Fan blade segmentation

When you create a Fan Noise force, each fan blade is automatically segmented into rectangular strips, or segments, for which an acoustic dipole is created at the center of gravity of each strip.

Each fan blade is segmented by the software as a function of the input fan blade geometry, maximum frequency of interest, and the fluid speed of sound. The segment size is selected to be much smaller than the acoustic wavelength to create a compact acoustic load. The CFD pressure-versus-time function is then converted into a force-versus-time function based on the segment area. The fan rotation is defined using the right-hand rule about the fan axis to determine rotation direction, and must always be in the positive sense.

Fan blade segments and dipoles. (1) Fan blade segment, (2) Dipole, (3) Fan rotation axis, (4) Fan rotation direction

Fan blade force versus time

Fan segmentation equation

The maximum fan blade segment size is computed using the formula:

where:

= Fan blade segment size (mm)

= Speed of sound

= Maximum computation frequency (Hz)

= Number of segments per wavelength = 4

Note:

The computed segment size will be smaller than the acoustic wavelength and will be rounded down to the nearest millimeter.

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Fan blade segmentation, Simcenter 3D 2021.1 Series

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