Solution

Past exam of the mathematics course of the University of Cambridge / 2023 / ii / Paper 2 / 39C / c / ii / Solution

{title2=$D=8\pi\mu U$}

For the zero-circulation flow around a circle, $e:e=8U^2a^4/r^6$. Integration over the exterior plane gives dissipation $8\pi\mu U^2$ per unit axial length and hence drag $D=8\pi\mu U$ per unit length.


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 Incoming links: Drag on a two-dimensional circular bubble from outer-flow dissipation