Engine Test Facilities - Issue Three

Engine Test Facilities

12. The Engine Test Facility

At present, the Engine Test Facility has five altitude Test Cells which can arrange engine and component tests at ground level or under simulated altitude conditions. Also included in the Facility is a general purpose sea level test bed.

The Cells can test a wide range of engines at various flight speeds and altitudes. Engineering experience in the gas turbine field has shown that performance presentation of altitude, speed and range can be somewhat misleading because the limits do not depend on plant alone, but are also related to the engine demand; consequently, any performance diagram relates to a particular engine choen to present the case and a different test envelope may result if another engine is chosen to show plant output. Where limited information on performance is given in this brochure it should be relasied that the information provides the broad trend of Cell capacity rather than specific detail of total N.G.T.E. capability and further information should be sought, as indiciated in Section 1. An outline of the testing capacity of the five different Test Cells is given in Table VIII.

Table VIII
Capacity Of Plant At N.G.T.E. For Engine Testing

Broadly speaking,Cell 1 carries out free jet testing and Cell 2 connected jet testing; both Cells having altitude capabilities of 3.5 inches of mercury absolute. The two Cells are sited adjacent to each other and have many common services. Cell 3 carries out connected testing over a much wider range of inlet air and altitude conditions and has air processing equipment which can reproduce temperatures from -70°C to 600°C. Cell 3 West carries out connected tests on large turbofan engines with large volume engine exhaust suction, but atmospheric low temperature inlet conditions. On the other hand, Cell 4 carries out free jet tests on engines with complete supersonic intake configurations.

Figure 6 shows diagrammatically the arrangement of the air mains and reference to the code indicates the pressure, vacuum and the dryness that is available in various flow circuits to the Test Cells. The diagram illustrates the manner in which the pipes to the various plant facilities are inter-connected with each other, this arrangement being a deliberate feature of the E.T.F. which gives wide flexibility in operation. However, the inter-dependence of the Test Cells and Laboratories on a pipework system which provides many different flow routes, makies it essential to programme tests in different Cells so that they do not interfere with each other, and consequently there is a rota procedure which allows each test plant to have testing facilities in turn. In addition, a safety procedure guarantees that all valves are correctly set according to the particular requirements of the experiments on hand and the appropiate safety instructions are put into effect both before and during every test. This vital step is aimed at protecting personnel working in or around sections of the pipework system not involved in the test on hand, as well as safeguarding expensive plant which could be damaged if it were not isolated.

13. Cell 1 and 2 Test Plant

Test Cells 1 and 2 are used for full-scale testing of turbojet and ramjet engines as well as for component development work under sea level and simulated altitude conditions. Cell 2 has also been used for the testing of solid propellant rocket motors at altitude. Figure 39 shows the layout and it can be seen that the two cells are sited adjacent to each other. Cell 1 is for free jet testing and is provided with a means of varying the incidence of the supersonic blowing nozzle as shown in Figure 40. Cell 2 is normally used for connected rig or combustion chamber testing and Figure 41 shows this type of installation when used in conjunction with sea level exhaust conditions.

Fig. 39 Layout of E.T.F. Cells 1 and 2

Fig. 40 Cell 1 set up for high altitude conditions

Fig. 41 Cell 2 installation of turbo-jet engine

The compressed air supplies from either the Air House G.E.C. sets or the Plant House Metropolitan-Vickers sets are connected to the Cells as shown in Figure 6. The pipeline connecting the Air House to the Cells is 54 inch diameter and this restricts the air capacity in Cells 1 and 2 to the output from three G.E.C. sets. The standard arrangement is to use air from either 1, 3, 5 or 7 machines, but if these particular sets are not available, it is possible to make special plans to supply Cells 1 and 2 from the other compressor/exhausters using the interconnecting cross-over main originally provided to allow the G.E.C. sets to operate in cascade at 1:81 pressure ratio. This improvisation restricts the simultaneous operation of Cells 1 and 2 with Cell 3. Figures 42 and 43 show photographically the general arrangement.

Fig. 42 View of Cells 1 and 2 showing air mains

Fig. 43 View of Cells 1 and 2 with No. 1 (free jet) in foreground

In addition to supplying the needs of engines under test, pressure air is used to operate ejectors which create altitude conditions inside the Cells. Sometimes, when high altitudes are simulated, the pressure of the air entering the test engine is less than atmospheric and consequently the engine requirements are drawn from atmosphere. For this purpose the Cell plant incorporates a silenced air-intake through which the engine draws its incoming supply during high altitude tests.

To drive the ejector plant, air of 9:1 pressure ratio from the G.E.C. compressors is used to supply the primary side of four separate air ejectors. The individual performance of one of these ejectors is given in Table IX and is shown graphically in Figure 44. Each ejector consumes 100 lb/s of G.E.C. driving air.

