6.4. Minimal Pressure Reflection Boundary

The minimal pressure reflection (MPR) approach is based on the treatment for boundary conditions proposed by Azab and Mustafa [1]. In Ansys Fluent, the MPR method has been modified using AI techniques in order to minimize pressure-wave reflections from the boundary, but not eliminate them completely. The amount of reflectiveness is carefully optimized in order not to contaminate the solution.

The MPR approach uses a linear system of equations consisting of Euler equations in full nonlinear multidimensional form, the MPR condition, and boundary conditions. The pressure variation at the MPR boundary can be expressed in terms of variations of conservative variables for any gas law:

(6–1)

where

where is density, , , and are , , and velocity components, respectively, and is total energy.

The term is used in the MPR condition to minimize the pressure wave reflection from the boundary were it is applied.

Note the following limitations when using the MPR treatment:

  • The MPR treatment is available only for the density based solver.

  • The material of the working fluid should be compressible.

  • Currently the MPR treatment is available for the following boundary conditions:

    • pressure inlet

    • pressure outlet

    • velocity inlet

The procedure for assigning the MPR condition to selected boundary faces is as follows:

  1. Enable beta feature access as described in Introduction.

  2. Enter the following text command in the console:

    solve/set/advanced/non-reflecting-boundary-treatment

    The text submenu of the available boundary types is printed in the console:

    • pressure inlet

    • pressure outlet

    • velocity inlet

  3. Select the boundary types where the MPR treatment will be applied during a simulation, and at the prompt, enable or disable the MPR treatment. For example:

    solve/set/advanced/non-reflecting-boundary-treatment pressure-inlet

    Enable minimal pressure-reflection treatment? [no] yes

  4. For boundaries where you want to use the MPR treatment, enable the non reflecting option for the acoustic wave model either in appropriate boundary condition dialog boxes or in the text user interface (TUI).

Bibliography

[1] M. Azab and M. I. Mustafa. "Numerical solution of inviscid transonic flow using hybrid finite volume-finite difference solution technique on unstructured grid". Aerospace Sciences and Aviation Technology. 14. 1–9. 2011.