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

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 dual nature of the dead-water phenomenology: Nansen versus Ekman wave-making drags.

A ship encounters a higher drag in a stratified fluid compared to a homogeneous one. Grouped under the same "dead-water" vocabulary, two wave-making resistance phenomena have been historically reported. The first, the Nansen wave-making drag, generates a stationary internal wake which produces a kinematic drag with a noticeable hysteresis.

Scattering of Co-Current Surface Waves on an Analogue Black Hole.

We report on what is to our knowledge the first scattering experiment of surface waves on an accelerating transcritical flow, which in the analogue gravity context is described by an effective spacetime with a black-hole horizon. This spacetime has been probed by an incident co-current wave, which partially scatters into an outgoing countercurrent wave on each side of the horizon. The measured scattering amplitudes are compatible with the predictions of the hydrodynamical theory, where the kinematical description in terms of the effective metric is exact.

Wave-current interaction as a spatial dynamical system: analogies with rainbow and black hole physics.

We study the hydrodynamic phenomenon of waves blocking by a countercurrent with the tools of dynamical systems theory. We show that, for a uniform background velocity and within the small wavelength approximation, the stopping of gravity waves is described by a stationary saddle-node bifurcation due to the spatial resonance of an incident wave with the converted "blueshifted" wave. We explain why the classical regularization effect of interferences avoids the height singularity in complete analogy with the intensity of light close to the principal arc of a rainbow.

Oscillation-induced sand ripples in a circular geometry.

This study deals with the observation of sand ripples in a circular geometry under oscillatory flow. We characterize the observed patterns as a function of the excitation parameters. We report the time evolution of the corrugated front invading the flat bed.

Physical distinction between rolling-grain ripples and vortex ripples: an experimental study.

We have performed an experimental study of the transition of rolling-grain ripples toward vortex ripples. In particular, we have looked for the influence of the grains' diameter, the frequency of oscillation, and the grains' cohesion. We demonstrate that the rolling-grain ripples are transient patterns which do appear as soon as we are close to the threshold for grain motion, whereas vortex ripples are always the final patterns observed and are the only patterns observed if one is far from the threshold for grain motion.

Wavelength selection of rolling-grain ripples in the laboratory.

We have performed an experimental study, at very high resolution, of the wavelength selection and the evolution of rolling-grain ripples. A clear distinction is made between the flat sand bed instability and the ripple coarsening. The observation of the initial wavelength for the rolling-grain ripples is only possible close to the threshold for movement which imposes a constraint on the parameters.