Some aspects of turbulent mixing in two phase flows

François-Xavier Demoulin, COmplexe de Recherche Interprofessionnel en Aérothermochimie (CORIA), Rouen, France

The goal of this lecture is to show some aspects of two-phase flows that are driven by turbulence. The presented applications concern the injection of liquid fuel and the following processes leading eventually to combustion. Thus, combustion is the result of several phenomena starting with atomization, followed by liquid dispersion, vaporisation, mixing and chemical reaction.

In the aim of accelerating these processes different methods are to be used. To promote atomization processes injection takes place with strong velocity gradients leading to turbulent regime. As an example, in Diesel or Rocket engines, the Reynolds and Weber numbers are high enough, thus allowing that liquid dispersion be similar to the turbulent mixing. In this case, the two-phase flow can be modelled as a single turbulent flow carrying two species: the liquid and the gas. Nevertheless, this turbulence is characterized by strong density variations. The droplets resulting from the atomisation are often small enough, so their Stokes numbers (based on the Kolmogorov time scale) are such that they become segregated. The focus will be on how these processes can influence the vapour distribution and finally the combustion.