Direct numerical simulation (DNS) of turbulent two-phase flows at a leadership computing facility allows achievement of unprecedented level of detail and can answer fundamental questions about the interaction between the complex and evolving interfaces between flow phases and turbulence. The detailed simulation of all turbulent structures using a DNS approach as well as interface evolution in turbulent flows (in the form of bubbles, droplets, and wavy interfaces between liquid and steam in various flow regimes) will allow the collection of statistical information about two-phase flow parameters at unprecedented Reynolds numbers and levels of detail. An advanced data collection approach coupled with interface-tracking methods will help process large data sets provided by the simulations.

Three subprojects will generate two-phase flow results highly relevant to nuclear reactor flows, including (i) bubbly flow through pressurized water nuclear reactor fuel bundles with complex geometry spacers, (ii) complex two-phase flow regimes (slug and churn flow) as well as (iii) droplet interactions with reactor structures during accident scenarios. Major statistical parameters, such as flow rate, mean velocity and gas volume fraction will be assessed against experimental data while the higher order statistics will bring new knowledge about two-phase flows. With the help of the Leadership Computing Facilities detailed data will be provided for new closure laws which will allow reliable application of multiphase computational fluid dynamics to nuclear reactor systems. This will improve the safety margin predictions for existing light water reactors and facilitate the development and design of next generation energy systems.