External Fan boundary condition

[Anonymous]

Hello,

I am trying to run a CFD simulation to see the flow of air inside an oven. The oven has got a circulation fan at the top of it which circulates air inside the oven. Can I use 'external fan' boundary condition to simulate circulation?

If yes, what data of fans do I need?

If no, can anyone please help how I can simulate this condition?

Thank you.

[frederic.gaillard.7 · Accepted solution]

Hello @Anonymous, 

here are the step to follow to apply correctly an external fan BC : 

External fan is another way to move flow in or out of a device. An external fan is defined as a head-capacity curve, resulting in an inlet flow rate that varies with the pressure drop of the device. This is a convenient way to determine the operating point of a fan for a particular flow path.

To assign an External Fan condition:

1. Set the Type to External Fan, and set the Unit type.
2. Enter the rotation speed of the fan in the Rotational Speed field.
3. If needed, change the rotational direction by clicking Reverse Direction. The direction is drawn with an arrow.
4. Specify the fan curve by clicking the Fan Characteristic Edit button.
   • Click Insert to add rows between defined rows.
   • Click the Plot button to view the plot.
   • The Import button imports a comma separated variable (CSV) file, and the Save button saves the curve information to a CSV file.
   • To enter a fan that pulls flow (at an outlet), enter all flow rate and pressure values as negative.
5. Enter a slip factor (between 0 and 1) in the Slip Factor field.
6. Click Apply.

Note: The slip factor is the ratio of the true rotational speed of the flow to the rotational speed of the fan blades. Due to inefficiencies in the fan, slip can result in a slower flow tangential flow velocity than expected. Autodesk® CFD determines the flow tangential velocity component by multiplying the slip factor by the user-supplied fan rotational speed. The default slip factor is 1.0. This means that the rotational speed of the flow is the same as the rotational speed of the fan.

does it answer to your question ? 
If you have other question don't hesitate 

Fred 

[jrohit1110]

How do you even know the values of pressure head and flow rate for a BLDC?.(I'm Simulating a drone.) I have no proper testing facilities or methods to test pressure heads and flow rates of fluids. I could go with a thumb rule or something. I'm using 2200kv motors at 4000rpm. Is there any other option to make an analysis? Is there a tutorial video online demonstrating the same?

Regards.  

[Anonymous]

I am having the same problem

CFD2019

[Anonymous]

For my own curve, I used two bits of information typically found on a fan spec sheet.  The first is the max flow.  This value is always presented with the understanding that max flow exists when there is no pressure head.  That gives you your first point.  The second value is max pressure.  Likewise, the max pressure is always given with the understanding that it pertains to no flow.  That gives you your second point.  You can enter those points into the "Fan Characteristic" sheet when you're assigning values to the "external fan" boundary condition.  The program will do the rest.

Hope that helps.

[Anonymous]

Thanks for this.

Now it is very clear

[itamar.ladelsky.21]

Hello,

I am trying to set up an external fan so i can get a better idea of how different RMPs of the fan effect the airflow thru the space. im a bit confused regarding what numbers to out in the pressure rate and flow rate section of the columns. 

Any adivce would be much appriciated!

\thanks,

Itamar Lilienthal