Fig. 44 Performance of Cells 1 and 2 ejector plant

Fig. 45 Altitude performance of Cells 1 and 2

The overall altitude performance of the ejector plant with all four units operating is shown in Figure 45. The test envelope shown has been calculated using the demand of an Olympus 320 engine. When test conditions so demand, the engine inlet air can be preheated in a 3 MW heater. The unit is built in two 1.5 MW sections each of which can operate independently. The total heater performance is shown in Figure 46, the maximum air delivery temperatures being 350°C. Inlet air temperatures to the heater depend on the mode of operation used, but when G.E.C. air is involved they can be as high as 210°C.

Fig. 46 Calibration of Metropolitan-Vickers 3 MW air heater

When air is supplied direct to Cells 1 and 2 from the Air House, the minimum temperature that can be obtained from the G.E.C. after-coolers is 70°C. However, by indirectly routing the air through the Cell 3 cold air plant, a lower temperature of 30°C can be obtained; with wintertime low ambient temperatures this figure can be reduced to 10°C. The maximum air weight flow at this low temperature is 200 lb/s.

Inlet air and altitude pressure conditions in Cells 1 and 2 can be automatically maintained at pre-set levels with varying engine air flows. Alternatively, simulated flight plans involving varying altitude conditions can be programmed and automatically followed. The engine installation and control room layout is shown in Figures 47 and 48.

Fig. 47 A typical engine installation within the free jet cell

Fig. 48 The main control room for Cells 1 and 2

Both Cells have an air filter in the inlet pipework, the elements of which can withstand a pressure difference of 30 lb/in² but the filter elements are normally changed when the pressure drop reaches 5 lb/in²in. Each filter can handle 600 lb/s throughput at a maximum air temperature of 350°C. The equipment is designed to BSS 1701 which specifies that dust particles of larger than 10 microns should be filtered out. The pressure vessel is capable of withstanding 12 atmospheres.

The plant fuel system, as distinct from the test engine fuel system, installed in Cells 1 and 2 delivers fuel at flows up to 16,000 gal/h at pressures up to 1,500 lb/in². A secondary plant fuel system is also available which delivers 8,000 gal/h at pressures up to 1,500 lb/in².

Engine exhaust cooling is achieved by direct water injection through spray nozzles. Two systems are available giving maximum injection rates of 180,000 gal/h at 80 ft head and 190,000 gal/h at 125 ft head respectively. The maximum amount of cooling water injected for a particular test is governed by evaporation losses and the capacity of the Cell water extract pumps, currently 216,000 gal/h. A total water storage capacity of 600,000 gallons is available and the Cells operate on a re-circulatory basis so that only evaporation losses need to be made good.

Engine operation during transient acceleration cycles can be measured in addition to the usual performance observations under steady state conditions, and all engine test information is normally fed through an on-line SDS 9300 computer with a PDP7 unit for data acquisition in support. As an alternative, the experimental information can be recorded by photographic means in special instrument rooms. However, this method is time consuming as the photo records must be processed before they are analysed. The details of the instrumentation services are listed more comprehensively in paragraph 23.

14. Cell 3 Test Plant

Unlike Cells 1 and 2 which are driven by ejectors, Cell 3 uses the Air House G.E.C. and the Parsons No. 9 and No. 10 exhausters to produce altitude conditions. Most tests also demand that compressed air shall be blown at the engine under test and this service is also provided by the Air House plant in its compressing role (see para 2.2.) An extensive system of air pipework circuits closely integrates Cell 3 with the Air House installation and, as shown in Figure 2.3, there are different circuits for compressed air supply and sub-atmospheric exhaust gas streams. The diagram particularly shows how the high pressure pipes supply compressed air to the forward end of Cell 3 while the suction mains are connected to the opposite end. For each of the eight compressor/exhauster sets there is a pressure main of 54 inches diameter and a suction main of 84 inches diameter. In every test a certain number of compressors (according to engine demand) supply inlet air to the engine under test whilst a matched capacity of exhausters suck away the exhaust gases. No. 1 G.E.C. compressor is not connected directly to Cell 3 but this particular limitation is overcome, if machine availability makes it essential to use the No. 1 set, by routing the air through a cross-over main and using this circuit to supply the pressurised air to Cell 3.

To reduce the emitted noise the whole structure of Cell 3 is submerged below ground level in a concrete trench as shown in the photographs and diagrams of the area and thus there is little outward appearance of the complicated engineering installation which forms Cell 3.

Figure 49 shows a cross section through the Cell from air inlet to suction exhaust manifold and a general view of the area is illustrated in Figure 50. The total length of the cell is 318 ft of which the working section accounts for 56 ft, the diffusing section 64 ft, the cooler and flame trap sections 90 ft, the rest being accounted for by the suction main manifold. The diameter of the working section with its inlet plenum chamber is 20 ft and it has a removable section in the roof so that test engines and associated equipment can be lowered into the Cell. The diameter of the diffuser and cooler sections is 10 ft and 30 ft respectively.

