  Air curtains are installed in open doorways of a building to reduce
buoyancy-driven exchange flows across the doorway. Although an air curtain
allows an unhampered passage of humans and vehicles, the interaction of this
traffic with an air curtain is not well understood. We study this problem by
conducting small-scale waterbath experiments with fresh water and salt water
solutions. As a model of human passage, a vertical cylinder is pulled through a
planar jet representing an air curtain and separating two zones at different
densities. For a fixed travel distance of the cylinder before and after the air
curtain, the average infiltration flux of dense fluid in light fluid side
increases with increasing cylinder velocity. However, we find that the
infiltration flux is independent of density difference across the doorway and
the travel direction of the cylinder. As a consequence, the sealing
effectiveness of an air curtain reduces with an increasing cylinder speed and
this reduction is independent of the direction of the buoyancy-driven flow. Dye
visualisations of the air curtain and the cylinder wake are used to examine the
re-establishment process of the air curtain after its disruption by the
cylinder. We observe that the re-establishment time of the air curtain and the
infiltration in the cylinder wake increases with an increasing cylinder speed.
