Open Conference Systems, DDAYS LAC 2024 Main Conference

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83 years after the seminal work by Kolmogorov the statistics of turbulent velocity fluctuations remain a riddle
Eberhard Bodenschatz

Building: Cero Infinito
Room: 1401
Date: 2024-12-10 02:30 PM – 03:00 PM
Last modified: 2024-11-22

Abstract


In 1941, the mathematician Andrei Nikolajevitsch Kolmogorov put forth the hypothesis that turbulent flows should exhibit universal statistical self-similar properties. Similarly, Ludwig Prandtl reached a comparable conclusion four years later. Subsequently, the Nobel laureates Werner von Heisenberg, Carl-Friedrich von Weizsäcker and Lars Onsager each reached the same conclusion.  Over time, the anticipated power laws have been refined, yet it has remained unfeasible to quantify them at the requisite high turbulence levels. Simulations of fully developed turbulence on the world's most powerful computers provide evidence of this statistical universality. It should be noted that these simulations are highly idealised, taking place within a periodic box and with energy introduced globally on large scales. The generation of this kind of turbulent flow is not feasible in any experiment.In light of the aforementioned considerations, it is pertinent to inquire as to the findings of experimental studies in this domain.  For over a century, the wind tunnel has been the established standard for studying turbulent flows. When a fluid flows through a grid at high velocity, vortices form and decay after a short time, exhibiting the universal statistical properties of turbulence.  The latest technological developments permit the measurement of velocities at the smallest length scales and highest Reynolds numbers. The results of experiments conducted in the Max Planck Variable Density Turbulence Tunnel  (VDTT) at the highest controllable and measurable Reynolds number will be presented, which demonstrate that universality in accordance with the Komogorov hypothesis is not observed. Our findings indicate a spatially dependent logarithmic dependence of the power-law exponents, which require further theoretical investigation. Additionally, results on Lagrangian particle tracking in the VDTT will be presented.