MechE Colloquium: Interactions between vertical and horizontal convections: from nuclear safety to the eye of cyclones
Event details
| Date | 09.12.2025 |
| Hour | 12:00 › 13:00 |
| Speaker | Dr. Michael Le Bars, IRPHE, CNRS, Aix-Marseille Université |
| Location | Online |
| Category | Conferences - Seminars |
| Event Language | English |
Abstract: We investigate heat transfer and flow dynamics in a thin cylindrical fluid layer with imposed heat fluxes at the bottom and top boundaries and a fixed temperature along the sidewall. This study is motivated by the In Vessel Retention strategy for severe nuclear accidents, where molten radioactive fuel and reactor materials form a Corium layer that must remain confined within the reactor vessel, cooled from the side to prevent failure. Combining Direct Numerical Simulations, model experiments, and theoretical analyses, we derive scaling laws for the mean temperature, velocity, and temperature differences in the system. Two distinct asymptotic regimes emerge, driven respectively by radial and vertical heat transfers. Realistic conditions combine these two regimes, leading to unexpected dynamics. In particular, experiments at application-relevant Rayleigh numbers reveal a persistent, large-scale radial branch pattern that drifts over time, governing long-term heat flux fluctuations critical for nuclear safety. Through linear stability analysis, we trace the origin of this pattern to a novel 3D instability arising from the interplay of convective and shear instabilities, significantly lowering the instability threshold compared to either mechanism alone. When global rotation is included, the system also serves as a dry model for hurricane-like vortices, enabling experimental and numerical investigations of the mechanisms behind eye formation in cyclones.
Biography: Michael Le Bars is a CNRS Senior Researcher at IRPHE (Marseille, France), where he leads the "Nature, Environment and Universe" group. His research combines laboratory experiments, theory, and numerical simulations to investigate fundamental fluid processes involving rotation, stratification, and convection. He has coordinated several interdisciplinary projects on topics such as tidal, librational, and precessional instabilities and their associated dynamos in planetary cores; vortices and jets in Jupiter’s atmosphere; and wave–mean flow interactions in geophysical and astrophysical contexts. His expertise also extends to fluid dynamics problems relevant to nuclear safety, including hydrogen risk and in-vessel retention of corium. He is the recipient of the CNRS Bronze Medal (2012) and the Leconte Prize of the French Academy of Sciences (2019).
Biography: Michael Le Bars is a CNRS Senior Researcher at IRPHE (Marseille, France), where he leads the "Nature, Environment and Universe" group. His research combines laboratory experiments, theory, and numerical simulations to investigate fundamental fluid processes involving rotation, stratification, and convection. He has coordinated several interdisciplinary projects on topics such as tidal, librational, and precessional instabilities and their associated dynamos in planetary cores; vortices and jets in Jupiter’s atmosphere; and wave–mean flow interactions in geophysical and astrophysical contexts. His expertise also extends to fluid dynamics problems relevant to nuclear safety, including hydrogen risk and in-vessel retention of corium. He is the recipient of the CNRS Bronze Medal (2012) and the Leconte Prize of the French Academy of Sciences (2019).
Practical information
- General public
- Free