[jinny]

Hello guys !

I wonder why the vortex-identification method needed ?

(such as, Lambda-2 criterion, Q-criterion, etc.)

If we do not use the vortex-identification method, we cannot visualize a vortex
and swirling motion of fluid ?

Thanks in advance

[FMDenaro]

Originally Posted by jinny

Hello guys !

I wonder why the vortex-identification method needed ?

(such as, Lambda-2 criterion, Q-criterion, etc.)

If we do not use the vortex-identification method, we cannot visualize a vortex
and swirling motion of fluid ?

Thanks in advance

If you do not use a vortex-identification method how can you be able in visualize a vortex? vortex is not vorticity...

[lovecraft22]

I disagree. You don't necessarily need a vortex identification method to visualize a vortex. Most of the time looking at some of the flow variables will be enough.

[FMDenaro]

Originally Posted by lovecraft22

I disagree. You don't necessarily need a vortex identification method to visualize a vortex. Most of the time looking at some of the flow variables will be enough.

yes, you can see the pressure field or visualize the vector plot to have some idea and avoiding further computational cost but that does not say you about a "vortex" if you need it.
Specifically, what should be identified (in 3d) is a "vortex-tube", according to the mathematical definition a tube having zero normal vorticity at its surface.
Pressure and velocity cannot provide a clear picture. Worst when you need to detect coherent vortices

[Florent]

it is easy to visualize a vortex when it is alone in a flow (such as a laminar von Karman street). It is more difficult to track coherent structures or vortical structure in a fully developed turbulent flow. This is why people have developed "automatic" criterion to identify coherent structures as lambda or Q-criterion