Tuesday, November 27th, 2018: The physics of smashing smoke rings: Cascades and cataclysmic changes

Event Date: 

Tuesday, November 27, 2018 - 3:45pm

Event Date Details: 

Refreshments served at 3:30pm.

Event Location: 

  • Broida 1640
  • Physics Department Colloquium

Many of the big problems we are facing involve far from equilibrium systems that entail a cataclysmic change. Climate, turbulence and earthquakes, developmental biology, aging death, and even evolution. These phenomena are rare (sometimes occurring only once) and are entirely irreversible. While understanding the physics of such irreversible processes is of both fundamental and practical importance, these problems also pose unique challenges. These challenges, as they manifest in turbulence, were beautifully portrayed by Richardson:

“Big whirls have little whirls that feed on their velocity, and little whirls have lesser whirls and so on to viscosity”

Lewis Fry Richardson (1922)

In his short verse, Richardson captures the essence of the turbulent cascade—the conveyance of kinetic energy across scales that underlies the universal dynamics of turbulent flows. Indeed, such conveyance of important physical quantities (energy, stress, frustration and even information) down and up a vast range of scales underlines the dynamics of many systems. The challenge in understanding these systems is in capturing the events as they occur, keeping up with the dynamics on all scales and at all times. Here, I will discuss the emergence of a turbulent cloud when two vortex rings are smashed together. This collision between two initially laminar structures rapidly generates small scale flows via a dynamic cascade of instabilities. The advantage of this system is that the critical vortex dynamics are stationary in the laboratory (computational) frame, which makes their detailed probing possible in real time and real space. Capturing these events required developing new tools and offers unique insight into the physical mechanisms underlying the turbulent cascade and to the possibility of singularity in the equations of fluid motion.

Shmuel Rubinstein, Harvard