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Transient growth underpins superstructures and near-wall scales in turbulent convection.

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Title: Transient growth underpins superstructures and near-wall scales in turbulent convection.
Authors: Zhou, Zisong1 (AUTHOR), Zhu, Xiaojue1 (AUTHOR) zhux@mps.mpg.de
Source: Journal of Fluid Mechanics. 6/25/2026, Vol. 1037, p1-18. 18p.
Subjects: Rayleigh-Bénard convection, Coherent structures, Thermal boundary layer, Heat convection, Turbulent boundary layer, Energy transfer
Abstract: Content of image described in text. Turbulent convection is a fundamental transport process that shapes weather and climate, powers flows in planetary interiors and stars, and limits the performance of energy and heat-transfer technologies. Yet how these flows organise simultaneously into large-scale 'superstructures' and small-scale near-wall patterns remains unclear. Here, using Rayleigh–Bénard convection with large domain size, we show that both structures are captured by optimal linear modes that maximise transient energy amplification, identified via linear analysis based on turbulent mean profiles. Two amplification regimes emerge with clear scale separation: large-scale modes spanning the full central domain with horizontal wavelengths tilde 6 ∼ 6 ${\sim} 6$ times the plate separation and small-scale modes confined near the walls at tilde 11 ∼ 11 ${\sim} 11$ times the thermal boundary layer thickness. These results indicate that linear energy amplification plays an important organising role in multiscale turbulent convection and establish a unifying link to analogous non-modal processes in wall-bounded shear turbulence. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:Content of image described in text. Turbulent convection is a fundamental transport process that shapes weather and climate, powers flows in planetary interiors and stars, and limits the performance of energy and heat-transfer technologies. Yet how these flows organise simultaneously into large-scale 'superstructures' and small-scale near-wall patterns remains unclear. Here, using Rayleigh–Bénard convection with large domain size, we show that both structures are captured by optimal linear modes that maximise transient energy amplification, identified via linear analysis based on turbulent mean profiles. Two amplification regimes emerge with clear scale separation: large-scale modes spanning the full central domain with horizontal wavelengths tilde 6 ∼ 6 ${\sim} 6$ times the plate separation and small-scale modes confined near the walls at tilde 11 ∼ 11 ${\sim} 11$ times the thermal boundary layer thickness. These results indicate that linear energy amplification plays an important organising role in multiscale turbulent convection and establish a unifying link to analogous non-modal processes in wall-bounded shear turbulence. [ABSTRACT FROM AUTHOR]
ISSN:00221120
DOI:10.1017/jfm.2026.11669