[bineet_aero]

Hello,

The sign convention for helicity or vorticity is +ve for a anti clockwise circulation and vice versa. But in starCCM it shows to be opposite. A +ve helicity is associatd with a clockwise vortex and a -ve helicity is associated with an anticlockwise vortex.

Any inputs on this ? Something here is wrong?

Thanks

Bineet

[LuckyTran]

I've always thought right-hand rule applies and +ve is clockwise.


edit* hahaha I guess it depends which orientation you are looking from whether it is clockwise or anti-clockwise.

[LuckyTran]

Right hand rule applies no?

[bineet_aero]

this is the reply i got from STARCCM official forum

"Note that there is no sign convention involved for both quantities since they are precise defined:

vorticity = w = curl of velocity field
helicity = h = v.w (scalar product)"

[LuckyTran]

That's quite a non-sense response from the Star crew because vorticity is a vector that characterizes a rotation. It is precisely defined as such, having a length and direction, but the direction of that vector is linked to the direction of rotation via the right-hand rule.


Maybe you can go back and ask them what happens when the magnitude of a vector is negative, which way it points? That is a cop-out answer to say "the precise definition is here," also not helpful to somehow like you who has a legitimate question. Are they going to say there's no sign convention for vector direction because vectors always point in the positive direction? Honestly, I'm shaking my head.

[bineet_aero]

Thanks a lot for your input. I am going to supply them some contours and streamlines for a detailed explanation. Will let you know.

Regards

[bineet_aero]

Hello


I think its all ok. I got confused from the reply of STARCCM.

Please find attached two images for a better interpretation. Image 1 is the channel geometry with a pair of vortex generators (Main flow is along x axis, u = some value, v=w=0).

Image 2 shows the streamline and contours of helicity at some streamwise cross sectional plane shown in image 1 (+ve x axis in image 2 is into the plane of the paper away from the reader). Looking at image 2 from +ve x axis we see an anticlockwise vortex (right side one z >0). For this vortex, vorticity or helicity should have a +ve sign according to right hand thumb rule which is actually the case in helicity plot for the right side vortex. So its ok i guess.

But i did not understand when starCCM said there is no sign convention for vorticity in STARCCM.

Regards
Bineet