Two-phase flows, dynamics and transfers

M.-C. Duluc, D. Juric, N. Grenier, A.-H. Ebo Adou, B. Xu, with contributions of V. Daru (AERO), J. Chergui (P2I), P. Le Quéré (ETCM)


Massively parallel DNS 3D code for multiphase flows: BLUE

BLUE has been developed by LIMSI in strong collaboration with S. Shin (Hongik Univ., Seoul, Korea), see our previous scientific reports. It has been successfully run on up to 65536 processors on the IBM BlueGene/Q machine at IDRIS with good scalability performance. The modular program structure allows for the application of the code to a wide variety of two-phase flow simulations: free-surface instabilities, flow of bubbles or drops with coalescence and breakup, thermal and species transport with phase change, droplet impact or flow around immersed solid objects for microchannel flows. We have thus been able to simulate cases of the Faraday instability with non-periodic pentagonal motifs for the interface. The Faraday problem has been extended to the spherical case with radial oscillations. BLUE has also been used for simulating oscillations in the Kelvin-Helmholtz Instability or a drop undergoing Leidenfrost levitation, thus meeting various experiments conducted at PMMH. BLUE is also the basis for collaboration contracts with Air Liquide, including an ANR project jointly proposed also with FAST.


Weakly compressible two-phase flows

Previous work on two-phase flows, liquid with weakly compressible gas, was based on the concept of dual fluid with appropriate Low Mach Number numerical scheme developed by V. Daru (AERO group); the interface was described with the Front Tracking method, which raised some difficulties with respect to mass conservation.

Recently, another approach has been tested that now uses a diffuse interface description based on a compressible two-fluid model, and overcomes those difficulties. In the new approach, both liquid and gas phases, either fully conservative, are numerically present at each space point and are modelled as one compressible medium with either stiff or smooth equation of state. A specific numerical scheme has been used that prevents from excessive numerical dissipation in the Low Mach regime, especially when the liquid is modelled with a high speed of sound . The two approaches (one dual fluid, or two fluids) were compared for some 1D, dynamic, and non-isothermal test-cases formerly developed by V. Daru and M.C. Duluc. As shown by Illustration 1, results are satisfactory. The two-fluid approach, currently being implemented in the in-house one-fluid compressible parallel platform CHORUS, will thus be extended in order to include phase change.

Test-case of a water plug surrounded by two gas pockets, heated on only one side). Thermodynamic pressure in each gas pocket (P1 and P2).