Tutorial: Performing Flow Simulation of an Aerofoil
In this tutorial, we are going to be taking a look at running flow visualization simulations on a basic aerofoil (or “airfoil”), which will hopefully be of use to those of you in aerospace engineering courses—or maybe you just like designing RC aircraft and want to simulate your wings before chopping up a load of balsa wood.
Before we can start simulating however, we need to design our aerofoil. This is relatively straightforward, as there is a wealth of aerofoil coordinate data libraries online, and we can import those coordinates into SOLIDWORKS by using the Curve Through XYZ function.
For this tutorial, we will be using a NACA 4415 aerofoil.
You can copy the NACA 4415 aerofoil coordinates from the University of Illinois at Urbana-Champagne aerofoil database website, or you can obtain it from the AirfoilTools website here. Note, the AirfoilTools site has a nice visualization tool that shows you how the shape of the aerofoil geometry changes as you modify the NACA parameters, which is great if you want to know exactly what those NACA numbers mean.
The raw coordinates need cleaning up a little before we can import them into SOLIDWORKS.
Open up Microsoft Excel and copy/paste them into the first cell. You will notice that both X and Y coordinates have been copied into a single column, so in order to make them usable we need to separate them into individual columns.
Highlight Column A in Excel, click on Data, and select Text to Columns.
On the first page of the Text to Columns Wizard, we want to select Delimited, if it isn’t already selected by default. Then click Next.
On the second page of the Wizard, check the Tab and the Space delimiter boxes. This should separate the X and Y coordinates into two columns. Then click Finish.
Now that we have two columns with separated X and Y coordinates, we are going to need to create a third column full of zeros so that SOLIDWORKS can import it. These zeros represent the Z coordinate, but as this is a two-dimensional curve, we have no need for a Z coordinate, and, hence, we set them to zero. Type “0” into the top cell in the third column, and click the little box at the bottom of the cell, or drag the box to the bottom of the data set in order to populate the third column with zeros.
Now we have our X, Y and Z coordinates in three columns. We can click File>Save As and select Text (Tab Delimited) from the drop down menu. Select a location to save the file to, pick a name for your file and click Save.
If an Excel warning appears, just click Yes to ignore it.
You can now close Excel and open SOLIDWORKS.
Loading the Aerofoil Coordinates
Open SOLIDWORKS, open a new part file and on the top of the screen select:
Insert> Curve > Curve Through XYZ Points
This will open the Curve File pane. Click Browse, and then locate the text file containing the cleaned up coordinate data that you exported from Excel. It will load the coordinates into the pane, as seen below.
Click OK, and you will see the aerofoil curve appear in the design window, as seen in the image below.
Of course, being a curve, it is still not useful for creating geometry, so select the Front Plane from the design tree and click Sketch from the Sketch tab.
Now click Convert Entities from the Sketch tab, and in the Convert Entities panel, select the aerofoil curve from the design window.
Next, we want to make a centreline from the trailing edge to just beneath the leading edge. This will represent the chord length of the aerofoil, and once we have constrained it we can alter the chord length at will.
After the chord line is sketched, we need to put another line connected to the last line near the leading edge. This new line needs to be tangential to the aerofoil, as shown below.
Then, we can select both the chord line and the tangent line, and constrain them so that they are perpendicular to each other. Why? Because when we rotate the sketch or extend the chord length, we want it to retain shape, and the perpendicular constraint will ensure that the whole thing remains aerofoil-shaped.
Now that the sketch is constrained, we can just double-click on the chord line and enter a value for how long we want the chord to be. In this case, let’s set it to 1.6 meters.
Congrats! You have now converted your aerofoil curve into a sketch entity. Now we can model our solid aerofoil.
2D to 3D
This part is easy. Simply select the aerofoil sketch and extrude it to 4 metres. This will provide us with a basic constant-chord (i.e., non-tapered), rectangular wing. This type of wing, incidentally, is referred to colloquially as a “Hershey Bar”.
And there it is. Our Hershey Bar wing is now ready for some flow simulation!
Flow Simulation Time!
Load up the Flow Simulation add-in by clicking Tools > Add-ins and checking the SOLIDWORKS Flow Simulation box. Once it is loaded, select the Flow Simulation tab and click the Wizard button to start the Flow Simulation Wizard.
On the first page of the wizard (Project Name), name your project and click Next.
On the second page (Unit System), select your preferred unit system. For consistency, we will select SI units here (m-kg-s). Then click Next.
On page three (Analysis Type), we can select Internal or External study. Internal studies are for simulating flows that are constrained by some kind of vessel, such as a pipe, and external studies are for simulating flows around the outside of a body such as a truck or an aerofoil. So, we click External, and then press Next to advance to the next page.
The next page (Default Fluid) allows us to select the fluid in our study. This is an aerodynamic study, so we select Air from the top list and click Add. Once the default fluid has been added, we can click Next.
We can skip over the next page (Wall Conditions) by clicking Next.
The final page that we need to deal with in the wizard is the Initial and Ambient Conditions page. This is where we set the temperature and pressure of the environment and the velocity of the flow in the x-direction. We have set the temperature and pressure to SSL (standard sea level) values and the velocity in x-direction to 55m/s (about 200km/h).
