View source for OpenFOAM-version-7/C2/Creating-2D-Channel-Geometry-and-Mesh-in-OpenFOAM/English

'''Title of the script''': Creating 2D Channel Geometry and Mesh in OpenFOAM

'''Author''': Ashley Melvin

'''Keywords''': OpenFOAM, ParaView, channel flow, blockMesh, meshing, structured mesh, graded mesh, pre-processing, video tutorial



{| border = "1"
|- 
|| '''Visual Cue'''
|| '''Narration'''
|- 
|| Slide: Opening Slide
|| Hello and welcome to this tutorial on '''Creating 2D Channel Geometry and Mesh in OpenFOAM'''.
|- 
|| Slide: Learning Objective
|| In this tutorial, we will learn to:
* Create a '''2D channel''' geometry using '''blockMeshDict'''
* '''Mesh''' a geometry
* Label the '''boundary patches''', and
* View the '''mesh''' in '''ParaView'''
|- 
|| Slide: System Specifications
|| To record this tutorial, I am using,
* '''Ubuntu Linux''' OS version 18.04
* '''OpenFOAM''' version 7
* '''ParaView''' version 5.6.0, and
* '''gedit Text Editor'''

You may use any other '''editor''' of your choice.
|- 
|| Slide: Code Files
|| 
* The files used in this tutorial are available in the '''Code Files''' link on this tutorial page 
* Please download and extract them
* Make a copy and then use them while practising
|- 
|| Slide: 2D Channel Flow
|| The problem description of '''2D flow in a channel '''is as shown in the diagram.
|- 
|| Slide: Channel Geometry
|| This is the geometry for''' 2D flow in a channel'''.
|- 
|| Slide: Faces
|| The '''faces''' of the geometry are:
* '''Inlet''' and '''outlet'''
* Bottom and top walls
* Back face, and Front face
|- 
|| CTRL + ALT + T
|| Open the '''terminal''' by pressing '''Ctrl, Alt''' & '''T''' keys.
|- 
|| [Terminal] Type:


'''cd $FOAM_RUN'''
|| At the '''prompt''', type the following '''command''' to go to the '''RUN directory'''.
|- 
|| Only Narration
|| Here onwards, please remember to press the '''Enter''' key after typing each '''command''' in the '''terminal'''.
|- 
|| [Terminal] Type:


'''cp -r $FOAM_TUTORIALS/incompressible/pimpleFoam/LES/channel395 .'''
|| Let us now copy the '''case''' of '''flow in a channel''' from the '''TUTORIALS directory''' into the '''RUN directory'''.


Type the following '''command''' to do so.
|- 
|| [Terminal] Type:


'''rm -r channel395/0'''
|| We will only be creating and '''meshing''' the geometry.


Hence, we do not need the '''boundary conditions''' folder.


Type the following '''command''' to delete the '''boundary conditions''' folder.
|- 
|| [Terminal] Type:


'''gedit channel395/system/blockMeshDict'''
|| The '''blockMeshDict''' file is located in the '''system''' folder.


Let us open it in any '''text editor'''.


I am doing it in '''gedit Text Editor'''.
|- 
|| [gedit - '''blockMeshDict''']
|| We can now see the '''blockMeshDict''' file.
|- 
|| [gedit - '''blockMeshDict'''] Highlight


'''Selection in the Text Editor >> Delete'''
|| Select the contents of the file from '''vertices''' to the end of the document, as shown.


We don’t need the selected content as we will be entering the '''input parameters'''.


Hence, delete the selected section.


The remaining content is common for all '''blockMeshDict''' files.
|- 
|| [gedit - '''blockMeshDict'''] Highlight


'''convertToMeters 1'''
|| The unit of the coordinates entered in the '''blockMesh dictionary''' needs to be specified.


It is defined using the '''keyword convertToMeters.'''


The value '''1''' indicates that the values of all the '''coordinates''' are in '''meters'''.
|- 
|| [gedit - '''channel''']
|| Open the '''channel.txt''' file, that you had downloaded, in a '''text editor'''.
|- 
|| [gedit - '''channel'''] Highlight


'''Selection in the Text Editor >> Copy '''
|| Copy the entire content of the text file.
|- 
|| [gedit - '''blockMeshDict''']
|| Let me switch back to the '''blockMeshDict''' file.
|- 
|| [gedit - '''blockMeshDict''']

'''Paste'''
|| Paste the copied contents into the '''blockMeshDict '''file as shown.
|- 
|| Slide: Vertices
|| The vertices of the '''channel''' geometry are numbered as indicated.


