Abstract: Aerodynamic noise source generated by tip leakage flow in circumferential skewed axial fans was studied by CFD simulation and experiments under offdesign conditions. Relationship between tip leakage flow and aerodynamic noise was analyzed based on vortexsound theory of low speed homentropic flow. Synergy between acoustic source and tip leakage vortex was discussed. Pressure test on casing wall and acoustic far field test were conducted to find how the different circumferential skewed direction control acoustic characteristics. The results show that the acoustic source generated by tip leakage vortex of circumferential skewed blades is an important noise source under offdesign conditions. The angle between velocity vector and vortex vector controls the strength and the distribution of the acoustic source in tip clearance region. The acoustic source in tip clearance region is related with the acoustic far field under offdesign conditions.

Key words:  circumferential skewed, off-designed, tip leakage vortex, vortex acoustic, synergy