We report experiments on buoyant-thermocapillary instabilities in differentially heated liquid layers. The results are obtained for a fluid of Prandtl number 10 in a rectangular geometry with different aspect ratios. Depending on the height of liquid and on the aspect ratios, the two-dimensional basic flow destabilizes into oblique traveling waves or longitudinal stationary rolls, respectively, for small and large fluid heights. Temperature measurements and space–time recordings reveal the waves to correspond to the hydrothermal waves predicted by the linear stability analysis of Smith and Davis [J. Fluid Mech. 132, 119 (1983)]. Moreover, the transition between traveling and stationary modes agrees with the work by Mercier and Normand [Phys. Fluids 8, 1433 (1996)] even if the exact characteristics of longitudinal rolls differ from theoretical predictions. A discussion about the relevant nondimensional parameters is included. In the stability domain of the waves, two types of sources have been evidenced. For larger heights, the source is a line and generally evolves towards one end of the container leaving a single wave whereas for smaller heights, the source looks like a point and emits a circular wave which becomes almost planar farther from the source in both directions.

An experimental study of a turbulent von Kármán flow in a cylinder is presented. The mean flow is stationary up to a Reynolds number $\mathrm{Re}={10}^4$ where a bifurcation takes place. The new regime breaks some symmetries of the problem and becomes time dependent because of equatorial vortices moving with a precession movement. In the exact counterrotating case, a bistable regime appears and spontaneous reversals of the azimuthal velocity are registered. A three-well potential model with additive noise reproduces this dynamic. A regime of periodic response is observed when a very weak forcing is applied.

We study the magnetic induction in a confined swirling flow of liquid sodium, at integral magnetic Reynolds numbers up to 50. More precisely, we measure in situ the magnetic field induced by the flow motion in the presence of a weak external field. Because of the very small value of the magnetic Prandtl number of all liquid metals, flows with even modest $R_m$ are strongly turbulent. Large mean induction effects are observed over a fluctuating background. As expected from the von Kármán flow geometry, the induction is strongly anisotropic. The main contributions are the generation of an azimuthal induced field when the applied field is in the axial direction (an Ω effect) and the generation of axial induced field when the applied field is the transverse direction (as in a large scale α effect). Strong fluctuations of the induced field, due to the flow nonstationarity, occur over time scales slower than the flow forcing frequency. In the spectral domain, they display a $f^{\text{−1}}$ spectral slope. At smaller scales (and larger frequencies) the turbulent fluctuations are in agreement with a Kolmogorov modeling of passive vector dynamics.

We report an experimental study of the magnetic field $\overrightarrow{B}$ induced by a turbulent swirling flow of liquid sodium submitted to a transverse magnetic field ${\overrightarrow{B}}_0$. We show that the induced field can behave nonlinearly as a function of the magnetic Reynolds number, $R_m$. At low $R_m$, the induced mean field along the axis of the flow, $⟨B_x⟩$, and the one parallel to ${\overrightarrow{B}}_0$, $⟨B_y⟩$, first behave like $R_m^2$, whereas the third component, $⟨B_z⟩$, is linear in $R_m$. The sign of $⟨B_x⟩$ is determined by the flow helicity. At higher $R_m$, $\overrightarrow{B}$ strongly depends on the local geometry of the mean flow: $⟨B_x⟩$ decreases to zero in the core of the swirling flow but remains finite outside. We compare the experimental results with the computed magnetic induction due to the mean flow alone.

The features of hydrothermal waves that appear when a liquid layer is laterally heated are presented. A bifurcation is observed from a steady regime to a regime of a basic flow with superimposed traveling waves. Measured characteristics of waves are shown and compared with some recent theoretical predictions.