From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Patent specification for a prime mover with a two-stage, double-intake centrifugal compressor.
| Identifier | ExFiles\Box 147\2\ scan0195 | |
| Date | 24th July 1936 guessed | |
| 4 461,887 losses depend upon the area of internal surfaces swept by the working fluid, and it therefore follows that an increase of mass flow without any corresponding in- 5 crease of swept surfaces will reduce the proportion of loss due to this cause. Shock losses can be kept down chiefly by careful design, but it is believed that the proportion of this loss will also be 10 diminished if the mass flow is increased without any corresponding increase in size. As bearing friction is independent of the mass flow, it is obvious that the pro- 15 portion of this loss will decrease with in- crease of mass flow. It is therefore the chief purpose of this invention to provide a gas turbine in which the mass flow of working fluid is far greater in propor- 20 tion to the size of the components than has ever previously been contemplated. According to this invention a prime mover of the type described comprises a centrifugal compressor having two in- 25 takes, one on each side of the plane of rotation of the impeller. In a preferred form of the invention, the prime mover comprises two first-stage, double-intake, centrifugal compressors 30 each supplying one intake of a second- stage, double-intake, centrifugal com- pressor. According to another feature of this in- vention, the working fluid delivered from 35 the compressor is divided, one part going to one or more turbines to give the useful power and the other part going to one or more turbines to drive the compressor or compressors. Alternatively the working 40 fluid may be delivered to a single turbine which provides the useful power and also drives the compressors; as further alterna- tives the working fluid may be delivered to two or more turbines in succession, one 45 or more of which provides useful work and the other or others drives the com- pressor; also as a further alternative the working fluid may be delivered to a tur- bine having two oppositely-rotating 50 wheels, one delivering useful power and the other driving the compressor. Other features of the invention will be described with reference to the accom- panying drawing which is a diagrammatic 55 representation of one embodiment of the invention. The compressor as illustrated is a two- stage centrifugal compressor of which there are two similar units indicated 60 generally by the reference 10, 11 to effect the first stage of compression. Each of these units comprises an impeller 12 and a casing 13 formed with strengthening ribs 14, and is of the general form described 65 in the specification of my co-pending patent application No. 14285/35. Each of these units is provided with a fluid in- take 15, 16 on each side of the plane of rotation of the impeller, and the impeller 70 delivers fluid into a primary diffuser 17 which takes the form of a bladeless radially-disposed chamber communi- cating with a volute 18. This volute or scroll 18 delivers the partially compressed 75 fluid through a suitable conduit 19, which acts as a second diffuser, to the intake of the second-stage centrifugal compressor indicated generally by the reference 20. This unit 20 is situated between the two 80 units 10, 11, and is also of the double- intake type, each intake being served by one of the first-stage compressors. The conduit 19 aforesaid communicates with a volute chamber 21 which opens into the 85 annular intake 22 of the second-stage com- pressor. The impeller 23 delivers the compressed fluid through a diffuser cham- ber 24 to a volute or scroll chamber 25. The three impellers are arranged co- 90 axially and their construction is prefer- ably similar to that described in my speci- fication No. 14285/35 aforesaid, and the whole assembly is driven by means of a turbine at each end. The compressor unit 95 is therefore of symmetrical construction comprising a central second-stage com- pressor, a first-stage compressor on each side of it, and a turbine beyond each first- stage compressor. 100 In the arrangement illustrated some of the compressed air from the volute 25 of the compressor 20 is delivered into a helical combustion chamber 26 in which there is provided a fuel burner; the first 105 part of this combustion chamber may be of tapering form so as to constitute a secondary diffuser for the compressor 20, and the discharge end of the chamber which may incorporate a nozzle, delivers 110 the heated fluid to a volute chamber 27 supplying a turbine nozzle 28 which delivers the gas to the buckets or blades 29. The working fluid then passes to the exhaust through a suitable conduit 30. 