Ventilation of the enclosure is provided by a ship cooling fan. The ventilation air exits the enclosure package via the exhaust stream downstream of the recuperator.
External to the enclosure are three separately mounted modules, the FW/SW intercooler, the lubrication module and the control system. The control system is a full authority digital controller (FADEC) known as the Electronic Engine Controller (EEC). The EEC controls the WR-21 system in response to commands from either the ships monitoring and control system or from the local man machine interface. The major functions of the controller include start/stop sequencing, steady state and transient control surveillance, fault detection and emergency stop procedures.
Ease of maintenance of the engine system was a key consideration during the design phase. A maintenance working group was established between the contractors and the Navies and appropriate design features were incorporated. These included additional borescope ports, easy access combustors, VANs, bleed valves and the retention of the aero modular concept. The aero RB211 parent is assembled in modules that are each individually balanced and feature a curvic coupling. This facility enables individual modules (compressors or turbines) to be replaced without the requirement for trim balancing. In 1999 the WR-21 completed its development testing. Over 2000 hours of testing has been accomplished since 1994 including two endurance tests. This testing has been supported by extensive rig and module testing and the use of analytical tools to investigate the effects of engine operation at all environmental conditions. Significant advancements in the available analysis tools have greatly reduced the amount of actual engine testing required and ensured that the actual testing undertaken is focused on the key areas.
Testing has been undertaken at both the Royal Navy test facility at Pyestock, Farnborough, UK and at the US Navy test facility at Philadelphia, USA. The latter facility was used to undertake the second endurance test that subjected the engine to the most arduous operating conditions. This test included cyclic and high power running coupled with intake salt ingestion and 1% sulphur fuel. The successful completion of this test and the subsequent engine inspection and post test review enabled the production standard to be declared and approved by the US, Royal and French Navies ready to enter the Introduction to Service Phase. The Introduction into Service consists of the engine system undertaking to an endurance trial and shock test. The endurance trial consists of 3000 hours of creep, performance and cyclic profiles representing the most extreme conditions seen in service by the navies of the world. The test shall be conducted at elevated cycle temperatures to simulate the extremes of ambient conditions likely to be experienced by the Navies during service. For marine application airborne salt is an obvious hazard and so to simulate the effects of compressor fouling and corrosion, the endurance trial shall be conducted with various levels of salt solution injected into the air intake.
Finally there is a direct relationship between the percentage of sulphur in the fuel and corrosion of the hot end of an engine. The range of sulphur content fuels likely to be encountered will depend upon economic, geographical and legislative factors with 1% sulphur by weight perceived to be the most likely worst fuel to be used. Thus for all the development tests and for the 3000 hour endurance trial 1% sulphur fuel is used. Figure 7 summarises the engineering and development programme undertaken since 1992.
