At this point, you will have either the source data saved to files or the sound pressure signals computed, or both. You can process these data to compute and plot various acoustic quantities using FLUENT's FFT capabilities. See Section 28.10 for more information.
Writing Acoustic Signals
If you chose to perform the acoustic calculation "on the fly'', you will need to write the sound pressure data to files. To do so, select Write Acoustic Signals under Options in the Acoustic Signals panel (Figure 21.3.6) and then click Write. The computed acoustic pressure will be saved from internal buffer memory into a separate file for each receiver you defined in the Acoustic Receivers panel (e.g., receiver-1.ard).
Solve Acoustic Signals...
Reading Unsteady Acoustic Source Data
Computing the sound pressure signals using the source data saved to files is done in the Acoustic Signals panel (Figure 21.3.6) .
Solve Acoustic Signals...
To compute the sound data, use the following procedure:
| You can use any number of source data files. However, note that you should select only consecutive files.
Optionally, you can click the Receivers... button to open the Acoustic Receivers panel and define additional receivers.
| If you enabled both the
Export Acoustic Source Data and
Compute Acoustic Signals Simultaneously options in the
Acoustics Model panel, you will need to first select the
Write Acoustic Signals option in the
Acoustic Signals panel after the flow simulation has been completed. If you select the
Read Unsteady Acoustic Source Data Files before writing out the "on-the-fly'' data in such a case, the data will be flushed out of the internal buffer memory. To avoid such a loss of data, you should save the
FLUENT case and data files whenever you begin to do an acoustic computation in the
Acoustic Signals panel. The sound pressure data calculated "on the fly'' will then be saved into the
.dat file. Finally, after the "on-the-fly'' data is saved, make sure to change the file names of the receivers before doing a sound pressure calculation with the
Read Unsteady Acoustic Source Data Files option enabled, to avoid overwriting the "on-the-fly'' signal files.
| Note that you can compute and write sound pressure signals only when the FW-H acoustics model has been enabled. See Section
21.3.1 for details about exporting source data (e.g., for SYSNOISE) without enabling the FW-H model.
Pruning the Signal Data Automatically
Before the computed sound pressure data at each receiver is saved, it is by default automatically pruned. Pruning of the receiver data means clipping the tails of the signal where incomplete source information is available.
The acoustic source data is tabulated from time
. Without auto-pruning, the receiver register begins receiving the earliest sound pressure signal at
, the sound accumulated on the receiver register does not include the contribution from the entire source surface area, and thus the sound pressure data received during that time is not complete. The same thing occurs during the period from
define models acoustics auto-prune text command.
Although auto-pruning can be disabled, it is expected that you will use only the complete sound pressure data.
Reporting the Static Pressure Time Derivative
The RMS value of the static pressure time derivative ( ) is available for postprocessing only on wall surfaces, which are at the same time sources of sound, when the FW-H acoustics model is used.
You can select Surface dpdt RMS in the Acoustics... category only when you specify at least one wall surface, which is also marked as an acoustic source, in the relevant postprocessing panels.
Using the FFT Capabilities
Once the sound pressure signals are computed and saved in files, the sound data is ready to be analyzed using FLUENT's FFT tools. In the Fourier Transform panel (Figure 28.10.1), click on Load Input File... and select the appropriate .ard file. If the receiver data is still in FLUENT's memory, then it can directly be processed using the Process Receiver option. See Section 28.10 for more information on FLUENT's FFT capabilities.