Experimental observations of the onset of unsteadiness for buoyant airflow along smooth and rough vertical isothermal walls

ABSTRACT

The buoyant airflow along a vertical isothermal wall, under conditions close to transitional, is studied. The schlieren technique and miniature thermocouples are employed for qualitative (flow unsteadiness) and quantitative (heat transfer coefficient and local air temperature) observations. For the smooth surface, the phenomena are found to be sensitive to the enclosure configuration surrounding the plate. Roughening the heated surface with staggered rib segments of proper dimensions leads to increased heat transfer, ascribed to the onset of unsteadiness close to the segments’ edges, together with a better redistribution of the flow thanks to a favorable hydrodynamic interaction between fluid and protrusions.

KEYWORDS:

• Natural convection
• transition
• isothermal vertical plate
• ribbed surface
• schlieren

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/08916152.2024.2357175.