When originally designed, the air inlet ducting of Cell 3 limited the throughput to 400 lb/s; however, modifications to the inlet ducting have since increased the throughput to 600 lb/s. The maximum allowable temperature has been reduced for this higher flow becuase the total cooling capacity of the gas cooler remains unaltered.

Fig. 49 Cross-section of Cell 3 test plant

Fig. 50 General view of Cell 3 area

As described in para 12, the operating performance of a test cell is intimately associated with the engine demand. However, Figure 51 shows the test boundaries which can be obtained for Cell 3 for a typical 400 lb/s gas turbine engine with reheat. This case will be very close to that which would be obtained with the Olympus 593 engine for Concorde. Pictorial illustrations of engines as mounted in the Cell are shown in Figures 52 and 53 whilst Figure 54 shows the engine control room layout.

Fig. 51 Typical test envelope for a 400 lb/s engine with reheat

Fig. 52 View of Cell 3 engine installation

Fig. 53 Concorde Olympus 593 mounted in simulated altitude nacelle in Cell 3

Fig. 54 General view of control room for Cell 3

Cell 3 is designed to cater for a wide range of turbine engine performance and hence facilities are provided to give an extensive air temperature range. Both hot and cold air processing plants are installed which can be used to set up the required air temperature within the working range. Figure 55 shows the air temperature circuits diagrammatically. The inlet air temperature field that can be obtained in Cell 3 is shown in Figure 56.

Engine thrust can be measured in Cell 3 and Figure 57 shows the oil borne bearing frame which supports the engine, permitting the movement on which thrust measurement depends.

Fig. 55 Diagrammatic arrangement of Cell 3 air mains

Fig. 56 Cell 3 inlet air temperature field

Fig. 57 Cell 3 engine test frame

A major part of Cell 3 installation is devoted to engine exhaust gas cooling. The gas cooler consists of 20 similar elements arranged radially within the 30 ft diameter pressure shell, as shown in Figure 58. The pressure shell is 1¼ inches thick and designed to withstand full vacuum and an explosion pressure of 127 lb/in². The engine exahust gases are first passed through an oil burning torch system which ensures than any unburnt fuel is ignited, thereby eliminating the explosion risk. Then the exhaust is cooled in an indirect cooler which can handle a throughput of 320 lb/s from 1,740°C to 150°C at pressures between atmospheric and 4.5 lb/in² abs. At low flow the cooler will handle 35 lb/s at 0.5 lb/in² abs., at this condition the design pressure drop is 1.4 inches of mercury. A further 100°C temperature drop to the G.E.C. maximum inlet temperature of 50°C is achieved by evaporative cooling in a number of water-washed flame traps which form the final stage of the cooling system. Treated water is used in the cooling circuit, the maximum flow being 2,500,000 gal/h on a closed circuit using five cooling towers working between 27°C and 57°C as described in para 41. The gas cooler section is shown in Figure 58.

Fig. 58 Cell 3 gas cooler

If desired, the G.E.C. sets may draw air from the Ceca air drying plant so that Cell 3 tests can be conducted with dry air. Alternatively, an injector in the cell air supply system enables up to 100 lb/s of dry air to be directly induced from the Ceca air dryer

Four fuel systems are available for use in Cell 3. Three of these supply fuel at ambient temperature but the other, described in para 18, supplies fuel heated by mineral oil at temperatures up to 250°C at 15 to 165 lb/ln², the maximum flow being 40,000 lb/h. Two of the normal fuel systems give maximum flows of 6,000 and 12,000 gal/h at 2,000 lb/in², while the third supplies 4,200 gal/h at 2,000 lb/in², the two larger systems are operated in a spill arrangement which enables acceleration work to be carried out at substantially steady supply pressures.

Engine operation during transient acceleration cycles can be measured in addition to the usual performance observations under steady state conditions and for this purpose engien test information is normally fed through an on-line SDS9300 computer with a PDP7 unit for data acquisition in support. As an alternative, experimental information can be recorded by back-up photographic methods. Paragraph 23 lists the available instrumentation in greater detal.

15. Cell 3 Air Heating Plant

The Cell 3 heater is shown in Figure 59 and consists of a vertical oil fired cylindrical furnace, 80 ft hight and 20 ft diameter, with the walls lined with tubes through which the air supply is passed. Heat is tranferred to the air tubes by radiation from the 12 oil burners which are fitted on the floor of the furnace and arranged to fire upwards. The air inlet mainfold is mounted at the top and the outlet manifold is situated under the furnace floor, thus the air flow direction is downwards. The heater is arranged to be manually operated during the starting cycle and switched to automatic control once the desired operating temperature has been reached. The heater performance data is given in Table X.

