[AS_Aero]

Hi
I have posted about this recirculation previously as well.

Now I have a doubt, I am running a steady state Rotor-Stator configuration simulation and I increased the outflow region to 10times the rotor diameter and still I could see huge recirculation after the step as shown in the image.
Can someone tell me if this is physical or could there be something wrong in my computation ? And will this recirculation affect my rotor performance and simulation as well ? Or should I do transient simulation ?

[Gert-Jan]

It is common practice to put the outlet outside the recirculation. So it should be put further downstream.

And is it realistic? I have no reason to doubt on these results. I would advise to go outside on a windy day and find out yourself if the windspeed is much lower behind a building ;-)

Will it affect your results? It depends on what question you are trying to answer using CFD. Is it the efficiency of your rotor? Then I doubt if you will see any effect. But you should determine that yourself. Put the outlet further away and determine the result.

[AS_Aero]

Hi Gert JAn

Yes its all about calculating the power from the rotor. And I was thinking if the rotor gets some negative velocity due to this recirculation and then it will affect the power. But as I run it longer the recirculation diameter changes or moving .So I am not sure how to quantify it. This I can see only in a transient simulation right ?
This I ran for 3000 iterations so I will use this as a restart for unsteady simulation. Will that be ok ?

[ghorrocks]

The magnitude of these effects vary simulation to simulation so you will have to do a sensitivity study as Gert-Jan recommends to determine how important it is in your case.

Yes, you can use a steady state simulation (even a partly converged one) as an initial condition for transient simulations. This is providing you don't care about the startup transient, only the periodic pseudo-steady state conditions are of interest to you.