News and Views
Nature 409, 993-995 (22 February 2001) | doi: 10.1038/35059196
Turbulence: Go with the flow
by Itamar Procaccia
It is about the Bodenschatz experiment with the special detector from electron-positron collider. The only ‘strange’ thing is why in 2001 the comparison is with hot-wire:
At present, the standard probe for turbulence research is the hot-wire anemometer. This consists of a thin wire that is heated by the passage of an electrical current and is kept at a constant temperature by means of a feedback loop. The wire is placed at right angles to the average flow of a turbulent fluid. The fluid cools the wire and, because the cooling effect depends on the fluid’s velocity — the faster the fluid flows, the more the wire is cooled — the velocity can be measured as a function of time. As would be expected for turbulent fluids, an erratic time series is obtained.
Of course, hot wire couldn’t give this picture:
At any moment in time the trio defines a triangle that is fully determined by a scale R, the Euler angles of its orientation in space, and two internal angles. Theory focuses on ‘statistically preserved structures’ which are determined by the distribution on internal angles and the scale. These structures dominate the statistical theory.
Well, of course we also like these cuts:
But theorists dream about measuring scale-dependent information from points that move with the flow — the so-called ‘lagrangian’ trajectories
offer new possibilities in following the detailed motion of fluid particles. This progress promises an exciting and fruitful interaction between theory and experiments in turbulence in the coming years.