OpenFOAM/C2/2D-Laminar-Flow-in-a-channel/English

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Tutorial: Simulating Laminar flow in a channel.


Script and Narration : Rahul Joshi


Keywords: Video tutorial,CFD,laminar flow,simpleFoam,channel


Visual Cue
Narration
Slide 1 Hello and welcome to the spoken tutorial on Simulating Laminar Flow in a Channel using openfoam
Slide 2 : Learning Objectives In this tutorial I will show you


2D geometry of channel


Meshing the Geometry


Solving and Post Processing results in Paraview


Validation with analytic result

Slide 3: System requirement To record this tutorial


I am using Linux Operating system Ubuntu 12.04 .


OpenFOAM version 2.1.1


ParaView version 3.12.0


Note that OpenFOAM version 2.1.1 is supported on ubuntu version 12.04


Hence forth all the tutorials will be covered using OpenFOAM version 2.1.1 and ubuntu version 12.04

Slide 4: System Requirement The tutorials were recorded using the versions specified in previous slide

Subsequently the tutorials were edited to latest versions

To install latest system requirements go to Installation Sheet


Slide 4 : Pre-requisite You should know how to create geometry using OpenFOAM


If not, please refer to the relevant tutorials on our website

Slide 5 : About flow in a channel Channel flow problem description
Slide 5 : boudnary patches The boundary names and inlet conditions are shown in this figure
Slide 6 : The flow develpoment length is given by the formula

L= 0.05 * Re * D

Slide 6 : Re which is the Reynolds number


and D which is the channel height



Slide 6 : Using the formula length of the channel comes out to be 5 meters


and height is kept as 1 meters.


The Inlet velocity is 1 meters per second


And we are solving this for a Reynolds number ( Re ) equal 100

Slide : file structure of the case This is a steady state problem


Therefore we are using a steady state incompressible solver for this case

Create a floder and name it as channel in simpleFoam folder


right click >> new folder

I have already created a folder in


simpleFoam folder of incompressible flow solvers

Nmae the folder channel The folder is named as channel


Now let me switch to the folder

copy 0,constant and system from pitzDaily to this channel folder Copy 0,Constant and System folders of any other case file in the simpleFoam directory
I have copied the file structure of case of pitzDaily
Paste it in the channel folder created and


make the necessary changes in the geometry,


boundary faces and boundary condition

Now let me open the command terminal
Press Ctrl+Alt+t keys simultaneously To do this press Ctrl+Alt +t keys simultaneously on your keyboard



run and press enter In the terminal

Type run and press enter

now type cd space tutorials and press enter
incompresible and press enter now type cd space incompressible and press enter
simpleFoam and press enter type cd space simpleFoam and press enter
channel and press enter now type cd channel and press enter
ls and press enter now type ls and press enter
You will see three folders 0 , Constant and System
Type in command terminal

cd constant and press enter

now type cd constant and press enter
ls and press enter now type ls and press enter
polymesh folder and 2 other files In this you will see files containing


properties of fluid and a folder named polymesh

gedit RASProperties and press enter RASProperties contains Reynolds-averaged stress model
Transportproperties transportProperties contain the transport model


and


kinematic viscosity (nu) is set at 0.001 m²/s.

cd polyMesh and press enter Now type cd polyMesh and press enter
ls and press enter Now type ls and press enter
you will see the blockMeshDict file here
gedit blockMeshDict and press enter To open the blockMeshDict file in the


terminal type gedit blockMeshDict and press enter


Scroll down

In the blockMeshDict file covertTometers is set to 1


Set the vertices for channel

The geomery is in meters so the convertTometers is set to 1


next we have defined the vertices of the channel

Mesh size for channel We have used a 100 X 100 mesh size here and cell spacing is kept as ( 1 1 1 )
Boundary conditions and types Next we have the boundary conditions and their types which are set as inlet ,outlet,top,bottom



FrontAndBack boundary type as empty Since it is a 2D problem frontAndBack is kept as empty
Due to a 2 dimensional geometry Also this being a simple geometry


mergePatchPair and edges are to kept empty.


