| 摘要 |
By suppressing generation and growth of a blade tip vortex at that portion of a blade outer circumference which is not surrounded by a bellmouth, the noise (i.e., the operating sound), as might otherwise be generated when the blade tip vortex and a fan guard collide, is reduced. The setting is made so that H1/H0 = 0.40 to 0.65, where the height of the portion overlapping the outer circumference portion (P) of a blade (13) Out of the axial heights in the bellmouth (5) is designated by H1 and the axial height of the outer circumference portion (P) of the blade (13) is designated by H0. With this setting, the growth of the leakage current (i.e., the blade tip vortex) from the positive pressure face to the negative pressure face of the blade (13) is suppressed at that portion of the outer circumference portion (P) of the blade (13) which is not surrounded by the bellmouth (5), while keeping the suction flow from the outer circumference portion (P) of the blade (13).
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