Torricelli's curtain: Morphology of horizontal laminar jets under gravity

Viscous fluid exiting a long horizontal circular pipe develops complex structure comprising primary jet above and smaller secondary below with thin curtain connecting them. We present here combined experimental, theoretical numerical study of this 'Torricelli's curtain' phenomenon, focusing on the factors that control its morphology. propose model for in which particle trajectories result from composition two motions: component corresponding to evolving axial velocity profile an axisymmetric viscous jet, vertical due free fall under gravity. The predicts well trajectory but somewhat less jet. suggest remaining discrepancy may be explained by surface tension-driven (Taylor-Culick) retraction Finally, direct simulation reveals recirculating 'Dean' vortices sections placing Torricelli's firmly within context flow curved pipes.