Abstract:

In this talk, we will present our newest results on fully developed turbulence. We mainly focus on two systems, Rayleigh-Bénard and Taylor-Couette flows, which share many similar features. In Rayleigh-Bénard turbulence, for the first time in two-dimensional numerical simulations we find the transition to the ultimate regime, namely at critical Rayleigh number Ra*= 1013. We reveal how the emission of thermal plumes enhances the global heat transport, leading to a steeper increase of the Nusselt number than the classical Malkus scaling. Beyond the transition, the temperature profiles are only locally logarithmic, namely within the regions where plumes are emitted, and where the local Nusselt number has an effective scaling Nu∝Ra0.38, corresponding to the effective scaling in the ultimate regime. In Taylor-Couette turbulence, we show how wall roughness greatly enhances the overall transport properties and the corresponding scaling exponents associated with wall-bounded turbulence. We reveal that if only one of the walls is rough, the bulk velocity is slaved to the rough side, due to the much stronger coupling to that wall by the detaching flow structures. If both walls are rough, the viscosity dependence is eliminated, giving rise to asymptotic ultimate turbulence — the upper limit of transport — the existence of which was predicted more than 50 years ago. In this limit, the scaling laws can be extrapolated to arbitrarily large Reynolds numbers.

Brief Biograph:

Dr. Xiaojue Zhu (朱晓珏) obtained his PhD in February, 2018 from the Physics of Fluids Group at the university of Twente in the Netherlands. He is currently a postdoctoral researcher in the same group. Dr. Zhu received his Bachelor degree in Engineering Mechanics from Hohai university in 2010, Master degree in Fluid Mechanics from Institute of Mechanics, Chinese Academy of Sciences in 2013. His research interests include Turbulence, Fluid Structure Interaction, Surface Nanobubbles and Nanodroplets, and Computational Fluid Dynamics.

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