The arrangements according to the invention and the methods according to the invention serve to seal a gap 20 against a primary fluid 10 by means of a secondary fluid 11 in a fluid-dynamic and non-contact manner, which primary fluid 10 flows over the gap 20. The secondary fluid 11 forms a preferably rotating vortex flow 13 in the gap in at least one or more sections along the gap. The flow of the secondary fluid 11 is preferably guided in a chamber 26, which is arranged in the gap 20. The chamber 26 is designed as a rotary chamber along the entire gap 20 or also as a local chamber 226 extending only locally along the gap. The secondary fluid 11 may be supplied via supply conduits 40, in which the gap 120 itself may be utilized for supplying secondary fluid 115 to the chamber 126. As further elements for the guidance of the vortex flow, guiding lips 50, undercuts of the chamber contour 351, and guiding elements 160 may be arranged in the gap. Furthermore, a mechanical seal 370 arranged in the gap on that side of the chamber which is remote from the primary flow may additionally seal the gap 320 mechanically. A typical embodiment of the invention is shown in FIG. 1. A second arrangement according to the invention relates to a slalom chamber 690, which is arranged in S-shaped undulations along the gap 620.