Wind-Tunnel Experiment of Heavy Gas and Passive Scalar Emission in a Turbulent Boundary Layer

Abstract The aim of this study is to experimentally investigate the dynamics of a heavy gas release and highlight its main differences compared to that of a passive gas. To achieve this, we examine the vertical emission of both heavy and passive gases from an elevated source, situated within a turbulent boundary layer. The wind tunnel experiment is designed to simulate a realistic release of oxygen at T = $$-\,40\,^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>-</mml:mo> <mml:mspace/> <mml:mn>40</mml:mn> <mml:mmultiscripts> <mml:mspace/> <mml:mrow/> <mml:mo>∘</mml:mo> </mml:mmultiscripts> </mml:mrow> </mml:math> C, following a similar setup to the study performed by Schatzmann et al. (Atmos Environ 27:1105–1116, 1993). The release is characterised by means of simultaneous velocity and concentration measurements along vertical and lateral profiles at various downwind distances from the source. The data were used to estimate the turbulent mass flows, the turbulent Schmidt number, and the high-order statistics of the scalar field. Furthermore, we conduct an in-depth analysis of the production and dissipation terms of the concentration variance. These are subsequently used to estimate the typical time scale for turbulent mixing using two different micro-mixing models that parametrize the effects of molecular diffusion. These findings are crucial for improving the accuracy of operational dispersion models that simulate localised releases of dense gases in the atmosphere.