cfx intro 12.0 ws3 room study

5/28/2018 CFX Intro 12.0 WS3 Room Study

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WS3-1ANSYS, Inc. Proprietary

2009 ANSYS, Inc. All rights reserved.April 28, 2009

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Workshop 3

Room Temperature Study

Introduction to CFX


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WS3: Room Temperature Study



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Workshop SupplementIntroduction

In this workshop you will be analyzing the effect of computers and

workers on the temperature distribution in an office. In the first stageairflow through the supply air ducts will be simulated and the outlet

conditions for the duct will be used to set the inlet conditions for the

room. Although both components could be analyzed together,

separating the two components allows different room configurations to

be analyzed without solving the duct flow again.


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Workshop SupplementDuct Simulation

The operating conditions for the flow are:

The working fluid is Air Ideal Gas

Fluid Temperature = 21 [C]

Inlet: 0 [atm] Total Pressure

Outlet: 0.225 [kg/s] (per vent)

Inlet

vent1

vent2


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Workshop SupplementStarting CFX in Workbench

1. Open Workbench

2. Drag CFX into the Project Schematic from the Component Systemstoolbox

3. Change the name of the system to duct

4. Save the project as RoomStudy.wbpj in an appropriate directory

5. Double-click Setup


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Workshop SupplementImport Mesh

1. Right-click on Meshin the Outlinetree and select Import Mesh > ICEM

CFD

2. Select the file duct_mesh.cfx5

3. Make sure Mesh Unitsare in mand click Opento import the mesh

The first step is to import the mesh that has already been created:


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Workshop SupplementCreate Domain

1. Double-click on Default Domainin the Outlinetree to edit the domain

2. On the Basic Settings tab, set the Fluid 1 Material setting toAir Ideal

Gas

3. Switch to the Fluid Models tab

4. Set the Heat Transfer Option to Isothermal

Heat Transfer is not modeled, but since the working fluid is an ideal gas

we need to provide a temperature so its properties can be calculated

5. Set the Fluid Temperature to 21 [C]

6. Change the Turbulence Model Optionto Shear Stress Transport

7. Click OKto commit the changes to the domain

You can now create the computational domain:


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Workshop SupplementCreate Boundary Conditions

1. INLET Boundary Condition Name: INLET

Boundary Type: Inlet

Location: INLET

Mass and Momentum Option:

Total Pressure (stable)

Relative Pressure: 0 [Pa]

3. VENT2 Boundary Condition

Name: VENT2

Boundary Type: Outlet

Location: VENT2


Mass Flow Rate

Mass Flow Rate: 0.225 [kg/s]

Now create the following boundary conditions:

2. VENT1 Boundary Condition Name: VENT1


Location: VENT1


Mass Flow Rate



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Workshop SupplementSolver Control

1. Double click on Solver Control from the Outlinetree

2. Enable the Conservation Targettoggle

3. Click OKto commit the settings

The default Conservation Target is 1%. This means that the

global imbalance for each equation must be less than 1% (i.e.

(flux influx out)/flux in < 1%). The solver will not stop untilboth the Residual Target and the Conservation Target have

been met (or Max. Iterations is reached).


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Workshop SupplementMonitor Point

1. Double click on Output Control from the Outlinetree

2. Switch to the Monitortab and enable the Monitor Optionstoggle

3. Under Monitor Points and Expressions, click the New icon

4. Keep the default name Monitor Point 1

5. Set the Option to Expression

Monitor points are used to monitor quantities of interest during the

solution. They should be used to help judge convergence. In this caseyou will monitor the velocity of the air that exits through the vent. One

measure of a converged solution is when this air has reached a steady-

state velocity.


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6. In the Expression Value field, type in:areaAve(Velocity w)@VENT1

7. Click OKto create the Monitor Point


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Workshop SupplementWrite Solver File

1. Close CFX-Pre to return to Project window

2. Save the project

3. Right-click on Solution and select Edit

4. Choose Start Run

You can now save the project and proceed to write a definition file for

the solver:


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Workshop Supplement

1. Examine the residual plots for Momentum and Mass and Turbulence

2. Examine the User Pointsplot

3. When the run finished close the Solver Manager

4. View the results in CFD-Post by double-clicking Results in the Project

window

CFX Solver Manager

Monitor point

Residual plot


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Workshop SupplementCFD-Post

1. Select File > Export

2. Change the file name to vent1.csv

3. Use the browse icon to set an appropriate

directory4. Set Type as BC Profile and Locationsas

VENT1

5. Leave Profile Type as Inlet Velocity and

click Save

6. Similarly export a BC profile of VENT2 tothe file named vent2.csv

7. Quit CFD-Post and return to the Project

Schematic

Now we will export a Boundary Condition profile from the outlet regions for

use in the next simulation.


