= Line source
{title2=$w(z)=\frac{Q}{2\pi}\log(z-b)$}
In a planar <incompressible flow>, a <line source> injects <volume flux> $Q$ per unit length perpendicular to the plane. Its radial <velocity> is $u_r=Q/(2\pi r)$, since integrating the outward <velocity> around a <circle> gives $2\pi r u_r=Q$. Its <complex potential of a two-dimensional potential flow> is $w=Q\log(z-b)/(2\pi)$ and its <complex velocity> is $w'=Q/[2\pi(z-b)]$. Here $Q>0$ means outward flow; a <line sink> has negative $Q$. Away from $b$, this is an <irrotational flow> as well as an <incompressible flow>.
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