National Gas Turbine Establishment

The Aeronautical Activities Of The National Gas Turbine Establishment

(A Lecture by D/NGTE to the Manchester Branch of the R.Ae.S on 12th Dec. 1973)

THE AERONAUTICAL ACTIVITIES OF
THE NATIONAL GAS TURBINE ESTABLISHMENT

The modus operandi of the National Gas Turbine Establishment still reflects its growth from two widely diverse roots, one in government research and the other in industry. The Establishment originated in 1944 from a merger of the Gas Turbine Division of the RAE with the original UK jet engine company founded by Sir Frank Whittle, i.e. Power Jets Ltd. The combination first ran as a company, Power Jets (R&D) Ltd, but in 1946 the latter was hived off as an exploitation organisation and the main body reconstituted as the National Gas Turbine Establishment under the Ministry of Supply.

FUNCTIONS

However, the total research programme s itself less than half of the Establishment activity for, setting aside the non-aeronautical interests, the work of NGTE as a whole is as shown in Figure 1. This diagram is functional and does not reflect organisation which can be dismissed with the observation that DD(Operations) is the Chief Engineer and DD(R&D) the Chief Scientist of the Establishment. There is, however, no fragmentation in the workings of the whole. Not only does the staff move freely between the various blocs depicted, but the practical links between these are so numerous that if illustrated they would make the illustration look like a "cat's cradle".

FIGURE 1

Whilst such a talk as this should aim to present an account of the Establishment that is based on interesting features in its past and present activities, it will be realised that in the time available only very few examples can be considered. To set these in context, a certain amount of attention must therefore be given to the underlying structure and functions.

THE RESEARCH AREA

From such a set-up one may deduce that the purpose of the research programme is the advancement, not of science, but of technology. Also that NGTE will not necessarily conduct the research, only ensure that it is done. In practice the research leading to or concerned with particular projects is generally sponsored in industry and that of a basic nature in the universities. Intramurally, the Establishment retains a middle slice together with certain items that require such massive specialist equipment as the Engine Test Facility, or that may be connected with possible legislation; for example matters relating to airworthiness, noise control, or atmospheric pollution.

In Figure 2, which gives the names and functions of the six research departments, it may be seen that the name of a department may not closely describe its activities. For example the term "Installation Aerodynamics" in Engine Research covers all aspects supersonic and subsonic intake and exhaust systems, including considerations of wave and form drag and the special problems of variable pitch fans, thrust reversers, exhaust gas and foreign object ingestion etc. In the other half of that department, the work on powerplant dynamics and control, including fuel systems exercises a quite different set of skills. As Engine Research is a typical research department comprising some 20 professionals, it can be seen why not only the group as a wholee but most of its 20 members are required to be multi-disciplinary in their scientific outlook and its practical application. This requirement for the rounded man rather than th e specialist, for the scientific engineer rather than the engineering scientist, is a prime characteristic of the Establishment.

FIGURE 2

As such people cannot be found, one of the continuing NGTE activitics is their training from an initial base of engineering science, physics or occasionally mathematics, chemisty or metallurgy.

From the detail of Figure 2 it will further be seen that the disciplines of aerodynamics, physics, thermal engineering & etc are practised by more than one department, so that each member of staff is able to move naturally around the territory of that illustration in the formative first ten to fifteen years of his or her career.

As might be expected from such staff mobility in a multi-disciplinary operation, the "Old boy net" ensures extensive collaboration between departments that extends not infrequently to the sharing of equipment and in which the Performance and Design Research Department plays a central part. Whilst this stems largely from its formal responsibilities for projected powerplant assessment, the engine architectural aspects of the design research activity also strengthen the role. But it should be observed that there is no question of any department becoming primus inter pares. Each is interdisciplinary and each is led by senior staff who have served in one or more of the others, so that any professional rivalry is of a healthy kind that promotes the cohesiveness which is so essential to a stimulating environment. And of course that cohesiveness is by no means restricted to the DD(R&D) area, but embraces all the functions of Figure 1 together with the non-aeronautical interests.

Another characteristic of NGTE and one which tends to strengthen cohesion is that Performance and Design Research is not the only department that deals with the powerplant as a whole, three others being Engine Research, Acoustic Aerodynamics, and of course the Engine Test Department under DD(Operations). Thus the staff in each of those departments is concerned not only with scientific problems, but has need to test, tease and otherwise deal with a wide variety of engines of which the Establishment is wont to run (and occasionally break) not a few in the course of a normal year's work.

To illustrate the way in which a new research situation is approached it is necessary to consider only one example - the NGTE history in aircraft noise research.

