Difference between revisions of "OpenFOAM/C2/2D-Laminar-Flow-in-a-channel/English"

2D geometry of channel

Meshing the Geometry

Solving and Post Processing results in Paraview

Validation with analytic result.

System Requirement

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.

If not, please refer to the relevant tutorials on the Spoken Tutorial website

L= 0.05 * Re * D

The pipe is of length 5 m and height 1 m.

Inlet velocity is 1 m/s.

Reynolds number ( Re ) is 100.

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

SimpleFoam in incompressible flows

The folders should be created inside the solver type you choose.

Create a floder and name it as channel in simpleFoam folder

copy 0,constant and system from pitzDaily to this channel folder

The folder is named as channel

Copy 0,Constant and System folders of any other case file in simpleFoam

Here 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

We will now see the file structure

Type in command terminal

run and press enter

tutorial and press enter

incompresible and press enter

simpleFoam and press enter

channel and press enter

ls and press enter

In the command terminal type the path for channel case

Type run and press enter

type cd tutorials and press enter

type cd incompressible and press enter

type cd simpleFoam and press enter

type cd channel and press enter

now type ls and press enter

cd constant and press enter

ls and press enter

polymesh folder and 2 other files

gedit RASProperties and press enter

gedit transportProperties and press enter

In terminal type

cd polyMesh and press enter

in terminal type:

gedit blockMeshDict and press enter

type cd constant and press enter

type ls and press enter

in this you will see files containing properties of fluid and a folder named polymesh

RASProperties containes Reynolds-averaged stress model

transportProperties contains transport model and

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

Now type cd polyMesh and press enter

Now type ls and press enter

This contains the file blockMeshDict

To open the blockMeshDict file in the terminal type gedit blockMeshDict and press enter

in terminal cd space .. twice and press enter

In terminal type:

cd space 0 and press enter

type ls and press enter

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

next we have defined the vertices of the pipe

we have used a 100 X 100 mesh size here and cell spacing of

( 1 1 1 )

In the command terminal type cd (space ) .. and press enter

Again type cd (space) .. and press enter

next we have the boundary conditions and their types which are set as inlet ,outlet,top,bottom

Since it is a 2D problem frontAndBack is kept empty.

We have entered here the type of boundary and their faces

Arcs and mergePatch pair is kept empty.

Close the blockMeshDict file

Type cd ..(dot dot and press enter after each) twice to go back to the channel folder

Now type cd 0 (Time directory) and press enter

Type ls and press enter

Slide 7 : formula to calculate epsilon and k.

Do not chnge the values of nu,nuTilde and R

Change only the boundary names

in terminal type : cd .. and press enter

System folder is kept default

It should contain various files named epsilon ,k, nu ,nuTilda which are the wall functions and

p , R and U are initial conditions of the flow

Calculate epsilon and k from the formula given in the

figure and enter it in the file.

Where Ux, Uy and Uz are the velocity components in the x, y and z direction

And U' = 0.05 times u actual

Calculate epsilon from the formula given

Where epsilon is the rate of 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 in each of the above folder.

Note that the values of nu,nuTilde and R are to kept default

Rest of the files should contain initial value for each of the boundary faces.

Now in the terminal Type cd (space) ..(dot dot) and press enter

There is no change in the system folder

We need to mesh the geometry

Meshing is done

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

Iterations running will be seen in the terminal.

The iterations will stop once the solution is converged or it reaches end time value.

type: paraFoam and press enter

type paraFoam and press enter

This will open up the paraviw window

Solid color to U

initial state at inlet boundary

click on the play button

final contour of velocity

toggle color legend on from left hand side top

The geometry can be seen here.

In top of active variable control menu change the drop down menu from solid color to capital U.

You can see the initial state of velocity magnitude at inlet.

On top of the paraview window click on the play button of VCR control menu

you can see the final value of velocity magnitude.

Also toggle on the color legend from left hand side top of active variable control menu.

Using openfoam we obatain a velocity of 1.48 m/s which is a good match.

File structure of channel

Obtained solution using steady state solver

Viewed the geometry in paraview

Validation with analytic results

Assignment

Solve the problem for Reynold Number 1500 and validate it with the analytical result

this brings us to the end of the tutorial

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