Doublet (potential flow)

A doublet is a potential-flow singularity formed by a source and an equal sink brought together while their product of strength and separation stays finite, giving a velocity potential that falls off as 1/r^2 in 3D. Superposing a uniform stream with a doublet produces the classic flow past a sphere or, in 2D, a cylinder, which is why doublets are the building block for body representation in panel methods. Distributing doublets (dipoles) over a hull surface, alongside sources, lets a boundary element method enforce the no-penetration condition and represent lift through a doublet wake. It carries the inviscid, irrotational assumptions of potential flow.