GB1265761A - - Google Patents

Abstract

1,265,761. Boundary layer control. NATIONAL RESEARCH DEVELOPMENT CORP. 19 Dec., 1969 [3 Jan., 1969], No. 557/69. Heading F2R. [Also in Division F1] A fan or the like, e.g. for cooling automobile engines, comprises a rotor which is mounted in a cylindrical duct 2, Fig. 2, and has radiallyextending blades 3 with spanwise-extending apertures 7 therein for discharging fluid substantially tangentially over the blade outer surfaces. The blades are hollow and of substantially circular cross-section as shown, and may be interdigitated with blades of aerofoil crosssection with or without discharge apertures. The aperture 7 is in the trailing region of each blade relative to the direction of rotation, so that during operation the air flow around the blades induces air from within the blades to flow through the apertures 7, the latter flow drawing air through the duct 2. The ratio of mean aperture width to blade chord may be 0À01. The aperture width may vary radially from a minimum at the hub 4. Each blade may have more than one aperture, and the apertures may be arranged to discharge in opposite directions at will for reversing the flow through the fan without reversing the direction of rotation. Each blade may be provided with diametricallyopposite slots at its tip for fluid flow therethrough to reduce losses at the tip. The flow circulating in or around the duct 2 may be controlled by discharge of fluid through at least one aperture formed in the duct wall. The air flow through the aperture 7 and thereby the flow through the fan, can be controlled by a valve 8. In an alternative embodiment, Fig. 4 (not shown), the air flow through the apertures is delivered thereto by a vane-type compressor (9) and is controlled by a valve (10) arranged upstream of the compressor.