Ricerc@Sapienza

The project addresses the evaporation/condensation of liquid droplets transported by a turbulent flow. In technological applications, e.g. internal combustion engines, aeronautical engines or power plants combustion chambers, the droplet transport, evaporation and vapor mixing is crucial for the overall efficiency of the device.

The phase change in a turbulent flow is a multi-scale phenomena ranging from the nano scales where the vapor is formed at the liquid interface, to the micro and macro scales of the turbulent flow which transports both the droplets and the vapor.

This multi-scale process poses several issues. Nowadays, the set of equations for the carrier phase in presence of mass, momentum and energy transfer is still formulated on phenomenological ground as well as the models which provide the macroscopic mass and energy fluxes.

In this project a rigorous derivation of the fluid flow equations will be carried out. The methodological path starts from the low-Mach number equations for the carrier phase endowed with appropriate boundary conditions at the droplet surface. In the limit of small droplets size, a rigorous decomposition of the flow field in terms of a background plus a disturbance (density, velocity and temperature), allows to reallocate the boundary conditions at the droplet surface as appropriate source terms for the carrier phase. These sources follow from a solution of a five dimensional unsteady Stokes problem without any ``ad hoc'' assumptions.

The methodology still needs mass and energy fluxes at the droplet positions. New models will be pursued starting the investigation at the nano scale where the evaporation/condensation naturally occurs via Molecular Dynamics simulations. The models will be checked against well targeted experiments of a single droplet evaporation/condensation and will be employed in the Direct Numerical Simulation of a droplet laden turbulent jet to be further validated against experimental measurements.