Like a lot of people right now, I’ve been working from home and wearing home-made face masks to help slow the spread of COVID-19 whenever I go out on essential errands. I thought it would be interesting to use a tool like SOLIDWORKS Flow Simulation to see the difference these kinds of masks can make. Contrary to what you may think, it is surprisingly easy to set up these types of simulations. I hope this article will help remove some of that intimidation and encourage you to experiment as well.
Before we dive in, I want to add the disclaimer that what I’m going to cover only scratches the surface of what is possible using this tool. There are so many variables and options to be considered that I can’t cover them all. Hopefully, this will inspire others to explore alternatives to the example I’ve done and share their findings.
Step 1: A Face Model to Build From
For this project, what we are doing in production terms is engineering a component to fit onto an existing part. In this case, a human face. For a starting model, I used a 3D scan that I took of my face using an Artec Space Spider. However, you can just as easily use a model you download off of a site like GrabCAD.
Step 2: Drafting a Mask Design Over the Model
Once I imported the face model into SOLIDWORKS CAD, I started to draw the base model using splines that roughly matched the outer contours of my face. These did not have to be perfect since the final product (made of cloth) would not be perfect either. To start, I used cross-sections of the model around my nose and chin. Then I created a solid body using a boundary surface to connect them and add thickness.
Step 3: Adding a “Mouth”
I modified my face model with a small extruded cut at the mouth to use it as the inlet for the flow study to represent my breath.
Step 4: Setting Up the Study Parameters
For this type of test, the setup I used was basic. I used the Flow Simulation Wizard with almost all the default settings for an external flow study.
- Analysis type: External
- Working fluid: Air (Pre-Defined) with Humidity enabled
- Inlet Volume Flow: 0.0005m^3/s (approx. speed of human breath)
One change I made was to reduce the default computation domain around my model. By default this is big, so to speed up computational time, I shrank it down to just the area around the front of the face.
Step 5: Setting Up the Study Material
I wanted to call out this step separately as this is probably the step that someone would end up changing the most as they experiment. In this case, selecting the Porous Medium would represent the material used to create the face mask.
For this specific example, I did my best to enter the values I thought would best represent T-shirt fabric material. As you can imagine, there is a multitude of materials you can test in this situation, and my values are just an approximation. Finding the mesh settings was a particular challenge since you have to find a density you can measure through but won’t take an excessive amount of time to solve.
Step 6: Looking at Results
Looking at the results, we can see that there is a definite impact from wearing the mask. As you can see, a good amount of the airflow is going through the front of it. There are also some small leaks around the gaps near my nose and chin, which matched pretty well with my real-life experiences and having my glasses fog up when I wore the prototype.
For sake of comparison and control, I ran the study with the same parameters but without the mask model and you can see the significant difference.
Conclusion and a Friendly Challenge
By performing this study there are some immediate takeaways that show us where we can make changes and improve the design.
- We can see where there is airflow around the model and can further mitigate leaks by improving how the design conforms to the shape of the face, maybe with the use of a metal band or strip across the bridge of the nose.
- We can also experiment with other material settings to see if one material does a better job of containment than another.
The great thing about having this model and study done in SOLIDWORKS is that I can make modifications to my original design and re-run the exact same study without having to set it up again. This would allow me to see the results of my changes almost instantly.
There are so many variables that can be considered in a project like this one, and my results are in no way conclusive. It is my hope that now that I’ve shown you all how easy it is to set up a study like this, you are encouraged to take this experiment further. Try your own designs and materials. I would love to know what you discover and how I can make my own experiment even better as a result.
I’m going to continue working on this project and I would love to hear about your results and improvements in the comments below