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ON THE K-TYPE TRANSITION IN NATURAL CONVECTION BOUNDARY LAYERS

DOI: 10.1615/ICHMT.2014.IntSympConvHeatMassTransf.590
pages 779-788

Yongling Zhao
School of Hydraulic, Energy and Power Engineering, Yangzhou University, Jiangsu, 225127, China; Centre for Wind, Waves and Water, School of Civil Engineering The University of Sydney, Sydney, NSW 2006, Australia

Chengwang Lei
Centre for Wind, Waves and Water, School of Civil Engineering The University of Sydney, Sydney, NSW 2006, Australia

John C. Patterson
Centre for Wind, Waves and Water, School of Civil Engineering, The University of Sydney Darlington, NSW 2006, Australia

Аннотация

A three-dimensional direct numerical simulation is carried out to study the K-type transition in vertical natural-convection boundary layers adjacent to an isothermally heated wall. By introducing superimposed Tollmien-Schlichting (TS) and oblique waves of the same frequency into the upstream boundary layer, the typical aligned Λ-shaped vortices characterizing the K-type transition are observed in the downstream boundary layer. The tips of the Λ-shaped structures appear at the peak locations of the oblique waves, which is another significant feature characterizing the K-type transition. A similar feature of the K-type transition in Blasius boundary layers has been reported by Berlin et al. [1999]. It is also found that there exists a local double-layer longitudinal vortex system in the boundary layer, which is qualitatively similar to the vortical structure inferred by Jaluria & Gebhart [1973] for a transitioning natural convection boundary layer adjacent to an iso-flux surface. The boundaries between the inner layer and outer layer vortex rolls in the present study and that of Jaluria & Gebhart [1973] are both approximately at the edges of the thermal boundary layers. However, the outer vortex rolls in this study are always confined within the velocity boundary layer, whereas the outer vortex rolls reported in Jaluria & Gebhart [1973] extended well beyond the velocity boundary layer. This difference may be attributed to the different thermal boundary conditions and different perturbation amplitudes.

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