Fig. 59 Cell 3 air heater

Table X
Air Heater Performance Data

The air is routed from the heater to the Cell, as shown in Figure 55, by way of stainless steel ducting. Air leaving the heater can be controlled over the range 300°C to 600°C as dictated by the test in progress and final temperature control is obtained by mixing heated and unheated G.E.C. air in the mixing sphere.

16. Cell 3 Cold Air Plant

The cold air plant works in conjunction with a precooler and pressure dryer to reduce ice formation; temperatures down to -70°C can be obtained by use of a cold air expansion turbine which is designed to give a maximum flow of 100 lb/s. Temperatures between ambient and -70°C can be achieved by mixing warm air from the G.E.C. machines with that from the cold air plant in the mixing chamber which has special large valves to meter the supply. When necessary, ambient air can be drawn into the chamber and blended with the cold supply; the circuits which make this possible are shown in Figure 55.

Figure 60 shows the temperature/air weight flow relationship obtained from the cold air plant and the cold air expansion turbine alternator is illustrated in Figure 61. The power generated by the air expansion turbine is absorbed by an alternator of five megawatt output and the electrical current is returned to the N.G.T.E. grid supply.

Fig. 60 Cell 3 cold air plant temperature characteristics

Fig. 61 Cell 3 cold air plant

17. Cell 3 Ice-making Facilities

Ice particles in air-breathing engine intakes can have a serious effect on performance. Consequently, two special ice-making plants are installed in association with Cell 3 so that all altitude effects can be investigated. The two plants are:

1. The ice crystal plant, and
2. The super-cooled water droplet plant.

The former has the capacity to produce ice blocks which are cut into small particles and injected into the engine under test. Ice blocks can be produced at the rate of one ton every twenty-four hours and facilities exist for storing four to five tons of ice for an indefinite period. The plant produces particles between 500 and 4,000 microns in size. The particle injection rate is variable between 5½ and 152 lb/min.

Alternatively, super-cooled water droplet plant can produce a spray of super-cooled water droplets within the engine inlet duct. These will freeze out on contact with the cold engine inlet surfaces and so build up ice formations. The basic air and distilled water system can deal with a water injection rate of up to 600 gal/h but some operational difficulties have been experienced with the spray nozzle atomisers. if a water droplet size of 20 microns is expected, the total flow is limited to 148 gal/h; this may be increased to 185 gal/h if the droplet size is expanded to 30 microns. The water concentration in the engine intake depends on the volume flow.

18. Cell 3 Hot Fuel Supply

To simulate engine operating conditions at high speed in test plant at ground level it has become necessary to preheat engine fuels to correspond with flight conditions where elevated fuel temperature occur when fuel is used to cool the aircraft structure and skin.

A plant, located near Cell 3, has been installed to provide a service to heat fuel up to 250°C and pipelines have been laid to service Cell 3.

Mineral oil, heated in two oil fired heater units to temperatures up to 300°C, is passed through coils in a 9,000 gallon capacity dwell tank to heat the engine fuel up to 100°C. The engine fuel is pumped from this dwell tank to Cell 3 via heat exchangers in which the fuel is given a second stage of heating by the mineral oil to raise the fuel temperature to the required level. The system supplies an engine under test with up to 40,000 lb/h of fuel at temperatures up to 250°C and pressures up to 160 lb/in². Higher fuel flows up to 60,000 lb/h are possible but at correspondingly lower temperatures. A spill system, incorporating a dump cooler, is used and transient flow conditions are possible with substantially steady inlet pressures.

The circuits used for fuel at temperatures above 100°C, including the heat exchangers, are constructed from 18/8 stainless steel.

19. Cell 3 West

To ground test, under simulated flight conditions, the new technology fan engines such as the Rolls-Royce RB207 and RB211, a new engine chamber of a very large diameter has been constructed at the west end of the Cell 3 suction manifold. The triple shaft design and high by-pass ratio of these engines create a test demand which absorbs the whole of the present N.G.T.E. exhauster resources, namely all eight G.E.C. and the Parsons No. 9 and No 10 machines. (See Figure 5).

A cold air plant capable of cooling an air capacity corresponding to the maximum engine requirement has been built as part of the Cell 3 West scheme. The cooler, described later, uses a 30 per cent aqueous ammonia solution precooled to -50°C in a cold store which is reactivated between individual cold test runs. At maximum design conditions there is sufficient 'cold' stored to permit the RB211 engine to run for approximately 30 minutes but with less arduous air flow and temperature demands the test duration can be proportionately longer. The engine chamber can be run both with and without cold air; in the latter case air can be drawn either direct from atmosphere through an intake silencer or through the cooler with no coolant circulation. In all cases the engine is directly coupled to the intake so that all tests are of the connected type.

Provision has been made on the engine chamber for a pressure connection from the G.E.C. machines in order than the chamber can be converted to a blown test bed when required at a future date.

