circle with a radius of 20 chord lengths.

On the Momentum

tab, set the gauge static pressure to 73048 Pa

We need to input static pressure for a far-field boundary. We can calculate this from the total pressure, which was atmospheric at 101325 Pa

for the wind-tunnel test. In the case of a real external aerodynamic simulation,

rather than a wind tunnel, the static pressure (at a given altitude) would actually be the same as the total pressure in the far field, because the air in the far field would be stationary.

We have already set the operating pressure to zero, so we are now working in absolute pressure values. Hence the gauge static pressure input will be equal to the

absolute static pressure value, which we will calculate to be 73048 Pa.

Pa 73048

3871.1

7.0No.Machair for 4.1

pressurestatic101325pressuretotal

where

211

12

==

====

==

+=

pppM

pPap

Mpp

o

o

o



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Boundary Conditions Set the Mach Number to 0.7 and flow direction components as shown. The angle of attack () in this numerical case is 1.53 deg. The x-component of

the flow is cos

and the y-component is sin . It is common practice to adjust the numerical

from the experimental

in order to match the lift obtained in the wind tunnel, and then to determine the drag associated with this lift. This adjustment of

is carried out to counter the effects of the wind tunnel enclosure.

Set a reasonable boundary condition for the far field turbulence:

In reality the far-field air would be stationary. Wind tunnels attempt to replicate this by using filters and grids to obtain a low turbulence intensity at the inlet.

Select Intensity and Length Scale Set an intensity of 0.01% Choose a length scale proportional to

the boundary layer thickness. Based on an estimated maximum boundary layer thickness of 50mm*, a suitable length scale is 0.4 x 0.05m = 0.02m

* taken from a previous simulation



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Boundary Conditions Select the thermal tab.

The wind tunnel operating conditions for validation test data give the total temperature as T0

= 311 K We can therefore calculate the static temperature to be 283.24 K

K 24.283so and 098.1

7.0 number Machair for 4.1

etemperaturstatic K 311 etemperatur total

where

211

0

0

20

====

==

==

+=

TTT

M

TT

MTT



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Boundary Conditions For both walls representing the airfoil, leave the default settings

which correspond to a no-slip condition for momentum and adiabatic for thermal.



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Reference Values Set the reference values: These are not used in the actual solution,

but are used for reporting coefficients, such as Cp. Use the freestream conditions as a reference, so choose compute from

then select pressure-far-field-1

in the drop down list.

Note the reference values for density, enthalpy, pressure, temperature,

etc. will update from the freestream values you specified in the pressure-far-field-1 boundary.

Set the reference length (which is not updated from the far field boundary values). In this 2D case, we will use the airfoil chord length, of 1m.



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Solution Methods The CFD computation is now defined. However the solver settings

need to

be modified. These dictate how fast, stable and accurate (within the mesh and BC constraints) the solution will be.

Select Solution Methods in the LHS tree.

Keep the default settings for the implicit formulation and Roe-FDS flux type. The explicit formulation is only normally used for cases where the characteristic

time scale is of the same order as the acoustic time scale, for example the propagation of high Mach number shock waves.

The implicit formulation is more stable and can be driven much harder to reach a converged solution in less time.



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Solution Methods Change the gradient method to Green-Gauss Node Based.

This is slightly more computationally expensive than the other methods but is more accurate.

Select Second Order Upwind for flow and turbulence discretization. To accurately predict drag, select the Second Order Upwind

schemes.



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Solution Controls The Courant number (CFL) determines the internal time step and

affects the solution speed and stability. The default CFL for the density-based implicit formulation is 5.0. It is

often possible to increase the CFL to 10, 20, 100, or even higher, depending on the complexity of your problem. You may find that a

lower

CFL is required during startup (when changes in the solution are

highly nonlinear), but it can be increased as the solution progresses.

As we will be using automatic solution steering, the choice of CFL at this stage is not important for this case.

Keep the default under-relaxation factors (URFs) for the uncoupled parameters.



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Solution Monitors Set up residual monitors so the convergence can be monitored

Monitors > Residuals > Edit Make sure plot

is on

Turn off convergence checks by setting the criterion to none. This means that the calculation will not stop based on the residual plots convergence, but you can still see their progress.