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Workshop SupplementOperating Conditions

The working fluid is Air Ideal Gas

Computer Monitor Temperature = 30 [C]

Computer Vent Flow Rate: 0.033 [kg/s] @ 40 [C] (per computer)

Ceiling Vents: Profile Data, Temperature=21 [C]

The operating conditions for the flow in the room are:

outlet

vent1

vent2


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Workshop SupplementStarting Room Simulation in Workbench

1. Drag CFXinto the Project Schematic from the Component Systems

toolbox

2. Change the name of the system to room

3. Double-click Setup in the room system


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Workshop SupplementImport Mesh

1. Right-click on Meshin the Outlinetree and select Import Mesh > ICEM

CFD

2. Select the file room.cfx5

3. Make sure the Mesh Unitsare in mand click Opento import the mesh

The first step is to import the mesh that has already been created:


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1. Edit Default Domainfrom the Outlinetree

2. On the Basic Settings tab, set the Fluid 1 Material setting toAir Ideal

Gas

3. Set the Buoyancy Option to Buoyant. Set the Buoyancy settings as

shown:

Gravity X Dirn. = 0 [ m s^-2 ]

Gravity Y Dirn. = 0 [ m s^-2 ]

Gravity Z Dirn. = -g (first, click theEnter Expression icon )

Buoy. Ref. Density = 1.185 [ kg m^-3 ]

You can now create the computational domain:

Enabling Buoyancy allows for natural convection due to density

variations. The buoyancy force is a function of density variations

relative to the buoyancy reference density. Since density

variations can be very small, using a reference density help avoid

round-off errors. The reference density should be a typical fluid

density in the domain.


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4. Switch to the Fluid Models tab

5. Change the Heat Transfer Option to Thermal Energy6. Change the Turbulence Model Optionto Shear Stress Transport

7. Switch to the Initialisation tab

8. Check the Domain Initialisation box

9. Set the Temperature OptiontoAutomatic with Value. Set the

Temperatureto 21 [C]

10. Click OKto commit the changes to the domain

For most cases, setting an initial condition for domain

temperature is not necessary since the solver can

automatically calculate initial conditions. However, if you input

a value that is closer to the final solution than what the solverwould automatically calculate, you will reach a converged

solution faster.


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Workshop SupplementProfile data initialization

1. Select Tools>Initialise Profile Data

and choose the Data File asvent1.csv. Click OK

CFX-Pre reads the file and creates

functions that point to the variables

available in the file (see the User

Functions section in the Outline tree).

Boundary conditions can be set byreferencing these functions. E.g.VENT1.Velocity u(x,y,z)refers to

the Velocity u value in the VENT1

function with the local coordinate values

x, y and z passed in as the arguments.

Any value with the correct dimensions

can be passed in as an argument, butusually the local coordinates are used.

2. Similarly initialise profile data for

vent 2 by choosing vent2.csv


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Workshop SupplementCreate Boundary Conditions

1. vent1 Boundary Condition Name: vent1


Location: VENT1

Select Use Profile Data and choose

VENT1 as the Profile Name

Click Generate Values

This will create expressions for the

Mass and Momentum option on the

Boundary Details tab that reference the

profile functions

On the Boundary Details tab check that

the expressions make sense

Heat Transfer Option: Static

Temperature

Static Temperature: 21 [C]

Now create the following boundary conditions:


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2. vent2 Boundary Condition

Name: vent2


Location: VENT2

Select Use Profile Data and choose VENT2as the Profile Name

Click Generate Values

The Mass and Momentum Option will be automatically updated Heat Transfer Option: Static Temperature


3. workers Boundary Condition

Name: workers

Boundary Type: Wall

Location: WORKERS

Heat Transfer Option: Temperature

Fixed Temperature: 37 [C]

Create Boundary Conditions


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4. outlet Boundary Condition

Name: outlet

Boundary Type: Opening

Location: OUTLET

Mass and Momentum Option: Opening Pres. and Dirn

Relative Pressure: 0 [Pa]

Heat Transfer Option: Opening Temperature

Opening Temperature: 21 [C]

5. monitors Boundary Condition

Name: monitors

Boundary Type: Wall

Location: monitors

Heat Transfer Option: Temperature

Fixed Temperature: 30 [C]



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6. computerVent Boundary Condition

Name: computerVent


Location: COMPUTER1VENT, COMPUTER2VENT,

COMPUTER3VENT, COMPUTER4VENT

Mass and Momentum Option: Mass Flow Rate


Heat Transfer Option: Static Temperature



S S


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7. computerIntake Boundary Condition

Name: computerIntake


Location: COMPUTER1INTAKE, COMPUTER2INTAKE,

COMPUTER3INTAKE, COMPUTER4INTAKE

Mass and Momentum Option: Mass Flow Rate


Mass Flow Update Option: Constant Flux

This enforces a uniform mass flow across the entire boundary region, rather

than letting a natural velocity profile develop. It is used here to make sure the

flow rate through each intake is the same.


