## Outline

PSI-BOIL (Parallel SImulator of BOILing phenomena) is an in-house Computational Fluid Dynamics (CFD) code developed at Paul Scherrer Institute. The main purpose of the code is basic research of new models for turbulence, multi-phase flows, with interface tracking and particle tracking, and phase change. Numerical models developed by using PSI-BOIL are a conservative two-phase flow model (Sato and Niceno, 2012a), bubbly flow model using coarse grid (Badreddine et al., 2015), a modelling for wetting phenomena (Badillo, 2015), a contact line treatment (Sato and Niceno, 2012b), phase change models based on a sharp interface (Sato and Niceno, 2013) and a phase field approach (Badillo, 2012) and an immersed boundary method (Niceno et al., 2013). As applications of the code, Large Eddy Simulation (LES) of muptiple impinging jets (Draksler et al., 2014) and convective nucleate boiling flows (Lal et al., 2015; Sato et al., 2013) were published. The code is parallelized with MPI, running on Monte Rosa and Piz Dora at Swiss National Supercomputing Center. Currently, the authors plan to implement GPU programming in order to use the full capability of Piz Daint.

## Description of the code

The code is based on a single-block, Cartesian-grid, 2nd order accurate finite volume method for incompressible flows. Single-block is chosen for efficiency of pressure solution, the most time-consuming part of the solution procedure of incompressible flows, and is based on generalization of additive correction multi-grid procedure. Since the PSI-BOIL’s code main purpose is basic research, Cartesian grid is a good choice, since it offers relatively straightforward implementation of new physical models. The variables are arranged in the staggered fashion, i.e. pressure and other scalars are defined in cell centers, whereas velocity components are at the cell faces. This arrangement offers robustness of the solution procedures, significantly eases implementation of semi-explicit non-iterative time-advancing schemes and ensures good transfer between potential and kinetic energy for the scale-resolving (DNS or LES) simulations of turbulence. As the name implies, the code is developed for parallel computational architectures using the message passing interface. It is written in standard C++, and compiled with automake tool, making it very portable. It has been compiled on various computational platforms, ranging from desktop PCs running Linux, Windows an iOS to mainframe parallel clusters. Efficiency of the multigrid solver for pressure, together with staggered arrangement allows user to run it on very fine meshes, allowing for much of the interface and turbulence details to be resolved. Simulations with up to two billion cells are reported for DNS with interface tracking, and up to 600 million cells for LES.

Physical models in PSI-BOIL comprise sub-grid scale models for LES, interface tracking methods, dispersed flow resolving methods, phase change methods, and micro-region/layer models for boiling. Sub-grid scale models comprise the standard Smagorinsky model and the WALE model. PSI-BOIL has been used for LES of flows at supercritical pressures (Niceno and Sharabi, 2013) and for multiple impinging jet simulations (Draksler et al., 2014). To simulate fluid flow around solid object of arbitrary shape, an immersed boundary method (Niceno et al., 2013) is used, which can also take into account the conjugate heat transfer between fluid and solid.

In spite of successful use of the code in single-phase situations, its main strength lies in the ability to model multiphase flows. The main framework is the single-fluid approach, with interface tracking method based on third-order accurate CIP-CSL2 (Constrained Interpolation Profile – Conservative Semi-Lagrangian 2nd order) method. The developers of the code, most notably Dr. Yohei Sato, made significant improvements of the field, by proposing improved interface sharpening (Sato and Niceno, 2012a), new contact line treatment (Sato and Niceno, 2012b) and sharp-interface phase-change model (Sato and Niceno, 2013). As applications of the code, convective nucleate boiling flows (Lal et al., 2015; Sato et al., 2013) were published. In parallel to CIP-CSL2, an accurate modelling for wetting phenomena (Badillo, 2015) and a phase change model (Badillo, 2012) are developed using a phase-field approach in order to understand thoroughly the corresponding phenomena. Owing to the accuracy and originality of the models in PSI-BOIL, it is already used by researchers in the group of Prof. D. Lucas at Helmholtz-Zentrum Dresden-Rossendorf, in the group of Prof. R. Walker at Imperial College in London, and in the group from Prof. L. Cizelj at Josef Stefan institute in Ljubljana. So the user base of the code is expanding in academia, which means that the code itself is subjected to scrutiny by leading experts in the field.

In addition to the innovative methods for phase-change outlined above, the code also features an original method for dispersed flow simulations (Badreddine et al., 2015), which combines the characteristics of interface tracking and Lagrangian particle tracking. The method allows simulations of many thousands of bubbles, as one would expect from Lagrangian particle tracking, but yet resolves interaction of the dispersed phase with the flow structures in the carrier phase.

## Source code

The code is available on the next web-page.

https://github.com/Niceno/PSI-BOIL

## Publications

**Single phase LES**

- Niceno, B., Sharabi, M. (2013). Large eddy simulation of turbulent heat transfer at supercritical pressures. Nuclear Engineering and Design, 261(0), 44-55. DOI: 10.1016/j.nucengdes.2013.03.042
- Draksler, M., Niceno, B., Končar, B., Cizelj, L. (2014). Large eddy simulation of multiple impinging jets in hexagonal configuration - Mean flow characteristics. International Journal of Heat and Fluid Flow, 46, 147-157. DOI: 10.1016/j.ijheatfluidflow.2014.01.005
- Draksler, M., Končar, B., Cizelj, L., Ničeno, B. (2017). Large Eddy Simulation of multiple impinging jets in hexagonal configuration – Flow dynamics and heat transfer characteristics. International Journal of Heat and Mass Transfer, 109, 16-27. DOI: 10.1016/j.ijheatmasstransfer.2017.01.080