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Solution Monitors Set up a monitor for the drag coefficient on the airfoil. Select both wall zones and toggle on Print, Plot

and Write. Remember that

is 1.53

so we need to use the force vector as shown. -Lift and drag are defined relative to the wind, not the airfoil.

Press OK, then follow the same process to setup a monitor for Lift. The settings are identical except for the File Name (cl-history instead of cd-history) and the

Force Vectors defined as shown here:

You can specify

which window

FLUENT uses to display plots. For now, accept th

e defaults.



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Solution Initialization Initialize the flow field based on the far-field boundary:

Select Solution Initialization from the model tree Compute from > pressure-far-field-1 Press Initialize.

Solution Steering enables the robust first order discretization in the early-stages of the computation, then blends to the more accurate second order schemes as the solution stabilizes. Select Run Calculation, and toggle on Solution Steering Change the flow type to transonic and keep default options

Full-Multi-Grid Initialization will compute a quick, simplified solution based on a number of coarse sub-grids. This will then be used as a starting point for the main calculation. FMG can help to get a stable starting point.



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Case Check Check the case file and make sure there are no reported issues.

Use Run Calculation > Check Case

Any potential problems with the case setup will be raised in the

case check panel if there are no problems this panel will not appear. In this case there is a recommendation to check the reference values for

the

force monitors. Since we have already set these we can ignore this warning.

Save the case file. File > Save Project (if running under workbench)



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Run Calculation Although the calculation is ready to compute, It is good practice (but

not strictly necessary) to run the FMG and then check the coarse FMG solution before starting the main calculation iterations.

Set the number of requested iterations to zero, and press Calculate.



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Run Calculation Check the pressure and velocity contours to make sure that no

spurious values are predicted. Go to Graphics and Animations in the LHS tree, choose Contours

and Set Up



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Run Calculation Choose Contours of Pressure > Static Pressure and Filled Display. If you need to autoscale the display press A Zoom in as required. Examine the min and max reported values. Repeat for Contours of Velocity> Mach Number.



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Run Calculation There are no spurious results from the FMG, so proceed to the main

calculation. Return to Run Calculation

in the LHS tree.

Change the number of windows to three (for the residual, drag and lift monitors that we set up earlier).

Request 900 iterations. Calculate



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Run Calculation After 900 iterations the calculation has fully converged.

Note that the CFL has been updated during the calculation in a number of stages, ramping up from 5 to 200 as we requested. This can be seen in the CFL window and the effect on the residuals is also evident. By the end of the calculation the residuals have converged well and are

no

longer changing. The drag and lift monitors are also stable.



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Post Processing [FLUENT] Select Graphics and Animations

in the LHS menu

Examine the contours of static pressure. Turn off Filled

to just display the

contour lines. Adjust the Levels to increase the

number of contour lines.

The contour will display in the active window (click a window to activate). Alternatively, use the drop down menu to return the display to a single window as shown here



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Post Processing [FLUENT] Plot contours of Velocity > Mach Number and notice that the flow

is

now locally supersonic.



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Post Processing [FLUENT] Select Plots

in the LHS menu.

Plot Pressure Coefficient along the top and bottom airfoil surfaces.



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Post Processing [FLUENT] Compare experimental pressure coefficient plots which we can

import and plot here alongside the numerical prediction. Click on Load File

and browse for the files in your directory.



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Post Processing [FLUENT] Once loaded, plot the CFD and experimental Cp plots together. A good agreement can be seen.



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Post Processing [FLUENT] In order to obtain a good drag prediction, and for the turbulence

model to work effectively, we need to have a mesh that is well resolved near to the wall, such that the first grid point is in the viscous sub-layer. Ideally we want a Y+ value of 1 or less.

Plot Turbulence > Y+, along both of the airfoil walls. Deselect the Pressure Coefficient File Data.

We can see that this is achieved here, the max Y+ is 0.75



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Post Processing [FLUENT] Compare the predicted Cl and Cd against the experimental values.

From Reference 1 Cl = 0.241 and Cd = 0.0079

From the console window, we have predicted Cl = 0.241 and Cd = 0.0083

Again, good agreement can be seen.



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Post Processing Save the project from the FLUENT file menu .