Cell 3 West assists the commerical exploitation of large fan engine design by enabling full flow cold air tests to be undertaken at flight operating altitudes. The performance of Cell 3 West operating with the RB211 engine is shown in Figure 62.

Fig. 62. Cell 3 West typical test envelope with Rolls Royce RB211 engine

Figure 63 shows Cell 3 West generally, whilst Figure 64 shows the front of the Cell with the end dome and inlet ducting removed to expose the inside compartment and a RB211 engine installation. The removal of the complete front end dome permits easy access for the engine at the time of installation.

Fig. 63 General view of Cell 3 West

Fig. 64 View of Cell 3 West engine chamber with the front dome removed

The Cell 3 West engine chamber is 25 ft diameter and 40 ft long and an extension of the Cell 3 exhaust manifold, which is 15 ft diameter, is directly coupled to the exhaust end of the cell. Unlike Cell 3, Cell 3 West has been built at ground level unlike Cell 3 and consequently the exhaust manifold passes through two cascaded right angle bends in order to accommodate the height difference. The Cell 3 West exhaust manifold is fitted with bulkhead doors which are shut in non-testing periods if the suction mains are in use for Cells 3 and Cell 4. The atmospheric to exhaust mainfold pressure difference helps to keep a pressure tight seal. Figure 65 shows the arrangement of the engine chamber relative to the eight G.E.C. suction mains and it should be noted that a similar isolating bulkhead is located on the Cell 3 end of the manifold so that installation and modification work can proceed in Cell 3 whilst Cell 3 West is operational.

Fig. 65 Cell 3 West Test Area

To maximise exhauster performance, an internal exhaust gas diffuser is sited in the parallel section of the exhaust duct immediately downstream of the engine exhaust nozzle. The vertical exhaust duct from Cell 3 West which joins the exhaust manifold is fitted with direct injection water cooling sprays and an inbleed valve for altitude trimming purposes.

It is possible to measure engine thrust in Cell 3 West as the engine mounting includes special features to permit the movements required for thrust and drag measurements. The engine is clamped to a support frame which is itself supported from flexible rods attached to the roof of the cell. The mounting permits the small deflections which are needed to measure thrust and draft on Davey United Ltd. load cells. The engine installation includes an automatic-connect bulkhead arrangement so that a large proportion of engine instrumentation and other service supplies to the engine are automatically made when the engine is lifted into its finally installed position. This arrangement is identical to sea level installations at Rolls-Royce, so that it is possible to make speedy interchange of engines which are sea level tested at Derby and altitude tested at Pyestock. In the past, the installation work associated with engine instrumentation has frequently delayed engine testing programmes.

The inlet ducting which connects with the cooler is 77 ft long, of which 43.5 ft is external to the cell and the rest internal. This ducting includes an air flow measuring section as well as air straightening gauzes which improve the air distribution at the engine entry plane.

Both steady state and transient instrumentation is available; test information is normally fed through the on-line SDS 9300 computer with the PDP7 data acquisition unit in support. Certain back-up information by photograph recording is alos provided. Altogether the instrument installation is able to provide 300 pressures and 200 temperature points for steady state conditions and 30 channels of U.V. and 28 channels of magnetic tape for transient conditions. A local control room adjacent to the Cell is used to operate the test plant, the engine and its associated auxiliaries. Further details of the instrumentation service is given in paragraph 23.

The fuel system is tapped off from that used in Cell 3 and is of similar design. A spill return line is situated close to the engine supply tee-off and fuel in excess of that required by the engine is returned to the plant fuel supply tank. This arrangement eliminates the need to accelerate large quantities of fuel through the long supply pipework during engine transients.

The spray cooling water system operates on a recirculatory basis with a make up supply to replace water evaporated into the air stream. Two banks of spray nozzles are provided and each is fitted with on-off and flow control valves. The quantity of water injected is carefully controlled to ensure than just enouhg is sprayed into the gas stream to maintain an acceptable gas temperature at inlet to the exhausters.

20. Cell 3 Cold Air Plant

The air intake cooler consists of 33 modules built in three rows of eleven modules. Each module has 18,500 ft run of 1 in o.d. x 16 B.G. mild steel pipe of plain section. The tubes are galvanised externally and the module headers are interconnected toegether in such a way as would allow the cooler modules to be removed for emergency repairs. Altogether, when all modules are interconnected, the cooler has a total length of 61 ft 5 in with frontal dimensions of 27 ft x 29.5 ft. The assembly is mounted on its own wheeled carriage and the cooler can be wheeled out of position along its own track if required. Figure 66 shows the cooler assembly cold store tanks and refrigeration plant.

Fig. 66. View of Cell 3 West cooler assembly

The cold store of aqueious ammonia is reactivated in twenty-four hours using the refrigeration plant which is sited adjacent to the cooler unit. This refrigeration plant includes the necessary condensers, evaporators, pumps, etc., and is of conventional design rated at 2.25 million B.t.u./h.

