In two-stage jet fan, the sound pressure level and specific noise level of the symmetry blade fan became low compared to that of aerofoil blade fan. In the case of two stage jet fan, the noise of the rear rotor was higher than that of front rotor because the turbulent flow generated from the front rotor flowed into rear rotor and the rear rotor cut the wake generated from a motor support plate. When the case of an airfoil form was attached to circular power cable, the width of wake became narrow and the fan noise was reduced. It was clarified experimentally that the noise characteristics of single-stage jet fan was improved compared to that of the ordinary tow-stage jet fan.
