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Aviation History
1955
1955 - 1079.PDF
5 August 1955 191 flame round to the other three. The combustion system has beendesigned to operate on either kerosine or wide-cut type fuels. The performance of the whole system so far has been most satis-factory and, on one engine, the cans have not yet been removed at 400 hr. The rear of each combustion chamber forms the turbine-inletcasing, the inner gas passages being formed from thin Nimonic sheet, run at high temperature and carrying no load apart from thatdue to the dynamic head of the gas and a very small pressure differential. Air flows around the outside of these casings, passesbetween the turbine casing and shroud, through a final restrictor and mixes with the main products of combustion further down-stream. The nozzle rings themselves are thermally free to expand, being mounted on radially sliding dogs, anti-rotational pins be-ing employed to take the gas reaction on the blades. The second- stage nozzle blades have inner and outer platforms and are boltedto the external casing. Both stages of blades are cast in X40 material, a tungsten alloy resembling high-speed steel. Owing to the unusual purpose of the Oryx, the turbine has tooperate against a high back pressure, and the leaving velocity and swirl are such that the diffusion required upstream of the collectorvolute is small. Two reaction-type stages are employed, with an expansion ratio of 3.14:1. The two discs are machined fromforgings in DNS 116 steel (a Napier specification) mounted over flank-fitting splines on a relatively short shaft supported at thefront by a roller bearing and at the rear by a ball bearing. These two bearings are carried by strong tubular radial struts, the frontset of struts being attached to the exterior tubular frame of the engine and the rear row to the turbine discharge casing. As in the Eland, the turbine section can readily be broken upinto units; for example, a seal failure during test-running was repaired in situ on the bed with a minimum loss of time. Therotor blading is of Nimonic 90 in the first stage and of Nimonic 80A in the second. The blades are attached by fir-tree rootswhich permit limited tip-rock to allow for differential expansion of the blades and discs. The first-stage blades are carried onextended platforms and a segmented ring is arranged around the first-stage rotor, the segments acting as "fire bricks," air blowing asa blanket between these segments adjacent to the blades and the cool casing. In any gas turbine the pressure drop is far higher across thenozzles than across the turbine discs themselves and, in conse- quence, there remains a large unbalanced end-load across thedisc in line with the inter-stage nozzle blading. A labyrinth seal is incorporated at this point and, in order to maintain the maxi-mum concentricity of this seal at all temperatures, the disc itself is mounted on swinging links for limited radial movement.To the rear of the turbine the gear-type coupling shaft already described transmits the drive to the four-stage auxiliary com-pressor. In spite of the low pressure ratio required (1.80:1) this number of stages was selected in order to obtain a compressorwith a high efficiency (values of the order of 90 per cent having been obtained on test) and with wide-range characteristics. Thewhole assembly, including the balance-piston and seals, is mounted on a splined shaft and is clamped together by means of ring nuts.Conventional bearings are employed, ball at the inlet and roller at the outlet end. Both bearings are pressurized with clean airfrom the sixth-stage filter (this air is dumped into the shaft and out through the normal breathing channel to the auxiliary intake)and the roller bearing is, as previously mentioned, in the same chamber as the rear turbine bearing, to ensure oil-mist lubrica-tion of the coupling-shaft gears. As in the main compressor, all blading is of Hidurax 1/12Aaluminium-bronze alloy, the rotor blades being secured by fir- tree roots to steel discs. All four stator stages are shrouded, thecomplete assemblies being bolted into the upper and lower halves of the RZ5 magnesium-zirconium alloy casing. Owing to the factthat, in the Oryx, two compressors are both matched to one turbine, a row of adjustable inlet guide vanes has, in development engines,been arranged around the intake to the auxiliary compressor (in production engines these vanes will be fixed). The setting of thesevanes can be finely adjusted to the optimum value but is not variable during running. The vanes are mounted in the annular i i 1 i I i 1 -MAX.POWER I I I 2I9OO ENGINE R.P.M: t TOO MAX CONTINUOUS ZIOOO ENGINE R.P.M.- MAX. POWER 2I9OO ENGINE RPM MAX CONTINUOUS 2IOOOENGINE R.PM. a UJ * 500$e 4OO mm mm ••• mm *m 9 21 91 mm 9C m X Mi mm E - N< ZIOCm ;INE >OE RPM. IP>E » R MM mm mm A. mm m •• mm I I I I I I I I I 2I9OOENGINE R.PM B600 n" SEA LEVEL 5OOO lOOOO ALTITUDE (ft) I5OOO 2OOOO Performance of the Oryx at NOr. 1 rating, plotted against altitude. This level of performance is already established, and development is progressing to higher powers. intake, which is another casting in RZ5 alloy. There remain to be described the collector and valve units,which are items peculiar to the Oryx. The collector is situated between the turbine outlet flange and the auxiliary compressorand is a stitched and Argonarc-welded assembly in stainless Nimonic 75 sheet. As the large drawing shows, the turbineefflux is collected in a birfurcated volute, divided into stream tubes by splitter sheets, to ensure a uniform distribution at theoutlet, which is turned upwards through 90 deg and exhausts vertically with an approximately square cross-section. Meanwhile,the delivery of cool air from the auxiliary compressor fills the space surrounding the hot-gas volute and thereby keeps the outercasing cool. This flow is also turned vertically upwards and is expelled as an outer tube of cool air screening the hot flow ofgas from the remainder of the engine. This arrangement results in depressed metal temperatures throughout the collector, and theassembly has been shown to have a long life. On top of the collector is mounted a two-position non-throttlingvalve, also manufactured of Nimonic 75. A piston-ring-sealed expansion joint is situated between the collector outlet flange and Longitudinal section (or, in American parlance, inboard profile) of the Napier Oryx, emphasizing the disposition, and relative sizes, of the major components. The circular unit under the main compressor is the filter of sixth-stage air for pressurizing and cooling purposes.
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