Take the middle option Continue after replacing settings file) Close FLUENT (File > Close FLUENT) Additional post-processing will now be performed in CFD Post. Return to the Workbench Project window. Click on Update Project

and notice the Results panel update.

Right click on cell B2 (Results) and select edit. This will launch CFD Post.



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Post Processing Note that CFD Post works in 3D, so a unit thickness will be added to

the 2D airfoil, with symmetry side boundaries.



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Post Processing Insert a new Contour and accept the default name Contour 1

Top menu > Insert > Contour Choose the location as symmetry-1 Choose the variable to be pressure and Apply

(zoom in)



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Post Processing A useful feature in CFD Post is the ability to compare two different

sets of CFD data. Verify that the file NACA0012-mach-0.5-conv.dat.gz

is in your working

directory. File > Load Results

Browse to your working directory.

Under Case options

make sure keep current cases loaded

is checked. Open the File NACA0012-mach-0.5-conv.dat.gz.

Click OK if an Information/Warning dialog box appears.

We now have two data sets loaded and can do a case comparison.



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Post Processing Make sure that two windows are open, and select the respective

cases in a different window. Lock the views so they are synchronised.



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Post Processing Toggle on location Symmetry 1

in each case.

Select Contour 1

and apply. We can compare the two pressure plots.



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Post Processing Finally, we can plot the difference between the two. In the Outline view, double-click Case Comparison. The Case Comparison details view appears. Select Case Comparison Active and click Apply. A third viewport opens that displays the pressure difference between

the two cases.



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Summary In this tutorial we have used FLUENT within a Workbench project to

compute the transonic, compressible flow over a naca0012 airfoil.

We have imported a mesh that was generated in Gambit.

We have used the density based solver with solution steering.

We have compared the results to published experimental data and seen good agreement.

We have seen how FLUENT can be linked to CFD Post in a Workbench project, and we have explored some of the features within CFD Post.



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References T.J. Coakley, Numerical Simulation of Viscous Transonic Airfoil

Flows,

NASA Ames Research Center, AIAA-87-0416, 1987.

C.D. Harris, Two-Dimensional Aerodynamic Characteristics of the NACA 0012 Airfoil in the Langley 8-foot Transonic Pressure Tunnel,

NASA Ames Research Center, NASA TM 81927, 1981.




Workshop 3

Room Temperature Study (Part 1)



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WS3: Room Temperature Study

Introduction

In this introductory workshop you will be analyzing the effect of computers and workers on the temperature distribution in an office. In the first stage, the simulation of airflow through the duct will be carried out and then the outlet conditions for the duct will be saved and provided as the profile data for the inlet condition(s) of the room



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Duct Simulation: DescriptionThe operating and boundary conditions for the flow are: The working fluid is Air Fluid Temperature = 294 K Inlet: 0.45 kg/s @ 294 K Outlet: 0.225 kg/s (per vent)

Inlet

Vent 2

Vent 1

Inlet



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Starting FLUENT in Workbench

1. Open the Workbench (Start > Programs > ANSYS 12.0 > ANSYS Workbench)

2. Drag FLUENT into the project schematic3. Change the name to Duct4. Double click on Setup5. Choose 3D and Double Precision under Options and retain the

other default settings



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Import Mesh

1. Under the File menu select Import> Mesh2. Select the file duct.msh and click OK to import the mesh3. After reading the mesh, check the grid using Mesh>Check option

or by using Check under Problem Setup>General

This starts a new FLUENT session and the first step is to import the mesh that has already been created:



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Setting up the Models1. Select Pressure Based, Steady state solver Problem

Setup>General>Solver2. Specify Turbulence model

Problem Setup > Models > ViscousDouble click and Select k-omega (2 eqn) under Model and SST under k-omega model and retain the default settings for the other parameters

3. Make sure that the Energy Equation is disabled Problem Setup > Models> Energy



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MaterialsDefine the materials.

