SimScale CAE Forum

Pollution exhaust in a garage


Hi everyone,

I am doing some practice on the following project (
as I am planning to do something similar for my dissertation thesis and I have some unclarities, I’ll be really grateful if you can help me figure them out.
First, how did you managed to get the CO concentration in PPM in the sections you posted ?? Is it a built-in feature in SimScale cause I couldn’t find it.
As I saw in the videos provided for this simulation as support, T1 represents the amount of CO in the garage, but I cannot find what’s the measuring unit for T1?
Second, I saw that you made some calculations of how much CO (2.77E-08 kg/m3 s) is initially in the garage, I was wondering where is this value taken into consideration in the simulation?
And third thing, how did you calculated the exhaust flow based on the initial CO concentration (2.77E-08 kg/m3 s) ???

Thank you !


Hey @grosua!

I would assume that this was achieved using a script which has been used inside Paraview (or the calculator filter) - as far as I know the formula for the concentration was given somewhere in a webinar but would have to check myself first. Let me tag @vaibhav_s here who might help out in this case. Doing some investigations regarding this and your other questions in the meantime!




Hi @jousefm

Thank you for your quick reply and for taking time to help me, looking forward to find out how the simulation works.

Kind regards!


Hi there,

The T1 passive scalar is set to 1 1/s if you go to the advanced tab. And because scalars are independent regarding unit, they can be interpreted in the way we define them, according to

In this case the project poster calculated a uniform distrbution of the CO of 2.77e-8 kg/(m^3 *s), hence we simply multiply the T1 result with this value and divide by the air mass in 1m^3, and finally multiply with 1000000, to get a mg/kg corresponding with ppm. I loaded the simulation results into paraview and entered “(T1 * 2.77E-08)/(1.2041) *1000000” in the calculator. This is the result for the case with the fans:

Sorry for the different colormapping, but the number seem to be close, let’s wait for the original poster to correct me, if it is not correct.

Below you can see where you find where the flux is defined

Hope that answers some of your questions. Regarding the exhaust flow, I think that it is some sort of system, that has some flow rate capability and hence the poster chose that as a boundary condition. However, you could pick any value and see how that helps the overall CO distribution. Which makes this a really cool simulation I think. That’s why I also went ahead and tried to answer your question, because otherwise I would not have seen this project.

Kind regards,


Hi @tcakir

Thank you for your time, your answers are really helpful, now it makes more sense. I wasn’t aware of the possibility to export the results and process them on different software.
As you said, there is a small difference (12ppm) between your results and the initial results in the simulation even the same results were processed in ParaView, this can have an impact on the validation of the ventilation system, so I am wondering where this difference comes from? Did you assume the value of air density at 20 degrees C right? maybe another value for density was considered? or different results were processed?
Maybe simulation master can share a thought on this ?? @vaibhav_s

Thank you!
Kind regards!


Nice one Tolga!!

I was quite sure that we worked with a script but the calculator is indeed the fastest and easiest way to achieve this. Also curious where this mistake comes from, would have also assumed that this is due to different density considerations.




The difference might also be in the colormap scale, I believe the original poster used a log scale, which might make it appear to be different. However, the results in paraview should always give the same values, because the data that i exported is the same, regardless of how many times I export it. Also, I just apply a simple calculation on the T1 value, so data should always give the same result in paraview.

Yes, I just googled air density at 20 c, that is the 1.2041 value. And indeed I do not know which value the orignal poster used in his results. But looking at order of magnitude I think I am pretty close to the original poster.

Hope that helps you further along the road. Would love to hear what kind of simulation you want to look into and maybe be of any help in that. You know where to find us :slight_smile:

Warm regards,