The computational fluid dynamics(CFD)technique combined with the acoustic analogy theory is employed to study the blade passing frequency(BPF)noise caused by the volute casing surface dipole and the blade rotating dipole in a centrifugal fan. A 3D unsteady turbulent internal flow is obtained by CFD at three different flow rates. The volute surface dipole is extracted based on the FW-H equation and the blade noise is modeled by the Lowson's formula. The multi-domain direct boundary element method is applied to study the noise propagation including the interior acoustic problem and the exterior acoustic problem
and these two models established are coupled together at the casing inlet and outlet openings. It is considered that the interior noise will spread outside through the casing openings by the sound scattering effect of the casing. The results show that the pressure fluctuation on the casing surface had the clear BPF component while there was no obvious BPF fluctuation on the blade. The volute tongue was the main contributor to the BPF fan noise. In addition
the casing noise strength was increased dramatically with the flow rate and the BPF blade noise was smaller than the casing noise
especially at large flow rates.
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references
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