THE NOISE RESEARCH ACTIVITIES

Whilst the appropriately weighted Perceived Noise Decibel (PNdB) scale had already been proposed and in some measure tested by Bolt, Beranek and Newman Inc, consultants to the Port of New York Authority, the real problem was not to devise a scientific measure but to establish one that would be politically acceptable throughout the Western World. As an acceptable unit of measurement must precede any meaningful analysis of aircraft noise, which study must in turn lead the research towards its reduction through the evolution of quieter engines, NGTE therefore entered the noise scene by pioneering a new style of phsycho-acoustic experiment in which:

1. The subjects were phsyiologically random members of the general public.
2. Their random selection was ensured by coercion rather than attraction.
3. There was no foreknowledge of the experiment on the part of the subjects.
4. Psychological conditioning ensured that the result was a measure of purely physio1ogica1 response (thus ensuring accurate, repeatable, objective results).

The resulting series of experiments ran from 1959 to 1968, involved many thousands of subjects and covered all aspects of both fixed wing aircraft and helicopter rotor noise. In this way it established both the proposed PNdB scale that is now widely used for aircraft noise control and the proposed Effective PNdB (EPNdB) scale that was ratified by the International Standards Organisation as the basis of state legislation on both sides of the Atlantic. Figure 3 shows the interior of the mobile psycho-acoustic laboratory.

FIGURE 3

Once that assessment technique was launched, the Establishment moved into the business of understanding and controlling, one-by-one, the many diverse sources of powerp1ant noise. By way of a product, Figure 4 illustrates the advance that was made between 1959 and 1972, and in this two features may be noted:

1. The reduction in overall noise as measured by the worst polar 'balloon'.
2. The extent to which the noise pattern has been balanced by adjusting the sizes of the individual 'balloons'.

FIGURE 4

To achieve this effect work was required on a very broad front and, in turn, this demanded comprehensive facilities as well as extensive collaboration with other organisations. Indeed, it should be made clear at this stage that, however measured, less than one quarter of the necessary research was in fact executed by NGTE, the bulk having been sponsored in industy and the universities.

Nevertheless, whoever may be conducting the research, facilities are required for the measurement of the fore and aft lobes of fan noise and for the sound emanating from the after end of the engine, with special arrangements for discrimination between the divers noises of the turbine, the jet pipe furnishings and of course the jet itself. In addition some facility is needed for the measurement of the aero-acoustic performance of the sound absorbing structures that may be used to reduce the noise output from all of those sources except the propulsive jet. All such equipment is provided at NGTE and illustrated here in Figures 5 to 8, of which the last shows the largest anechoic chamber in course of construction as it is not due for completion until November 1973.

FIGURE 5

FIGURE 6

The extent of collaboration is illustrated by Figure 9, which depicts the distribution of the Government sponsored, NGTE managed aircraft engine noise research programme in UK over the many university, industrial and government laboratories concerned. Indeed, even this does not paint the broadest picture as, where international projects are concerned, there is appreciable ad hoc collaboration with Europe.

That account of the noise activity, covering everything from psycho-acoustics to propagation studies, from helicopter rotors to jets and from the conduct of basic research to the monitoring of a national network is an indication of the manner and extent of the NGTE involvement in aeronautical affairs through its Acoustic Aerodynamics Department. As comparable policies prevail in respect of the other five research departments, multiplication by six to account for the rest of Figure 2 affords a reasonable measure of the total research based NGTE involvement with UK, European and World aeronautical affairs.

But, lest one should form an impression that NGTE leads only from behind, Figure 10 comprises a list of those among the NGTE published titles that can justly be deemed source papers in the noise field.

FIGURE 10

THE OPERATIONS AREA

Originally NGTE had a Flight Test Section that incorporated a wide variety of aircraft, starting with the original E28/39, Figure 11, and F9/40 or Meteor. Figure 12 shows the Ashton and Lincoln flying test beds in formation with the rest of the flight - Canberra, Meteor and Hunter - in 1958. There was also a Ram Jet Section that mounted its firing trials at the Royal Aircraft Establishment rocket range at Aberporth in Cardigan Bay, Figure 13. So far as on-site plant was concerned there was at that time among the several air supplies none that exceeded a calibre of 120 lb/sec at a pressure ratio of 6.0, and so virtually no alternative to flight testing engines and other powerplant components in aircraft.

FIGURE 11

FIGURE 12

FIGURE 13

The relevant change of policy took effect in the early 1960's when the Flight Section was disbanded and 'flight' testing was transferred to a ground complex that has become known as the Engine Test Facility and now has, so far as is known, a combination of calibre and flexibility that is unique in the world. The heart of the complex is an air house, Figure 14, that contains eight three spool compressors each of which is rated at 44,000 shp and, by an appropriate selection of valves, can either exhaust or pressurise (ie suck or blow) the test cells.

