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ISSN Imprimer: 1064-2285
ISSN En ligne: 2162-6561
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Experimental Study of the Transition and Developed Turbulent Flow Regimes in Free Convection Boundary Layer Near a Vertical Heated Surface
RÉSUMÉ
The results of an experimental study of a free-convective boundary layer formed on a vertical isothermally heated plane surface are presented. Three regimes of flow are studied: laminar, turbulent, and a laminar-turbulent transient flow, which is given a considerable amount of attention. The free-convective flow is generated by a vertical aluminum plate 90 cm in width and 4.95 m in height. The large height of the plate gave the possibility to obtain all three flow regimes such as laminar, transient, and a developed turbulent one. The study of the boundary-layer properties is based on the measurements of the average and fluctuational temperature and velocity components. When measuring the velocity characteristics, two components of velocity (streamwise and normal) are determined. Attention is specially paid to the near-wall flow region, in particular, to the measurement of the heat flux and the wall stress. New empirical dependences of these values within a wide range of the Grash of numbers are obtained, including three flow regimes: laminar, transient, and turbulent. Some features of the flow in the transient region which are appropriate only for a free-convective flow are described. Various criteria of the beginning and end of the transient region are analyzed. In the present work a fluctuational flow is analyzed in detail in a laminar-turbulent transient region. The results of the measurements of different boundary-layer characteristics (intensity of temperature and longitudinal velocity fluctuations) are presented. The results of the present study are compared in detail with the data given in other references.