Experimental Study of Noise Reduction in Centrifugal Blowers

Abstract

Several centrifugal blowers with forward, backward, and radial blades have been studied experimentally at various speeds, capacities, and pressures. Attention was concentrated on the methods of noise reduction that are applicable to blowers of any type. It is shown that sound at the blade‐passage frequency and its harmonics may be reduced as much as 12 dB either by locating the cutwater at the optimum clearance from the impeller (0.17 in. in the particular blower described), or by sloping the edge of the cutwater relative to the tips of the impeller blades. These two effects on sound‐pressure level are additive. Broadband aerodynamic noise originating within the impeller may be reduced 1 or 2 dB by twisting of the impeller blades. For the proper amount and direction of the twist, this latter noise‐control measure also results in an improvement of mechanical efficiency (up to 10%) though at the expense of decreased capacity (typically 5%–10%). Further noise reduction is achieved only with decreased efficiency.