Patent GB-785761-A (GB)
Title: Improvements in or relating to axial flow compressors
Inventor: FORSHAW JAMES ROBERT
IPC: F04D29/52
Filed: 1954-09-21
Abstract: 785,761. Axial-flow compressors and turbines. POWER JETS (RESEARCH & DEVELOPMENT), Ltd. Sept. 13, 1955 [Sept. 21, 1954], No. 27259/54. Classes 110 (1) and 110 (3). In an axial-flow compressor having structure forming a circumferentially extending wall bounding the working fluid flow path and rows of blades extending across the flow path, the wall structure comprises a number of wall portions each extending between adjacent blades of one row and each movable from an inoperative position where it complements the adjacent wall parts to afford a substantially smooth flow path to an operative position wherein it protrudes into the flow path to effect a local restriction in transverse area of the path. In the multi-stage compressor shown in Figs. 2 and 3, segmental resilient sheet metal strips 20, slotted as shown in Fig. 3 to accommodate stator blades 6, are secured at the upstream end by rivets or screws 18 within a circumferential recess 16 so as to form between each pair of adjacent blades 6 a wall portion 17 which is normally flush with the inner surface of the compressor casing 2. The portions 17 can be simultaneously bent into the position shown dotted in Fig. 2 by means of plungers 19, Figs. 2 and 4, so as to restrict the area of fluid flow. The plungers 19 are operated by a ring 22 having cam surfaces 24 which engage the heads 25 of the plungers 19. The ring 22 is rotated in a clockwise direction into the operative position by a compression spring 30 and a link 29. A fluid pump driven from the compressor shaft supplies fluid at 34 to a cylinder 33, so as to subject a piston 32 to a pressure which rises with the compressor speed, whereby the piston 32 rotates the ring 22 until it reaches the inoperative position shown at a prescribed proportion of the full load speed. Movement is limited by a stop 36 which engages a collar 31. The control, which may be in accordance with load instead of speed, may be for the purpose of preventing blade vibration due to surging at low loads or for maintaining the matching of the various stages at different load conditions. The flow restriction may be applied to more than one blade row. Fig. 7 shows an alternative construction, in which each wall portion 40 has a cranked end 40a whereby it is pivoted in a deepened upstream part 41 of the recess 16. Alternatively, the wall portion may be hinged at its upstream end. The plunger 19 is loosely pin-jointed to an eye 44 on the downstream end of the portion 40; this feature may also be applied to the first-described embodiment. Fig. 12 shows an arrangement in which wall portions 45 are carried by plungers 46 so as to be bodily movable in the radial direction. According to the Provisional Specification, the restriction of the flow area is effected by three rings which fit into an annular recess in the casing wall so that, in the inoperative position, they are flush at their inner peripheries with the inner surface of the casing. Each ring has diametrically opposed lugs which extend through the casing to limit movement of the ring to that diametrical direction. The lugs on the three rings are spaced equiangularly about 'the casing axis. Movement of each ring is effected by an eccentric which engages a slot in the corresponding lug, the three eccentrics being operated simultaneously by a toothed ring and pinions. The stator blades may have axially sliding roots which are entered into axially extending recesses from the annular recess which receives the rings. The invention may be applied to turbines.