Tutorial — Turbulence Modeling in Ansys Fluent — Lesson 4

Introduction

This tutorial focuses on turbulence modeling in Ansys Fluent, particularly for a flow simulation through an exhaust manifold. By the end of this tutorial, you'll be equipped to set up the physics for turbulent flow, define boundary conditions, utilize the Reynolds number for flow classification, and visualize your results using Ansys Fluent's post-processing tools.

Step 1: Define the Computational Domain

• Start by creating a computational domain that represents the exhaust manifold.
• Make sure to consider the geometry accurately to capture the flow characteristics.
• Use Ansys DesignModeler or import the geometry if it is already created.

Step 2: Set Up the Physics for Turbulence Modeling

• Navigate to the physics setup in Ansys Fluent.
• Choose a turbulence model suitable for your flow type. Common options include:
  • k-epsilon model
  • k-omega model
• Ensure that the selected model aligns with your specific flow characteristics.

Step 3: Specify Boundary Conditions

• Define boundary conditions for your model:
  • Inlet: Specify velocity or mass flow rate and turbulence intensity.
  • Outlet: Use pressure outlet conditions.
  • Walls: Define no-slip conditions for solid walls.
• Ensure that you set the boundary conditions according to the physical scenario of the exhaust manifold.

Step 4: Calculate Reynolds Number

• Use the Reynolds number to evaluate the flow regime:
  • Formula:

    Re = (density * velocity * characteristic_length) / viscosity
    

  • If Re > 4000, the flow is considered turbulent.
• Adjust your parameters if necessary to ensure you are modeling the correct flow regime.

Step 5: Run the Simulation

• Set up the solver settings:
  • Choose steady-state or transient analysis based on your needs.
  • Adjust the time step and convergence criteria.
• Start the simulation and monitor convergence.

Step 6: Post-Processing and Visualization

• Once the simulation completes, use the post-processing tools in Ansys Fluent:
  • Visualize flow parameters including:
    • Temperature distribution
    • Mass flow rates
    • Velocity vectors
    • y+ values (a measure of wall distance).
• Utilize contour plots and vector plots to better understand the flow patterns.

Conclusion

In this tutorial, you have learned how to model turbulence in Ansys Fluent, define boundary conditions, calculate Reynolds numbers, and visualize results effectively. By following these steps, you can confidently set up and analyze turbulent flow scenarios in various applications. For further learning, explore additional resources on Ansys’s website, and consider downloading free software for practical experience.