799,675. Axial-flow compressors and turbines. BRISTOL AERO-ENGINES, Ltd. Oct. 2, 1956 [Oct. 13, 1955], No. 29230/55. Classes 110 (1) and 110 (3). In an axial-flow compressor or turbine, gas is injected into the flow passage through an annular slot or an annular series of slots in a wall of the flow passage, with a component of motion which is directed upstream against the main flow, to reduce the effective flow area in the region of the slot or slots. In the compressor shown, air is tapped off from the delivery or an intermediate stage and passed through conduits 19 and 23 to annular galleries 16 and 22 respectively, from which the air is injected into the flow passage in an upstream direction at about 60 degrees to the compressor axis, through annular slots 18 and 20 respectively (or annular series of slots). The slots, which are of nozzle formation, are adjacent the inlet guide blades 13. The injected air adds energy to the vortices adjacent the tips of the rotor blades 10 which occur at low compressor speeds and which provide a rotating stall pattern, causing the vortices to join up into a single stabilized toroidal vortex. The resultant relative uniform annular stalled zone allows a smooth transition to the fully stalled zone. In addition, the annular zone reduces the effective cross-sectional area available to the main flow, thereby increasing the velocity of the main flow in the inlet stages of the compressor. This improves the matching between the inlet stages and the later stages so that a wider flow range is possible before surging occurs. The injection of air may take place from the outer wall only of the flow passage, either upstream or downstream of the inlet guide blades, or from both the inner and outer walls at a common radial plane upstream of the inlet guide blades. Where the maximum efficiency of the compressor is designed to occur at partial loading, air may be injected immediately upstream of the shortest rotor blades of the compressor, so that the tips of these blades are stalled at speeds above the design speed. The capacity of an axial-flow turbine can be reduced, for example for improving its matching with a compressor in a gas turbine engine at a speed below the design speed, by injecting gas into the turbine flow passage, preferably between a stator blade ring and the next downstream rotor blade ring. The gas may be tapped from the main gas flow passage of the turbine or of the engine or taken from another source. In either a compressor or a turbine, the supply of air or gas to the slot or slots may be controlled by a valve which closes progressively with increase of speed or with increase in the rate of delivery of fuel to the gas turbine engine. The blades may be shrouded.
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