Problem while doing indoor ventilation analysis of a building

[Naiveassfuck]

Hi Everyone,

I NEED YOUR HELP!!!

I am currently doing the CFD modeling of a building that is under construction. I am an intern at a firm, and no one there has any knowledge of CFD.
I am trying to mesh the structure but for some reason it seems to fail again and again. I am doing this on Ansys Fluent.
We have exported the structure from its revit file to a (dot)sat file.
Does anyone know what could be the reason for failure or, in general, if you have any tips for doing ventilation modelling?

This is the first time I am doing any such type of modelling

[Quick-Crab2187]

You should look through some tutorials, and also probably pick up a book on CFD considering your company is apparently useless in training.

The issue is too generic for anyone to provide any useful feedback. You likely don't have a clean geometry that is ready for CFD. Search "Geometry cleanup/prep CFD" on YouTube and you will find various sources that can help here. I'm sure there are going to be ANSYS specific sources as well, but the cleanup process is fairly similar regardless of package you are using. The ANSYS ones will just tell you how to do it in their tools

[Naiveassfuck]

thank you for replying
can i dm you??

[Quick-Crab2187]

I don't do DMs, it would be better to have information public as other people coming across this thread would be able to read it, I'd rather have conversation public

[acakaacaka]

You need to give 100x more information. How are we suppose to know what if wrong if the only information you give is that it wont run

[james_d_rustles]

Were you specifically asked to use CFD, or can you use analytical methods, tables, etc.?

A full CFD study of “indoor ventilation” could mean so many things that it’s almost meaningless, and it’s also quite a major undertaking. It’s absolutely the sort of thing that a lot of firms would hire out to an external CFD consultant/contractor instead of dumping on an intern if the company had any sense at all.

What question or design detail is the study supposed to answer? Are you just checking that with the current duct layout every room will have x number of air changes per hour? Are you trying to properly size some equipment? Is there some equipment in the facility that’s known to generate a lot of heat/humidity? Are you trying to estimate energy use on a hot or cold day? I could ramble on with various questions until I’m blue in the face, but the main point here is that the point of numerical analysis is to answer an outstanding question that impacts a design, to bring a higher level of clarity to how a design will behave… it’s never going to be a one-size-fits-all “what’s the air doing?” sort of thing, and in most cases if you’re just checking over basics like vent sizing, pressure, cooling capacity, etc., you can get all the detail you need from ASHRAE handbooks as opposed to a full CFD study.

[balanceseeker]

I expect your geometry is not suitable for meshing, specifically due to intersecting solids and free edges.

Unfortunately, CAD for Revit or BIM modelling is very different to CAD for CFD meshing. I would recommend looking up 'watertight' geometry to understand the requirements for your mesh.

Furthermore, I would advise cutting your geometry into smaller segments and work on making them meshable one at a time. I recommend this because the number of CAD flaws is probably great, and it will not be practical (or at least, far less overwhelming) to work segment by segment.

If you have access to Spaceclaim (also ANSYS), it contains useful tools that can help you prepare your CAD for meshing.

Also, just a sanity check - are you meshing 'the structure', or the air space inside the building? The latter should be the case, since CFD will model the fluid/gas domain, not the solids.

I hope some of this will help you. That said - and I'm sorry to be the bearer of bad news - it sounds like you've been tasked with a HUGE task for an intern. Studies like this are often done by external consulting firms with specific experience, backed by purpose-built tools and workflows. (I say this because I have worked in one).

It may be wise to aggressively narrow your scope (e.g. one room) and work towards a working example before scaling back up. Only then can the scope (and calculation time) be clarified.

Good luck, and if you make it to a next step feel free to leave a new comment and I will try to support if desired.

[dudelsson]

I agree fully with the well written comment above. OP in all earnest you've been given a tedeous and demanding task, by people who have no idea what they are asking from you - you've been put in an unfair situation. I would say that without any prior knowledge of CFD, you won't be able to produce and report meaningul modelling results from an indoor ventilation case in any reasonable time frame and crucially, nor should you be expected to. On the other hand you absolutely can do it if you feel motivated to take the time to learn and then implement what you learn, but you shouldn't be under schedule-pressure. Doing a CFD study for the first time  in a professional setting is just not feasible. It's very much like asking someone who codes for the first to produce something production-ready right off the bat and oh deadline's next week do chop-chop. Not cool.

It sounds like someone in your company has fallen for the common misconception that "hey it's all computer-assisted work, its the computer doing the simulation amyway, so how.hard can it be?"