GB877989A - Centrifugal flow turbines - Google Patents

Abstract

877,989. Turbines. AMERICAN MACHINE & FOUNDRY CO. Sept. 24, 1957, No. 44109/60. Divided out of 877,988. Class 110 (3). In the contra-rotating outward-flow steam turbine shown in Fig. 3, the output shaft 32 and a concentric shaft 37 are connected by means of gear teeth 42, 46 and idler pinions 43a so as to rotate in opposite directions. Shaft 37 carries a rotor disc 36, and shaft 32 carries a rotor disc 30a connected through blading 14 to a further rotor disc 30 which in turn is connected through blading 20, disc 31 and blading 92A to a rotor disc 91A. Steam can be bled from the turbine upstream of stator blading 21 through an annular duct 82 and a scroll 9. Convergent stator blading 13 expands the steam to unity Mach number at the trailing edges of the blades, expansion continuing in the divergent flow beyond the blades to increase the velocity to a Mach number of about 1.3. In a preferred mode of operation, this velocity is the highest absolute velocity attained in the turbine, the absolute velocity decreasing through the subsequent rings of rotor blading, but having a constant radial component. Expansion occurs in each ring of rotor blading, the degree of convergence of the rotor blading increasing from stage to stage so as to keep the relative exit velocity at a nearly constant Mach number. The angle of deflection of the rotor blades decreases from stage to stage. The degree of reaction is about 0.5. Diffuser blading 27 discharges the steam to an exhaust scroll 1 which may be insulated from an outer wall 2 by aluminium foil. In a non-preferred mode of operation, the radial component of the absolute velocity increases or decreases from stage to stage. In a modification, the discs 31, 91A are omitted and the stages beyond the bleed duct 82 are of single-rotation type comprising rotor blade rings carried by the disc 36 and alternating with stator blade rings. Fig. 9 shows a gas turbine in which shaft 924 carries a rotor disc 931 while the oppositely-rotating shaft 923 carries a rotor disc 929 which is connected through the last rotor blade ring 916 to a rotor disc 930 carrying all the other rotor blade rings which rotate in the same direction as ring 916. Disc 930 may be extended as shown to rest on a bearing 940. Cooling air is supplied by way of a duct 933, a toroidal manifold 950 and circumferentially-spaced orifices 951, 952 to cooling channels 953 in the first rotor blading row 901. Part of the cooling air is diverted through further orifices (not shown) to a chamber 954, where it cools heatreflecting members 955 before entering cooling channels 956 in the expansion blading 900. The cooling air finally joins the motive gases entering through a central inlet duct 932. Any gases or cooling air leaking past labyrinth glands towards bearings such as 927 are conveyed by a pipe 957 to the exhaust scroll 921. In a modification, the rotor blading is carried by two oppositely-rotating rotor discs, the left-hand disc being connected through the first ring of rotor blading to the inner shaft, and the left-hand disc being carried by the outer shaft. In a further modification, the turbine is of single-rotation type with rotor blade rings carried by a single disc and alternating with stator blade rings. Expansion occurs in both the stator and rotor blade rings. The constructions described in Specification 877,988 in connection with centripetal compressors may be applied to outward-flow turbines.