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Steady-state Flows



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J Fluid Mech 2001 vol 426 pp 355 386 c 2001 Cambridge University Press Printed in the United Kingdom 355 Steady state flows in an enclosure ventilated by buoyancy forces assisted by wind By G R H U N T AND P F L I N D E N Department of Applied Mathematics and Theoretical Physics University of Cambridge Silver Street Cambridge CB3 9EW UK Received 10 March 1998 and in revised form 7 July 2000 We examine ventilation driven by a point source of buoyancy on the floor of an enclosure in the presence of wind Ventilation openings connecting the internal and external environment are at high level on the leeward fac ade and at low level on the windward fac ade so that the wind driven flow in the enclosure is in the same sense as the buoyancy driven flow We describe laboratory experiments that determine the parameters controlling the ventilation under these conditions and compare the results with predictions of a theoretical model Previous work has shown that when ventilation is driven solely by a single localized source of buoyancy flux B a stable two layer stratification and displacement flow forms The steady height of the interface between the buoyant upper layer and the lower layer at ambient density is independent of B and depends only on the effective area A of the openings the height H of the enclosure and entrainment into the plume For wind assisted flows the ventilation is increased owing to the wind pressure drop between the windward and leeward openings The two layer stratification and displacement flow are maintained over a range of wind speeds even when the wind induced flow far exceeds the flow induced by the buoyancy force The steady height of the interface depends upon the Froude number Fr 1 2 H B 1 3 and the dimensionless area of the openings A H 2 Increasing the wind speed raises the position of the interface and decreases the temperature of the upper layer as does increasing A H 2 while increasing B lowers the level of the interface and increases the



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