 Solution

ID: past-exam-of-the-options-i-course-of-the-university-of-oxford/2008/k/k1/ii/solution

The vorticity points normally to the plane and has scalar component

ω_{z} = v_{x} - u_{y} = 2 sin x cos y = 2 ψ .

It is nonzero in general, so the flow is rotational.

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