Miscible displacement flows in near-horizontal ducts at low Atwood number

International audienceWe study buoyant displacement flows with two miscible fluids of equal viscosity in the regime of low Atwood number and in ducts that are inclined close to horizontal. Using a combination of experimental, computational and analytical methods, we characterise the transitions in the flow regimes, between inertial and viscous dominated regimes, and as the displacement flow rate is gradually increased. Three dimensionless groups largely describe these flows: F r (densimetric Froude number), Re (Reynolds number) and Ø (duct inclination). Our results show that the flow regimes collapse into regions in a two-dimensional (F r, Re cos Ø/F r)-plane. These regions are qualitatively similar between pipes and plane channels, although viscous eAEects are more extensive in pipes. In each regime we are able to give a leading order estimate for the velocity of the leading displacement front, which is eAEectively a measure of displacement e±ciency