| 摘要 |
PURPOSE:To enable to lower the noise level of a fan, by forming recesses on the surface of a hub portion of an impeller, and producing noise silencing effect by the resonance function of the recesses. CONSTITUTION:A plurality of recesses 14 having an adequate depth are formed in the surface of a hub portion 12 of an impeller to extend substantially perpendicularly to the surface of the hub portion 12. When the impeller is set into rotation, noises produced by air flowing along the surface 13 of the hub portion 12 between adjacent two blades 11 are absorbed by the recesses 14 formed in the surface 13 which function like resonance tubes and the energy of the noises possessed by the air flowing along the surface 13 is absorbed effectively, so that the noise level of the impeller can be lowered. |
