Setting Up a User-Defined Noise Source

Monopole (the pressure field is defined for a single cell), dipole (two cells), and quadrupole (four cells) noise sources are typical examples of user-defined noise sources.

For example, the analytical expression of the monopole source is:

where:

• $A$ is the amplitude.
• $R$ is the radius.
• $\omega =2\pi f$ and $f$ is the frequency of the source.
• $r$ is the radial location in the domain.
• $k=\omega /c$ and $c$ is the speed of sound.

The corresponding field function that you need to apply for the monopole source is:

where $V$ is the cell volume.

As a monopole source is a point source, the acoustic source definition in this case needs to be divided by the cell volume (in order to make it free of volume), since the noise sources on the right-hand side of the wave equation undergo a volume integration using the finite volume method:

• Acoustic perturbation-based source: $-\frac{1}{c^2}\int \frac{{\partial }^2{P}^{\prime }}{\partial t^2}dV$
• User-defined source: $\int S_{\text{user}}dV$

Ideally, the monopole source should be a sphere or a point source, but this is not possible with a finite volume mesh. For this reason, expect to see some difference between the analytical and computational solution.

The acoustic pressure field that is generated by the monopole source is illustrated below:

To set up a user-defined noise source: