## A fluid mechanic’s analysis of the tea-cup singularity

In 1926 Einstein published a short paper explaining the meandering of

rivers. He famously began the paper by discussing the secondary flow

generated in a stirred tea cup — the flow now widely known to be responsible for the

collection of tea leaves at the center of a stirred cup of tea. In 2014, Luo

and Hou presented detailed numerical evidence of a finite-time

singularity in a rotating, incompressible, inviscid flow. The key driving mechanism of

that singularity is the secondary tea-cup flow. The present work is not aimed at

proving the existence of a singularity in this flow, nor is it aimed at

generating more highly resolved numerical evidence for the singularity than

already exists. Rather, I will assume that the flow simulated by Luo

and Hou genuinely develops a singularity. My goal is to understand, from a

fluid-mechanics perspective, why.