Abstract
Downhill flows of granular matter colliding in the lowest point of a valley, may induce a self-organized jet. By means of a quasi two-dimensional experiment where fine grained sand flows in a vertically sinusoidally agitated cylinder, we show that the emergent jet, that is, a sheet of ejecta, does not follow the frequency of agitation but reveals subharmonic response. The order of the subharmonics is a complex function of the parameters of driving.
Highlights
Downhill flows of granular matter colliding in the lowest point of a valley, may induce a self-organized jet
Homogeneous granular jets falling in gravity undergo a similar instability, e.g.3–6, despite the fact that there is no surface tension
Very similar jet-like splashes can be observed when a sphere is dropped into a loose packing of granular material[20,21,22,23,24,25,26]
Summary
Downhill flows of granular matter colliding in the lowest point of a valley, may induce a self-organized jet. Self-organized granular jets are observed when downhill flows of granular matter collide at the lowest point of a valley At this point, the incoming rapid convergent flows parallel to the ground come suddenly to rest, such that the energy which cannot be dissipated through particle collisions gives rise to a vertical jet emerging from this point. In the present paper we adopt this setup to produce sequences of granular jets, similar to the oscillon instability[35] with two important differences: First, the novel type of jet appears in each period of the driving vibration unlike the oscillon which is a subharmonic effect of second order. In contrast to the oscillon, the periodic appearance of the jet is superposed by another subharmonic instability whose order is a function of the parameters of driving, amplitude and frequency The latter type of subharmonic oscillation is the main subject of the present paper. We observed this novel effect to occur as an subharmonic effect of up to order 11
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