MechE Colloquium: The onset of turbulence in shear flows - a matter of life and death
Event details
| Date | 30.04.2019 |
| Hour | 12:15 › 13:15 |
| Speaker | Prof. Björn Hof, IST Austria |
| Location | |
| Category | Conferences - Seminars |
Abstract:
Past studies of the transition to turbulence in pipes and related shear flows could neither agree on a critical point nor on the nature of the transition. The main difficulty is that in this class of flows turbulence arises despite the linear stability of the laminar flow and that it results from perturbations of finite amplitude. I will show that under such circumstances the transition is driven by a stochastic spreading process: each turbulent spot will eventually die but it may produce offspring beforehand. This setting precisely corresponds to the rules of a stochastic process called ‘directed percolation’. By introducing periodic boundary conditions in laboratory experiments we demonstrate for Couette and pipe flow that the transition to turbulence indeed falls into the directed percolation universality class. In particular I will also show that insights into the transition process can be exploited to control turbulence. Moreover, if time permits, I will discuss how the transitional regime can be connected to high Reynolds number turbulence.
Bio:
Björn Hof is professor of experimental physics at the Institute of Science and Technology (IST) Austria in Klosterneuburg, Austria. He obtained his PhD in physics at the University of Manchester, UK in 2001. After postdocs in Manchester and the TU Delft he was a lecturer in the Physics Department in Manchester and later a research group leader at the Max Planck Institute of Dynamics and Self-Organization in Göttingen, Germany. He joined IST Austria in 2013. His main research interests are the transition to turbulence, turbulence control and instabilities in complex fluids.
Past studies of the transition to turbulence in pipes and related shear flows could neither agree on a critical point nor on the nature of the transition. The main difficulty is that in this class of flows turbulence arises despite the linear stability of the laminar flow and that it results from perturbations of finite amplitude. I will show that under such circumstances the transition is driven by a stochastic spreading process: each turbulent spot will eventually die but it may produce offspring beforehand. This setting precisely corresponds to the rules of a stochastic process called ‘directed percolation’. By introducing periodic boundary conditions in laboratory experiments we demonstrate for Couette and pipe flow that the transition to turbulence indeed falls into the directed percolation universality class. In particular I will also show that insights into the transition process can be exploited to control turbulence. Moreover, if time permits, I will discuss how the transitional regime can be connected to high Reynolds number turbulence.
Bio:
Björn Hof is professor of experimental physics at the Institute of Science and Technology (IST) Austria in Klosterneuburg, Austria. He obtained his PhD in physics at the University of Manchester, UK in 2001. After postdocs in Manchester and the TU Delft he was a lecturer in the Physics Department in Manchester and later a research group leader at the Max Planck Institute of Dynamics and Self-Organization in Göttingen, Germany. He joined IST Austria in 2013. His main research interests are the transition to turbulence, turbulence control and instabilities in complex fluids.
Practical information
- General public
- Free