The Role of Direct Numerical Simulations in Validation and Verification

The role of direct numerical simulations (DNS) of multiphase flows, where all continuum length and time scales are fully resolved, in validation and verification of models for the average flow, is discussed. Although DNS are usually limited to relatively small problems and are generally impractical for predictions of full-scale multiphase systems, DNS offer unprecedented data and insight. Indeed, if correctly done, DNS provide an essentially exact solution for the system under study. With the growing ability to conduct DNS of increasingly larger and more complex multiphase systems, they are bound to play a major and critical role in the development and validation of models designed for the predictions of the average or large-scale behaviour of industrial flows. Methods designed for DNS of multiphase flows are briefly discussed and two examples where DNS have lead to fundamentally new insight are reviewed. In the conclusion we look at the immediate needs for further development of multiphase DNS and how such development will impact multiphase flow modelling.