Combined acoustic and aerodynamic investigation of the effect of inlet geometry on tip leakage flow noise of free-inlet free-exhaust low-speed axial flow fans

Abstract

The performance and the emitted noise of a free inlet – free exhaust axial flow fan are influenced by the inlet geometry. In the present paper, the effect of bellmouth entries with various sizes on the tip leakage flow (TLF) noise is discussed. The aerodynamics phenomena are investigated using inlet velocity profile measurements and computational fluid dynamics (CFD) simulations. Noise source maps have been derived from phased array microphone measurements using the Rotating Source Identifier (ROSI) beamforming algorithm. The aerodynamic and acoustic data are evaluated in a combined manner. The results showed that with the use of a bellmouth entry of proper size, the TLF can be moderated, the double-leakage flow (DLF) can be eliminated, and the sound pressure level of the emitted noise can be reduced by 5–6 dB.