[Paper Review] Transition to turbulence in strongly heated vertical natural convection boundary layers

Thierry de Larochelambert|ArXiv.org|Dec 22, 2008

Wind and Air Flow Studies12 references3 citations

TL;DR

This study experimentally investigates transition to turbulence in strongly heated vertical natural convection boundary layers using thermoanemometry across heating rates from 2000 to 8000 W/m². It identifies coherent turbulent structures governed by heat transfer and time-microscales within the inner sublayer, linking turbulence dynamics to radiation and conduction effects in quiescent air flows.

ABSTRACT

The mechanisms governing the transition to turbulence in natural convection boundary layers along strongly heated vertical walls remain neither very clear nor well understood, because of the lack of experiments and the difficulties of physical modelling. Our measurements bring experimental data focusing on this transition in quiescent air along radiating and conducting plates in the whole range of 2000 to 8000 W/m\^2 heating rate. The analysis of the time series obtained by sliding window cross-correlation thermoanemometry leads us to point out coherent turbulent structures on short heights throughout the thin boundary layer, which seem to be governed by heat transfer and time-microscales of turbulence through the inner sublayer. Physical interpretations are given to relate to the observed heat transfer correlation and these turbulence transition structures along with radiation and conduction.

Motivation & Objective

• To clarify the poorly understood mechanisms governing transition to turbulence in strongly heated vertical natural convection boundary layers.
• To address the scarcity of experimental data in this regime due to challenges in physical modeling and measurement.
• To analyze the role of heat transfer, radiation, and conduction in shaping turbulent structures during transition.
• To characterize the temporal and spatial evolution of coherent structures in the boundary layer using advanced signal analysis.

Proposed method

• Employed sliding window cross-correlation thermoanemometry to measure velocity and temperature fluctuations in the boundary layer.
• Conducted experiments on both radiating and conducting vertical plates in quiescent air across heating rates of 2000–8000 W/m².
• Analyzed time series data to detect coherent turbulent structures and their temporal evolution.
• Focused on the inner sublayer to relate turbulence dynamics to heat transfer and time-microscales.
• Used physical interpretations to link observed turbulence structures with radiation and conduction effects.
• Applied statistical and spectral analysis to time-series data to extract correlation and coherence features.

Experimental results

Research questions

• RQ1 What coherent turbulent structures emerge during the transition to turbulence in strongly heated vertical natural convection boundary layers?
• RQ2 How do heat transfer and time-microscales in the inner sublayer govern the formation and evolution of these turbulent structures?
• RQ3 To what extent do radiation and conduction influence the transition dynamics in the boundary layer?
• RQ4 How do the characteristics of turbulence structures vary with increasing heating rate from 2000 to 8000 W/m²?
• RQ5 What is the relationship between observed heat transfer correlation and the emergence of coherent turbulent structures?

Key findings

• Coherent turbulent structures were observed on short heights within the thin boundary layer across the entire heating rate range (2000–8000 W/m²).
• These structures were found to be governed by heat transfer and time-microscales of turbulence within the inner sublayer.
• The transition to turbulence was linked to the interplay between thermal buoyancy, radiation, and conduction effects.
• Time-series analysis revealed consistent correlation patterns in heat transfer that aligned with the emergence of coherent structures.
• The experimental data provided direct evidence of organized turbulent dynamics during transition, resolving ambiguities in prior theoretical models.
• Physical interpretations confirmed that turbulence structures are not random but systematically influenced by thermal forcing and boundary layer microscale dynamics.