Freestream BC, HELP PLEASE!
 

Hello everyone,

I am pretty new to Openfoam and I am trying to model a 2d airfoil in a time varying free stream velocity. From the airfFoil2D tutorial I got I need to set the type of the boundaries to "freestream" for all inlet,outlet, top and bottom patches and the wind velocity in the tutorial has been set as follows:
type freestream;
freestreamValue uniform (25.75 3.62 0);

is there any way that I can change the freestreamValue to a time varying value using the same boundary type (freestream)?
(I should mention that for some reason I prefer to keep the type of the boundaries as freestream)
Thank you.

Example from groovyBC instruction page(mimics inletOutlet):

outlet
{
type groovyBC;
valueExpression "vector(0,0,0)";
gradientExpression "vector(0,0,0)";
fractionExpression "(phi > 0) ? 0 : 1";
value uniform (0 0 0);
}

fractionExpression: Direchlet(1) or Neumann(0) BC
gradientExpression: for Neumann BC
valueExpression: for Direchlet BC

You can change the expressions to be time varying

Thank you for your reply. Could you please send me the link of the page?
what does "phi" stand for?

Thank you for your reply. Could you please send me the link of the page?
what does "phi" stand for?

https://openfoamwiki.net/index.php/Contrib/groovyBC

phi is the flux

Awesome. Actually the good thing about the "freestream" is that it treats each cell as a single patch, therefore instead of having inlet/outlet/bottom/top a circular boundary can be considered and the freestream can be applied. However for groovyBC it is necessary to have inlet and outlet.( please correct me if I am wrong)

Thank you for your help.

Hi

I want to use freestreampressure but combined with having the pressure prescribed as a value:
"Prescribed pressure; with allowed in/outflow reversal"
Is this possible in OpenFoam? Thanks,

PS: more details:
It is a wind engineering in-compressible flow simulation.
I have a prescribed inlet velocity BC (Fluctuating Inlet). We usually combine this with a zeroGradient Pressure BC on the inlet.
I want to have Inlet/Outlet condition on the Top, Sides and Outlet. However, a pressure value should be described on some boundary. Usually we use a fixedValue 0 for pressure. Is there a way to combine this with freestreampressure?