TRANSITION TO TURBULENCE IN STRONGLY HEATED VERTICAL NATURAL CONVECTION BOUNDARY LAYERS

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 the observed heat transfer correlation and these turbulence transition structures along with radiation and conduction.

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