## Fluids

#### Interior Fan Boundary Condition

• bervyngoh
Subscriber

Hello all,

My problem is that of ventilation in a room. Imagine a square room with a duct passing from left to right. There are cut outs from the duct that allow cooled air to flow into a room and fans that help to improve cool-air flow into the room at the cut-outs.

I can only select, 'intake-fan' and 'exhaust-fan' but there is no 'fan' boundary condition (with the swirl velocity) that I can select as seen after doing some research online.

How can I model the fans that simply redirect air-flow from the ducts into the room, without having to input a temperature value (like in 'intake-fan' and 'exhaust-fan').

I am only using a rectangular surface to model the fan.

Your help will be greatly appreciated!

• Karthik R

If you are not modeling the actual fan and are simply looking for an inlet condition to your room, you could use any of the following - mass flow inlet (if your flow is induced) or intake fan. Again, the inlet value you use depends on what your knowns are. Mass flow inlet works if you have the knowledge of your inlet mass flow rate. Intake fan, which models an external intake fan, relies on pressure jump.

For both these cases, if you are modeling the heat transfer, you will need to provide an inlet air temperature.

Thanks.

Karthik

• bervyngoh
Subscriber

Hi Karthik.

I already have inlets into the room (air-con) with an inlet air temperature. What I am trying to model is just a fan inside the room that redirects air. Perhaps it will be useful to think of a normal study room with an air-conditioner and just a table-top electric fan to improve ventilation. I have managed to include the boundary condition for the air-con as "velocity-inlet" with an inlet air temperature. But I am unsure how to model the fan that I have described above. My plan was to use a simple surface to model the fan instead of drawing the actual fan (with blades) itself for simplicity. WIll that be possible?

I only have the volume flow rate and rpm of the fan.

Thank you once again!

• Karthik R

Thank you for explaining your modeling needs.

You should be able to use the fan boundary condition. Without actually modeling fan geometry, you should be able to use a thin surface to define this condition. Here, the fan model is a lumped parameter model that can be used to determine the impact of a fan with known characteristics upon some larger flow field. You will either need the relationship between the pressure head and flow rate or the radial and tangential components of the swirl velocity.

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v201/en/flu_ug/flu_ug_sec_bc_fan.html?q=fan%20boundary%20condition

If you are looking for specific instructions on how to open this link, I'd recommend that you check this post.

https://forum.ansys.com/forums/topic/how-to-access-the-ansys-online-help/

There are a lot of videos available on YouTube related to this boundary condition and how to use it. I'd strongly recommend that you go through these videos. They should provide you with a strong starting point.

Thank you.

Karthik

• bervyngoh
Subscriber

Hi Karthik,