Rémi Zamansky

Radiation induces turbulence in particle-laden fluids

When a transparent fluid laden with solid particles is subject to radiative heating, non-uniformities in particle distribution result in local fluid temperature fluctuations. Under the influence of gravity, buoyancy induces vortical fluid motion which can lead to strong preferential concentration, enhancing the local heating and more non-uniformities in particle distribution. By employing direct numerical simulations this study shows that the described feedback loop can create and sustain turbulence. The velocity and length scale of the resulting turbulence is not known a priori, and is set by balance between viscous forces and buoyancy effects. When the particle response time is comparable to a viscous time scale, introduced in our analysis, the system exhibits intense fluctuations of turbulent kinetic energy and strong preferential concentration of particles.

Influence of skin depth on convective heat transfer in induction heating

We investigate convection driven by induction heating of a horizontal fluid layer with direct numerical simulations (DNS). This problem is of particular interest in the context of nuclear severe accident mastering. In a real severe accident, the molten core is subjected to homogeneous internal sources resulting from nuclear disintegrations. This situation is mimicked in the laboratory using induction heating as the internal source. In induction heating however, heat sources are localized in the skin layer. Consequently, this concentration of heat may modify the flow and wall heat transfer, compared to the case of homogeneous internal sources. DNS are carried out for three typical skin depths and three total deposited powers. Skin depth variations show surprising results regarding flow structures and heat transfer. It is found that the heat sources heterogeneity has a weak effect on flow structures. Consequently, models of heat transfer in the case of homogeneous sources remain valid even with strong localized heating near the bottom.

Experimental study of bubble detection in liquid metal

Bubble detection in liquid metal is an important issue for various technological applications. For instance, in the framework of Sodium Fast Reactors conception, the presence of gas in the sodium flow of the primary and secondary loops is a problematic of crucial importance for surety and reliability. Here, the two main measurement methods of gas in sodium are Ultrasonic testing and Eddy-current testing; we investigate the second method in our study. In a first approach, we have performed experiments with liquid metal – galinstan – containing insulating spherical beads of millimeter order. The liquid metal is probed with an Eddy-current Flowmeter (ECFM) in order to detect the beads, and characterize their diameter and position. Results show that the signal measured by the ECFM is correlated to the effect of these parameters. Finally, an analytical model is proposed and compared to the experimental results.

Magnetoconvection transient dynamics by numerical simulation

Abstract.We investigate the transient and stationary buoyant motion of the Rayleigh-Bénard instability when the fluid layer is subjected to a vertical, steady magnetic field. For Rayleigh number, Ra, in the range 103-106, and Hartmann number, Ha, between 0 and 100, we performed three-dimensional direct numerical simulations. To predict the growth rate and the wavelength of the initial regime observed with the numerical simulations, we developed the linear stability analysis beyond marginal stability for this problem. We analyzed the pattern of the flow from linear to nonlinear regime. We observe the evolution of steady state patterns depending on

Particle-laden flows forced by the disperse phase: Comparison between Lagrangian and Eulerian simulations

Ra/Ha^{2}

Turbulent thermal convection driven by heated inertial particles

Ra/Ha2 and Ha. In addition, in the nonlinear regime, the averaged kinetic energy is found to depend on Ra and to be independent of Ha in the studied range.Graphical abstract