Problem Setup > Materials 1. Double click on air to open Create/Edit Materials panel2. By default, Density and Viscosity of air are set as 1.225 kg/m3 and

1.7894e-05 kg/(m-s) respectively3. Retain those values and close the panel



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Operating Conditions Under Problem Setup >Cell Zone Conditions (operating

conditions are also in BC panel)Click on Operating Conditions and set the Operating

Pressure (Pascal) to 101325



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Boundary ConditionsUnder Problem Setup > Boundary Conditions

1. Select inlet under Zone and choose Pressure-Inlet from the drop down menu under Type

2.Now double click on inlet under Zone

Input all the parameters in Momentum tab as shown below



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1.Select vent1 under Zone and choose mass-flow-inlet from the drop down menu under Type

2.Now double click on vent1 under Zone

Input all the parameters in Momentum tab as shown below



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1.Select vent2 under Zone and choose mass-flow-inlet from the drop down menu under Type and set the conditions similar to that of vent1

NOTE: Under the Direction Specification Method, we may also use Outward Normal condition for both the vents



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Solution Methods Set the Solution methods which decides the

Pressure-Velocity coupling. Under Solution>Solution Methods setup the

parameters as shown in the image.



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Solution ControlsUnder Solution>Solution Controls setup the parameters as shown below



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Monitors

Residual Monitoring

Solution > Monitors1.Double click on Residuals (By default it is on)2.Enable Plot under Options. Deselect Check Convergence for all the variables.



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Monitors

Solution > Monitors > Surface Monitors 1. Click on Create to create a new surface monitor2. Type velocity-monitor under Name3. Enable Printing and Plotting of monitors by marking check boxes

under Options4. Select Area-Weighted Average from the drop-down menu under

Report Type5. Select Velocity as the Field Variable and select Velocity

Magnitude under Velocity variable

Monitor points are used to monitor quantities of interest during the solution. They should be used to help judge convergence. In this case you will monitor the Velocity of the air that exits through the door. One measure of a converged solution is when this air has reached a steady- state temperature.

Surface Monitors



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Monitors6. Select one of the vents as the Surfaces to be monitored7. Click on OK to create the monitor and to close the panel

We can also write the above values to a file by clicking the check box next to Write.



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Write Case File

1. To save the project File>Save Project

2. To write the case files File>Export>Case..

You can now save the project and proceed to write a case file for the solver:



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InitializationBefore starting the calculations we must initialize the flow field in the entire domainSolution > Monitors > Solution Initialization1.Initializing the flow field with near steady state conditions will result in faster convergence2.In this case, from the flow rate and the area of the duct we can get an estimate of the velocity at steady state3.Click on Initialize to initialize the solution



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FMG Initialization

Flow convergence can be accelerated if a better initial solution is used at the start of the calculation. The Full Multigrid initialization (FMG initialization) can provide this initial and approximate solution at a minimum cost to the overall computational expense.Note: FMG initialization is not available through GUI

1.Press in the console to get the command prompt ( >).2.Enter the text commands and input responses outlined in green, as shown, accepting the default values by pressing when no input response is given

Note: The FMG initialized flow field can be inspected using FLUENT's postprocessing tools.



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FMG Initialization



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Run Calculations

The solution process can be started in the following mannerSolution >Run Calculation

Enter 200 for Number of Iterations and click on Calculate

During the iteration process, both the residual plot and monitor plots will be shown in different windows. If the velocity monitor is not changing we can stop the iterations. You may specify further iterations if the monitors are still changing significantly.

The magnitude of change of a monitor per iteration can be observed from the console (enabled by clicking on Print to Console while creating the monitor)

Note: Iterations can be stopped in between using the Cancel button.



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Residue & Monitor plots

The results included are obtained after running for 370 iterations.



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Other Checks (optional)We can check the mass balance at the inlet and outlet boundary as follows:Results > Reports> Fluxes1.Click on Setup2.A new dialogue box for Flux Reports will come3.Select Mass Flow Rate under Options4.Select inlet, vent1,vent2 together under Boundaries5.Click on Compute6.Mass flow rate on all these boundaries will be printed and we can see that the Net Results is in the order of e-06 which indicates very good convergence



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Exporting the Profile at the Outflow boundaryWe need to export the outflow velocity profile at the Vents to provide the same as an input for the room case.Exporting the Profile:1.Export the velocity profile at vent1 from the file menu

File>Export>Profile2.Select vent1 from Surfaces 3.Select X,Y,Z Velocity and Turbulent Kinetic energy(k) and Specific dissipation rate (Omega)as the Values to be exported 4.Save the file as vent1.prof



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Exporting the Profile at the Outflow boundary