The vertex numbering starts from 0.
|- 
|| [gedit - '''blockMeshDict'''] Highlight


Vertices List



|| The coordinates of the vertices are entered as shown.


Note that the vertices are entered in the ascending order of their vertex numbers. 
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''(0 0 0)'''
|| Vertex '''0''' is located at the '''origin'''.


Its coordinates are entered as shown. 
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''(4 0 0) '''
|| The''' x, y '''and''' z '''coordinates''' '''of vertex''' 1 '''are '''4, 0''' and '''0''' respectively.


Its coordinates are entered as shown.
|- 
|| [gedit - '''blockMeshDict'''] Highlight 


'''(0 2 0) '''and''' (4 2 0)''' 
|| Similarly, the coordinates of vertex''' 2 '''and''' 3''' are entered as shown.
|- 
|| Only Narration
|| The '''z '''coordinate of all the points on the front face is 2.
|- 
|| [gedit - '''blockMeshDict'''] Highlight 


'''(0 0 2) to (4 2 2)'''
|| The coordinates of front face vertices''' 4, 5, 6 '''and''' 7''' are entered as shown.
|- 
|| Only Narration
|| For '''meshing, OpenFOAM''' requires '''3-dimensional blocks''' to be defined.


The '''blocks''' are specified using the vertices that define them.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


Blocks List 
|| We use a single '''block''' in our geometry.


The '''block''' is defined as shown.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''hex'''
|| We use '''hexahedral blocks''' for '''meshing'''.
|- 
|| Only Narration
|| The order in which the vertices are specified, define the '''block'''.


We first enter the vertices of the lower '''xy-plane''', in this case, the back face.


We start from the '''origin''' and enter the vertices of the face.


When viewed along the '''negative z-direction''', the vertices should be ordered counterclockwise.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''0 1 3 2 '''
|| The vertices of the back face are defined as shown.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''4 5 7 6'''
|| The vertices of the front face are entered in the same order as that of the back face.
|- 
|| Only Narration
|| Let us start defining the '''meshing parameters''' of the '''block'''.


We first define the number of '''cells''' in each direction of the '''block'''.
|- 
|| [gedit - '''blockM''', '''eshDict'''] Highlight:


'''40 25 1'''
|| The number of '''cells''' in each '''direction''' is defined as shown.


This indicates that there are 40 '''cells''' in '''x direction''' and 25 '''cells''' in '''y direction'''.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''1 '''
|| There is only one '''cell''' along '''z direction''' indicating that the '''simulation''' is '''2D''' in '''xy-plane'''.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''simpleGrading'''
|| Next, let us define how the '''mesh''' is '''graded'''.


We use '''simpleGrading''' as the '''cells''' have '''uniform expansion''' in all directions.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''1 1 1'''
|| Let us now define the '''expansion ratios''' in each direction. 


'''Expansion ratio''' along a direction is the ratio of width of the '''end cell''' to that of the '''start cell''' in that direction.


Since the '''cell''' width is uniform in all directions, the '''expansion ratio''' is '''1'''.
|-
||Narration only.
|| Please refer to the '''"Additional Reading Material"''' on this tutorial page for details.

It has more details on defining a '''block'''.
|- 
|| Only Narration
|| Now, let us define the '''edges'''.


'''Edges''' are used to define '''arc''' or '''spline edges'''.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


Edges List
|| Since all the '''edges''' of '''channel''' geometry are straight lines, we leave it empty. 
|- 
|| Only Narration
|| Let us label the '''boundary patches'''.


The labels are used to impose '''boundary conditions''' on the respective faces.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''boundary'''
|| '''Boundary '''labels are defined using the '''boundary''' list.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''bottomWall''' 
|| The bottom face of the geometry is named '''bottomWall'''. 
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''type''' 
|| The '''patch type''' of the '''boundary''' is defined using the '''keyword type'''.

|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''wall'''
|| The bottom face resembles the characteristics of a solid wall.


Hence, the face is of the '''type wall'''.
|- 
|| [gedit - '''blockMeshDict'''] Highlight: 


'''faces'''
|| Vertices define a face.


The vertices and their order for a face, is defined using the '''keyword faces'''.
|- 
|| Slide: Bottom Wall
|| Since the '''block '''face is a quadrilateral, it is defined by 4 vertices.


