Improved Noise Performance of Tubular fan with New Casing

The tubular fan is sometimes used to obtain the high pressure in axial flow equipment. The fan is consisted of the centrifugal impeller and axisymmetric casing. The air flows onto the impeller from the center of impeller and turns to radial direction in the impeller. The radial directional flow makes the large pressure rise in the impeller. After the impeller, the air turns to axial direction again. The flow pattern in the tubular fan is so complex that the large loss and noise are generated in the fan. We analyze the flow characteristics of the tubular fan with numerical simulation and pointed out the casing geometry that is composed of the constant radius cylinder is not suitable for the tubular fan. It is not obtained the sufficiently pressure recovery in the casing that the separation and reverse flows are occurred. The new geometry casing is proposed that is based on the concept of the diffuser effect. The spiral flow diffusion is considered that is included the centrifugal effect. It is obtained about 10 % large pressure rise and 2 to 5 dB(A) low in SPL(A) with the new casing compared to conventional casing.