We have investigated the stability of a double vortex street, induced in a rectangular container by a tape, or a rope, moving at high speed on its free surface. Depending on the tape velocity and on the geometrical aspect ratios, three patterns of flows are observed: (1) a vortex street with recirculation of the liquid along the lateral sides of the container, (2) the same recirculation but with no stable vortex array, (3) recirculation along the bottom of the container. We have investigated the spatial structure of the vortex street and found that this system explores the phase space available inside a stability tongue predicted at the end of the 1920s by Rosenhead for point vortices in a perfect fluid. Although this very surprising result contrasts with the wellknown von Kármán unique stability condition for point vortex streets in an infinite domain, this complements the theory inside a channel of finite breadth. In this paper, we present the very first experimental confirmation of this 90-year old theory. The Bénard-Von Kármán (BVK) vortex street is a 1 structure that can be observed in the wake of an obstacle 2 immersed inside a stationary unidirectional flow of large 3 enough velocity [1]. It was investigated experimentally for 4 the first time by Bénard [2] and modeled by von Kármán 5 [3] [4] at the beginning of the XXth century and has since 6 been extensively investigated. This phenomenon is ubiq-7 uitous in meteorology, oceanography, naval engineering, 8 vehicle design, modeling of the air flows around buildings 9 or piles of bridges, etc [5]. According to Von Kármán [3], 10 a vortex street of point vortices in a plane perfect flow can 11 be stable only if the wavelength of the vortex street, i.e.
In this “practice insight” we present a series of experiences run by Association Traces, injecting participatory approaches into science engagement activities by valuing the knowledge of the public rather than focusing on their ignorance. Starting from the observation that a sort of hybridization is occurring between cultural activities and public engagement with science on one side, and co-creation and participatory activities on the other, we provide some insight on the features of each approach. Examples are then used to highlight the potential value of this hybridization: as a way of making participatory activity more recognizable and accessible to a wide audience; to ensure that scientists have a professional interest in engaging in the communication activity; to raise a sense of ownership and empowerment in the audience, etc. These examples will eventually show that participation may lead to science communication practices that are socially-inclusive and/or productive for research, and ideally both.
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