GB1078112A - Improvements in and relating to impeller blades and impellers for fans and the like machines - Google Patents

Abstract

1,078,112. Centrifugal blowers and compressors. AEREX Ltd. Jan. 30, 1964 [Feb. 22, 1963], No. 7279/63. Heading F1G. An impeller blade for a radially outward flow blower, compressor or the like, has a radially inner surface formed with a chordal contour comprising three curved parts, each of substantial chordal extent, the parts being an intermediate concave part, a convex leading edge part and a convex trailing edge part (which may be curved throughout or may have a plane or flat face towards the trailing edge). The blade is disposed with its chord at an angle to the radial direction, so that the surface 1 is the radially inner surface. The surface 1 has convex portions 2 and 3 adjacent the leading edge 7 and trailing edge 9, respectively, with a concave intermediate portion 4. At midchord, the distance between the surface 1 and the chord is preferably not greater than 0À45 of the chord. A mathematical expression for the contour of the surface 1 is given in the Specification. A close approximation can be obtained by joining end to end three suitably located circular areas of approximately equal radius. The radially outer surface may, as shown, be convex over the greater part 6 of its length from the leading edge 7, with a plane or concave part 8 adjacent the trailing edge 9. For good performance and low weight, the maximum thickness D should be between 0-05 and 0À10 of the blade chord. The thickness may be locally increased to take fixing screws. The included trailing edge angle # should be between 6 and 12 degrees. The leading and trailing edges should be rounded off, with a radius of between 0-0050 and 0À010 of the blade chord. The blade may be cast, machined from solid stock or machinefinished from an extruded blank. Alternatively, the blade may be rolled or pressed from a plate or lamina so that it is of constant thickness with the radially outer contour similar to the radially inner contour. The blade may instead be of constant thickness over the extent of the concave intermediate part, the portions of the radially outer surface adjacent the leading and trailing edges being machined flat.