Learning Forum

[puh69]

Hello,

 

I have been running a rotor grid with rotational periodic boundary conditions (non-matching).  I have notice that whenever I use the Pressure Far-field boundary condition on the outer surface of the cylindrical grid that my solution begins to diverge, however if I set this to an inviscid will I will find a converged solution. My initial test case is purely axial flow because issues arise with pressure waves escaping the domain when I add the tangential velocity due to this BC issue!  Happy to provide more details where requested.

 

Thanks

[Rob]

Pictures may help. Far field is really intended for external aero models such as aerofoils etc where there isn't anything around the object of interest. I've never seen them used with periodic boundaries, so don't know if the are designed to work together. 

[puh69]

Rob, 

 

Thanks for the detail. The idea here is that the rotor would be spinning in free air. It appears that the current limitation is that any wall used on the outer component prevents the pressure wave from escaping. Any alternative suggestions would be appreciated.

[Rob]

There shouldn't be any/much of a pressure wave hitting the outer face looking at the above. If you plot pressure when it's a wall what are you seeing? Pressure outlet with reverse flow direction from neighbouring cell ought to do it. 

[puh69]

Rob, my converged case has always been purely axial flow. As I introdouce tangential flow we start to see the following contours for both pressure and velocity and this is where I'm guessing the source of error is coming from. 

 

[Rob]

Possibly, but shouldn't the flow remain as mostly axial?