Coolant from the pre-cooled store of aqueous ammonia is circulated through the cooler which is divided into three stages for this purpose. Each stage of the cooler has an independent flow control system and coolant is recirculated wherever possible to ensure maximum use of the "cold". Eventually the coolant is returned to the cold store where an interface, formed between the "warm" and "cold" coolant, travels down the tank as testing proceeds. The duration of a run is dependent on the rate at which coolant is drawn from the tank and the position of the interface. Under some circumstances the length of test run may be limited by the falling off in heat transfer coefficient due to ice building up on the outside of the cooler tubes.

The cooler has been designed to give thirty minutes running time at -37°C with an air throughput of 800 lb/s assuming air inlet conditions of 7.3°C dry bulb temperature and 100% relative humidity. Operating times and temperatures at other air flows and inlet conditions have yet to be established but an approximation of the performance expected based on inlet conditions of 0°C and 18°C with relative humidities of 100 per cent and 50 per cent respectively is given in Figure 67.

Fig. 67 Cell 3 West estimated performance of air inlet cooler using one cold store tank

21. Cell 4 Test Plant

When gas turbine engines are chosen to operate in supersonic aircraft, there is a need to test the engine in close association with the aircraft air intake system which is designed to reduce the air speed at the compressor face to an acceptance velocity thus converting the forward ram velocity into high engine intake pressure with a resultant bonus in power plant performance.

Although the engine an intake problems arising in supersonic flight are inter-related, a true simulation of all relevant factors is only achieved if full-scale free jets are possible; Cell 4 provides this capability for engines such as the Rolls-Royce Olympus 593 engine for Concorde and it is possible to test this engine and similar power plants with their intakes and control systems under high speed flight conditions. The Cell provides a means of observing on the ground the interaction of the intake and engine at changing altitude, Mach number and incidence. The performance range of Cell 4 is given in Figure 68. Figures 69 and 70 show actual views of the Cell 4 plant and associated machinery and some idea is obtained of the size and engineering complexity of full-scale free jet tests. In addition to testing in the free jet supersonic mode, the cell has also been used for subsonic free jet testing of the engine and intake. Also, by removing the blowing nozzle, connected testing of engines with reheat has been successfully undertaken with an experimental thrust measurement system installed in the engine mounting frame. Figure 71 shows the Rolls-Royce Olympus 593 engine installed in the Cell 4 engine chamber; this view is taken from the engine tailpipe end with the propelling nozzle in the immediate foreground, looking forward to the bulkhead which divides the engine chamber from the intake working section. Figure 72 shows the air circuit diagram for Cell 4 which is designed to handle a maximum flow equivalent to two G.E.C. sets, i.e. 400 lb/s, under pressure conditions, with the capability of increasing this flow to 600 lb/s at lower pressures by the use of an injector system.

Fig. 68 Performance envelope for Cell 4 plant

Fig. 69 General view of Cell 4

Fig. 70. Cell 4 plenum chamber

Fig. 71. Rolls-Royce Olympus 593 for Concorde installed in Cell 4 engine capsule

Fig. 72. Cell 4 process air diagram

The total air mass flow can be provided as dry air from the Ceca air dryer which is described in para 11. Normally, the Cell air supply maximum inlet pressure does not exceed three atmospheres absolute and the temperature ranges from 70°C to 470°C using the air heater described in para 15. The Cell is built parallel to Cell 3; the relative position of these plants is shown in Figure 6 which also shows the inter-connecting ducting with the G.E.C. and No. 9 and No. 10 exhausters.

Flight speed is simulated by a supersonic blowing nozzle which has an adjustable throat and wall contour to provide variable Mach number operation. This nozzle is mounted on a universal carriage which enables aircraft pitch and yaw conditions to be simulated up to angles of +/- 10° at rates of up to 20° and 10° per second respectively. The total weight of the nozzle and moving carriage assembly is approximately 75 tons. Figure 73 shows the carriage assembly with the 25 square foot nozzle in position viewed through the plenum chamber with the 20 foot diameter inlet cone removed.

Fig. 73 Cell 4 carriage assembly and supersonic blowing nozzle

To match engine performance more closely two variable nozzles are available; the first is 12 sq ft in area, giving a Mach number ange of 1.5 to 3.5 while the second is 25 sq ft in area giving a Mach number range of 1.7 to 2.5.

A general cross sectional view of Cell 4 is shown in Figure 74. The diagram illustrates how the aircraft intake is mounted in the working section immediately downstream of the blowing nozzle with the engine coupled behind.

