Intermittency and Lagrangian dynamics of velocity gradients in fluid turbulence
| Quand ? |
Le 20/03/2023, de 11:00 à 12:00 |
|---|---|
| Où ? | Salle des Thèses |
| Participants |
Charles Meneveau |
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Small-scale intermittency continues to pose modeling challenges for turbulent flows. As a descriptive tool, the velocity gradient tensor in three dimensions provides a rich characterization of its salient statistical and geometric features. We review a recent model for isotropic turbulence involving a set of stochastic differential equations for the Lagrangian time evolution of the velocity gradient tensor at multiple scales. Dominant terms in the model could be derived directly from the Navier-Stokes equations while phenomenological models for unclosed pressure and viscous terms are still required. We show that instead of having to integrate this set of SDEs in time at multiple levels or scales, the same predictions can be obtained based on a single level that recursively modulates the model terms interpreted at arbitrarily higher levels. Statistical properties compare very well to direct numerical simulation and experimental data at different Reynolds numbers. The proposed formalism represents a new type of multifractal intermittency model that can be connected directly to terms in the Navier-Stokes equation and is capable of predicting many intricate statistical and geometric features of turbulent flows, over a wide range of Reynolds numbers. We also summarize applications of a single-scale version of the model implemented as a subgrid-scale model in Large Eddy Simulations of dispersed deforming droplets in channel-flow turbulence. The work to be presented arose from the contributions of Drs. L. Chevillard, M. Wilczek, P. Johnson and Y. Luo, and benefitted from partial support from NSF and the work of the JHTDB team, also supported by NSF.