Relation between irrotational and inviscid

[haisol]

I want to know the relation between irrotational and inviscid.
Is it irrotational if the fluid is inviscid? Or inviscid if it's irrotational?

That's because my professor always write these two together as a constraint.
And he sometimes says that it can be rotational even if it's inviscid, for the case of shockwave.
Then is it always inviscid if it's irrotational? I'm so confused.

 

[boneh3ad]

The two terms are not one in the same. A fluid is irrotational if the curl of the velocity field is identically zero everywhere - it has no vorticity. For an inviscid fluid, vorticity cannot be generated, so a fluid that begins irrotational will remain irrotational indefinitely. For a viscous fluid, the effect of viscosity allows an otherwise irrotational fluid to generate some vorticity on its own such as in a shear layer or von-Karman shedding behind a cylinder.

 

[haisol]

thank you very much!