Classical hydrodynamics for analogue space–times: open channel flows and thin films

Abstract

Here we review the way to build analogue space–times in open channel flows by looking at the flow phase diagram and the corresponding analogue experiments performed during the last years in the associated flow regimes. Thin films like the circular jump with different dispersive properties are discussed with the introduction of a brand new system for the next generation of analogue gravity experiments: flowing soap films with their capillary/elastic waves. This article is part of a discussion meeting issue ‘The next generation of analogue gravity experiments’.

The next generation of analogue gravity experiments

“…Germain & Hamid [43] share with us the ‘plumber’s expertise’: they summarize the necessary tools to observe the Hawking effect in 1 + 1-dimensional water experiments and insist on the combined influence of hydrodynamics and dispersion on the output spectrum. In the second part of their article, they enrich the family of analogue gravity experiments with a new experimental platform—flowing films of soap—and demonstrate the creation of flows with horizons.…”

Wave Patterns of Gravity–Capillary Waves from Moving Localized Sources

“…The two families are independent at this current speed, that is, their domains are not overlapping. The demarcation line of the families, the asymptote (17), is shown in magenta. The classic Kelvin cone is given by a black solid line for reference.…”

“…212. One should note that amplitudes are vanishing at the demarcation asymptote at β m where κ = 1 (17). At the line of quasi-dispersion β group (25) and (52) the amplitudes are not zero but asymptotically decaying slower than in close directions.…”

Non-linear Processes and Stimulated Hawking Radiation in Hydrodynamics for Decelerating Subcritical Free Surface Flows with a Subluminal Dispersion Relation

“…The frequency of some waves or modes may become negative if it is measured in a coordinate system which is moving faster than the phase velocity of dispersion-less waves [3][4][5][6][7][8]. A resulting amplification of outgoing positive energy modes (the universal Hawking effect) that are propagating away from the horizon towards an asymptotic observer is predicted by the very appearance of the outgoing negative ones inside the horizon of real black holes or their analogues [8][9][10][11][12][13][14][15].…”

“…In 1981 Unruh, willing to observe in the laboratory such an effect, transposed the reasoning of Hawking to dumb holes featuring a trapping supersonic region due to a trans-sonic flow for non-dispersive acoustics waves propagating in a flowing air and he predicted an analogue acoustic Hawking radiation [19]: the Newton escape velocity plays the role of an analogue current flow velocity in a trans-sonic regime that reaches the speed of waves at the horizon [9][10][11][12]. Barcelo [12] and a special issue after a Royal Society of London Meeting [14] have recently summarized the current state of affairs in the growing field of "analogue space-times" or "analogue gravity" and the recent achievements in the comprehension of Hawking radiation seen as a universal phenomenon common to astrophysics (Hawking's original prediction) and condensed matter physics (including classical hydrodynamics as discussed in the review issue included in [15] and our own works [20][21][22][23][24][25][26][27][28][29][30][31][32]).…”