GB827670A - Improvements in or relating to rotors for axial flow fans and the like - Google Patents

Abstract

827,670. Axial-flow fans. DAVIDSON & CO. Ltd. Dec. 19, 1957 [Jan. 23, 1957], No. 2493/57. Class 110 (1). In an impeller for an axial-flow fan or the like, the blade base has an ellipsoidal contour whereby the annular area of the passage decreases from the impeller inlet towards the impeller outlet, the geometrical pitch of the blades progressively increases towards the impeller outlet, and the geometrical pitch does not decrease from root to tip in any one plane which is parallel to the axis of rotation. The geometrical pitch varies from root to tip to equalize the absolute velocities at the outlet from the blades. Fixed impeller blades 13 may be followed by auxiliary blades 29 which may be detachable or adjustable, or both, in the manner described in Specification 702,312. The gap, measured in the axial direction, between the blades 13 and 29, is of the order of 0.01 to 0.03 of the overall chord, and may extend over part only of the radial lengths of the blades. The elliptical contour of the impeller hub 15 is continued by a fairing 30 which may be stationary as shown or may be attached to the hub 15. The blades may be of aerofoil or laminar form, the centroids of the blade sections being such that bending stresses are relieved by the centrifugal forces. The mean camber line may be parabolic or may be curved to a radius which varies from root to tip but is not less than that at the root. The fairing 30 may be omitted, and the impeller blade tips and the adjacent part of the fan casing may have a shape which is inverse to that of the ellipsoidal impeller hub. The impeller blades may have a solidity ratio greater than unity and may overlap when viewed in the axial direction.