[quent9]

Hello guys,

I'm working on my master's thesis, it's about a vertical axis wind turbine and I would like to create a field function like :

int(p - p atm)dS to calculate the drag

I don't find in the user guide how we could write a field function with a integral operator.

Could someone help me please ?

Thanks.

[DCK]

Hi,

I am not sure what you mean with p atm. Assuming it is the reference pressure (Continua -> Physics -> Reference Values -> Reference Presure) the following should work:

1. Create a Surface Integral Report. Field Function: Pressure. Parts: your area "S". It's default Name will be "Surface Integral 1"

2. Create a Field Function. Definition: ${SurfaceIntegral1Report}

That's it.

[quent9]

Thanks DCK for your interesting reply.

In fact, I think this is the good way but one thing disturb me in your arguments :

I have to choose the part for the integral and I can't choose the frontal area of my VAWT. I just can choose the part that compose the regions...

Do you have any solution ?

Thank you again !

[fluid23]

Why are you creating a report that already exists? Force reports can be customized to report only pressure forces and by selecting the proper axis definition you can get pressure drag back out. You are making this way more difficult than it needs to be.

Also, you should never select a part for a report. Always choose a region, ...so you are on the right track there already.

Create a force report:
-right click Reports and select New Report > Force

-choose your units

-define your direction. (for VAWT drag you will want to use your freestream velocity vector)

-change force option to pressure and set reference pressure to 0 atm. (this is a gauge pressure, not absolute so 0 will reference whatever you have input into continua > physics > reference values > reference pressure.)

-assign your blade regions (and any other surface regions that contribute to the drag value you want)

Easy as 3.141592653589793238462643383279502884197169399375 1058209, right?

[fluid23]

Field functions should only be used to to calculate variables that are distributed in space. Not the integration, summation or derivation of variables that are distributed in space that result in a uniform scalar value.