2. The acoustic model of the pump was also used to determine the
ideal sound sources that generate acoustic fields equivalent to
the sound emission by fluid-dynamic blade–tongue interaction
at different flow-rates. For flow-rates below nominal, the ideal
sources identified were two monopoles closely located at the
tongue region of the volute that approximately behave like a
dipole. For nominal and high flow rates, the ideal sources are
two dipoles also located at the tongue region of the volute,
which behave approximately as a lineal quadrupole.