Dandelion Seeds Fly Using ‘Impossible’ Method Never Before Seen in Nature

The Reynolds number is only part of the picture. You also need a measure of the strength of the turbulence. A common measure is the "turbulence intensity", which you can think of as the standard deviation of the velocity divided by the mean of the velocity. (Though that's only exactly true in "isotropic turbulence".)

In certain circumstances you can compensate for a higher Reynolds number with a lower turbulence intensity. The bristles of the dandelion may have a turbulence reduction ability, so perhaps this is already being done. I'm not certain how to reduce the turbulence level further as in this case it's mostly an ambient property which is beyond the control of the dandelion. Some sort of honeycomb structure upstream of the bristles might help, or it might hurt; it depends on the details.

Here are some examples:

Pipe flow can remain laminar for higher Reynolds numbers if the turbulence intensity is low enough. Though special turbulence control approaches (e.g., eliminating vibrations which could trigger transition to turbulence) laminar pipe flows have been observed at a Reynolds numbers of about 100000, about 50 times higher than the typical Reynolds number where laminar flow ends.

Here's a quote from a review article:

https://www.annualreviews.org/doi/abs/10.1146/annurev-fluid-...

> The impression gained from presenting data in this way is that there is a transition between two definable states. One is the relatively rare but well-defined state of motion, laminar flow, and the other is the more common and ill-defined state of turbulence. Experimental evidence suggests that the laminar state can be achieved in pipe flows over a wide range of Re with the record standing at Re = 100,000 by Pfenniger (1961). Reynolds himself managed to achieve Re = 13,000, and Ekman (1911) later improved on this to ∼50,000 using Reynolds’ original apparatus. [...] Achieving laminar flows at high values of Re is an indication of the quality of an experimental facility and gives some confidence that the observations will not be contaminated by extraneous background disturbances such as entrance flow effects, convection, and geometrical irregularities.

Matching the turbulence intensity of two wind tunnels is often necessary to make the results comparable between the two wind tunnels. In the first volume of Sidney Goldstein's "Modern Developments in Fluid Dynamics", there's a plot showing (if I recall correctly) the Reynolds number at which the "drag crisis" occurs as a function of turbulence intensity. This basically means that the drag coefficient can be very sensitive to the turbulence intensity, at least in special circumstances.

(Why I wrote this: In my dissertation, I have an entire section about how turbulence intensity is too frequently neglected in analyses, particularly for the problem I'm studying for my PhD.)

Evolution is crazy good at finding and exploiting quirks in physics.

It can be shown mathematically, using a technique called parabolized stability equations (PSE), that small disturbances amplify rapidly thorough non-linear interactions in the frequency space. Hence, although it's possible to create a laminar flow at high Re number in the lab, it's extremely hard to achieve in nature.

One interesting case of this is the Rutan's Voyager airplane in the 80s. It was designed to have a laminar flow over its wing to reduce drag. It worked quite well until it faced rain drops at some point which messed up the aerdynamics of the wing and caused the airplane to stall. At that point, they had to add vortex generators on the wing to prevent the stall.