4. Similarly export the Velocity profile of vent2 and save the file as vent2.prof



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Write Case & Data File


2. To write the case/data files File>Export>Case & Data..





Workshop 3

Room Temperature Study (Part 2)



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Room: Operating Conditions

The operating conditions for the flow at room are: The working fluid is Air Worker Temperature = 310 K Computer Monitor Temperature = 303 K Computer Vent: 0.033 kg/s @ 313 K (per computer) Ceiling Vents: profile data, Temperature=294 K



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Room Geometry and Details

Vent 2 Vent 2Outlet

Workers

Monitors Computer CPU



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Starting FLUENT in Workbench

1. Return to the Project window2. Drag FLUENT into the Project Schematic3. Change the name to Room4. Double click on Setup5. Choose 3D and Double Precision under Options and retain the

other default settings



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Import Mesh

1. Under the File menu select Import> Mesh2. Select the file duct.msh and click OK to import the mesh3. After reading the mesh, check the grid using Mesh>Check option

or by using Check under Problem Setup>General

This starts a new FLUENT session and the first step is to import the mesh that has already been created:



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Reading the ProfilesRead the profile files that were written in the Ducts case at Vent Boundaries1.Under the File menu select Read> Profile2.Select the file vent1.prof and click OK to read the profile3.Similarly read vent2.prof file



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Models1. Select Pressure Based, Steady state

solver Problem Setup>General>Solver

2. Specify turbulence model Problem Setup > Models > Viscous Double click and Select k-omega (2 eqn) under Model and SST under k- omega model and retain the default settings for the other parameters

3. Enable the Energy Equation. Problem Setup > Models> Energy



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MaterialsDefine the materials.

Problem Setup > Materials 1. Double click on air to open Create/Edit Materials panel2. Select incompressible-ideal-gas from the dropdown menu of Density3. Retain other default values of Specific heat and Viscosity. Select

Change/Create to implement the changes then Close

NOTE: The incompressible ideal gas law for density is used when pressure variations are small enough that the flow is fully incompressible but you wish to use the ideal gas law to express the relationship between density and temperature



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Operating ConditionsProblem Setup >Cell Zone Conditions

Click on Operating Conditions and set the Operating Pressure (Pascal) to 101325

Enable Gravity and specify Z-component of Gravitational Acceleration as -9.81 m/s2

Enter Operating Density as 1.225 kg/m3

Note: Enabling gravity will allow the solver to take into account the buoyancy effect due to the change in the density of the air.



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1.Select vent1 under Zone and choose velocity-inlet from the drop down menu under Type. For this boundary we will specify the parameters using the previously read profile file

2.Now double click on vent1 under Zone

3. Go to Momentum tab, set Components as Velocity Specification Method

4.Select vent1 x-velocity from the dropdown menu for X-Velocity. (make sure you select the velocity variable vent1 x-velocity not the grid variablevent1 x. Do likewise for all the other variables (y-velocity, z- velocity, turbulent kinetic energy and specific dissipation rate).

5.In the Thermal tab, set a constant Temperature of 294K:



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6. Similarly, select vent2 under Zone and set all the quantities. This time choose the profile quantities starting with vent2



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1.Select outlet under Zone and choose Pressure-outlet from the drop down menu under Type. For this boundary we will specify the parameters using the previously read profile file

2.Now double click on outlet under Zone

3.Go to Momentum tab, set Gauge Pressure (Pascal) as 0

4.Set the backflow conditions for the turbulence quantities to have a Backflow Turbulent Intensity and Backflow Turbulent Viscosity Ratio of 5% and 5 respectively

5. In the Thermal tab, set a constant Backflow Total Temperature of 294 K



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1.Select computer1intake under Zone and choose Mass-Flow inlet from the drop down menu under Type.

2.Set the Mass Flow Rate as 0.033 kg/s and keep the Direction Specification Method as Outward Normals

3.Set Turbulent Intensity (fraction) and Turbulent Viscosity Ratio as 5% 10 respectively



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Boundary ConditionsTo save time, the conditions for computer1 can be copied over to the boundary

conditions for the other 3 computers in the simulation.

