2

Consider if it is necessary to use a Window Function in the Aeroacoustic Flow Source. This is typically the case if the source domain is not selected in the entire acoustic domain.

3

Solve the flow problem using one of the available fluid-flow Turbulence model type options (LES, DES, or SST-SAS) to resolve the structure of the turbulence. This problem is solved on an appropriate mesh for the flow with appropriate time stepping settings. This typically consists of several steps, for example, first solving a stationary RANS model to get a good initial condition for the transient flow problem. Then the detailed initial flow model (LES, DES, or SST-SAS) has to be solved to get a fully developed turbulent flow. In this step the solution only needs to be stored at the end time. Finally, the flow model (LES, DES, or SST-SAS) is run with the fully developed turbulent flow as initial condition. Here, the solution is stored with an appropriate time resolution defined in the Output times.

4

As an alternative to solving one of the fluid-flow models in COMSOL, the CFD solution can also be imported into COMSOL Multiphysics using CGNS data. For this purpose use The Imported Fluid Flow Interface. The same requirements apply to the quality and time resolution of the CFD data.

5

Map the solution from the CFD mesh to the acoustics mesh (or directly from the imported CGNS data). This is done by using the Transient Mapping study step. The input to this study step is only the Time step Δt used in the CFD study. For imported CGNS data, the time step can be seen in the Information section on the CFD Data (CGNS) function.

6

Transform the mapped flow sources to the frequency domain using the Time to Frequency FFT study step. In the Study Settings for the study step, the End time is set to Tend and Maximum output frequency is set to fmax. In the Time to Frequency FFT study step it is also only the Aeroacoustic Flow Source Coupling that is solved for.