CFD with OpenFOAM: Backward Facing Step Flow Simulation, Learn Flow Separation and Reattachment with the Classic Backward Facing Step CFD Benchmark.
Course Description
The Backward Facing Step (BFS) is one of the most fundamental benchmark cases in Computational Fluid Dynamics (CFD). It is widely used in both research and industry to study flow separation, recirculation, and reattachment—phenomena that are central to aerodynamics, turbomachinery, environmental flows, and many engineering applications. With its simple geometry yet complex physics, the BFS case is an excellent teaching and validation tool for turbulence models, making it an essential part of every CFD engineer’s learning journey.
In this course, you will learn how to set up, run, and analyze the backward facing step case using OpenFOAM, the world’s leading open-source CFD software. The course is designed to be practical and hands-on, walking you step by step through geometry creation, mesh generation, boundary condition setup, solver execution, and post-processing.
We begin with the geometry and mesh setup, where you will understand the channel with a sudden expansion and learn how to use blockMesh to create a structured mesh. We also cover mesh refinement strategies to ensure accuracy in capturing separation and reattachment zones.
Next, we move to the boundary conditions and case setup, where you will specify inlet velocity profiles, outlet conditions, wall functions, and turbulence parameters. You will become familiar with the OpenFOAM folder structure (0/, constant/, and system/) and understand how each file contributes to the simulation workflow.
A dedicated section is focused on turbulence modeling, where you will explore commonly used models such as k–ε, k–ω, and Spalart–Allmaras. You will learn their theoretical foundations, practical implementation in OpenFOAM, and when to choose one model over another based on flow features.
After the case setup, we dive into running the simulation. You will learn how to execute solvers like simpleFoam for steady-state turbulent flow, monitor residuals, and check for convergence. For larger cases, we introduce parallel computing in OpenFOAM, teaching you how to decompose the domain, run with mpirun, and reconstruct results efficiently.
Post-processing is performed with ParaView, where you will visualize velocity contours, pressure distributions, and turbulent kinetic energy fields. You will also learn how to generate streamlines, line plots, and animations that clearly illustrate flow separation and reattachment downstream of the step. These visualization skills are crucial for preparing professional reports and presentations.
The course also includes a mini-project assignment where you will create and simulate BFS cases with different inlet velocities. This project reinforces your understanding of parametric studies, solver stability, and the physical effects of changing Reynolds numbers on separation length and recirculation intensity.
By the end of the course, you will:
1: Understand the physics of backward facing step flow.
2: Gain hands-on experience in setting up and running turbulent flow simulations in OpenFOAM.
3: Be able to select and configure turbulence models appropriately.
4: Master the workflow from geometry creation to post-processing.
5: Build confidence to extend these skills to more complex real-world CFD problems.
This course is ideal for students, researchers, and professionals in mechanical, aerospace, civil, and chemical engineering who want to strengthen their CFD foundations using open-source tools. Whether you are new to turbulence modeling or looking to validate your CFD setup, this course provides the skills and confidence to take your simulations to the next level.
