GB701576A - Improvements in or relating to compressors - Google Patents

Abstract

701,576. Axial-flow compressors. ROLLSROYCE, Ltd. June 26, 1951 [June 28, 1950], No. 16217/50. Class 110 (1). [Also in Group XXIX] When a multi-stage axial-flow compressor is operating below a selected speed which is less than the design speed, additional working fluid is injected into the initial stages to increase the velocity of the working fluid over the radially outer portions of the blades to a greater extent than over the radially inner portions. In an axial-flow compressor which may form part of an aircraft gas turbine plant, the stator blades 12g, Figs. 4 and 5, of each of several of the later stages are attached, as by brazing, to an annular member 17 which, in turn, is attached by flanges 17a to spacer rings 15 carried by the casing 11a. A rotary valve 24 is formed with ports 25 to register with ports 23 in the annular member 17, to permit air to be bled from the later stages by way of ports 19. The air passes by way of longitudinal ducts 33, 34, Fig. 8, and annular ducts 37a, 37b to the compressor inlet, where it is injected over about the outer third of the length of the inlet guide vanes 13 whereby to prevent stalling at low speeds. Valve 24 carries a peg 26 which engages a slot 28, Fig. 7, in 'a bar 29 which is moved longitudinally by a servomotor (see Group XXIX) so as to rotate the valve into the closed position when the rotational speed of the compressor rises above a selected value. The speed at which the valve commences to open may be made slightly different in value, as by making the slot 28 wider than the peg 26. The inlet guide vanes 13 may be of variable pitch as shown, so as to provide increased swirl at rotational speeds below the selected value. The vanes 13 are interconnected by radius arms 45 which engages a notched rotatable ring 46, and the spindle 40 of one vane is connected by a radius arm 42 to a servomotor 31. Preferably, the injection of additional air and the adjustment of vanes 13 are done simultaneously, but may instead be done consecutively, in which case the adjustment preferably takes place at a higher speed than the injection. Instead of the rotational speed, the control factor may be an operational variable dependent on the rotational speed, such as the corrected rotational speed (corrected, that is, for temperature variations), the delivery pressure or the pressure ratio. Thus, the control means may comprise a diaphragm or capsule subjected to the delivery pressure or two diaphragms or capsules subjected respectively to the delivery and intake pressures and connected to opposite ends of a pivoted beam which will be rocked when the pressure ratio. passes through a selected value. Instead of being bled from later stages, the additional air injected into the intake may be obtained from a separate source.