Wall roughness induces asymptotic ultimate turbulence

Abstract

Turbulence is omnipresent in Nature and technology, governing the transport of heat, mass, and momentum on multiple scales. For real-world applications of wall-bounded turbulence, the underlying surfaces are virtually always rough; yet characterizing and understanding the effects of wall roughness for turbulence remains a challenge, especially for rotating and thermally driven turbulence. By combining extensive experiments and numerical simulations, here, taking as example the paradigmatic Taylor-Couette system (the closed flow between two independently rotating coaxial cylinders), we show how wall roughness greatly enhances the overall transport properties and the corresponding scaling exponents. If only one of the walls is rough, we reveal that 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 thoroughly eliminated in the boundary layers and we thus achieve asymptotic ultimate turbulence, i.e. the upper limit of transport, whose existence had been predicted by Robert Kraichnan in 1962 (Phys. Fluids {\bf 5}, 1374 (1962)) and in which the scalings laws can be extrapolated to arbitrarily large Reynolds numbers.

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Cited by in corpus (13)

• Transition to the ultimate regime in two-dimensional Rayleigh-Bénard convection
• Supergravitational turbulent thermal convection
• An efficient phase-field method for turbulent multiphase flows
• Evidences for the existence of the ultimate regime in supergravitational turbulent thermal convection
• Bubbly drag reduction using a hydrophobic inner cylinder in Taylor-Couette turbulence
• Direct numerical simulations of Taylor--Couette turbulence: the effect of sand grain roughness
• Characterizing the turbulent drag properties of rough surfaces with a Taylor--Couette setup
• Controlling secondary flow in Taylor-Couette turbulence through spanwise-varying roughness
• Asymptotic turbulent friction in 2D rough-walled flows
• The influence of wall roughness on bubble drag reduction in Taylor-Couette turbulence
• Towards DNS of the Ultimate Regime of Rayleigh--Bénard Convection
• Two-layer Thermally Driven Turbulence: Mechanisms for Interface Breakup
• Geophysical flows over topography, a playground for laboratory experiments