Natural ventilation forced by wind fluctuations: theoretical analysis and experimental study

This study investigates the dynamics of a naturally ventilated room in which a point source provides a steady buoyancy source, when an opposing unsteady wind occurs. The wind is modelled as a stochastic forcing, which aims to simulate realistic velocity fluctuations as observed in the lower atmosphere, due to atmospheric turbulence. By doing so, we expand the analysis already conducted for deterministic wind, following both a theoretical approach and an experimental one. Firstly, regarding the theoretical approach, we compute some numerical simulations, which highlight how the stochastic forcing affects and changes the dynamics of the system. Namely, a structural change of the mean behaviour of the system occurs: the warm–cold air interface does not fluctuate around the elevation exhibited when wind is constant, but oscillations occur around a new interface elevation, which is significantly lower. We provide the physical explanation for such a counterintuitive behaviour and show its dependence on (i) wind characteristics (intensity and timescale of fluctuations) and (ii) relative strength of wind over thermal loads. Secondly, concerning the experimental approach, we perform some experiments in wind tunnel in order to compare the measures with the numerical results. The experimental results are in reasonable agreement with theoretical predictions, and confirm the key role of stochastic components in naturally ventilated systems.