Onset of thermal ripples at the interface of an evaporating liquid under a flow of inert gas

peer reviewe

Scroll waves in isotropic excitable media : linear instabilities, bifurcations and restabilized states

Scroll waves are three-dimensional analogs of spiral waves. The linear stability spectrum of untwisted and twisted scroll waves is computed for a two-variable reaction-diffusion model of an excitable medium. Different bands of modes are seen to be unstable in different regions of parameter space. The corresponding bifurcations and bifurcated states are characterized by performing direct numerical simulations. In addition, computations of the adjoint linear stability operator eigenmodes are also performed and serve to obtain a number of matrix elements characterizing the long-wavelength deformations of scroll waves.Comment: 30 pages 16 figures, submitted to Phys. Rev.

Clarifying the meaning of mantras in wildland fire behaviour modelling: reply to Cruz <i>et al.</i> (2017)

International audienceIn a recent communication, Cruz et al. (2017) called attention to several recurring statements (mantras) in the wildland fire literature regarding empirical and physical fire behaviour models. Motivated by concern that these mantras have not been fully vetted and are repeated blindly, Cruz et al. (2017) sought to verify five mantras they identify. This is a worthy goal and here we seek to extend the discussion and provide clarification to several confusing aspects of the Cruz et al. (2017) communication. In particular, their treatment of what they call physical models is inconsistent, neglects to reference current research activity focussed on combined experimentation and model development, and misses an opportunity to discuss the potential use of physical models to fire behaviour outside the scope of empirical approaches

The different equations of motion of the central line of a slender vortex filament and their use to study perturbed vortices

A comparison between the equation of motion of the central line of a slender vortex filament deduced from a matched asymptotic expansion(A. Callegari and L. Ting) and the expansion of the equation of motion of the ad-hoc cut-off methods(S. Crow) with the cut-off length as the small asymptotic parameter is performed. It justifies the cut-off methods and gives the link between the cut-off lengths and the thickness of a viscous or inviscid vortex with an axial velocity component. The asymptotic equation of motion for an open filament is then simplified in case of a perturbed straight filament and different regimes are displayed. They depend of relatives values of the amplitude of the perturbation and the small thickness of the filament

Linear and nonlinear analyses of convective instabilities in evaporating liquid layers

peer reviewe

Influence of evaporation on Bénard-Marangoni instability in a liquid-gas bilayer with a deformable interface

Bénard-Marangoni instability in a bilayer liquid-gas system with a deformable interface is investigated. The present work is devoted to a linear approach. We discuss the influence on the onset of stability of the following parameters: initial temperature profile, relative thickness of the gas and liquid layers, deformation of the interface, influence of the evaporation process, and the wetting parameter

On the use of Galerkin-Eckhaus method to study the nonlinear regime of Marangoni-Bénard instabilities in an evaporating liquid layer

We investigate theoretically Marangoni-Bénard instability in an evaporating liquid layer surmounted by its vapor and an inert gas. A Galerkin-Eckhaus method, based on a slaving principle and an iterative algorithm, and a direct finite element method are used to determine the evaporation rate above the convective threshold. Both methods provide precise quantitative results, even far from the linear stability threshold. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200647.20.Ky Nonlinearity, bifurcation, and symmetry breaking, 47.20.Hw Morphological instability; phase changes, 47.20.Dr Surface-tension-driven instability, 47.55.pf Marangoni convection,

Bénard instabilities in a binary-liquid layer evaporating into an inert gas: stability of quasi-stationary and time-dependent reference profiles

This study treats an evaporating horizontal binary-liquid layer in contact with the air with an imposed transfer distance. The liquid is an aqueous solution of ethanol (10 % wt). Due to evaporation, the ethanol mass fraction can change and a cooling occurs at the liquid-gas interface. This can trigger solutal and thermal Rayleigh-B´enard-Marangoni instabilities in the system, the modes of which corresponding to an undeformable interface form the subject of the present work. The decrease of the liquid-layer thickness is assumed to be slow on the diffusive time scales (quasi-stationarity). First we analyse the stability of quasistationary reference profiles for a model case within which the mass fraction of ethanol is assumed to be fixed at the bottom of the liquid. Then this consideration is generalized by letting the diffusive reference profile for the mass fraction in the liquid be transient (starting from a uniform state), while following the frozen-time approach for perturbations. The critical liquid thickness below which the system is stable at all times quite expectedly corresponds to the one obtained for the quasi-stationary profile. As a next step, a more realistic, zero-flux condition is used at the bottom in lieu of the fixed-concentration one. The critical thickness is found not to change much between these two cases. At larger thicknesses, the critical time at which the instability first appears proves, as can be expected, to be independent of the type of the concentration condition at the bottom. It is shown that solvent (water) evaporation plays a stabilizing role as compared to the case of a non-volatile solvent. At last, an effective approximate Pearson-like model is invoked making use in particular of the fact that the solutal Marangoni is by far the strongest as an instability mechanism here