1. Make sure that the inlets for the other computers are all of type mass- flow-inlet

2. In the Boundary Conditions Panel, click the Copy... button. This will open the Copy BCs panel

3. In the From Zone list, select the zone that has the conditions you want to copy: computer1intake

4. In the To Zones list, select the zones to which you want to copy the conditions to: computer2intake, computer3intake, computer4intake

5. Click Copy. FLUENT will set all of the boundary conditions for the zones selected in the To Zones list to be the same

as the conditions for the zone selected in the From Zone list.



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Boundary ConditionsUnder Problem Setup > Boundary Conditions1.Repeat the instructions on the previous 2 slides in order to set the conditions for the

computer vents.2.So, first make sure all vents are of type mass-flow-inlet.3.Set the conditions for computer1vent as in the image below.4.In the Thermal tab, set a constant temperature of 313 K5.Copy this boundary condition from computer1vent to the other 3 computers.



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1.Select monitors under Zone and choose wall from the drop down menu under Type.

2.Now double click on monitors under Zone

3.Go to Momentum tab, set it as Stationary wall with No Slip

4.In the Thermal tab, set a constant Temperature of 303 K



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Boundary Conditions Under Problem Setup > Boundary Conditions1. Select workers under Zone and select wall from the drop down menu

under Type.2.Double-click on workers under Zone.3.On the Momentum tab, specify a stationary wall with no slip.4.On the Thermal tab, set a constant wall temperature of 310 K.



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Solution MethodsSet the Solver Controls

Under Solution>Solution Methods setup the parameters as described below

Select Coupled Scheme Specify the discretization schemes as shown below



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Solution ControlsUnder Solution>Solution Controls

1. Set a Courant Number of 100 with Explicit Relaxation Factors for Momentum and Pressure as 0.25 each

2. Set Under Relaxation Factors of Density, Body Forces, Turbulent Kinetic Energy, Turbulent Viscosity and Specific Dissipation Rate as 0.5 each

3. Keep an Under Relaxation Factor of 1.0 for Energy



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Monitors

Residual Monitoring

Solution > Monitors1. Double click on Residuals (By default it is on)2. Enable Plot under Options. Deselect Check Convergence for all the variables.



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Monitors

Solution > Monitors > Surface Monitors 1. Click on Create to create a new surface monitor2. Type temperature-monitor under Name3. Enable Printing and Plotting of monitors by marking check boxes

under Options4. Select Area-Weighted Average from the drop-down menu under

Report Type5. Select Temperature as the Field Variable and select Static

Temperature under Temperature

Surface Monitors



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Monitors

6. Select outlet under Surfaces 7. Click on OK to create the monitor and to close the panel



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Write Case File


2. To write the case files File>Export>Case..




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Initialization

Solution > Monitors > Solution Initialization

1. Initialize the flow field with inflow conditions by selecting vent1from the dropdown menu under Compute from

2. Click on Initialize to initialize the solution



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Run Calculations

The solution process can be started in the following mannerSolution >Run Calculation

Enter 100 for Number of Iterations and click on Calculate

Monitor the solution and see if the Temperature monitor is not changing further. You can instruct FLUENT to perform more iterations if the monitors are still changing significantly. You can stop iterating if the monitors are stabilized.



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Residue & Monitor plots

The results included are obtained after running for 554 iterations.



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Write Case & Data File


2. To write the case/data files File>Export>Case & Data..




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Post processing(1)

We can create isosurfaces at various locations of the domain to examine the results at any location within the domain, not just at the boundaries.An isosurface can be created in the following manner:1.Select Surface>Iso-surface from the toolbar2.Select Mesh under Surface of constant drop down menu and select Y- Coordinate under Mesh

If we click on Compute it will report the minimum and maximum values

3.Enter 2.4 under Iso-Values4.Specify a surface name under New Surface Name5.Clicking Create will generate the new surface

You may want to create more iso-surfaces at different critical locations to observe different parameters.



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Post processing(2)

Display the contours of Temperature: Go to Results > Graphics and Animation

Select Contours under Graphics and click on Set Up Select Contours of Temperature then Static Temperature Select the Surfaces on which we wish to see the temperature Zoom into the area of interest by using middle mouse buttonOverlay a wireframe representation of the room: On the Contours Panel, Check the Draw Mesh box. Select Edges (not Faces), and Outline. Under Surface Types, select

Wall which will select all the walls. Display then Close (mesh display panel) : Display (contours panel)Display the Vectors of Velocity: Go to Results > Graphics and Animation

Select Vectors under Graphics and click on Set Up Change the Scale to 15, and plot on the surface of interest.