FIGURE 14

With the addition of two later air houses, both of which provide exhauster capacity only, [Number 9 Exhauster and Number 10 Exhauster] the total air moving capacity exceeds 1,700 1b/sec and the available, modular sink or source pressure levels are:

• On suction: 1/81, 1/27, 1/9 and 1/3 atmospheres
• On pressure: 3 and 9 atmospheres

FIGURE 15

FIGURE 16

FIGURE 17

The test cells themselves are five in number, each having been developed to meet some specific need and so being different from its fellows. The only ones that constitute a pair with some degree of interchangeability are the 12 ft diameter cells, 1 and 2, Figure 18. Normally, however, Cell 1 is run as a free jet cell and Cell 2 in the connected mode. In this latter technique, Figure 19, the engine on test is coupled to an air supply with extensive inlet survey instrumentation, so that thrust can be measured accurately with correction for all inlet momentum effects & etc. The simulation of flight conditions is therefore by an appropiate scheduling of pressure, temperature and, where appropriate, icing conditions.

FIGURE 18

FIGURE 19

In the free jet mode, Figure 20, there is no thrust measurement but the cell acts as a propulsion wind tunnel in which the engine, or on occasion the model is 'flown' in a free jet that may be supersonic, transonic, Figure 21, or of course subsonic as appropriate. The limitations of Cells 1 and 2 are that they cannot accommodate engines of larger calibre than the Pegasus, Figure 22, and that their flight simulation is static rather than dynamic. That is, when the 'flight' Mach number, altitude or angle of attack is changed, the transition from one set condition to another is by a route that is not meaningful in flight and represents 'dead' testing time.

FIGURE 20

FIGURE 21

FIGURE 22

For dynamic environmental testing in which such aircraft motions as pitch, yaw and the variation of pressure and temperature during acceleration or deceleration can be reproduced in real time one uses the larger cells of which Cell 3, Figure 23, is the first. This was first used in earnest on the ill fated TSR2 project, is 20 feet in diameter, will take all but the largest big-fan engines and is normally used in the connected mode. An indication of its range is that it can cover almost the entire flight envelope of Concorde or of any military aircraft that can reasonably be envisaged, the exception being altitudes under a few thousand feet for which testing on a sea-level bed such as the Glen Test House, Figure 24, will suffice. Whilst Figure 23 showed the 'flange-to-flange' Olympus 593 engine for Concorde being lowered on to the thrust frame, Figure 25 shows the simulated aircraft nacelle in position for environmental trials including all the accessories and cabin air conditioning equipment etc.

FIGURE 23

FIGURE 24

FIGURE 25

For big fan engines such as the RB2ll, Cell 3 West, Figure 26, was constructed with a diameter of 25 feet and, as Figure 27 shows, such tests are done in the connected mode with the engine thrust frame. Again, virtually the whole flight envelope is covered and indeed, because of its size, flow and icing capability, Cell 3 West is also used in the free jet mode for airframe trials - Figure 28.

FIGURE 26

FIGURE 27

FIGURE 28

Cell 4, the supersonic free jet cell, Figure 29, is the largest of all and was itself an engineering project that took 11 years of R&D, design and construction from its conception to its commissioning. The whole structure is some 400 feet long with a plenum chamber diameter of 30 feet and a Mach number range up to 3.5 at which the inlet temperature is 470°C for correct flight simulation. In covering the flight envelope of an aircraft like Concorde the cell reproduces all significant dynamic conditions including acceleration and pitching and yawing manoeuvres of which the rate is up to 10 degrees per second. Figure 30 shows the inlet of the 75 ton variable Mach number nozzle with its pitching and yawing machinery, Figure 31 the outlet end with the Concorde intake in position in its shock diamond and Figure 32 the inside of the engine capsule.

FIGURE 29

FIGURE 30

FIGURE 31

FIGURE 32

From the fact that the equipment of the Engine Test Facility is used not only for development trials but up to 20 per cent by the research departments which also have their own facilities including air supplies that total over 200 lb/sec and range from 1/15 to 50 atmospheres pressure with appropriate temperatures to match, it may be appreciated that NGTE enjoys a considerable and in several respects unique technological resource on its 200 acre NGTE site at Pyestock. Indeed the measure of its plant is a fourth feature which makes NGTE unusual among research establishments.

It may serve as a reminder of the first three features of scientific catholicism. overall cohesiveness and a 'down-to-earth' approach to engineering hardware, to note that the following film was made in 1968 by the Combustion and Instrumentation Department to present a research of the Engine Research Department at the request of the Acoustic Aerodynamics Department that required it for the last of their subjective noise measurement experiments on members of the public.

With thanks to Richard Pinker for the scans