Patent GB-933222-A (GB)
Title: Improvements relating to axial-flow blowers
IPC: B64C21/04
Filed: 1959-07-31
Abstract: 933,222. Turbines; axial-flow blowers. N. LAING. July 31, 1959 [Aug. 1, 1958], No. 26284/59. Classes 110 (1) and 110 (3). [Also in Group XXXIII] An axial-flow blower comprises a rotor mounted for free rotation and having at least one blade, openings in the trailing portions of each blade for the ejection of air from the blade to produce a " jet flap " effect and also to drive the rotor by reaction, and an auxiliary blower disposed in the rotor to supply air to each blade under pressure. The " jet flap " effect is that already proposed for use in aircraft, wherein air is ejected from a slot at the trailing edge of an aerofoil to form an air jet having the effect of a flap but with greatly reduced losses. The air jet increases the lift of the aerofoil and reduces flow separation on the suction side of the aerofoil. Figs. 1 and 2 show a ceiling fan rotor 9 comprising a pair of blades 10 carried by a hub 11 supported by ball-bearings 12 for free rotation about a housing 1. A double-entry centrifugal impeller 8, driven by an electric motor 2 and supported by ball-bearings 4, draws in air through a port 16 in the trailing edge of each blade tip, via a channel 14 in each blade and a central space 17 in the hub 9. In addition, some air is drawn into the central space 17 through holes in the wall of the housing 1, as shown by arrow 17a, passing over the motor 2 to cool it. The impeller 8 discharges through channels 15 in the blades to slots 19 formed along the trailing edges of the blades, the slots 19 being directed for ejection of air rearwardly and slightly downwardly with respect to the blade chord, to cause rotation of the rotor 9 by jet reaction and to produce a " jet flap " effect which improves the circulation around each blade and hence the lift. The removal of air from the blade tips through the ports 16 reduces eddying at the tips and consequent noise. Further noise-suppression is effected by soundabsorbing means 21, 22 in the channels 14, 15. Fig. 4 shows a ceiling fan rotor 40 supported for free rotation on a post 41 and comprising a single hollow blade 42 counterbalanced by a blower 43 and its driving motor 44. The blower draws in air at 46 and discharges it through a slot 47 along the trailing edge of the blade. The slot 47 is so constructed that more air is discharged through its outer part 49 than through its inner part 51. The major part of the reactive thrust is associated with the outer part 49 where, moreover, the moment arm is longer; while the " jet flap " effect has its major influence at the inner part 51, where breakaway of flow is more likely. In a further embodiment, a two-bladed fan used in a cooling tower is supplied with air for propulsion and " jet flap " effect by an electrically-driven axial-flow blower projecting within the fan hub. The guide blades of the blower are supported by and within the fan hub. The major part of the air leaves the fan blades at their outer region, at only a slight angle to the plane of rotation, to produce a strong reactive drive, while a minor part leaves the blades at their inner region, at an angle to the plane of rotation which increases towards the fan hub for the purpose of preventing breakaway of flow at the inner region.