| 摘要 |
PROBLEM TO BE SOLVED: To reduce noise by providing a plurality of spherical concave portions of a predetermined size on the fin surface of the impeller such that the turbulence of the discharged airflow is reduced, and thus reducing the air resistance at the discharge portion. SOLUTION: A plurality of spherical concave portions c having diameters of approximately 0.5 mm to 3 mm, and depth of approximately 0.2 mm to 1 mm are provided on surfaces of each fin b of an impeller portion 5. Generally, when air parts from a spherical surface, turbulence acting as an air resistance is generated. The amount of turbulence generated is smaller when a separation point is located toward the back. By providing the spherical concave portions c on the fin b surface of the impeller 5, the separation point is pushed back, which narrows down a range of a turbulent swirl at the air discharge portion. Accordingly, a turbulent flow acting as the air resistance is reduced. As described above, providing a plurality of spherical concave portions c having diameters of approximately 0.5 mm to 3 mm and depth of approximately 0.2 mm to 1 mm narrows down the separation point at which turbulence of airflow by swirl on the surfaces of each fin b is generated, reducing air resistance, and thus reducing noise.
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