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Post processing(3)We can also find out the Maximum and Minimum of a variable in the following wayGo to Results > Reports>Volume IntegralsSelect Maximum under Report TypeSelect Temperature under Field Variable followed by Static Temperature Select fluid-19 under Cell ZonesOn clicking Compute, the maximum value of the Temperature is calculated.

Note: The location of Maximum temperature, say, can be found out by creating an iso-surface of temperature in the same process as mentioned in the slide-54



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Post processing(4)

Contours of Temperature on a plane at Y=2.4 m

Plane location



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Results Summary

Mass Weighted Average of Temperature at Outlet: 298.02K Minimum temperature in the domain: 293.6K Maximum temperature in the domain: 313.1K (at the region near the outlet

of Computer2vent) Mass Weighted Average of Velocity at Outlet: 0.697 m/s



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Further Steps (Optional)

Following steps can be done so as get the flow patterns at various planes etc.1.Observe the density variation at various planes2.Create a streamline from each of the vents3.Animate the streamlines4.Create an isosurface based on different temperatures



Workshop 4

Electronics Cooling with Natural Convection and Radiation




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WS4: Electronics Cooling

Goals In this workshop, you will model

the heat dissipation from a hot electronics component fitted to a printed circuit board (PCB) via a finned heat sink.

The PCB is fitted into an enclosure which is open at the top and bottom.

Initially only the heat transfer via convection and conduction will be calculated. The effect of thermal radiation will then be included as a later stage.



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Mesh Import (Workbench) This workshop can be done either inside or outside of ANSYS

Workbench.

If working outside of Workbench, you should skip this page.

Open a new Workbench session and select a new FLUENT session from Component Systems

Use Save As to save the session.

Import the the mesh file. Right-click on the Setup cell. Change Files of Type to Fluent

Mesh File Select the mesh file heatsink.msh Click Open.

Launch FLUENT using the default options.

Drag



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Mesh Import (Stand-alone)

(If working with FLUENT as Standalone)

Start a 3D FLUENT session from the icon or from the Windows Start menu

Select either File Read Mesh from the top

menu Open File icon from toolbar

Open the file heatsink.msh

Check the grid to verify that there are no errors in the mesh.



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View the model: Display the mesh and color the faces by ID:

Select Graphics and Animations Highlight Mesh, then Setup just below

Set Faces to on, and Edges to Feature Deselect all currently selected faces Select Surface Types Wall, Pressure Outlet

and Velocity Inlet (note effect on Surfaces list) Select Colors and Color by ID. Display

Select the Lights button, and turn on headlight.

Make the outer walls transparent Use Scene button Select wall_left, wall_right and wall_top Select Display and set transparency to roughly

50 Apply and close Display Property panel Apply and close Scene Description panel

Redisplay the image (Use Setup and Display buttons as above)



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Model setup1. Display the mesh and adjust the

display settings.a) Highlight Mesh and click Setup.

i. Select Feature and Edges. Set Edge Type to Feature.

ii. Deselect all currently selected facesiii. Select Surface Types Wall, Pressure

Outlet and Velocity Inlet (note effect on Surfaces list)

iv. Select Colors and Color by ID.v. Click Display

2. Change temperature units to C Define Units

1. Select Temperature as a Quantity2. Select c as the temperature units.3. Close the panel.

3. Enable the energy equation.a) Select the Models tree itemb) Double-click on Energy and enable the equation.



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Comments on Model setup General

It is good practice to display the grid after import to check for any boundary zone misassignment and that you have opened the correct model.

Workbench uses SI units (meters, kg etc) but if importing a mesh from another source check the scale and dimensions are correct.

Check mesh is used to confirm the mesh is suitable for use in a CFD simulation.

Report Quality is a backup to the quality tools available within the meshing application.

By default the energy equation is not solved to reduce CPU load because many problems are isothermal. In this case, temperature must be calculated so the energy equation needs to be enabled.