When viewed from inside the '''block''', the vertices of the face should be ordered clockwise.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''0 1 5 4'''
|| Keeping this in mind, the vertices of the bottom wall are ordered as shown.
|- 
|| [gedit - '''blockMeshDict'''] Highlight: 


'''topWall '''definition
|| Following the same convention, the top face is named '''topWall''' and is defined as shown.
|- 
|| Only Narration
|| We are creating the geometry for a '''2D simulation''' in '''xy-plane'''.


We do not need to solve in the '''z''' direction.


Hence, we keep the front and back faces empty.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''Back '''and''' front '''planes definitions 
|| The back and front faces are defined as shown.
|- 
|| Only Narration
|| The '''inlet''' and '''outlet''' faces need the application of '''boundary condition'''.


Since they do not contain any geometric or topological information, a '''generic''' label would suffice.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''patch'''
|| Such generic '''boundaries''' are labelled using the '''keyword patch'''.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''Inlet '''and''' outlet '''planes definitions
|| The '''inlet''' and '''outlet''' faces are defined as shown.
|- 
|| Only Narration
|| We have finished labelling all the '''boundary patches'''.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''mergePatchPairs'''
|| Next, we merge faces using the '''mergePatchPairs '''field.


We merge faces when a '''patch '''face from one '''block''' is connected to a '''patch '''face of another '''block'''.
|- 
|| [gedit - '''blockMeshDict'''] Highlight:


'''mergePatchPairs '''List
|| Our geometry has only one '''block''' and there are no '''patches''' to merge. 


Therefore, we leave the '''mergePatchPairs field''' empty. 
|- 
|| [gedit - '''blockMeshDict'''] 


Save >> Close the window
|| We have entered all the necessary '''fields'''. 


Save and close the file.
|- 
|| [Terminal] Type: 


'''cd channel395'''
|| In the '''terminal''', type '''cd (space) channel395'''.
|- 
|| [Terminal] Type:


'''blockMesh '''>>''' Enter'''
|| Let us '''mesh''' the geometry.


Type '''blockMesh''' and press '''Enter''' to do so.
|- 
|| [Terminal] Highlight: '''End'''
|| The '''meshing''' is complete.
|- 
|| [Terminal] Type:


'''paraFoam '''>>''' Enter'''
|| To view the '''mesh''' in '''ParaView''', type '''paraFoam''' and press '''Enter'''.
|- 
|| [ParaView]


Click on '''Apply'''
|| Click on the green coloured '''Apply''' on the left side of your window in the '''Properties''' tab.
|- 
|| [ParaView]


Click on '''Surface''' >> Click on '''Surface with Edges'''
|| Click on '''Surface''' available in the '''Representation Toolbar''' and change it to '''Surface with Edges'''.


You can now see the '''mesh''' structure of the front face.
|- 
|| [ParaView] Close the window
|| Close the '''ParaView''' window.
|- 
|| Only narration
|| With this we have come to the end of the tutorial.


Let us summarize.
|- 
|| Slide: Summary
|| In this tutorial, we have learnt to:
* Create a '''2D channel''' geometry using '''blockMeshDict'''
* '''Mesh''' a geometry
* Label the '''boundary patches''', and
* View the '''mesh''' in '''ParaView'''
|- 
|| Slide: Assignment
|| As an assignment:
* Create a '''geometry''' having dimensions '''5 metres, 4 metres''' and '''3 metres''' along '''x''', '''y''' and '''z axis'''
* Mesh the geometry such that it has 50, 40  and 1 '''cell''' along '''x, y''' and '''z axis''', and
* View the '''mesh''' in '''ParaView'''
|-
|| Slide: About the Spoken Tutorial Project
|| The video at the following link summarises the Spoken Tutorial project.


Please download and watch it.
|-
|| Slide: Spoken Tutorial Workshops
|| We conduct workshops using spoken tutorials and give certificates.


Please contact us.
|-
|| Slide: Spoken Tutorial Forum
|| Please post your timed queries in this forum.
|-
|| Slide: FOSSEE Forum
|| 
* Do you have any general/technical questions?
* Please visit the forum given in this link.
|-
|| Slide: FOSSEE Case Study Project
|| 
* The FOSSEE team coordinates solving feasible '''CFD''' problems of reasonable complexity using '''OpenFOAM'''.
* We give honorarium and certificates to those who do this.
* For more details, please visit these sites.
|- 
|| Slide: Spoken Tutorial 
|| The Spoken Tutorial project is supported by MHRD, Govt. of India.


The script for this tutorial is contributed by Ashley Melvin.


And this is Swetha Sridhar from IIT Bombay signing off.


Thank you for joining.
|-
|}