Wind Direction in CFD Analysis

[Anonymous]

Hi,

I want to work on natural ventilation. In my case, wind direction plays an important role for CFD analysis.

I didn't see any input for wind direction. 

Is it possible to input this data in Autodesk CFD?

Wait for your answer.

Thanks for your consideration.

Regards,

Helia

[matt.bemis]

Hi @Anonymous,

This would be done via a velocity boundary condition. FYI you will need an outlet somewhere. Probably on the opposite end of the model? 0 pressure gage.

Thanks,

[Anonymous]

Matt,

Thanks alot for your reply.

Actually, I mean that I want to have the wind direction for the boundary condition of of the inlet (and even outlet). Since I want to work on Natural Ventilation and simulate it in a room, and I want to have an inlet and outlet which are expose to the outside condition. I want to see that is I use the wind direction of the outdoor condition, what will be happen for the natural ventilation inside the room.

Thanks for your consideration.

Regards,

Helia

[David.Short.]

Hi Helia,

Only normal / perpendicular directions can be applied to flow boundary conditions. To achieve alternate wind directions one approach would be to change the angle of the inlet in CAD.

I hope that helps,

David

[David.Short.]

Hi Helia,

I must correct my last response. It is possible to apply any angle to the flow at the inlet usin "Component" method in the boundary condition edittor.

Thanks and sorry for any confusion,

David

[Anonymous]

David,

Thanks alot for your reply and information.

I searched for Component Method and I didn't find that, would you please tell me how can I change the method?

Besides, it is a better solution to make a big surrounding box around the room and make wind direction with the big box inlet and outlet? Or you think that it is not a good solution for natural ventilation?

Thanks alot for your respond.

Regards,

Helia

[Jon.Wilde]

Typically, we run with a larger box (drawn in CAD) around the building with a wind direction at the inlet and a P=0 at the outlet. This then naturally ventilates the building, might that work for you?

To apply components, check out the page here. It isn't really recommended though and I can't really see how it would be useful 😉

Go with the external air domain and draw it in CAD so you don't have a gap underneath.

[Anonymous]

Jon,

Thanks alot for your reply.

I didn't understand completely. You told that I can have a domain box and have wind direction in the inlet and 0 pressure in the outlet. But I see that you told it is not suggested.

Am I understand right?

Thanks,

Regards,

Helia

[Jon.Wilde]

The component approach is a little weird and I would say go with the external domain. There you don't need components, just a normal velocity - much like a wind tunnel.

Does that help?

[Anonymous]

Dear Jon,

Thanks alot for your reply. I just try to built an external environment several times. But the problem is that when I want to make a domain, and I input the dimension in X, Y and Z, the software cannot do it and after an hour of thinking, it becomes "Not Responding". My model is a 30 x 30 x 10 ft room and I try to make an external domain to simulate natural ventilation for it.

I hope I can conduct this simulation.

Thanks alot for your consideration.

Regards,

Helia

[matt.bemis]

Hi @Anonymous,

When exactly does CFD get hung up and stop responding? During the external volume creation? During solve? Mesh? is your RAM maxed out? Send us a screenshot of when it gets frozen and what your screen is showing and we may be able to help.

If for some reason it gets hung up while creating the external domain (in geometry tools) then you could probably just create it in CAD and this import CAD to CFD. 

Thanks,

[Anonymous]

Matt,

Thanks alot for your consideration.

I tried again and could create an external volume. I push the Solve button, but the window which I attach to this reply is appeared. 

I tell you about the features that I assigned.

1- Air to the volumes of the external volume and my room.

2- Solar Window to the South Windows.

3- Solar Walls to the South Walls. 

4- No Boundary conditions for the surfaces and windows.

5- Temperature and Humidity Boundary Conditions to the inlet of the external volume.

6- Pressure=0 for the outlet of the external volume.

7- Slip/Symmetry to the surfaces of the external volume (except inlet and outlet).

8- In Solve: Heat Transfer, Flow and Radiation are checked.

9- I selected Raleigh for Solar Heating.

My goal in this simulation is simulating natural ventilation in summer design day for Raleigh. Besides, I want to take the solar heating which enters through windows in the calculation.

Thanks alot for your consideration.

Wait for your suggestions.

Regards,

Helia

[Jon.Wilde]

Do you have solar materials applied to surfaces like the error suggests?

[Anonymous]

I assigned Solar Window and Wall to the south windows and wall. I remove that material. and assigned air to the windows. 

But the problem is that, the air flow doesn't come inside of the room! 

I don't know how I can solve this. I read alot the tutorials, and tried to do the process right, but the air flow doesn't enter the room.

Thanks,

Helia

[David.Short.]

Hi @Anonymous,

I think we are going to need to see your .cfz to grasp what's going on her.

Please can you upload it.

Thanks,

David

[Anonymous]

David,

This is the file of my model. Is it enough or I should send other support files, too? (I mean the Design 1 and Scenario 1 folders)

Thanks alot for your consideration.

Regards,

Helia

[Jon.Wilde]

You need to save out a support file from the interface, a CFZ file 🙂

[Anonymous]

Thanks.

This is the CFZ file. 🙂

[David.Short.]

Hi @Anonymous,

You have modeled your building using single surfaces rather than volumes this is why you cannot assign the solar window and wall properties.

In reality the walls will have a thickness, thus making them a volume! You need to model the building just like in reality to produce usable results.

Didn't we already get a simulation up and running just without the external volume? Use that model and then just add an external volume.

As for the simulation without solar walls and windows there is a small amount of air entering and leaving the room which is probably quite realistic for the setup.

All the best,

David

[Jon.Wilde]

Also, you might want to consider adding the external volume in CAD so that you can place the building on the ground 😉