**Immersed boundary method**

- Niceno, B., Reiterer, F., Ylönen, A., Prasser, H. M. (2013). Simulation of single-phase mixing in fuel rod bundles, using an immersed boundary method. Physica Scripta, 88(T155), 014054.
- Badreddine, H., Sato, Y., Berger, M., Niceno, B. (2017). A Three-Dimensional, Immersed Boundary, Finite Volume Method for the Simulation of Incompressible Heat Transfer Flows around Complex Geometries. International Journal of Chemical Engineering, 2017, 14. DOI: 10.1155/2017/1726519

**Two phase flow model**

- Sato, Y., Niceno, B. (2012a). A conservative local interface sharpening scheme for the constrained interpolation profile method. International Journal for Numerical Methods in Fluids, 70(4), 441-467. DOI: 10.1002/fld.2695
- Sato, Y., Niceno, B. (2012b). A new contact line treatment for a conservative level set method. Journal of Computational Physics, 231(10), 3887-3895. DOI: 10.1016/j.jcp.2012.01.034

**Phase change model (Color function)**

- Sato, Y., Niceno, B. (2013). A sharp-interface phase change model for a mass-conservative interface tracking method. Journal of Computational Physics, 249, 127-161. DOI: 10.1016/j.jcp.2013.04.035
- Sato, Y., Smith, B. L., Niceno, B. (2018). Examples of Pool-Boiling Simulations Using an Interface Tracking Method Applied to Nucleate Boiling, Departure from Nucleate Boiling and Film Boiling Encyclopedia of Two-Phase Heat Transfer and Flow III (pp. 225-263): WORLD SCIENTIFIC. DOI: 10.1142/9789813229440_0007

**Pool boiling**

- Sato, Y., Niceno, B. (2015). A depletable micro-layer model for nucleate pool boiling. Journal of Computational Physics, 300, 20-52. DOI: 10.1016/j.jcp.2015.07.046
- Murallidharan, J., Giustini, G., Sato, Y., Niceno, B., Badalassi, V., Walker, S. P. (2016). Computational fluid dynamic simulation of single bubble growth under high-pressure pool boiling conditions. Nuclear Engineering and Technology, 48(4), 859-869. DOI: 10.1016/j.net.2016.06.004
- Giustini, G., Walker, S. P., Sato, Y., Niceno, B. (2017). Computational fluid dynamics analysis of the transient cooling of the boiling surface at bubble departure. Journal of Heat Transfer, 139(9), 091501. DOI: 10.1115/1.4036572
- Sato, Y., Niceno, B. (2017). Nucleate pool boiling simulations using the interface tracking method: Boiling regime from discrete bubble to vapor mushroom region. International Journal of Heat and Mass Transfer, 105, 505-524. DOI: 10.1016/j.ijheatmasstransfer.2016.10.018
- Sato, Y., Niceno, B. (2018). Pool boiling simulation using an interface tracking method: From nucleate boiling to film boiling regime through critical heat flux. International Journal of Heat and Mass Transfer, 125, 876-890. DOI: 10.1016/j.ijheatmasstransfer.2018.04.131

**Convective boiling**

- Sato, Y., Lal, S., Niceno, B. (2013). Computational fluid dynamics simulation of single bubble dynamics in convective boiling flows. Multiphase Science and Technology, 25(2-4), 287-309. DOI: 10.1615/MultScienTechn.v25.i2-4.110
- Lal, S., Sato, Y., Niceno, B. (2015). Direct numerical simulation of bubble dynamics in subcooled and near-saturated convective nucleate boiling. International Journal of Heat and Fluid Flow, 51(0), 16-28. DOI: 10.1016/j.ijheatfluidflow.2014.10.018

**Boiling in annular flow regime**

- Sato, Y., Niceno, B. (2017). Large eddy simulation of upward co-current annular boiling flow using an interface tracking method. Nuclear Engineering and Design, 321, 69-81. DOI: 10.1016/j.nucengdes.2017.03.003

**Phase change model (Phase-field method)**

- Badillo, A. (2012). Quantitative phase-field modeling for boiling phenomena. Physical Review E, 86(4), 041603. DOI: 10.1103/PhysRevE.86.041603
- Badillo, A. (2015). Quantitative phase-field modeling for wetting phenomena. Physical Review E, 91(3), 033005. DOI: 10.1103/PhysRevE.91.033005
- Szijártó, R., Badillo, A., Niceno, B., Prasser, H. M. (2017). Condensation models for the water–steam interface and the volume of fluid method. International Journal of Multiphase Flow, 93, 63-70. DOI: 10.1016/j.ijmultiphaseflow.2017.04.002

**Dispersed flow model**

- Badreddine, H., Sato, Y., Niceno, B., Prasser, H.-M. (2015). Finite size Lagrangian particle tracking approach to simulate dispersed bubbly flows. Chemical Engineering Science, 122(0), 321-335. DOI: 10.1016/j.ces.2014.09.037
- Badreddine, H., Lafferty, N., Niceno, B., Prasser, H. M. (2018). Corrective interface tracking approach to simulate finite-size bubbly flows. Chemical Engineering Science, 178, 61-69. DOI: 10.1016/j.ces.2017.12.028
- Badreddine, H., Niceno, B. (2018). Simulations of droplet merging with free surface and bubble column reactor with Finite-size Lagrangian particle tracking. Chemical Engineering Science, 176, 609-621. DOI: 10.1016/j.ces.2017.10.037

**Deep learning (Artificial intelligence)**

- Liu, Y., Dinh, N., Sato, Y., Niceno, B. (2018) Data-driven modeling for boiling heat transfer: using deep neural networks and high-fidelity simulation results, Applied Thermal Engineering, 144, 305-320. DOI:10.1016/j.applthermaleng.2018.08.041