Particles and swowflakes falling through turbulence
Event details
| Date | 11.02.2021 |
| Hour | 12:15 › 13:15 |
| Speaker | Prof. Dr. Filippo COLETTI of ETH Zurich |
| Location | Online |
| Category | Conferences - Seminars |
Abstract: Multiphase flows in which an inertial dispersed phase interacts with a turbulent fluid flow are ubiquitous in environmental, industrial and biomedical settings. Even stripped down to its minimal components, the problem remains complex because of the wide range of scales involved and the multiple physical parameters at play. In this talk, I will first focus on the seemingly simple case of dilute microscopic spherical particles falling through homogeneous air turbulence. A unique experimental facility is leveraged, in which hundreds of jets are individually controlled to produce the largest volume of zero-mean-flow homogeneous turbulence ever created. Using high-resolution laser imaging, I will show how inertial particles group in larger clusters than previously thought, experiencing anomalously large accelerations and a multi-fold increase in fall speed compared to their still-air terminal velocity. At concentrations found in dust storms, the particles also cause a substantial increase in turbulence intensity, at odds with most numerical simulations. The relevance of such observations is demonstrated by outdoor field measurements, in which snowflakes are illuminated and tracked over vertical planes about 30 m^2 using high-speed cameras. The snow particles display strikingly similar behaviors as seen in the laboratory, including self-similar clustering, anomalous accelerations, and turbulence-enhanced fall speed. These findings demonstrate that the fundamental phenomenology of particle-laden turbulence can be leveraged towards the predictive understanding of snow precipitation. They also demonstrate how environmental flows can be used to investigate dispersed multiphase flow physics at Reynolds numbers not accessible in laboratory experiments or numerical simulations.
Links
Practical information
- General public
- Registration required
Organizer
- Organizsation ETH & EPFL
Contact
- Contact ETH, Prof. George Haller, [email protected] Contact EPFL, Prof. John Kolinski, [email protected]