Close the blockMeshDict file

Terminal window In the command terminal Type cd space ..(dot dot) and press enter
Terminal window Again type cd space .. (dot dot) and press enter
In the terninal window type cd 0


type ls and press enter

Now in the terminal type cd space 0 (Zero) and press enter


Now Type ls and press enter

In terminal you can see these slides This contains the intial boundary conditions


and wall functions for the channel case

Wall functions : epsilon, k, nut, nutilda


initial flow conditions: p, R and U

It should contain various files named


epsilon ,k, nut,nuTilda


which are the wall functions


and


p , R and capital U which the are initial conditions of the flow

Slide 7 : formula to calculate epsilon and k. Calculate k which is the turbulent kinetic energy


from the formula given in the slide


Where Ux, Uy and Uz are the velocity


components in the x, y and z direction


And U' ( dash ) = 0.05 times u actual

Slide 8: calculate epsilon


epsilon


C mu - constant


l – length of channel

Calculate epsilon from the formula given


Where epsilon is the rate of disspiation turbulent kinetic energy


C mu is a constant and its value is 0.09


And l is the length of the channel


Let me minimise this

Change only the boundary names Change only the boundary names in each of the above files
Do not chnge the values of nu,nuTilde and R Note that the values of nut, nuTilda and R


are to kept default

Rest of the files should contain initial value


for each of the boundary faces

In the terminal window Now in the terminal Type cd (space) ..(dot dot) and press enter
No change in system folder There is no change to be done in the system folder
Mesh the geometry


terminal window type : blockMesh

We need to mesh the geometry


To do this


In the command terminal type blockMesh and press enter


Meshing is done


Let me switch back to the slide

Slide 8 : Solver type The type of solver we are using here is simpleFoam


It is a Steady-state solver for incompressible, turbulent flow


let me minimise this

Type simpleFoam and press enter In the command terminal type simpleFoam and Press enter
Iterations in terminal window Iterations running will be seen in the command terminal
Iterations running may take some time
Iterations converge or stop at end of time step The iterations will stop once the solution is


converged or it reaches its end time value

In terminal

type: paraFoam and press enter

To view the results in paraview in the terminal


type paraFoam and press enter


This will open up the paraview window

In paraview window


View the geometry

On let hand side of the paraview window click Apply


The geometry can be seen here.

Change from solid color to U On top of active variable control menu change


the drop down menu from solid color to capital U

Look at left side of the channel geometry You can see the initial state of velocity magnitude at inlet.
VCR control click PLAY button On top of the paraview window click on the


play button of the VCR control


you can see the final value of velocity magnitude

Color legend from top left Also toggle on the color legend from the


left hand side top of active variable control menu


Click APPLY again

In object inspector menu


click on rescale to data

Now go to display


Scroll down


You can see Rescale , click on it

Check the color legend for this We can see that once the flow has fully devloped


it attains a maximum uniform velocity at the center


Now let me switch back to the slides



Slide 8:Validation The results obtained can be validated with


the analytical solution for laminar flow in a


channel which is u(max)=1.5 Uavg


Using openfoam we obatain a velocity of 1.48 meters per second which is a good match


This brings us to the end of the tutorial

Slide 9 : Summary In this tutorial we learnt


The File structure of channel


Obtained solution using steady state solver


Viewed the geometry in paraview


Validation with analytic results

Slide 10 :

Assignment

As an assignment:

Solve the problem for Reynold Number 1500 and

validate it with the analytical result

Slide 11 : Abour spoken tutorials The video available at this URL:

http://spoken-tutorial.org/What_is_a_Spoken_Tutorial

It summarizes the Spoken Tutorial project.

If you do not have good bandwidth, you can download and watch it.

Slide 12 :

About Spoken tutorials

The Spoken Tutorial Project Team

-Conducts workshops using spoken tutorials

-Gives certificates to those who pass an online test

-For more details, please write to contact@spoken-tutorial.org

Slide:

Forum to answer questions

Do you have questions on THIS Spoken Tutorial?

Choose the minute and second where you have the question Explain your question briefly Someone from the FOSSEE team will answer them. Please visit http://forums.spoken-tutorial.org/

Slide:

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Questions not related to the Spoken Tutorial?

Do you have general/technical questions on the Software? Please visit the FOSSEE forum http://forums.fossee.in/ Choose the Software and post your question


Slide:

Lab Migration Project

We coordinate migration from commercial CFD software like ANSYS to OpenFOAM

We conduct free Workshops and provide solutions to CFD Problem Statements in OpenFOAM For more details visit this site: http://cfd.fossee.in/


Slide:

Case Study Project

We invite students to solve a feasible CFD problem statement of reasonable complexity using OpenFOAM

We give honorarium and certificate to those who do this For more details visit this site: http://cfd.fossee.in/


Slide 13

Acknowledgement


Spoken Tutorials are part of Talk to a Teacher project,

It is supported by the National Mission on Education through ICT, MHRD, Government of India.

More information on the same is available at the following URL link http://spoken-tutorial.org/NMEICT-Intro

About the contributor This is Rahul Joshi from IIT BOMBAY signing off.

Thanks for joining

Contributors and Content Editors

DeepaVedartham, Nancyvarkey, Pravin1389, Rahuljoshi

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