Browsing by Subject "Falling liquid films"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Open Access Linear stability analysis of evaporating falling liquid films(Elsevier, 2020) Mohamed, Hammam; Biancofiore, LucaWe consider the linear stability of evaporating thin films falling down an inclined plate. The one sided-model presented first by “Burelbach, J.P., Bankoff, S.G., Davis, S.H., 1988, Nonlinear stability of evaporating/condensing liquid films, Journal of Fluid Mechanics 195, 463–494. ” was implemented to decouple the dynamics of the liquid than those of the vapor at the interface, at which the evaporation is modeled based on a thermal equilibrium approach. We consider the base state solution derived by “Joo, S., Davis, S.H., Bankoff, S., 1991, Long-wave instabilities of heated falling films: two-dimensional theory of uniform layers, Journal of Fluid Mechanics 230, 117–146. ” which is based on the slow evaporation assumption. In previous works, only low dimensional models. i.e. the long wave theory, have been analysed for evaporating liquid films. Conversely in this paper, we extend the Orr-Sommerfeld eigenvalue problem for a film falling down a heated wall to include evaporation effects namely, vapor recoil and mass loss. As expected, we observe that the long wave theory fails in predicting the correct behavior when the inertia is strong or the wavenumber k is large. We confirm that the instability induced by vapor recoil (E-mode) behaves in a similar fashion to the instability due to the thermocapillary effect (S-mode). Both the S-mode and the E-mode can enhance each other, specially, at low Reynolds numbers Re. Moreover, we examine the perturbation energy budget to have an insight into the instabilities mechanism. We show that the presence of evaporation adds a new term corresponding to the work done by vapor recoil at the interface (VRE). We also find that the main contributor to the perturbation kinetic energy in the unstable E-mode is the work done by shear stress while VRE is negligible, unless Re << 1. Simpler analytical expressions of the energy balance terms near the instability threshold are obtained by using a long wave approximation.Item Open Access A spectral vanishing viscosity method for large-eddy simulations of two-fluid flow(2020-12) Khoshavaz, SolmazDNS studies of turbulent flows have proved to be inefficient in terms of time and computational resources. On the other hand, Large-eddy simulation (LES) is an effective approach towards modeling turbulence. The current research applies an extension of the Spectral Vanishing Viscosity (SVV) method to finite differences. This straight-forward LES technique allows turbulence modeling without the need for filtering or upwinding. The result is a hybrid DNS/LES Solver. The solver is applied to the two-fluid problem of falling liquid film in the presence of turbulent gas. Numerical simulation of falling liquid films requires a mathematical representation of the multiphase flow. A Direct Numerical Simulation (DNS) solver implementing finite volumes is used to solve the Navier-Stokes equations for the liquid phase. The Front Tracking method is used to model the moving gas-liquid interface. Gravity-driven falling liquid films are commonplace in engineering applications. Perturbed falling films dramatically increase the heat/mass transport across the interface compared to flat films, which highlights the significance of studying interfacial flows. The present research aims to develop a numerical tool, which will be used to further investigate falling liquid film phenomena.