Extending Inlet and Outlets to Help Avoid Divergence, Improve Mass Balance and Aid Accuracy

Autodesk Support

Dec 19, 2017

 Adding inlet and outlet extensions can be of huge benefit to many simulations where accurate flow predictions are paramount.

 For example:

  •  Extensions help to ensure that flow is fully developed as it enters and leaves the analysis domain.
  • Outlet extensions can also help to avoid recirculation of the flow over the outlet boundary condition which is seen in many simulations and can negatively impact the results, sometimes causing divergence and poor mass balance in the system.    

For best practice users should aim to have inlet extensions greater than or equal in length to 5 times the opening width and outlet extensions greater than or equal to 10 times the opening width.

The following Screencast provides a typical technique for adding inlet and outlet extensions. Autodesk Inventor CAD Modelling software has been employed and the geometry has been taken from the Electronics CFD tutorial.  

Once extensions have been added, the model should be exported to CFD via either creating a new study or updating the design in an existing study. The working fluid material must then be applied to ech extension and boundary conditions can then be implemented on the new locations of the inlet and outlet.

The following Screencast demonstrates the export process as well as assigning the working fluid and boundary conditions. Note that the boundary conditions correspond to those specified in the Electronics tutorial.

 


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