Could some one please explain what the purpose/concept/benefit/use of 'Non reflective boundary conditions'(beta function in CFX-11) is?

I am asking this in context of my another question posted at http://www.cfd-online.com/Forum/cfx.cgi?read=24989

How would it help to maintain the flow direction outward at some outlet?

Thank you so much, KK

Hi KK

Non-reflective boundary condition prevent the pressure fluctutaions to reflect back in your CFD domain. It helps to stabilise your numerical solution.

Kasim

Thank you very much Kasim

As opening type boundary conditions are supposed to make Large Eddy Simulations unstable because eddies are recirculated at the boundary, will NON-reflective boundary condition (opening) might help to make the LES simulation stable?

May be my question is not an appropriate one, I am new in CFD.

Thank you so much again, KK.

If you have set pressure at the outlet, pressure fluctuations can reach the outlet and de-stabilise the soilution by reflecting back in domain. In that case one should use non-reflective BC. I would suggest that you dont use Opening with non-reflective boundary condition for final solution. You can keep non-reflective BC but change your opening to Outlet once your solution has gained stability.

Kasim