Combined direct numerical simulation and long-wave simulation of a liquid film sheared by a turbulent gas flow in a channel

Abstract

In this work, the dynamics of a thin liquid film sheared by a turbulent gas flow are investigated numerically. It is known that even a constant interfacial shear stress affects film stability and dynamics. We are interested in the effect of turbulent fluctuations on the film development. A combination of a direct numerical simulation (DNS) of the turbulent gas flow and a long-wave theory for the liquid film evolution is used to study the effect of the turbulent shear stress fluctuations on the liquid film. The simulation is carried out in two steps. First, a DNS of a single-phase turbulent channel flow is conducted. The time-dependent turbulent shear stress at the lower wall is stored. In the second step, the time- and location-dependent turbulent shear stress serves as a boundary condition in a one-sided long-wave simulation of the liquid film to identify the effect of the turbulent gas flow on the film stability and dynamics. The resulting film deformation is simulated for different Reynolds numbers, and an analysis of the film deformation and stability as a function of the turbulent shear stress fluctuations is given. The numerical simulations are accompanied by a simplified linear analysis. The results show that the dynamics of the liquid film sheared by a turbulent gas flow depend not only on the average shear stress at the liquid-gas interface but also on the amplitude as well as the temporal and spatial scales of the shear stress fluctuations.