Flow Instabilities and Noise Generation in Vane Axial Fans Due to Rotating Stall and Surge

The main characteristic of axial flow fans is instabilities in their performance and noise characteristics in partial load operation. Those instabilities are a consequence of rotating stalls created in the rotor blade and/or in guide vane cascade. At some operation conditions the rotating stalls caused an appearance of surge representing the lowest region of fan operating stability. The rotating stalls and especially the surge appearances caused a steep increase in the emitted noise and lowered the performances of the fan. The present paper highlights the rotating stall generation phenomena and its influence on the emitted total noise level and noise spectra at axial flow fans with inlet and outlet guide vanes.