Study on the Effects of Concave Volute Tongues on Aerodynamic Performance and Noise of a Multi-Blade Centrifugal Fan

Two types of volute tongue are designed for a multi-blade centrifugal fan used in range hoods. One is an inner concave arc volute tongue and the other is an inner concave grooved volute tongue. The effects of the inner concave volute tongues on both the aerodynamic performance and the noise of the multi-blade centrifugal fan are studied by using the measurement and numerical simulation methods. Compared with the traditional tongue, the impact of the air flow discharged by the impeller on the surface of the volute tongue is weakened and the inverse pressure gradient of the flow field near the volute tongue is reduced when the inner concave arc and the inner concave grooved volute tongues are used. Under the condition that the total pressure and operating efficiency of the multi-blade centrifugal fan keep constant, the aerodynamic noise is reduced. Experimental results show that the sound pressure level of the multi-blade centrifugal fans with the inner concave arc volute tongue and the inner concave grooved volute tongue goes down by 1.4 dB and 1.7 dB, respectively. At the same time, the effective flow area at the fan outlet increases because the flow separation occurred near the volute tongue is suppressed. The vortex intensity and the corresponding influence area are reduced. These results show that the flow rate of the multi-blade centrifugal fan with the concave volute tongues effectively increases.