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Experimental study of the indoor flow behaviour transitions in a naturally ventilated single-zone building opposing wind and buoyancy

Abstract : Indoor flow behaviour can strongly impact safety in the case of a fire event. Indeed, when air inlet and outlet are correctly placed, stratification allows a fresh air layer to be maintained in the room that can be favourable for the egress. However, in the case of a naturally ventilated building, the presence of the wind will interact with the indoor flow pattern. Hence, fire smoke extraction in naturally ventilated buildings can strongly be influenced by the wind. Indeed, when wind opposed buoyancy, a change in the ratio between buoyancy forces and wind forces can impact the internal flow pattern resulting in a mixed ventilation mode, which is unfavourable for egress, in the case of a fire event. Flow pattern inside a room and their transitions are then a safety purpose. In this paper, natural ventilation of a singular room with two asymmetrical and opposed openings was studied experimentally when wind opposes buoyancy. The buoyant source was generated by an injection of an air/he mix. Varying wind and injection conditions, the ventilation regimes change as well as the indoor flow dynamic. Three ventilation regimes are experimentally observed depending on the balance between J and Fr :buoyancy-driven, bidirectional and wind-driven. From dimensional analysis, we shown that the ventilation regimes can be described via the Froude number, based on the injection flow rate Fr, and the momentum flux ratio J. in the literature, transitions between these regimes is still difficult to estimate as far as it depends on the assumption made on the initial indoor flow pattern (layered or fully mixed). Hence, an experimental investigation on the transition from each extreme regime (buoyancy-driven or wind-driven) to the bi-directional one, has been conducted. The transitions are found to follow a power low in the form Fr ∝ J3/4. A discussion on the inner flow pattern for this bi-directional regime is also proposed and a focus on how the knowledge of the behaviour of the inflowing flow contributes to improve the modelling is made.
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https://hal.univ-reunion.fr/hal-02961307
Contributor : Alain Bastide <>
Submitted on : Thursday, October 8, 2020 - 12:54:26 PM
Last modification on : Wednesday, October 14, 2020 - 4:21:46 AM

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Karim Khan Juhoor, Kevin Varrall, Olivier Vauquelin, Alain Bastide. Experimental study of the indoor flow behaviour transitions in a naturally ventilated single-zone building opposing wind and buoyancy. 2020. ⟨hal-02961307⟩

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