Vortex dynamics

Hurricanes, tornadoes, water swirling down a drain are all examples of vortices. Vortices are needed to close the valves at every beat of our heart, to mix fast milk and coffee and they are responsible for bird and airplane flight.


Destroying Aircraft Wakes 

An aircraft wake consists of powerful trailing vortices that live long after the airplane has flown by. This potential hazard imposes stringent safety distances, and pose  limiting constraint on airport traffic. We have developed high-performance Navier-Stokes solvers based on a hybrid particle-mesh approach and applied them to the study of a medium-wavelength instability on massively parallel machines.


Simulation of a medium-wavelength instability in a 4-vortex wake: vorticity magnitude

The Mechanics of Vortex Ring Decay

Vortex rings are one of the archetypal structures of fluid dynamics phenomena ranging from fish swimming to oil drilling. The instability of vortex rings has been the subject of several theoretical and experimental studies. Using massively-parallel direct numerical simulation methods we clarify the three-dimensional vortex dynamics during the nonlinear stage and determine the structure of the wake in the turbulent stage. The availability of the full three-dimensional vorticity field enables us to elucidate the origin and topology of the secondary vortex structures during the nonlinear stage of vortex ring decay.


Secondary vortical structures:Tsai–Widnall( short wavelength) instability leads to the formation of a dipole which is stretched and convected in the streamwise direction. See "The Secret Life of Vortices" for animations.

The Structure of Vortices for Animal  Propulsion
Vortices are shed at every stroke of a fish tail fin or a bird wing. In effect, they are the manifestation of momentum transfer between the swimmer/flyer and the fluid. Recent work by group members studied the relationship between the wake configuration and the swimming mode of eels.

Vorticity structures past anguilliform swimmers with optimal efficiency (left) and speed (right)

 

Other projects include flow control and drag reduction through the control of vorticity flux at the wall.

People:
 Philippe ChatelainMichael BergdorfJens WaltherBabak HejzialhosseiniMattia Gazzola

Collaborators: Alessandro Curioni (IBM), Wanda Andreoni (IBM), Prof. Anthony Leonard (Caltech)

Funding: Swiss National Science Foundation,  ETHZ

Student Projects: Aircraft wakes instabilitiesFluid-Structure Interaction in Vortex Particle Methods

Publications:
  • van Rees W.M., Gazzola M., Koumoutsakos P., Optimal shapes for anguilliform swimmers at intermediate Reynolds numbers. Journal of Fluid Mechanics, 722, 2013. (pdf)
  • Gazzola M., van Rees W.M., Koumoutsakos P., C-start: optimal start of larval fish. Journal of Fluid Mechanics, 698:5–18, 2012. (Abstract)(http://dx.doi.org/10.1017/jfm.2011.558(this article is featured in the JFM series: Focus on Fluids) (Cover of JFM)
  • Gazzola M., Chatelain P., van Rees W.M., Koumoutsakos P., Simulations of single and multiple swimmers with non-divergence free deforming geometries, Journal of Computational Physics, 230(19):7093–7114, 2011. (Abstract) (pdf)
  • Chatelain P., Gazzola M., Kern S., Koumoutsakos P., Optimization of aircraft wake alleviation schemes through an evolution strategy, Lecture Notes in Computer Science, 6649:210, 2011 (Abstract) (pdf)
  • Chatelain P., Curioni A., Bergdorf M., Rossinelli D., Andreoni W., Koumoutsakos P., Billion Vortex Particle Direct Numerical Simulations of Aircraft Wakes, Computer Methods in Applied Mechanics and Engineering, 197/13-16, 1296-1304, 2008 (Abstract) (pdf)
  • Fukagata K., Kern S., Chatelain P., Koumoutsakos P., Kasagi N., Evolutionary optimization of an anisotropic compliant surface for turbulent friction drag reduction, J. Turbulence, Vol. 9, N35, 1-17 (2008) (Abstract) (pdf)
  • Bergdorf M., Koumoutsakos P., Leonard A., Direct Numerical Simulations of Vortex Rings at Re=7,500, J. Fluid Mechanics, 581, 495-505, 2007 (Abstract) (pdf)
  • Kern S., Koumoutsakos P., Simulations of optimized anguilliform swimming, J. Experimental Biology, 209, 4841-4857, 2006 (Abstract) (pdf)