Phased array microphone measurement of a ducted low-speed axial flow fan at various operating points with the involvement of the acoustically transparent duct technique

The aeroacoustic investigation of ducted turbomachines is not evident. Wall-mounted and strut-mounted microphones placed in the flow field are both sensitive to installation, placement, and flow-related effects. Therefore, it is advantageous to place the microphone sensors outside of the ducting of the turbomachine while also accounting for the acoustic characteristic of the ducting. In this paper, a ducted low-speed axial flow fan is investigated with the acoustically transparent duct (ATD) and the phased array microphone (PAM) Rotating Source Identification (ROSI) beamforming techniques at design and off-design conditions. The combination of these methods is capable of identifying the dominant sound sources of the fan in a non-intrusive approach at stall condition, pre-stall operation, design condition, and part-load operating condition as well.