Flow Structure around a Polygon Mirror Inducing Aerodynamic Noise

Abstract

Two typical flow structures around the rotating polygon mirror were clarified with a Particle Image Velocimetry and a Laser Doppler Velocimetry measurement under the low rotating speed condition. One is the periodical fluctuating structure generated as a bow-shaped region and a pair of the vortex tubes near at the polygon mirror. This vortex tube structure induces the high frequency noise corresponding to the product of the number of the polygon corners and the number of rotations. The other is the alternative flow structure generated at the outside of the periodical structure (r/d>0.8). This flow structure is considered as one of the causes of the jittering of the polygon rotation. In addition, this flow accompanies the complicated three-dimensional vortices generated by the interaction between the vortex tubes on the outskirts of the alternative flow structure.