Fig. 74 Cross section of Cell 4 altitude test plant

Spill diffusers, which are shown more clearly in Figure 75, are mounted above and below the intake and are used to obtain altitude conditions in the working section by converting low pressure, high velocity air from the nozzle into higher pressure, low velocity air. As the downstream end of the spill diffusers are connected to exhausters it can be seen that the diffusers are a means of aiding the exhausters to obtain altitude.

Changes in altitude are obtained by varying the geometry of the diffuser.

Better use of the installed exhauster is obtained by sucking away the low energy air issuing from the supersonic blowing nozzle, normally about four per cent of the nozzle mass flow. This process is termed "working section bleed" and is performed by the No. 9 machine referred to in para 5.

As stated above, Figure 75 shows diagrammatically the flow paths in the supersonic nozzle, spill diffuser and engine intake. The geometry of the Concorde intake makes it necessary to provide additional ductwork to accommodate the "ramp bleed" and "dump door" flows which are an essential feature of the Concorde aircraft power plant. The ramp bleed flow is piped away from the upper part of the intake and returned to the working section to be sucked away by No. 9 exhauster machine. The dump door flow is sucked away through one of the two permanent plant blow-off ducts to join the main exhaust system further downstream.

Fig. 75 Cross section of Cell 4 intake assembly, and flow ducts for Rolls-Royce Olympus 593

As in all altitude cells, the heat exchanger needed to cool the engine exhaust is a major plant item. The Cell 4 gas cooler has two stages, the first stage cooler is shown pictorially in Figure 76 which also shows the six flame torches that ignite any unburnt fuel in the engine exhaust so that explosion risks are eliminated. The exhaust gases leave the water-cooled diffuser duct at temperatures up to 1,700°C to enter the first stage cooler where they are cooled to 1,000°C by a novel gasover-tube matrix; a water flow of 620,000 gal/h is circulated through the matrix. In the second stage cooler, where the gases pass through the tubes in a conventional manner, the temperature of the gases is reduced to 150°C. This second stage also has a water circulation of 620,000 gal/h. Additionally, the flow from direct injection water sprays is used as evaporative cooling to reduce the gas temperature further to 50°C, this latter temperature being the maximum for the inlet flow to the G.E.C. exahusters. The excess water from all the direct injection sprays drains from the air ductwork into a 40 ft deep barometric well. The well is divided into two sections. Clean water is drained into one section from which it is pumped back to the water storage ponds, and water that has been contaminated by the exhaust gases is drained into the second section from which it is pumped into the site sooty water plant described in Section 5. The total recirculating flow of all cooling water systems in Cell 4 under hot running conditions is 2.5x10⁶ gal/h. Losses up to 170,000 gal/h through evaporations, leakages and contamination are incurred.

Fig. 76 Cell 4 first stage gas cooler matrix

The exhaust cooling system is manufactured entirely from conventional ferrous materials. During non-running periods corrosion is arrested by filling the system with a solution of sodium suplhite and sodium hydroxide.

Altogether, Cell 4 has a total length of approximately 400 ft of which the 30 ft diameter inlet plenum chamber with its blowing nozzle contributes 36 ft and the working section 10.5 ft. The engine chamber itself has a diameter of 10 ft and a length of 16 ft and the exhaust diffuser 55 ft; the first and second stage coolers have diameters of 26 ft and 18 ft respectively, the total length of the two stages is 160 ft, whilst 105 ft of ducting at the rear end of the cell accommodates the seven G.E.C. exhauser connections.

The fuel system is teed off that serving Cell 3 and described in para 3.3. As both cells do not run at the same time, no inconvenience is suffered by having a common system. The fuel flow rates are 100 gal/min and 200 gal/min for engine and reheat systems respectively. Normally, the engine flight fuel pump is used on engines installed in Cell 4, therefore, the plant fuel system provides fuel to the engine low pressure pump at a set pressure of 25 lb/in²; however, if needed, fuel at pressures up to 100 lb/in² can be supplied.

Fig. 77 Cell 4 control room with test in progress

Figure 77 shows the main Control Room for Cell 4 with a test in progress. All test results are fed direct to the SDS 9300 computer which has a PDP7 computer in support. The engine stedy state pressures and temperatures are processed beforehand in a digital data aquisition unit so that the information can be handled by the computers. Back-up photographic recording equipment is also available.

The instrumentation installation permits 300 pressure and 200 temperature points to be measured during steady state processing. Twenty-eight channels of magnetic tape, 36 channels of U.V. recording and digital counters for engine speed and fuel flow are available for transient conditions. Further details of the instrumentation service are listed more comprehensively in para. 23.

22. Sea-Level Engine Testing Plant (The Glen Test House)

The facilities required for testing gas turbine engines under sea-level conditions are not so complicated as those needed for simulated altitude flight conditions which have already been described; however, userful and much less expensive development work can be conducted on sea-level static beds. Figures 78 and 79 show views of the N.G.T.E. plant built on the New Site and known as the Glen Test House.

