The condition of irrotationality for a two-dimensional flow is satisfied when rotation w everywhere is (less than — equal to — more than) zero.

Zero.

Explanation:

Lets take velocity V is given as in 2 dimensional flow

  V=u i +v j

V=f(x,y)

u=f(x,y)

v=f(x,y)

Rotational ability ω given as

If

ω=0 ,then flow will be  irrotational.

ω ≠0 ,then flow will be rotational.

So we can say that , ω will be zero every where for  irrotational  two dimensional flow .

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