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

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.
*