Fig. 78 External view of the 'Glen' test house

Fig. 79 Aircraft gas turbine installed in the 'Glen' test bed

The plant was originally installed for engines not greater than 250 lb/s air mass flow and 28,000 lb of thrust; but already engines of 320 lb/s and 35,000 lb thrust such as the Olympus 302 engine have been tested in the Glen Test House. Modifications are now in hand to increase the capacity still further so that the bed can accommodate the Olympus 593 for Concorde.

The test plant will shortly have an ability to accommodate 435 lb/s engiens giving 34,500 lb of thrust. An important part of the installation is the exhaust cooling and silencing system which was planned to keep the noise levels below 105 decibels at a radius of 250 ft from the test bed. The design allows engines to be tested with exhaust reheat systems in which the exit temperature may be as high as 2000°K; the engine throughput is diluted with a larger volume of induced air, 2:1 ratio approximately, which servers to cool the hot exhaust gases. The total silencer weight flow is therefore approximately 1,250 lb/s. Water cooling sprays have been added at the entrance of the exhaust tunnel to augment the exhaust cooling system.

There are two separate fuel systems, one for the engine supply and the other for reheat; in total, 12,000 gal/h is available at the engine test bed of which 2,000 gal/h, at pressures from 20-50 lb/in², is available in the engine supply and 10,000 gal/h, at pressures from 100 to 1,000 lb/in² in the reheat.

Figure 80 shows a plan view of the test facility which includes a fitting-out area in which engines can be installed on the test frames with their experimental instrumentation equipment so that actual installation time in the test bed can be kept to a minium.

Fig. 80. Plan layout of the 'Glen' test house

23. Instrumentation in the Engine Test Facility

Two groups of instruments measure engine test data, the first group give a direct display in the cell control room of engine and plant behaviour and are used to set-up and control the test in progress. The second group are installed to monitor more concisely the engine and plant parameters which are used to calculate test performance data. This latter group of instruments relay their information to a SDS9300 computer which records and calculates test data according to prearranged software programmes.

Generally, the driving instruments terminate at visual indicators on the engine driver's panel but those observations also required for performance calculations have circuits teed together so that readings are also routed to the computer. The driving instruments comprise manometers and gauges for pressure measurements, differential gauges for air and water flows, and thermocouples transmitting to visual pyrometers and chart recorders for temperature measurement; an accuracy of +/- 2 per cent of full scale deflection is normally acceptable for the engine control room instruments. The important air inlet and cell working pressures related to forward speed and altitude conditions are measures by bellows type maonmeters based on the R.A.E. 'Midwood' design and which have a high resolution over a wide working range. Increasingly, automatic control of plant is being introduced whenever operating costs or manpower can be reduced.

Permanent instrument pipelines and circuits originating at junction boards in the engine control compartment connects with the data acquisition system whilst short flexible temporary lines are used to connect this compartment with the sensing points in the engine; this system permits changes to be made in the instrumentation schedules for individual tests. Comprehensive scheduling nomenclature exists so that the permanent lines can be quickly identified and coupled to the individual engine sensing points.

The engine instrumentation installed enables both steady state and transient measurements to be made. The parameters that may be measured are temperature, pressure, speed, fuel flow, thrust, angles and areas. Table XI shows the range of instrumentation available to each cell.

Fig. 81. N.G.T.E. computer installation.

Figure 81 shows the main computer installation being operated during a test run. In steady state performance work, minimum accuracies of 0.25 per cent of full scale deflection are required, but in fact values of 0.1 per cent are frequently achieved. The arrangement of the steady state instrumentation is shown diagrammatically in Figure 82. The various measurements are fed to an electronic analogue/digital converter via a switching system and amplifier. The 17 digit output of the converted is then fed to the computer room.

Fig. 82. Steady state instrumentation arrangement.

Fig. 83. Transient instrumentation arrangement.

The computer itself is programmed to work ON-LINE and individual points are evaluated immediately. The computer has stored within itelf all necessary calibrations and one of its tasks after the input information is collected is to convert this data into engineering units, e.g. lb/in², degress absolute, gal/min, etc.

After meaning or averaging, selected data may be used to compute performance parameters ready for plotting the engine performance curves.

The maximum speed of data acquisition for steady state work is 100 points a second.

The transient instrumentation system is shown in Figure 83. DC signals from the various sensors and transducers are fed into a data distribution board from which ultra violet galvanometer recorders, analogue tape recorders and a computer are fed in parallel. Magnetic tape recording of the transient conditions is produced in the computer room and can be used as an input to the computer when required. By using the UV recording units, on-line visual examination may be made both in the control room and in the data centre. In addition, other visual systems such as chart recorders and decimal displays are installed.

A back-up photographic installation is available in all cells using manometers and pyrometers to record pressures and temperatures in an emergency or when checks on the normal instrument systems are desirable.

© Procurement Executive, Ministry Of Defence