## Introduction

Many processes for the production of drugs, fuels and plastic materials, as well as energy from coal or biomasses involve multiphase flows, which are composed by a combination of a fluid, either liquid or gas, and particles, droplets or bubbles. This type of flow is also naturally present in the environment. Examples are the formation of a mixture of air and solid particles due to volcanic eruptions, and particles of sand and other materials transported by the wind. Scientists and engineers use software to study how these flows behave in order to improve the yield of industrial processes, reduce their environmental impact, and energy consumption. The computer programs used to perform these studies solve complex mathematical problems, and require powerful computers to be able to obtain the results in a useful time. This project focuses on developing the next generation of computer software for the simulation of multiphase flows, enabling it to use the latest generation of computers which combine traditional and graphical processors for improved performance. This software will be released to the public and will enable, scientists and engineers from different research areas to tackle real-world problems by taking advantage of the latest developments in multiphase flow science, combined with the benefit of being able to use the software on powerful computer infrastructures. Students and educators will be able to use the software and learn about multiphase flows through the examples and the documentation that will be provided.

## Objectives

The project objectives are:

- The development of computational models for turbulent multiphase flows in the framework of quadrature-based moment methods
- The implementation of a suite of three solvers into OpenFOAM to tackle the following problems
- Solution of the population balance equation for particles with negligible inertia, such as nanoparticles in a fluid flow
- Description of gas-liquid flows, where the bubble inertia is small but not zero
- Description of gas-particle flows with highly inertial particles

- The creation of an interface between the OpenFOAM solvers and specific libraries to solve part of the problems on graphical processing units (GPU).
- The creation of documentation, verification and validation cases, and tutorials to favor the adoption of the software and external contributions to it
- The distribution of the developed software under the GNU GPL 3 license, and of its documentation under the GNU FDL in order to disseminate the results of the research and gather feedback

## Timeline

The project extends for three years, starting on October 1^{st}, 2014. The proposed timeline for the development of the software is the following:

**Year 1**- Formulation of turbulence models for quadrature-based moment methods (QBMM).
- Development of an interface between OpenFOAM and existing GPU libraries.
- Implementation of realizable quasi-second-order numerical schemes into OpenFOAM.
- Implementation, code review, pre-release testing and public release of a PBE solver with advection and size-dependent diffusion in the limit of small Stokes number.

**Year 2**- Verification of the PBE solver implemented at the previous point on simple test cases involving flows with small Stokes number. Public release of the verification results.
- Formulation of a generalized population balance equation (GPBE) solver with size-dependent advection, to describe flows with small but finite Stokes number (gas-liquid flows).
- Implementation, code review, testing and public release of the GPBE for low Stokes number problems using quasi-second-order realizable schemes.
- Verification of the GPBE solver for low Stokes number problems against test cases involving bubble columns. Public release of the verification results.

**Year 3**- Extension of the GPBE solver to turbulent polydisperse multiphase flows with moderate to large Stokes numbers, such as moderately dilute to dense gas-particle flows.
- Implementation, code review, pre-release testing and public release of the GPBE solver for moderate to large Stokes numbers into OpenFOAM.
- Verification of the GPBE solver against simple test cases involving gas-particle flows. Release of the results obtained during the verification process.
- Preparation of the final release of the source code, of the code documentation and test cases for the public release.

Updates on the development status can be found in the blog, and on twitter.