If the significance of the Reynolds number is:

Total Momentum Transfer / Molecular Momentum Transfer

Then what is the effect of angular momentum on the transition from laminar to turbulent as in a convective vortex? Waterspouts, in particular, seem to be obvious cases where a very large Rayleigh Number would be assigned, yet the systems are admitted by observational experts to be dominated by laminar flow!

  • $\begingroup$ What do You mean with that waterspout? The water streaming in the nozzle or the water jet in air? $\endgroup$
    – Georg
    Commented Nov 28, 2011 at 20:56
  • $\begingroup$ Waterspouts as in tornadoes over water. Lots of videos of them on youtube and its hard to imagine turbulent flows dominate them. $\endgroup$ Commented Nov 28, 2011 at 21:32
  • $\begingroup$ Ah, in a tornado hose! Why would someone assign high Reynolds numbers for those? $\endgroup$
    – Georg
    Commented Nov 28, 2011 at 21:40

1 Answer 1


This is a reasonable question. At the scale of a waterspout, the inertial forces of fast-moving air should be large compared to the viscous forces (i.e., very large Reynolds number). Yet the inflow along the surface of the water is laminar, where we would ordinarily expect boundary-layer vorticity (i.e., turbulence). A detailed description of the expected properties of suction vortexes (including the boundary-layer turbulence) can be found here:

Thermodynamic Tornadoes?

An hypothesis that directly addresses the anomalous behavior is here:

Tornadic Inflow

This work includes plenty of references in case you want to research it further. For example, you could read up on two-fluid simulations, which accurately describe the fast-moving, laminar flow along the surface (but beg the question of how two-fluid behaviors are instantiated in a well-mixed fluid such as the air).


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