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Introduction to RANS Turbulence Modeling in OpenFOAM
Rating: 5.0 out of 5(2 ratings)
13 students

What you'll learn

  • Describe the Reynolds-Averaged Navier–Stokes equations, the concept of Reynolds stresses, and the need for turbulence modeling.
  • Explain the Boussinesq hypothesis and how eddy-viscosity–based models close the RANS equations.
  • Compare Spalart–Allmaras, standard k–ε, RNG k–ε, k–ω, and SST k–ω models in terms of assumptions, strengths, and limitations.
  • Justify the choice of a RANS model for separated flows such as the backward-facing step.
  • Configure mesh, boundary conditions, turbulence properties, and solver settings for incompressible RANS simulations.
  • Use ParaView to extract and interpret velocity, pressure, and turbulent viscosity fields.
  • Describe the key ideas behind the LRR Reynolds Stress Model (RSM) and explain how it overcomes limitations of eddy-viscosity–based RANS models.

Course content

7 sections13 lectures1h 54m total length
  • Derivation of the Reynolds-Averaged Navier–Stokes (RANS) Equations8:34

    In this lecture, we will derive the Reynolds-Averaged Navier–Stokes (RANS) equations starting from the incompressible Navier–Stokes equations. By applying Reynolds decomposition and time-averaging, we will show how turbulent fluctuations introduce additional terms—known as the Reynolds stresses. This derivation lays the theoretical foundation for most turbulence models used in CFD and helps explain why turbulence modeling is essential for practical simulations.

  • The Boussinesq Hypothesis and Turbulence Closure Models4:42

    n this lecture, we introduce the Boussinesq hypothesis, a key assumption used to relate the Reynolds stresses to the mean velocity gradients via an eddy viscosity. This simplification allows us to close the Reynolds-Averaged Navier–Stokes (RANS) equations and forms the basis for many widely used turbulence models.

    We will also discuss different types of closure models, including zero-equation, one-equation, and two-equation models, and explain the trade-offs between accuracy and complexity when choosing a model.

Requirements

  • Ability to independently install, configure, and run OpenFOAM dot com (v2412 or newer) on a local system (Linux, WSL, or native setup).
  • Basic understanding of the Navier–Stokes equations and fundamental fluid mechanics concepts
  • Familiarity with CFD terminology such as velocity, pressure, boundary conditions, and meshes
  • Elementary knowledge of numerical methods and discretization (helpful but not mandatory)
  • Willingness to use the Linux command line for running simulations and post-processing
  • Comfortable using Ubuntu Linux for demonstrations; Windows and macOS users can follow along using Docker or WSL.

Description

This course offers a comprehensive, beginner-friendly introduction to Reynolds-Averaged Navier–Stokes (RANS) turbulence modeling using OpenFOAM, with a strong emphasis on eddy-viscosity–based models widely used in engineering CFD. The course is designed to bridge the gap between turbulence theory and practical simulation skills, making it suitable for students and early-career engineers who are new to OpenFOAM and turbulence modeling.

The course begins with the fundamentals of the RANS formulation, explaining Reynolds averaging, the closure problem, and the physical meaning of turbulent stresses. Building on this foundation, learners are introduced to the eddy-viscosity hypothesis and how it leads to commonly used turbulence models. The following models are covered in detail:

  • Spalart–Allmaras model (one-equation model)

  • Standard k–ε model

  • Standard k–ω model

  • SST k–ω model

Each model is discussed in terms of its governing equations, underlying assumptions, near-wall treatment, strengths, and known limitations. Special attention is given to how these models behave in separated and recirculating flows, which are common in practical engineering applications.

To reinforce the concepts, the course uses the backward-facing step as a canonical benchmark problem. Learners will set up the computational domain, generate meshes, specify boundary conditions, select appropriate solvers and turbulence models, and run steady-state and transient RANS simulations in OpenFOAM. Through systematic post-processing using ParaView, learners will analyze velocity fields, pressure distributions, turbulent viscosity, flow separation, and reattachment length, and compare predictions across different turbulence models.

The course also emphasizes best practices in CFD, including mesh quality considerations, near-wall resolution, convergence monitoring, and basic model validation against reference data. A brief discussion on Reynolds Stress Models (RSM), including the LRR model, is included to expose learners to advanced RANS approaches and to highlight the limitations of eddy-viscosity models.

To support learning, the course includes fully working OpenFOAM case files for all examples, along with additional downloadable PDF notes that consolidate all theoretical concepts, equations, and modeling details discussed in the lectures. These resources allow learners to revise the theory at their own pace and reuse the simulation setups for further practice or extension.

By the end of the course, learners will have a solid practical foundation in RANS turbulence modeling with OpenFOAM and will be able to confidently apply eddy-viscosity models to real-world engineering flow problems while understanding their limitations and proper use.

Who this course is for:

  • Undergraduate and postgraduate engineering students
  • Beginners in OpenFOAM
  • CFD enthusiasts and self-learners
  • Early-career CFD engineers
  • Researchers transitioning to OpenFOAM