115 The turbine blades are preferably specially adapted to withstand high work- ing temperatures, and the rotor is prefer- ably cooled by providing water-jackets closely adjacent to it. One of these 120 which also cools the bearing is shown at 31, and another water-jacket 32 is arranged in close proximity to the outer face of the turbine rotor; this jacket is formed on a filling-piece 33 in the exhaust 125 conduit 30 which is shaped so as to pro- vide a diverging exhaust for the gases to reduce back pressure on the turbine blades; internal ribs or flanges 34 may be used to control or direct the flow of the 130 cooling water. [Page 5] 5 The compressor unit 20 as stated above supplies the working fluid to each of the two turbines which drive the compressor units, and it also delivers the remainder 5 of the working fluid through a combustion chamber 35 to a useful power turbine which is mechanically independent, that is to say has no interconnecting mechan- ism with the compressor; it may be 10 situated away from the compressor in any convenient location and, in general, it is of similar construction to the turbines driving the compressor, or in accordance with the work it has to perform. 15 It will be seen that in this arrangement the working fluid is divided into three parts which flow in parallel respectively to the two small turbines driving the com- pressor and to the larger turbine deliver- 20 ing the useful power; the useful power turbine being mechanically independent of the compressor may, if desired, be made to rotate in the opposite direction in order to cancel out gyroscopic torques. Each 25 turbine is preferably fed from a single combustion chamber which discharges into the delivery channels 27, 36 so that the gases are fed to the bucketed wheels uniformly around the periphery, 30 thus securing full peripheral admission in furtherance of the general object of the maximum mass flow in pro- portion to size. The arrangement above described permits of very considerable 35 latitude in design, since for example, a number of compressor units may feed a single power wheel, or one compressor unit may feed several power wheels. Other arrangements of these principal 40 components are, however, possible. In the arrangement already described the whole of the expansion takes place in one pressure stage, but is divided between the three turbines shown. 45 Possible alternative arrangements are as follows:— (a) The whole of the expansion may take place in one pressure stage through a single turbine wheel, in which case a 50 two or three row Curtis wheel would be preferable. It is probable that with this arrangement it would be necessary to drive the compressor or compressors through gearing. 55 (b) Two stages of expansion may be em- ployed, one stage being sufficient to pro- vide the power necessary to drive the com- pressor or compressors, and the remainder for providing the net output of the engine, 60 turbines being used to transform the energy of each stage. (c) The whole of the expansion may take place in one pressure stage, and the whole of the working fluid passes through 65 two oppositely-rotating wheels in suc- cession, the said wheels being either con- nected by gearing or not connected at all, one being used to drive the compressor, and the other to provide the useful 70 power. Various ways of controlling the power unit may be provided, but it is preferred to effect control by variation of the fuel supply in conjunction with automatic 75 speed regulation. It is desirable that the speed of the compressor unit should remain constant irrespective of the load conditions of the power wheel and a speed governor on the compressor unit may be 80 used to regulate the proportion of the working fluid passing to the useful power turbine, or to regulate the proportion of the expansion taking place through the turbine of the compressor unit, when a 85 series arrangement of turbines is used. Any desired arrangements may be used for starting the engine, but it is preferred to provide means for speeding up the rotors of the compressor unit by the appli- 90 cation of independent power, with the turbine nozzle valves fully closed so that the mass flow is prevented until a suit- able speed of rotation has been attained; thereafter the admission of a small quan- 95 tity of air and the ignition of the fuel jet is sufficient to effect the starting of the compressor unit. The starting of the useful power turbine may then be achieved by opening its nozzle valve and 100 increasing the fuel supply. This invention provides a prime mover which, by virtue of its design and arrangement, permits a very high mass flow of working fluid, and therefore has a 105 high power weight ratio; as such it is suitable for use in aircraft, but its design is primarily intended for general use as a prime mover. Having now particularly described and 110 ascertained the nature of my said inven- tion and in what manner the same is to be performed, I declare that what I claim is :— 1. A prime mover of the type described 115 comprising a centrifugal compressor hav- ing two intakes, one on each side of the plane of rotation of the impeller. 2. A prime mover of the type described comprising two first-stage double-intake 120 centrifugal compressors each supplying one intake of a second-stage double-intake centrifugal compressor. 3. A prime mover according to claim 1 or claim 2 wherein the working fluid 125 delivered from the compressor is divided, one part going to one or more turbines to give the useful power, and the other part going to one or more turbines to drive the compressor. 130 4. A prime mover according to claim | ||