Airflow Simulation

[Anonymous]

Hello fellow CFD-modelers,

My task is to model the airflow in a 2-room appartment under various thermal and humidity conditions. As a result I must locate weak spots where condensate should appear.

I am having problems in setting the correct boundaries, I read the tutorials but somehow I can't make it going.

so the question is:

what boundaries should I set, to solve following:

outside : -25 Celsius, Humidity 75%

inside: 20 Celsius, Humidity 50%

for the airflow from outside i set up temperature and humidity at the inlets. but i can t figure out how to set the initial room temperature and humidity.

Thanks a lot!!!

Alex

[Anonymous]

Hi John,

I could set the volume flow rate at the outlet to 60 m3/h total. The two inlets provide a max of 30 m3/h each. However, the real life model has two ventilators who suck in 95 m3/h (total).

I will also need to simulate the airflow when the ventilators pump 65 respectively 110 m3/h for some scenarios. So it would be awesome if i could somehow set a maximal inlet limit.

Thanks,

Alex

[Jon.Wilde]

Where does the extra air go? 🙂

It sounds like you have an imbalance between in and out, is that a correct assumption?

[Anonymous]

Dear Jon,

I think I made a wrong assumption setting up the volume flow rate to 35 m3/hr. It is more accurate with the external fan, for I have the information regarding the information between the pressure and the volume flow rate of the fan.

However, the air inlet supply, does phyisically not let in more than 30 m3 per hr. And this is already a simplification, it can go also lower depending on the relative humidity inside. I dropped that part because things were getting to complicated.

Is mounting a filter who acts like a resistance at the inlets an option? I am pretty confused 😄

Thanks!

[Anonymous]

Dear Jon,

I'm still struggling with this matter. is it possible to limit the volume flow rate  through an inlet to a certain value?

I tried even building an extra outlet to be able to define the 4 existing ones but not succesful.

Any hints are highly appreciated 😄

Thanks a lot!!!

[Jon.Wilde]

I am still not clear on your setup.

You could have a resistance near the inlet but this would only cause a pressure drop really. As you are pulling air out of your model, the same volume of air is going to have to enter also. Is this not the case here somehow?

[Anonymous]

The air is sucked out by two ventilators (for who I have pressure-volume flow rate diagramm) and flows in through two inlets, who do not let more than 30 m3/h each.

[Jon.Wilde]

Hi,

I guess the important fact here is that air out = air in, that can't change so what I am thinking is this.

Why not model a resistance near the inlet (with a good length of air upstream also) and have your flow rates at the outlet. CFD will balance the flow coming in with what you are pulling out, but it may pull more air from one inlet than the other. Could that help?

For scenarios with lower flow, pull less air from the outlets?

[Anonymous]

Hello Jon,

Thanks for your answer!

It is no problem if more air is pulled from one inlet than the other so I will give this option a try.

Could you help me with some tipps regarding this resistance?

Thanks again!!

[Jon.Wilde]

Sure, the help has a good page. Make sure they have a good uniform mesh (4-5 elements through their thickness)

[Anonymous]

Hi Jon,

I did the required steps, used automatic sizing and refined then surfaces and gaps (5 elements through).
I still get a number around 11 milion elements and I don't succeed to reducing this number to 5-6 as you suggested. What should I do?


Thanks!!!

[Jon.Wilde]

Hi,

I am not sure my instructions were too clear 🙂

If you are using Gap Refinement, use 3 elements, any more tends to be a waste.

You need to manually refine the fans to ensure they have sufficient mesh through them.

Your final mesh count is not what I am referring to here - more ensuring that the mesh is of good quality. Does that help?

Thanks,

Jon

[Anonymous]

Hello Jon,

After doing surface and gap ref. with 3 elements, I got 4.3 mil elements. Is there any aspect I should consider other than these edits?

Thanks

[Anonymous]

P.s. As this is my first project in CFD ensuring a good quality mesh is like a pandora s box.

[Jon.Wilde]

Haha, somewhat although you soon get good at it 🙂

Yes, you need to uniform mesh the fans as above 😉

Other than that, see how it runs.

[Anonymous]

Dear Jon,

As my computing capacities do not tend to compliy with my 10 million elements, i would like to know how to use the cloud computing of autodesk.

With a lower element number, i get pretty ugly results, or maybe I am just not setting it up right. I am pretty frustrated with this. Last simulation lasted for 3 days, only for the stationary part.

Thanks,

Alex

[Amal.C]

Hello Alex,

It seems like you are using a student version.

Unfortunately, we do not provide access to the cloud to students. The cloud is only limited  to commercial use.

3 days is not a long time to solve locally a model with 10 Million elements  

I have by the way a question concerning your model. What do you mean by "Stationary part"? 

Thanks!

Amal

[Anonymous]

Hi and thanks for your reply,

I meant steady state solving.

I read about a possibility to buy credits and run the simulation.

Is that possible?

Sent from my iPhone

[Amal.C]

Hi Alex,

It is possible to buy the cloud credits only for commercial customers and subscriptions.

The cloud credits are unfortunatly not provided for educational purposes.

Amal,

[Amal.C]

Hi Alex,

Would it be possible to share your model with us to check if we should make some improvements on it?

Many thanks!

Amal,

[Anonymous]

Hello,

This is my model. I get pretty low results on the edge surfaces. Is it because of the model itself or am I missing a setting?

I started with the whole appartment but my computer was unable to run the simulations properly once I passed 5 million elements which apparently did not lead to real results.

Please help me out 😄

Thanks,

Alex