Fluent Tutorial 2005
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Fluent Tutorial
The Durham Fluent Tutorial. Introduction. This provides a short step by step guide to modelling an aerofoil using the Fluent package. The aim being to introduce you the important features of Fluent in the shortest possible space of time. Additional tutorials are available from the Help menu in fluent and gambit for more complex geometries.
Meshing the Aerofoil. Creating the Geometry. ●
Start gambit
●
Obtain the NACA5012 coordinates file (it should be on duo)
●
File> Import > Vertex Data (then select the file you just got off duo)
●
You should have a screen that looks like Figure 1:
Figure 1: Point Input to Gambit. ●
Now we want to create two edges from these points. Select the 2nd icon in the 2nd row of buttons at the top right of the screen. Right click on it and select NURBS. 1
Fluent Tutorial ●
●
Use the point picker, mouse and NURBS tool to make two edges, one of the bottom and one of the top surface of the aerofoil. Ideally we'd make just one but creating a face out of that later is tricky! Then we want to create the surface on which we will calculate the fluid flow. To do this we will create a domain around 1 chord lengths above and below the aerofoil and 1.5 chord lengths before and after. This is slightly arbitrary and we may want to change this after we look at the results!
●
Add points at (1.5,1),(1.5,1),(2,1) and (2,1)
●
Join these points together with straight lines. Your screen should look like Figure 2:
Figure 2: Edges in Gambit.
●
●
● ●
We now have six edges from which we construct our surface. We are going to construct two surfaces which we will then subtract to give us our final face. Join the outer edges into a wireframe face (Geometry Button > Face Button > Wireframe Button You may have to right click to find it!) Join the inner edges (the aerofoil) into a wireframe face Subtract the two faces. (Geometry Button > Face Button –> Subtract Button. You will find this by right clicking on the third icon from the left in the face group) 2
Fluent Tutorial Meshing the Surface. ●
●
For simplicity we are going to use an unstructured mesh. This may not be the best mesh for the problem! To do this we will apply an edge mesh to all the edges you have created and then put an unstructured mesh onto the surface. So mesh the inlet and the outlet with around twenty points. (Mesh Button > Edge Button) ●
●
●
The number of points is controlled by the interval count option (fourth division down from the top) you will have to change it as the default is interval size. You may want to put in a successive ratio that alters the spacing of the points as you go along the edge. In this example I've concentrated some points towards the centre of the edge as this is where the interesting flow effects will happen. Gambit has some idiosyncrasies in it's meshing selection, after you have asked it to mesh something you have to reselect the edge to make further changes.
●
Mesh the top and bottom with around twenty points as well.
●
Mesh the top and bottom of the aerofoil with around forty points.
●
Mesh the face. (Mesh Button > Face Button) you will need to select tri elements.
●
You should end up with something like Figure 3:
Figure 3: The meshed aerofoil. ●
We now need to tell gambit about the physical nature of the problem and then we can export to 3
Fluent Tutorial Fluent. ●
●
●
●
You will need to tell Gambit that we are going to use Fluent at this stage. Use the Solver Menu and select Fluent 5/6. Hit the Zone Button and then you have two other buttons: ●
Specify Boundary Types – use this to specify what is going to happen at each edge.
●
Specify Continuum Types – use this to specify fluids or solids.
Put the inlet on the left as a pressure inlet, the outlet on the right as a pressure outlet. Make sure you select edges as the “entity”. The top and bottom edges should be a symmetry plane (which is a bit of trick as we are not really interested in any symmetry).
●
The aerofoil should be a wall surface.
●
Specify Fluid as the Continuum type for the face.
●
You are now ready to export your mesh: File > Export > Mesh (Don’t forget to Save your Gambit files as well!) Push the 2D button as this is a 2D case.
Computing the Flow. The next step is much more straightforward. In CFD modelling flow most of your time will be taken meshing the problem and then analysing the results, computation is the easy bit. ●
Start fluent
●
Select 2D
●
File > Read > Case and select your file
●
Grid > Check (this should return no problems)
●
Display > Grid (so you can look at the grid if you want to)
●
You must then set a number of parameters to solve the flow: ●
Define > Boundary Conditions. I'd suggest 300 Pa for your pressure inlet value.
●
Solve > Initialise. Set this to compute from inlet.
●
Define > Models > Viscous. Set this to inviscid for now.
●
Solve > Monitors > Residuals. Select plot.
●
●
Solve > Iterate. Set this to 1000 or so and watch the computer work for you! The problem should converge in around 100 iterations or so. You can then view your results using Display > Contours and you might end up with
4
Fluent Tutorial something like Figure 4.
Figure 4: The Inviscid Flow Results.
Turbulence Models. The inviscid flow solution is fine for bulk pressure changes, but if we wanted to examine the flow under more realistic conditions we can use this solution as the basis for the next run. ●
●
Define > Models > Viscous. Then select SpallartAllmaras. The default values will be o.k. for now. Solve > Iterate. Then uses the inviscid velocity data etc. with the new turbulence model.
Summary You have now successfully meshed up and calculated a basic geometry. Other things you could try with the data: ●
Extend the problem into 3D
●
Tilt the aerofoil and examine the prediction of separation
●
Remesh the problem using a structured grid.
