[ansys_matt]

My CFD results include Q criterion, Raw Q criterion, Vorticity magnitude, and lambda2 criterion.

Is there any way to use these to determine direction of rotation for 2D flow? Especially when there are closed streamlines but it is a shear vortex so a gradient plot won't help.

[FMDenaro]

Originally Posted by ansys_matt

My CFD results include Q criterion, Raw Q criterion, Vorticity magnitude, and lambda2 criterion.

Is there any way to use these to determine direction of rotation for 2D flow? Especially when there are closed streamlines but it is a shear vortex so a gradient plot won't help.

what do you mean exactly for "direction of rotation for 2D flow"?



Clearly vorticity has a sign and its only component is normal to the plane.
If you compute the streamline field Lap psi = vorticity you can see the flow direction passing between two streamlines by the difference of the values of psi.
But you should provide more details.

[ansys_matt]

Hello,


I mean clockwise or counterclockwise rotation.

[aero_head]

Originally Posted by ansys_matt

Hello,


I mean clockwise or counterclockwise rotation.

In terms of vorticity, it is +'ve for counterclockwise rotation and -'ve for clockwise rotation.

You can also calculate the circulation and its magnitude will indicate whether it is CCW or CW (C>0 = CCW, C<0 = CW).

[ansys_matt]

Thank you.

Is there a general guide to recommended distance for the circulation calculation? Say I have identified a region of non-zero Vorticity Magnitude or Q-Criterion. I find the "center" coordinates. How big of a circle around the center would work? Something like 2x the average space between nodes?

[aero_head]

Sorry, I had edited my response to indicate also that in terms of vorticity, it is +'ve for counterclockwise rotation and -'ve for clockwise rotation. Not sure if you saw that.

[aero_head]

Originally Posted by ansys_matt

Thank you.

Is there a general guide to recommended distance for the circulation calculation? Say I have identified a region of non-zero Vorticity Magnitude or Q-Criterion. I find the "center" coordinates. How big of a circle around the center would work? Something like 2x the average space between nodes?

Just make a user surface defined by a contour of vorticity=1 [1/s]. Then do a surface integral of vorticity on that user surface using the function calculator.