Direct and large-eddy simulations of two-phase turbulent flows

Methodologies have been developed for accurate numerical simulations of unsteady two layer cocurrent and countercurrent turbulent flows driven by gravity and pressure. The basis of these methodologies is projection method within the bulk of each phase, with rigorously derived boundary conditions being imposed at the gas/liquid interface. A judiciously chosen high – order spatial discretisation allows for direct numerical simulations (DNS) of the turbulence in each phase. A method for conducting simulations with smallscale eddies modelled and largescale eddies resolved (wall – resolved LES), was also implemented. The gas/liquid interface is forced to remain flat so as to allow the a priori constructed structured mesh to adequately resolve the turbulent boundary layer around the interface for the duration of the simulation. The method is numerically efficient when applied to the flows where time scales (andj therefore kinematic viscosities) in the two phases are of the same order of magnitude, but no restriction is placed on the density or viscosity ratio. For example, flow of air over viscous oil can be efficiently simulated. Single phase versions of both the DNS and the LES codes are validated against the literature. Results for the two layer system provide insight into the structure and the energy budget of turbulence near a liquid film on a wall. The turbulence statistics in the less viscous phase are compared to those derived from those collected from singlephase flows over a moving wall. The results are used to validate (and possibly replace) semiempirical profiles used previously in stability analyses and to provide further information that is otherwise unknown