# Determining boundary conditions

Would like to ask to find out the best way to measure the volumetric flow rate (m3/h) of air through a main entrance (sliding door) into the office whenever the door opens/closes. Appreciate help as I have very little background info on this.

I am trying to define this boundary conditions for a Computational Fluid Dynamics (CFD) simulation of airflow into the office.

As it is, the entire office is cooled by only Ceiling Fan-Coil Units and the only source of fresh air is from this main entrance door (sliding door). Hence it is treated as the necessary outdoor fresh air.

Can I say that when the sliding doors opens, the following movement happens (in the picture) and I can measure the volumetric flow rate by measuring the:

• Air Velocity (by standing at the door when it opens, I have a Kestrel K5400 equipment that can measure velocity)

• Area of the sliding door (treating it like an air duct)

Extra Assumptions/Information:

• Iâ€™d like to assume that the airflow at the gap between the ground and the base of the sliding door is negligible.

• Iâ€™d like to assume the following convective heat transfer below and fresh air enters as a result of convective movement of air between the colder indoor air at 24 degrees C vs the outdoor indoor at 30 degrees C. Hence, the cold air leaves via the bottom and hot air moves in at the top. Is this considered as one full air change?

Interesting project!

I am looking for papers or some related simulations, in the meantime, do you have any suggestions here @CFD-SQUAD?

Best,

Jousef

Thanks. Really appreciate SimScale helping out beginners here. Any luck in finding papers or related simulations?

Hi, I have found a paper like this: https://www.aivc.org/sites/default/files/airbase_12996.pdf Will be discussing this with my Professor very soon but wondering if any simulation has been done before, especially with Fan-Coil Units? Thanks!

I have another question: Iâ€™ll be constructing the model in Autodesk Revit and how do I then prepare the human models ? Saw that cyclinders are used as stands-in for simulations on SimScale. In that case, what are the dimensions of the cylinder human models?

Thank you once again.

Hey there!

It doesnâ€™t really matter, for simplification you can use cylinders but we also used other approaches where we use human models: https://www.simscale.com/tutorial-thermal-comfort-of-a-meeting-room/ - I am not aware of norms in this regard but I know for example for crash tests that there have to be standardised models that have to be used for different scenarios (and which you can also buy on the internet ). A bit of research here might help but if you are free I would probably also go with cylinders.

Best,

Jousef

Hi,

Would like to check what are the boundary conditions that needs to go into creating this type of simulation for airborne transmission of bacteria (https://www.simscale.com/blog/2018/12/cfd-airflow-operating-room/).

I have read a few academic papers and it primarily indicates cough flow rate vs time and requires some complex calculations. This simulation does the same of using cough flow rate vs time but did not mention the boundary conditions. I do not need the exact numbers used for that simulation, but just want to know what are the units that is necessary to perform something like that simulation in SimScale.

Thanks for the help once again.

Hey @1701818!

I will find the project for you and share it here (assuming it is not under NDA).

Best,

Jousef

If you are trying to still calculate boundary conditions for your inlet you can do it based upon your exhaust rate in your building. The exhaust fans in your building would have specified ft^3/min or CFM they move at specific pressures and you can assume an equal mass transfer in most cases, unless major losses.

Also if you are trying to use a anemometer, you can create an array of points, based upon geometry of the door. And then measure along those points in the array and create a weight average.

Or you can possibly do both and verify one method with the other for a check.

Best,
Jake

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Hi,

I created the model but ran into a problem. Itâ€™s the creation of the flow region. In the earlier geometry â€śFinal Final Finalâ€ť I was able to create a closed inner region but felt that it was wrong as I could see the fan coil units at the top after the flow region was created.

I recreated the model in Revit and tried to create a flow region in the geometry â€ś19 Novâ€ť but failed with the error message â€śThe tool objects could not be combined. Please consider cleanup operations in your CAD toolâ€ť

Hi!

I noticed that you have a number of recently uploaded CAD models with a successful flow volume extraction operation. Have you been able to solve the issue in the meantime?

Cheers

Hi,

I have been able to do it and the simulation run was successful. I am trying to understand the post-processing part now.

Thanks!

Hi,

So far, I have performed the re-meshing (more coarse) on Automatic that did not distort the human body models unlike in the earlier meshes. But I ran into a problem:

Resource estimation:
duration: 304 - 457 min (exceeds maximum runtime)
compute resources: 81.2 - 121.8 core hours

I understand that it will halt the run halfway when it â€śexceeds maximum runtimeâ€ť. Is it possible for SimScale to assist to run. Really appreciate it as it is for a school assignment!

EDIT: Searched the forums further and saw the maximum runtime option and will try for that in the meantime! Thanks!

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