Fluent and Gambit have an extensive help system which you should use when you get stuck. Also note that this is a tutorial on how to use Fluent and Gambit. The flow model of the aerofoil produced captures bulk flow effects but for anything more refined you will have to carefully consider how to model the scenario! Grant Ingram 5
Fluent Tutorial 17 October 2005
6
The Durham Fluent Tutorial. Introduction. This provides a short step by step guide to modelling an aerofoil using the Fluent package. The aim being to introduce you the important features of Fluent in the shortest possible space of time. Additional tutorials are available from the Help menu in fluent and gambit for more complex geometries.
Meshing the Aerofoil. Creating the Geometry. ●
Start gambit
●
Obtain the NACA5012 coordinates file (it should be on duo)
●
File> Import > Vertex Data (then select the file you just got off duo)
●
You should have a screen that looks like Figure 1:
Figure 1: Point Input to Gambit. ●
Now we want to create two edges from these points. Select the 2nd icon in the 2nd row of buttons at the top right of the screen. Right click on it and select NURBS. 1
Fluent Tutorial ●
●
Use the point picker, mouse and NURBS tool to make two edges, one of the bottom and one of the top surface of the aerofoil. Ideally we'd make just one but creating a face out of that later is tricky! Then we want to create the surface on which we will calculate the fluid flow. To do this we will create a domain around 1 chord lengths above and below the aerofoil and 1.5 chord lengths before and after. This is slightly arbitrary and we may want to change this after we look at the results!
●
Add points at (1.5,1),(1.5,1),(2,1) and (2,1)
●
Join these points together with straight lines. Your screen should look like Figure 2:
Figure 2: Edges in Gambit.
●
●
● ●
We now have six edges from which we construct our surface. We are going to construct two surfaces which we will then subtract to give us our final face. Join the outer edges into a wireframe face (Geometry Button > Face Button > Wireframe Button You may have to right click to find it!) Join the inner edges (the aerofoil) into a wireframe face Subtract the two faces. (Geometry Button > Face Button –> Subtract Button. You will find this by right clicking on the third icon from the left in the face group) 2
Fluent Tutorial Meshing the Surface. ●
●
For simplicity we are going to use an unstructured mesh. This may not be the best mesh for the problem! To do this we will apply an edge mesh to all the edges you have created and then put an unstructured mesh onto the surface. So mesh the inlet and the outlet with around twenty points. (Mesh Button > Edge Button) ●
●
●
The number of points is controlled by the interval count option (fourth division down from the top) you will have to change it as the default is interval size. You may want to put in a successive ratio that alters the spacing of the points as you go along the edge. In this example I've concentrated some points towards the centre of the edge as this is where the interesting flow effects will happen. Gambit has some idiosyncrasies in it's meshing selection, after you have asked it to mesh something you have to reselect the edge to make further changes.
●
Mesh the top and bottom with around twenty points as well.
●
Mesh the top and bottom of the aerofoil with around forty points.
●
Mesh the face. (Mesh Button > Face Button) you will need to select tri elements.
●
You should end up with something like Figure 3:
Figure 3: The meshed aerofoil. ●
We now need to tell gambit about the physical nature of the problem and then we can export to 3
Fluent Tutorial Fluent. ●
●
●
●
You will need to tell Gambit that we are going to use Fluent at this stage. Use the Solver Menu and select Fluent 5/6. Hit the Zone Button and then you have two other buttons: ●
Specify Boundary Types – use this to specify what is going to happen at each edge.
●
Specify Continuum Types – use this to specify fluids or solids.
Put the inlet on the left as a pressure inlet, the outlet on the right as a pressure outlet. Make sure you select edges as the “entity”. The top and bottom edges should be a symmetry plane (which is a bit of trick as we are not really interested in any symmetry).
●
The aerofoil should be a wall surface.
●
Specify Fluid as the Continuum type for the face.
●
You are now ready to export your mesh: File > Export > Mesh (Don’t forget to Save your Gambit files as well!) Push the 2D button as this is a 2D case.
Computing the Flow. The next step is much more straightforward. In CFD modelling flow most of your time will be taken meshing the problem and then analysing the results, computation is the easy bit. ●
Start fluent
●
Select 2D
●
File > Read > Case and select your file
●
Grid > Check (this should return no problems)
●
Display > Grid (so you can look at the grid if you want to)
●
You must then set a number of parameters to solve the flow: ●
Define > Boundary Conditions. I'd suggest 300 Pa for your pressure inlet value.
●
Solve > Initialise. Set this to compute from inlet.
●
Define > Models > Viscous. Set this to inviscid for now.
●
Solve > Monitors > Residuals. Select plot.
●
●
Solve > Iterate. Set this to 1000 or so and watch the computer work for you! The problem should converge in around 100 iterations or so. You can then view your results using Display > Contours and you might end up with
4
Fluent Tutorial something like Figure 4.
Figure 4: The Inviscid Flow Results.
Turbulence Models. The inviscid flow solution is fine for bulk pressure changes, but if we wanted to examine the flow under more realistic conditions we can use this solution as the basis for the next run. ●
●
Define > Models > Viscous. Then select SpallartAllmaras. The default values will be o.k. for now. Solve > Iterate. Then uses the inviscid velocity data etc. with the new turbulence model.
Summary You have now successfully meshed up and calculated a basic geometry. Other things you could try with the data: ●
Extend the problem into 3D
●
Tilt the aerofoil and examine the prediction of separation
●
Remesh the problem using a structured grid.
Fluent and Gambit have an extensive help system which you should use when you get stuck. Also note that this is a tutorial on how to use Fluent and Gambit. The flow model of the aerofoil produced captures bulk flow effects but for anything more refined you will have to carefully consider how to model the scenario! Grant Ingram 5
Fluent Tutorial 17 October 2005
6
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