## Computational Fluid Dynamics Research Group

### Overview

The CFD group at AUB is a research group that includes a group of professors, graduate students and undergraduate students who undergo a wide range of studies and simulations related to computational fluid dynamics. Working with both development and applied numerical studies, the group have gained a great expertise and knowledge in the CFD domain, which is currently the widest as well as the most efficient fluid flow testing tool.

Computational fluid dynamics has started decades ago (early 1950's) where simple as well as limited fluid flow problems were attempted on early computers. This area of study has heavily relied on the electronics revolution, which in particular the rise of high performance computers. The work of famous CFD researchers (i.e. Patenkar) in the 1980's have furthur pushed this domain forward such that it is deemed after that to be a science on its own right.

Now CFD is considered the number one tool among all fluid testing units due to the availability of high tech computers besides commercial and open-source CFD packages and libraries accessible to almost every one.

Our mission at the CFD group at AUB is to help develop the science of CFD by devising new mathematical methodologies that render more robust CFD simulations. We also aim at conducting CFD analysis for different domains such as air-conditioing, oil and gas, aerodynamics, blood flow in arteries, heat transfer issues .. etc.

### History

Our work at AUB started in 1990 with the development of number of high resolution schemes such as the STOIC scheme, a family of bounded Skew Scheme, work on adaptive Very High Resolution Schemes and more recently on the implementation of High Resolution schemes in unstructured grids. The formulation of nearly all schemes was based on the Normalized Variable Diagram of Leonard., and a an extension developed by the group the Normalized Variable and Space Normalized Diagram.

Near the mid 90's we started researching pressure-based algorithm based on the SIMPLE algorithm of Spalding and Patankar. We worked on a unifying the formulation of large number of pressure based schemes such as PRIME, SIMPLEC, SIMPLER, PISO, SIMPLEX, PISOC, in addition to the SIMPLE algorithm. Basic characteristics for these scheme were established and tested in a range of flow test problems. This was followed by the re-formulation of these schemes for all speed flow simulation, hence accounting for density variation. Work continued on the extension of these schemes for the simulation of multi-fluid algorithm both compressible and incompressible.

Multifluid flow simulation became our research focus in the beginning of year 2000 and continues to form an important thrust for our research.

More recently we started working on acceleration techniques for flow simulation such as the use of multigrids and work on improveming pressure-based algorithms.

### Lectures

There are currently plenty of CFD courses offered at AUB by the mechanical engineering department:

1 - Computer Applications Course: A course dealing with the application of numerical techniques for the solution of a variety of mechanical engineering problems involving systems of linear or non-linear algebraic equations, systems of ordinary differential equations of the initial and boundary value types, systems of ordinary differential equations, and partial differential equations of the parabolic, elliptic, and hyperbolic types. Engineering applications are introduced through a number of case study problems. The studies are usually applied using the commercial CFD package Ansys Fluent.

2 - Computational Fluid Dynamics: A course that deals with discretization process in fluid dynamics, numerical approaches and applications, iterative and direct matrix methods and numerical implementation of turbulence models. This course has recently included extensive use of the popular open-source CFD library OpenFOAM. Below are some presentations related to the course:

3 - Advanced Topics in Computational Fluid Dynamics: A course on numerical solution of compressible unsteady flows, advanced turbulence modeling, the segregated approach, the multigrid technique, and an introduction to multi-phase flows.4 - Simulation of Multiphase Flows: A course that is intended to give an overview of the fundamentals involved in dispersed multiphase flows, and develop a working knowledge which would allow the student to predict these flows numerically. Multiphase flows are important to many engineering and environmental applications. The course examines the conservation equations for multiphase systems; discretization using the finite-volume method; pressure-based algorithms for multifluid flow at all speeds: mass conservation based algorithms and geometric conservation based algorithms (SIMPLE, SIMPLEC, PISO, etc.); the partial elimination and SINCE algorithms; weighted pressure correction; mutual influence of volume fractions; implicit volume fraction equations; bounding the volume fractions; numerical implementation; and applications. Below are some presentations:

- Phase Diagrams
- Driving Force for Solidification
- Nucleation
- Solute Redistribution
- Solidification Microstructure
- Enthalpy Method

5 - Modeling Solidification Processes: A course that seeks to impart a coherent view of solidification processes and how they are modeled. Topics for the first part of the course include: homogeneous and heterogeneous nucleation, with plane front, cellular and dendritic pattern, columnar and equiaxed grain growth. Phenomenaaffecting the quality of castings such as micro-segregation, constituent under-cooling, macrosegregation and porosity formation are also covered. In the second part solidification models are developed and applied in the context of casting operations. The course covers: heat flow in solidification processes; thermodynamics of solidification: nucleation and growth; binary phase diagrams, phase diagram computation; microstructure evolution, constitutional undercooling; columnar and equiaxed solidification enthalpy method; mushy zone modeling; phasefieldmethod; volume-averaging of conservation equations; multi-scale models; and modeling solidification defects.

6 - Advanced Finite Volume Techniques: A course that focuses on linear multigrid; non-linear multigrid; mesh agglomeration: structured and unstructured grids; mesh generation: structured and unstructured grids; free surface simulation; and solidification simulation.

*Contact:*

Mhamad Mahdi Alloush