Experimental and Numerical Investigation of the Blade Tip-Related Aeroacoustic Sound Source Mechanisms of a Ducted Low-Speed Axial Flow Fan

A combined aerodynamic and aeroacoustic study of a ducted low-speed axial flow fan at various operating points is presented herein, focusing on the blade tip-related noise sources. The investigation includes upstream and downstream phased array microphone measurements and computational fluid dynamic simulations. The downstream acoustic measurements are carried out by using an acoustically transparent duct. The resulting flow fields and noise source maps are evaluated simultaneously. The results show that at higher flow rates, the dominant noise source is the turbulent boundary layer - trailing edge noise. At lower flow rates, the dominating noise sources can be found at the blade tip's leading edge. These noise sources are found to be tip leakage flow related. Also, downstream microphone array measurements indicate strong noise sources at the blade tip's trailing edge. These are determined to be a combination of the turbulent boundary layer - trailing edge noise, tip leakage vortex impingement noise, and double-leakage noise.