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Natural ventilation driven by periodic gusting of wind

Published online by Cambridge University Press:  25 May 2011

RICHARD W. MOTT  and
ANDREW W. WOODS
RICHARD W. MOTT
Affiliation:
BP Institute, Madingley Rise, Cambridge CB3 0EZ, UK
ANDREW W. WOODS*
Affiliation:
BP Institute, Madingley Rise, Cambridge CB3 0EZ, UK
*
†Email address for correspondence: andy@bpi.cam.ac.uk
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Abstract

We investigate the mixing of a warm enclosed space by a series of discrete gusts of cold air from a high-level opening. Initially we examine the case of a series of gusts of identical size each modelled as a turbulent buoyant thermal. We develop a model of the filling box-like flow which develops in the space and identify the key parameter in the system as the ratio between the initial gust size and the product of the height of the room and the entrainment coefficient. We find an approximate analytic solution for the evolution of the density profile within the space which is in good agreement with a full numerical solution of the governing equations. We successfully test the predictions of the model with a series of new laboratory experiments. The experiments combined with the model also provide a new independent estimate for the entrainment coefficient of a thermal, ε = 0.37 ± 0.02, based on the propagation speed of a filling box front. We then examine the mixing produced by a series of thermals of non-identical size which we characterize in terms of a mean size and coefficient of variation. We find that as the coefficient of variation increases, the density profile becomes progressively more stratified owing to the asymmetry of dilution through entrainment of large and small thermals. We discuss the implications of these results for the ventilation of a building subject to gusts of wind.

JFM classification

Convection: Convection Convection: Plumes/thermals Turbulent Flows: Turbulent convection
Type
Papers
Information
Journal of Fluid Mechanics , Volume 679 , 25 July 2011 , pp. 58 - 76
Copyright
Copyright © Cambridge University Press 2011

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References

REFERENCES

Baines, W. D. & Turner, J. S. 1969 Turbulent buoyant convection from a source in a confined region. J. Fluid Mech. 37, 51–80.CrossRefGoogle Scholar
Bolster, D. & Linden, P. F. 2007 Contaminants in ventilated filling boxes. J. Fluid Mech. 591, 97–116.CrossRefGoogle Scholar
Caulfield, C. P. & Woods, A. W. 2002 The mixing of a room by a localized finite-mass-flux source of buoyancy. J. Fluid Mech. 471, 33–50.CrossRefGoogle Scholar
Germeles, A. E. 1975 Forced plumes and mixing of liquids in tanks. J. Fluid Mech. 71, 601–623.CrossRefGoogle Scholar
Hunt, G. R. & Kaye, N. G. 2001 Virtual origin correction for lazy turbulent plumes. J. Fluid Mech. 435, 377–396.CrossRefGoogle Scholar
Hunt, G. R. & Linden, P. F. 2001 Steady-state flows in an enclosure ventilated by buoyancy forces assisted by wind. J. Fluid Mech. 426, 355–386.CrossRefGoogle Scholar
Hunt, G. R. & Linden, P. F. 2005 Displacement and mixing ventilation driven by opposing wind and buoyancy. J. Fluid Mech. 527, 27–55.CrossRefGoogle Scholar
Kuesters, A. S. & Woods, A. W. 2010 The formation and evolution of stratification during transient mixing ventilation. J. Fluid Mech. 670, 66–84.CrossRefGoogle Scholar
Linden, P. F. 1999 The fluid mechanics of natural ventilation. Annu. Rev. Fluid Mech. 31, 201–238.CrossRefGoogle Scholar
Linden, P. F., Lane-Serff, G. F. & Smeed, D. A. 1990 Emptying filling boxes: the fluid mechanics of natural ventilation. J. Fluid Mech. 212, 309–335.CrossRefGoogle Scholar
Liu, P. C., Lin, H. T. & Chou, J. H. 2009 Evaluation of buoyancy-driven ventilation in atrium buildings using computational fluid dynamics and reduced-scale air model. Build. Environ. 44 (9), 1970–1979.CrossRefGoogle Scholar
Lishman, B. & Woods, A. W. 2008 On transitions in natural ventilation flow driven by changes in the wind. Build. Environ. 44 (4), 666–673.CrossRefGoogle Scholar
Lishman, B. & Woods, A. W. 2009 The effect of gradual changes in wind speed or heat load on natural ventilation in a thermally massive building. Build. Environ. 44 (4), 762–772.CrossRefGoogle Scholar
Morton, B. R., Taylor, G. I. & Turner, J. S. 1956 Turbulent gravitational convection from maintained and instantaneous sources. Proc. R. Soc Lond. A 234, 1–23.Google Scholar
Mott, R. W. & Woods, A. W. 2009 On the mixing of a confined stratified fluid by a turbulent buoyant plume. J. Fluid Mech. 623, 149–165.CrossRefGoogle Scholar
Richards, J. M 1961 Experiments on the penetration of an interface by buoyant thermals. J. Fluid Mech. 11, 369–384.CrossRefGoogle Scholar
Thompson, R. S., Snyder, W. H. & Weil, J. C. 2000 Laboratory simulation of the rise of buoyant thermals created by open detonation. J. Fluid Mech. 417, 127–156.CrossRefGoogle Scholar
Turner, J. S. 1973 Buoyancy Effects in Fluids. Cambridge University Press.CrossRefGoogle Scholar
Turner, J. S. 1986 Turbulent entrainment: the development of the entrainment assumption, and its application to geophysical flows. J. Fluid Mech. 173, 431–471.CrossRefGoogle Scholar
Woods, A. W., Fitzgerald, S. D. & Livermore, S. 2009 A comparison of winter pre-heating requirements for natural displacement and natural mixing ventilation. Energy Build. 41 (12), 1306–1312.CrossRefGoogle Scholar