| 摘要 |
A disc shaped impeller may comprise an upper face and a lower face. Concavities may be repeatedly arranged along a circumferential direction on the upper face and the lower face. Each concavity may include a front surface, a back surface, an inner surface, an outer surface and a bottom surface. Each front surface may include a front-inner area formed between an inner edge of the front surface and a middle portion of the front surface. Each front-inner area may be formed in a convex shape when viewed as a longitudinal cross-section. The longitudinal cross-section is defined as a cross-section through a longitudinal plane disposed so as to be aligned along the circumferential direction. |
