1988 年 54 巻 500 号 p. 883-889
The effect of the tip clearance between the blade tip and the fan casing on the noise generated by a diagonal flow fan is examined over a wide range of the flow rate of a fan and discussed in relation to the characteristics of flow measured at a cross section behind the fan rotor. Wake width, which controls the fan noise level, increases with decreasing the flow rate of the fan, which results in the increase in the noise level. The increase in the tip clearance causes the increase in the wake width especially in the tip region of a fan blade. A method to estimate the wake width by the known quantity of the deviation angle of the flow is proposed and verified experimentally to be useful, which enable us to estimate the noise level even in the low fan flow rate region.