Like cures like: how to destroy turbulence with turbulence

Like cures like: how to destroy turbulence with turbulence
Jakob Kühnen, IST Austria
Michael Riedl, IST Austria
Davide Scarselli, IST Austria
Björn Hof, IST Austria
DOI: doi.org/10.110...
Pipes and pipelines are essential for the distribution of fluids, ranging from small diameter tubes in domestic settings to pipes in industrial plants and large scale pipelines. The frictional losses encountered in these flows are responsible for a significant part of the global energy consumption. A huge amount of energy (pumping power due to frictional drag) could be saved if flows in pipes are laminar instead of turbulent. Pipe flow has a property that makes it particularly attractive for control methods which totally extinguish turbulence and establish a laminar flow, as the laminar state is stable to infinitesimal perturbations. Consequently, once relaminarization is achieved, the flow will remain laminar provided that the pipe is straight and smooth. We show that a rather simple, steady perturbation of turbulent flow in a pipe can lead to a complete collapse of turbulence and the flow fully relaminarizes.
See other videos from the 2017 Gallery of Fluid Motion: gfm.aps.org/

[@AndrewPa]

thank you for uploading this video. It is informative and interesting.It is interesting to know direction of rotation (sync/async, and how speed of rotation was impacting flow. Using passive scalars can be misleading about velocity distribution. Anyway danke ... a lot

[@NzeDede]

is it wrong to deduce that the motor helps in breaking down those large structures into small eddies, and due to the energy transferred from the motor to the smaller structure, this in turn helps it to transition into laminar after losing some of its energy to heat due to work down by viscous forces?

[@NzeDede]

In retrospect, one can say that the turbulent energy (or rather, the random increase and decrease in the mean velocity) carried by the smaller eddies is dissipated due to work done by viscous forces, thus leaving no room for further transport of properties to adjacent strata.

[@nikoskorobos100]

I agree, I believe that the rotors break-up the larger turbulent structures into smaller ones resembling isotropic turbulence conditions. Under such conditions viscus dissipation acts (microstructure) therefore the decay of turbulence is faster.

[@vishnusankar5335]

This is so counter-intuitive and very cool! Thanks a lot for sharing...

[@grezamisoit]

Nice video but we are missing a physical interpretation of the phenomen.

[@aeromodeller1]

Can passing it through a fine screen destroy the turbulence? It makes very fine grain turbulence which decays quickly.

[@vanhoot2234]

likely not

[@alikahraman5884]

It should be the same idea as the video, if you kill the large eddies into smaller ones they get dissipated, and then in the absence of a perturbation to create large eddies again the flow turns laminar. The question is, would the fine screen be able to properly kill the large eddies, or would sort of the "ghost" of the large eddy live through the screen.

[@Bobby-vz9eq]

That's interesting. Very Interesting. It's the frequency of the biggest structures somehow connected with the rotor speed? In particular, the rotor turn on the same frequency of them or it is sufficient that there is a perturbation like that and the rotor speed influence only the distance between the rotor section and the section where the velocity profile is almost laminar?

[@SugarBoxingCom]

How to desrtoy physics with CFD ...

[@rolandotillit2867]

How much does back pressure reduction with the rotors contribute?

[@BlissOn47]

Nice

[@573355415]

Isn’t this expected from turbulence physics?

[@professionalprocrastinator8103]

How is that expected?

[@Bobby-vz9eq]

theoretically if you have an armonic information it's sufficient to insert a perturbation at the same frequency but counterphase (the same principle used on the headphones with noise cancelling). But actually turbulence is random and caotic so I can't understand what the experiment is based on.

[@getsideways7257]

@@Bobby-vz9eq Indeed, I'm pretty sure it has nothing to do with counter-phasing, and the rotating parts seem to have constant characteristics too. Is this even real?

[@Nando-gc8kb]

@@getsideways7257 It seems to be, but I was not able to understand the physical mechanism behind this phenomenon. In the research paper this work is described in, only a numerical justification (using navier stokes) was presented, but as far as I read, no physical explanation was provided.

[@getsideways7257]

@@Nando-gc8kb Combating turbulence with more turbulence should theoretically be possible, but I seriously doubt that we can calculate the required input - let alone doing it in such a manner that the "straightened" flow remains laminar.