WS3 R T t St d


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Workshop SupplementSolver Control

1. Edit Solver Control from the Outlinetree

Due to nature of this flow it will take a long time for a steady-state conditionto be reached

2. Increase the Max. Iterations to 750

3. Change the Timescale Control to Physical Timescale

4. Set a Physical Timescale of 2 [s]

5. Enable the Conservation Targettoggle

6. Click OKto commit the settings

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1. Edit Output Control from the Outlinetree

2. Switch to the Monitortab and enable the Monitor Optionstoggle

3. Under Monitor Points and Expressions, click the New icon

4. Enter the Name as temp

5. Set the Option to Expression

Monitor points are used to monitor quantities of interest during the

solution. They should be used to help judge convergence. In this caseyou will monitor the temperature of the air that exits through the outlet.

One measure of a converged solution is when this air has reached a

steady-state temperature.

WS3 R T t St d


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6. In the Expression Value field, type in:massFlowAve(Temperature)@outlet

7. Click OKto create the Monitor Point

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Workshop SupplementWrite Solver File

1. Close CFX-Pre to return to the Project window and save the project

2. Select File > Import from the main menu in Workbench

3. Set the file filter to CFX-Solver Results File

4. Select the results file provided with this workshop, room_001.res

5. Change the name of the system to room results

You can now save the project and proceed to write a definition file for

the Solver:

The solution will take several hours to solve on one processor. To save

time, a results file is provided with this workshop. The Project

Schematic shows that the roomSolution has not been completed, soyou cannot view the results in CFD-Post yet. To view the results for the

file provided youll need to add the results to the project.



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Workshop SupplementProject Schematic



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Workshop SupplementCFX Solver Manager

1. Right-click on Solution in the room results system and select Display

Monitors

2. Examine the residual plots for Momentum and Mass, Heat Transfer

and Turbulence The Residual Target of 1e-4 was met at about 270 iterations, but the solver

did not stop because the Conservation Target had not been met

3. Examine the User Pointsplot

Air temperature leaving through the outlet did not start to reach a steadytemperature until >650 iterations. Using residuals as the only convergence

criteria is not always sufficient.

Now you can view the solution for the previously solved case.



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Workshop SupplementResidual and Monitor plot

Residual plot Monitor points



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Workshop SupplementCFX Solver Manager

6. Check the Domain Imbalances at the end of the .out file for each

equation You can right click in the text monitor, select Findand search for

Domain Imbalance to find the appropriate section

An imbalance is given for the U-Mom, V-Mom, W-Mom, P-Massand H-

Energyequations

It took 653 iterations to satisfy the Conservation Target of 1% for the H-Energyequationsee the Plot Monitor 1tab

7. Close the Solver Manager

8. View the results in CFD-Post by double-clicking Results in the

Project Schematic from the room system



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1. Select Location > Plane from the toolbar

2. In the Detailswindows on the Geometrytab, set the Definition

Method to ZX Plane

3. Set Yto 1.2 [m]

4. On the Colour tab set Mode to Variable

5. Set Variable to Temperature

6. Set Rangeto Localand clickApply

Observe the temperature distribution (for example, how the warm air

collects under the table)

Start by creating a ZX Plane at Y = 1.2 [m]



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1. ZX Planeat Y= 2 [m]

2. ZX Planeat Y= 5.1 [m]

3. XY Planeat Z= 0.25 [m]

4. When finished observing the temperature distribution, uncheck the

visibility boxes of the planes that you created

Using the same procedure, create several other planes displaying the

temperature profile:



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1. Click Insert > Vector from the main menu

2. In the Detailswindows on the Geometrytab, set Location to Plane 2

and Symbols Size to 3.0 in Symbol tab

3. ClickApply

4. After observing the flow behavior on Plane 2, switch the Location to

Plane 4

Plot vector plots on the planes that you created:



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Workshop SupplementFurther Steps (Optional)

1. Observe the density variation at various planes

2. Create a streamline from each of the vents

You may want to adjust the values on the Limitstab (Max. Segments)

3. Animate the streamlines

Right-click on the Streamlines in the 3D viewer and selectAnimate

4. Create an isosurface based on different temperatures (e.g., 22 [C],24 [C], etc.)

5. Calculate the areaAve of Wall Heat Flux on the workers

Click Tools > Function Calculator

Time permitting, you may want to try the following:

cfx intro 12.0 ws3 room study

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