Journal of Fluid Mechanics Webinar Series: Jane Bae, USA and Axel Huerre, France
- Date
- Friday 11 June 2021, 4:00pm BST/11am EDT
- Location
- Zoom
- External URL
- https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/fluid-mechanics-webinar-series
- Category
- JFM Webinar Series
Speaker: Jane Bae, Harvard University, USA
Date/Time: Friday 11th June 2021 4:00pm BST/11am EDT
Title: Nonlinear interaction of the self-sustaining process in the near-wall region of wall-bounded turbulence
Abstract: We investigate the nonlinear interaction in the self-sustaining process of wall-bounded turbulence. Resolvent analysis is used to identify the principal forcing (nonlinear) mode which produces the maximum amplification in direct numerical simulations of the minimal channel for the buffer layer. The identified mode is then removed from the nonlinear term of the Navier-Stokes equations at each time step from a direct numerical simulation of a minimal channel. The results show that the removal of the principal forcing mode is able to inhibit turbulence in the buffer layer, while the removal of subsequent modes only marginally affects the flow. Analysis of the dyadic interactions in the nonlinear term shows that contributions toward the principal forcing mode come from a limited number of wavenumber interactions. Using conditional averaging, the flow structures that are responsible for generating the principal forcing mode, and thus the nonlinear interaction to self-sustain turbulence, are identified to be spanwise rolls interacting with meandering streaks.
Speaker: Axel Huerre, Laboratoire Matière et Systèmes Complexes (MSC), Université de Paris
Date/Time: Friday 11th June 2021 4:30pm BST/11:30am EDT
Title: Freezing a rivulet
Abstract: We investigate experimentally the formation of the particular ice structure obtained when a capillary trickle of water flows on a cold substrate. We show that after a few minutes the water ends up flow-ing on a tiny ice wall whose shape is permanent. We characterize and understand quantitatively the formation dynamics and the final thickness of this ice structure. In particular, we identify two growth regimes. First, a 1D solidification diffusive regime, where ice is building independently of the flowing water. And second, once the ice is thick enough, the heat flux in the water comes into play, breaking the 1D symmetry of the problem, and the ice ends up thickening linearly downward. This linear pattern is explained by considering the competition between the water cooling and its convection.