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Generation of Stable Thermal Stratification by Turbulent Flows in a Partially Open Enclosure.


pdf icon Generation of Stable Thermal Stratification by Turbulent Flows in a Partially Open Enclosure. (1160 K)
Abib, A. H.; Jaluria, Y.

American Society of Mechanical Engineers (ASME). Fundamentals of Natural Convection. HTD-Vol. 264. 1993, Am. Soc. of Mechanical Engineers, New York, NY, 127-140 pp, 1993.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Keywords:

enclosures; stratification; turbulent flow; equations; flow fields; flow fields; velocity; temperature; heat transfer; ceiling jets; penetration

Abstract:

A numerical study of the turbulent flow induced by the energy input due to a heat source at the bottom boundary in a partially open rectangular cavity is carried out. Such flows are of interest in enclosure flows induced by localized sources such as fires and electronic components. The flow in the open cavity interacts with its surroundings through the opening. Of particular interest is the influence of opening height on the generation of thermal stratification within the cavity. Therefore, the effect of opening height is explored for an isothermal ambient medium using a wide range of Grashof numbers, spanning both laminar and turbulent regimes. A control-volume finite-difference method, in stream function vorticity formulation, is employed for the solution of the initial-value problem. A low Reynolds number kappa - epsilon turbulence model is used for the turbulent flow calculations. This model is particularly suitable for flows in which the possibility for re-laminarization exists. It was found that, for high Grashof numbers and for relatively small opening heights, particularly for doorway openings, a strong stable thermal stratification is generated within the cavity, with a cooler essentially uniform lower-layer and warmer linearly stratified upper-layer. As a consequence, turbulence is suppressed and the flow in the upper region of the cavity becomes laminar with turbulence confined to isolated places such as the thermal plume above the source and the shear-layer at the opening. The penetration distance and the height of the interface are both found to decrease with a reduction in the opening height. The Nusselt number for heat transfer from the source is seen to be affected to a small extent by the opening height.