That’s all we need to worry about with the wizard. Click Finish and the wizard will close.
You will notice that the wizard has created a box around the wing. This is our Computational Domain, where all the magic happens. Think of it as the inside of a wind tunnel. Everything inside it is part of the simulation, and everything outside it is irrelevant.
Note that a larger Computational Domain requires more processing.
Click on Computational Domain on the left hand panel (as seen below) and you will notice six handles appear on the box. Drag these handles until the domain box fits just around the wing model. Be sure to leave enough room at the fore and aft of the wing so we can get some sweet visualization of the fluid flow as it passes around the wing.
Next up, we want to set our goals.
The Goals in SOLIDWORKS Flow Simulation serve three purposes:
- Defines Design Goals and/or other important criteria
- Used for Convergence Control
- Finish the calculation
Being an aerodynamic simulation, we want to set goals that are relevant to this domain. So, go into the left-hand project simulation panel again, right click on Goals, and select Surface Goals. This will bring up a list of parameters that we wish to measure and visualise, and we can select the minimum, maximum and average for each goal.
First, we want to select the faces of the wing that we want included in the study. In the Surface Goals panel, click the blue Selection area to activate it and click all of the faces of the wing model.
Next, go down the list and check the minimum, maximum and average for the following parameters:
Note that we have selected Velocity (X), because this is the direction that the flow will be travelling in.
Click the green check mark to exit Surface Goals.
Next, we want to go into the study panel on the left, right click Input Data and select Calculation Control Options.
Check the iterations box and ensure it is set to 100 iterations. It may be that your simulation requires less, or even more. But for now, 100 iterations is fine. This should be enough for the goals to reach convergence. More iterations will generally give a better result, but after a point, the trade-off between accuracy and time-taken simply isn’t worth it. You can run the simulation all day long and the gains to accuracy will become very modest. So, 100 is fine in this case. Click OK to exit.
Now that our simulation is set up, we can run it. You can find the Run button in the top ribbon (as seen below). Click it and you will see the solver screen appear, informing you of how many iterations are left.
Displaying the Results
Now the calculations have finished, we can go into the study panel on the left and expand the Results section to show us a selection of graphs and plots. Right clicking any of these plots will allow you to insert the plot into the main window.
The first plots we will look at are cut plots. This type of plot will display a 2D slice (a plane) of the model, and you can drag the green arrow to move the slice along any part of the 3D model.
Right click Cut Plot, and select Insert.
In this instance, I select Front Plane, then I select Contours to show a contourplot. In the Contours section, you can see that the default parameter should be Velocity (X). We would like to see the pressure contours here, so we can click the parameters box and select Pressure.
Click the green check mark and you will see your plot appear in the main design window. You can move the slice along the length of the wing by using the green drag handle and you can rotate the plot as you would do your 3D model. The image below shows an isometric view and a side view. The color code shows how the colors relate to differences in pressure.
Because the results are already loaded into your computer, you can easily switch between data types by clicking the parameter name just beneath the colour scale and selecting new results to display.
So, if I want to change from a pressure contour plot to a velocity contour plot, I simply click Pressure beneath the colored scale (as seen above) and switch it to velocity. The main plot will change accordingly.Note, if you want to see the slice scan along the entire length of the wing, you can right click on Cut Plot and select Play for a little animation.
Cut plots are nice, but they don’t show the holistic view of what is going on; they simply show a 2D slice of the 3D whole. The trajectory plot is more useful for showing behavior over the full length of the wing at any given time. This is more like a wind tunnel with smoke injected into the chamber, which you may be more familiar with from university.
Right click on the Flow Trajectory option in the study pane, and select Insert. This will open the Flow Trajectories pane.
In this pane, select the faces that we want to be a part of the study as we did for the Cut Plot.
In the Number of Points box, type 15 and set the Spacing to 0.03m.
In the Appearance section, we select Static option, and then we select the appearance of the trajectory. In this instance we select Pipes, but feel free to play around here and experiment with different appearances.
Again, in this plot we will be looking at Pressure, so select that from the Appearance section, and then click the green check icon. The plot will appear in the main window, as you can see below.
Here we can see the variations of pressure as the air flows over the aerofoil, and also we can get some idea of the turbulence/vortices created by the wing tip.
OK, so you’ve done your first aerofoil flow visualization in SOLIDWORKS Flow Simulation.
After this tutorial you should now be able to do the following:
- Import aerofoil coordinate geometry
- Create a solid from imported coordinates
- Set up a fluid analysis
- Run the analysis
- Visualize flows in cut plots
- Visualise flows in trajectory plots
- Switch parameters from inside a plot
There are a lot of different visuals that can be created in Flow Simulation (and so little space to write about all the combinations).
The best way to discover them is to experiment with the different parameters and see for yourself!
About the Author
Phillip Keane is currently studying his PhD at the School of Mechanical and Aerospace Engineering at Nanyang Technological University, Singapore. His background is in aerospace engineering, and his current studies are focused on the use of 3D-printed components in spaceflight. He previously worked at Rolls-Royce and Airbus Military and served as an intern for Made In Space and the European Southern Observatory.