Patent GB-825967-A (GB)
Title: Improvements in turbines and in particular gas turbines
IPC: F01D5/18
Filed: 1957-03-25
Abstract: 825,967. Turbine blades; cooling gas turbines. POUIT, R. J. March 25, 1957 [March 28, 1956; July 10, 1956],No. 9772/57. Class 110(3). In a turbine means are provided for producing along at least a portion of the surface of at least some of the rotor blades, a laminar flow of a gaseous fluid cooler than the turbine working fluid, the blades being so disposed as to produce an acceleration of the turbine working fluid sufficient to stabilize the laminar flow. Means are also provided to prevent gas leakage between the tips of the rotor blades and the turbine stator. The blade 1 shown in Fig. 1 has a pair of shields 2 disposed along its leading edge, fluid under pressure being supplied through ducts 4 to the passages between the shields and the blade proper, the fluid discharging through gaps 3 and flowing over the concave and convex surfaces of the blade so as to provide a cool insulating layer between the turbine working fluid and the blade. The shields 2 are secured by means of a pin 29 which engages extensions of the shields which are entered in a slot 31 in the blade proper. The shields are also supported by means of flanges 32 thereon which are secured to the rotor periphery. A further supply of insulating fluid from the duct 5 issues through a slot 6 formed by a further shield 7 mounted on the convex side of the blade. The trailing edge of the blade is formed by a hollow member 9 to which fluid under pressure is supplied through ducts 10. The hollow member 9 and the shield 7 are supported by pins 29 and flanges 32 similarly to the shields 2. The means to prevent leakage of working fluid past the blade tips is shown in Fig. 21 and comprises an annular chamber formed in the stator casing 11 around the rotor blade tips, a ring member 12 of graphite being supported in the annular chamber closely adjacent the rotor blade tips so that no damage will occur should the blade tips come in contact with the graphite ring. Fluid under pressure discharging from the hollow member 9 causes any working fluid which has flowed in the clearance space 14 between the blade tips and the graphite ring to flow around the passage 15 and then to rejoin the working fluid flowing into the spaces between the rotor blades. In Figs. 31 and 32 an annular channel 16 is formed in the stator casing and partitions 18 extend between the hollow portions 9 of the blades. Air under pressure issuing from the hollow portions prevents working fluid leakage across the rotor blade tips. In Fig. 6 a shroud band 34 is secured to the rotor blade tips, the shroud band having apertures 33 through which air under pressure from the hollow members 9 of the blades 1 may pass. In this embodiment atomized liquid such as water is supplied through injectors 46 into the air under pressure passing to the hollow members 9. The shroud band 34 is formed so as to provide an annular expansion chamber 421 in which are disposed vanes 472, also an annular channel 38 in which are disposed vanes 471. The chamber 421 and the channel 38 are connected by ducts 48 and the channel is divided into two by means of a flange 39 of the stator casing. The water droplets in the air are separated out in the chamber 421 and the water passes to the annular groove 38 where it forms a sealing device to prevent leakage of fluid past the blade tips. The acceleration of the working fluid in the passages between the blades which is provided so as to stabilize the laminar flow of the gaseous fluid under pressure, is caused by giving the passages a convergent shape whereby the working fluid undergoes a partial expansion so producing a reaction effect.