| 摘要 |
A large air moving fan has a number of hollow airfoil blades extending generally radially from a rotatable hub. The tips of the blades are surrounded by a circumferential shroud leaving a narrow gap between the tips of the blades and the shroud. A fin on the tip of each blade extends substantially perpendicular to the transverse cross section of the blade. The outline of the fin corresponds approximately to the shape the airfoil at the tip of the blade and the fin is curved so as to be substantially parallel to the shroud. It is believed that the fin prevents direct radial flow of a boundary layer of air from the outside surface of the blade into the gap between the tip of the blade and the shroud. This reduces the turbulence adjacent to the tip of the blade since the air traveling radially along the blade does not mix as violently with air passing through the gap from the high pressure side of the fan to the low pressure side of the fan. Noise reduction in the order of 3 db is obtained. Further noise reduction is obtained by sealing any gap between the fin and the end of the blade for preventing air leakage adjacent to the fin. A vent, however, is provided for venting air from within the blade to the outside of the blade in a direction substantially along the concave surface of the blade.
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