SP3 ‘Intercooled Core’ Editorial

As outlined by our Chief engineer in the last NEWAC editorial, the aviation industry faces a big challenge in minimising the environmental impact of commercial aviation and meeting the ACARE targets.  Having previously participated in SILENCE(R), which was another pan-European project, co-funded by the EU and targeting noise reduction, I joined the NEWAC team well aware of the difficult task of developing cost effective technological solutions to meet these targets.

[Begleittext / Subline: Fig 1 – SP3 Intercooled Core ]

In our sub-project we are developing the concept of the intercooled core compression system. At the heart of the intercooled core lies a fundamental thermodynamic principle – if we are able to reduce the temperature and increase the density of the core gas stream part way through its compression cycle, then the work required to further compress the air prior to combustion can be reduced. 

In NEWAC the intercooled core is being studied in conjunction with the Lean Direct Injection (LDI) combustor technology in SP6, which is well suited to the high overall pressure ratio core design.  Reductions of up to 4% in C02 and 16% in NOx emissions are potentially achievable just from the SP3 and SP6 technologies, depending on how the technologies are exploited. 

The technological challenge lies in realizing the environmental benefits within the real engineering constraints of a compression system that is already highly optimised.  The 3-shaft engine architecture is particularly well suited to intercooling, since the split in compression between the Intermediate Pressure (IPC) and High Pressure (HPC) compressors provides a natural point at which to cool the core gas stream using readily available cooling air taken from the fan bypass air stream (see Fig. 1)

[Begleittext / Subline: Fig 2 – Intercooler Arrangement ]

The SP3 team has already made some great advances in the underpinning technologies for a successful intercooled core.  Studies of the engine intercase design have gone a long way towards answering the question of where and how best to duct the compressed air and cooling air to and from the heat exchangers, as well as how to arrange the heat exchangers for maximum effectiveness (see Fig. 2).  The optimisation of the duct aerodynamics has been carried out in parallel with the task of optimising the mechanical design of the intercase structure and validating its behaviour through whole engine mechanical modelling.

[Begleittext / Subline: Fig 3 – Duct aerodynamics testing ]

Scale models of the duct designs have now been tested (see Fig. 3) and the results have shown we are close to achieving our aggressive performance targets.  The design and manufacture of the heat exchanger itself is another key technology, and we are charting new territory in optimising a compact cross-corrugated heat exchanger design for this demanding environment.  The chosen matrix design and manufacturing processes have been determined and we are getting ready for prototype testing. 

Compressor design is critical to achieving the efficiency gains of the intercooled core, and as such, detailed computational studies have been carried out utilising the latest automated design methods to truly optimise the aerofoil shapes in the 3D environment.  At the same time, recognising that the operability of a compressor integrated with novel flow paths in a high overall pressure ratio engine is potentially challenging, stability enhancement technologies are being developed based on computational studies and backed up by low speed testing.   

[Begleittext / Subline: Fig 4 Compressor Rig ]

The compressor technologies are soon to be tested on a purpose built high-speed rig (see Fig. 4), which will validate these advances in both efficiency and operability.

With various rig tests now coming to fruition this is an exciting time for SP3. Validation of our design philosophy and environmental targets is the primary goal but there is also the chance to highlight further opportunities for improvement.

Nick Baker
SP Leader

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