Towards a multi-scale approach of two-phase flow modeling in the context of DNB modeling
Résumé
In this article, we present how Direct Numerical Simulation (DNS) is being used in the context of Departure from Nucleate Boiling (DNB) modeling. Two particular applications are analyzed: wall boiling and bubble column flow. An analysis of the relevant length scales involved shows that true DNS, where all the length scales are resolved, is necessarily restricted to flow configurations where one or a few bubbles are involved. In the context of DNB modeling, DNS can thus be used to study (i) the dynamics of the growth of a few bubbles with their eventual spreading and (ii) bubble column flows to predict the void fraction field in the near wall region. To account for collective effects in bubbly flows, we show that it is necessary to develop a new approach where the large turbulence structures and large interface deformations are captured whereas the smallest scales are modeled; this is the Interface and Subgrid Scale (ISS) method. The DNS and ISS methods are presented and preliminary results on the use of DNS for larger scales models are presented.