27 février 2020

Seminar Clara Marika Velte

Clara M. Velte received her Ph.D. in experimental and theoretical fluid mechanics from the Technical University of Denmark in 2009. After several extended stays abroad, she became Associate Professor in Fluid Mechanics at the Technical University of Denmark in 2012. She then received an ERC Starting Grant in 2018 to build a state-of-art laboratory facility to test the bounds of validity of the classical theory of turbulence. This was in 2019 supplemented with a Turbulence Centre of Excellence – a long-term collaboration with the Poul Due Jensen Foundation to develop improved models for turbulence. A strong focus on maintaining an interdisciplinary approach and tailoring the methods to the research question asked is central to the research philosophy of her group.
Dynamic Triad Interactions and the Evolution of Turbulent Power Spectra

The Navier-Stokes equation is generally accepted to describe all aspects of the momentum balance of fluid flows – both laminar and turbulent. However, due to the nonlinearity of the equation and the wide range of scales interacting through the nonlinear term, the Navier-Stokes equation is notoriously difficult to solve, especially for turbulent flows at large Reynolds numbers. Herein, we therefore investigate a time-dependent solution in one primary spatial dimension to the 4-dimensional Navier-Stokes equation, representing the momentum balance for the instantaneous fluid convection velocity. The solution retains all terms in the Navier-Stokes equation, including both pressure and dissipation. The purpose is primarily to learn about the peculiar effects of the nonlinearity of the Navier-Stokes equation in all 4 dimensions, by presenting some numerical calculations of the flow development with different representative (including measured) input velocity records. Including the temporal component in the decomposition results in the addition of a temporal frequency contribution in the triad interaction matching condition. The solution reveals the dynamic development of non-equilibrium turbulence towards equilibrium, where a soliton-like behavior is eventually attained. The numerical model is compared to experiments and analysis. The classical picture, as described by Kolmogorov 1941 and Richardson, is discussed in light of these numerical, experimental and theoretical developments.

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27 février 2020, 14h0015h00
LMFL Bâtiment M6
Avenue Paul Langevin

Villeneuve d'Ascq