A joint experimental and numerical study has been achieved on a low-speed axial ring fan
in clean inflow. Experimental evidence shows large periodic broadband humps at lower
frequencies than the blade passing frequencies and harmonics even at design conditions.
These sub-harmonic humps are also found to be sensitive to the fan process and
consequently to its tip geometry. Softer fans yield more intense humps more shifted to lower
frequencies with respect to the fan harmonics. Unsteady turbulent flow simulations of this …