The onset of turbulence is specified by the Reynolds Number (pipe flow) or Rayleigh Number (natural convection). Calculating these numbers using boundary conditions indicates that the flow will be laminar.



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Material properties The air density needs to change with

temperature (but not pressure) Select Materials Air Create/Edit Change density to incompressible

ideal gas All other properties remain unchanged Click Change / Create then close the

fluid materials window.

Define two additional solid materials (for the board and the heat sink). Select Materials Solid Create/Edit Click the FLUENT Database button. Change Type to Solid Select Copper Copy then close the database window



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Material properties Modify the copper material to produce two different materials.

The PCB is made of material Fr-4. Change Name to fr-4 Delete the chemical formula All other properties remain unchanged Click Change/Create. Click No when prompted to overwrite

copper. Selecting No will create a new material Fr-4,

but copper remains in the material list. Selecting Yes will overwrite the copper

material for the current case only. The heat sink is made of a different

material (named Component for this simulation).

Select solid material Copper Change Name to component Delete the chemical formula Select Change/Create. Select Yes when prompted to

overwrite copper.



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Comments on Material properties In most natural convection problems the change of density with

temperature drives the flow. The changes in pressure over the domain are minimal, and their effect on density negligible, hence the incompressible ideal gas density formulation can be used instead of fully compressible ideal gas.

The FLUENT database contains basic properties for many materials. These are generally set to the standard STP/RTP values, but always check these are suitable before proceeding.

Additional materials can be added to the database; refer to the user documentation. It is often easier to copy a material from the database and then modify it; alternatively, you can modify the default material of aluminium and then choose to not overwrite.



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Set Cell Zone Conditions Under Cell Zone Conditions click the

Operating Conditions button. Change the Reference Pressure location in

the y direction to -0.29 m Enable Gravity, and set the y component to

to 9.81 m/s2. Turn on Specified Operating Density and set

to 1.1096 kg/m3 Click OK.

There are no changes to the fluid zone (Cell Zone Fluid Edit) Observe that this contains material air which

is correct. Close the pop-up window



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Set Cell Zone Conditions Set the material properties for

the PCB: Select cell zone solid_board,

then Edit Change the material to fr-4 OK to close the window

Set the material properties for the heat sink: Heatsink is made of aluminium Select the cell zone

solid_heatsink Observe the default material

aluminium is already selected. No change is needed



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Set Cell Zone Conditions

Set the conditions for the component: We need to set both the material,

AND the thermal power (75W) dissipated by this component.

Select zone solid_heatsource Change the material to component Check Source Terms then go to the

Source Terms tab The components volume is

0.11808x10-3 m3. Hence, the volumetric source is 635000 W/m3.

Create 1 energy source with the above value.



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Set Boundary Conditions For the Inlet (Boundary Conditions > Inlet)

Change type to Pressure Inlet Keep the pressure at 0 Pa Under the Thermal tab set the temperature to 45 C, then OK

For the Outlet: Keep type as Pressure Outlet Select Edit and set 0 Pa Gauge Pressure, with direction From

Neighboring Cell Under the Thermal tab set backflow temperature to 45C, then OK



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Set Boundary Conditions Set the casing walls to be adiabatic:

Select boundary zone wall_left Under the thermal tab, check this is set to zero heat flux Repeat for wall_right and wall_top

Set the PCB outer surface thermal properties to be adiabatic. These are the external surfaces of the model The surfaces to set are wall_board_bottom and wall_board_side Set these to zero heat flux as above.

Note that the surface wall_board is the surface of the PCB that borders the fluid air region, and so is not an exterior boundary



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Comments on Cell and Zone Conditions Operating conditions

Gravity is required for natural convection. In many cases, unless buoyant forces are present, gravity can be left disabled.

Operating density is critical in natural convection problems, and should be set to the density at the far field temperature (ie inlet temperature).

Operating pressure position is related to the inlet/outlet pressure settings. In this example, it is positioned at the inlet.

Boundary zones Inlet and Outlet pressure set

to 0 Pa gauge, as it is at the operating pressure position.

Volume data The volume of an entity can be

requested in the Volume Integrals panel. Note that the solution must be initialized before the volume integrals are enabled.



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Comments on Cell and Zone Conditions External heat loss:

ansys fluent intro 12.0 1st-edition - workshops

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