Transpiration Cooling Systems for Jet Engine Turbines and Hypersonic Flight

This grant will deliver a step change in the understanding and predictability of next generation cooling systems to enable
the UK to establish a global lead in jet engine and hypersonic vehicle cooling technology.
We aim to make transpiration cooling, recognised as the ultimate convective cooling system, a reality in UK produced jet
engines and European hypersonic vehicles. Coolant has the potential to enable higher cycle temperatures (improving efficiency following the 2nd law of thermodynamics) but invariably introduces turbine stage losses (reducing efficiency). Cooling system improvement must enable higher Turbine Entry Temperature (TET) while using the minimum amount of coolant flow to achieve the required component life. For high speed flight, heat transfer is dominated by aerodynamic heating with gas temperatures on re-entry exceeding those at the surface of the sun. Any
reduction in heat transfer to the Thermal Protection System will ultimately lead to lower mass, allowing for decreased launch costs Furthermore, the lower temperatures could serve as an enabler for higher performance technologies which are currently temperature limited.

The highest temperatures achievable for both jet engines and hypersonic flight are limited by the materials and cooling
technology used. The cooling benefits of transpiration flows are well established, but the application of this technology to aerospace in the UK has been prevented by the lack of suitable porous materials and the challenge of accurately modelling both the aerothermal and mechanical stress fields. Our approach will enale the coupling between the flow, thermal and
stress fields to be researched simultaneously in an interdisciplinary approach which we believe is essential to arrive at the best transpiration systems. This Progreamme Grant will enable world leaders in their respective fields to work together to solve the combination of cross-disciplinary problems that arise from the application of transpiration cooling, leading to rapid innovations in this technology. The
application is timely since the proposed research would enable the UK aerospace industry to capitalise on recent
developments in materials, manufacturing capability, experimental facilities/measurement techniques and computational
methods to develop the science for the application of transpiration cooling.
The High Temperature Research Centre at Birmingham University will provide the means to cast super alloy turbine aerofoils with porosity. The
proposed grant would allow innovation in the cast systems arising from combining casting expertise with aerothermal and
stress modelling in recent EPSRC funded research programmes. It also builds upon material development of ultra-high
temperature ceramics and carbon composites undertaken in EPSRC funded research, by use of controlled
porosity and multilayer composites. It will also provide the first opportunity to undertake direct coupling of the flow with the
materials (porous and non-porous) at true flight conditions and material temperatures.
Recent investment in the UK's wind tunnels under the NWTF programme (EPSRC/ATI funded) at both Oxford University and
at Imperial College will allow for direct replication of temperatures and heat fluxes seen in flight and interrogated using
advanced laser techniques. Recent development of Fourier superposition in CFD grids for modelling film cooling can now
be extended to provide a breakthrough method to predict cooling flow and metal effectiveness for high
porosity/transpiration cooling systems.
The European Space Agency has recently identified the pressing requirement for alternatives to one-shot ablative Thermal
Protection Systems for hypersonic flight. Investment in this area is significant and transpiration cooling has been identified
as a promising cooling technology. Rolls-Royce has embarked upon accelerated investment in new technologies for future jet engines including the ADVANCE

will benefit the UK engine aero-engine manufacturing sector by addressing the need for blue-sky research to provide crucial engineering science for future engines. The sector is highly competitive (with fierce competition from the USA and growing competition from Asia) and research in this field is vital for future aerospace products. Our intent is that this grant will play a significant part in underpinning the hot stage technology that is vital for future turbofans and future hypersonic vehicles. Our grant is technically very ambitious and funding from EPSRC at this stage is essential for the UK to make the progress we need.

We expect our work to lead to other R&D / BIS funded research (co-funded by industry) to integrate the technology into engines - for example, research into air system innovations to remove particles from the cooling air. Several associated programmes have already been identified and confirmed in the letter of supports from Rolls-Royce, DSTL, MBDA and LMCO. We will disseminate the results internationally through conferences, journals and research networks which will broaden international collaboration and present opportunities for future international collaborations and funding.

The jet engines are likely to be manufactured in the UK. The UK aerospace sector employs over 300,000 people in the UK both directly in the OEMs and in the specialised supply chain. Salaries paid to the high value jobs in this successful sector benefit the UK economy and these benefits are especially welcome in the East Midlands and the Bristol areas where manufacturing employment is key to the economy.

Passengers will benefit from improvements in engine efficiency reducing fuel costs and ticket prices. Similarly, this technology will eventually enable commercial hypersonic flight and improve launch costs by moving to reusable air-breathing engines such as those proposed by Reaction Engines. The airlines will be able to improve competitiveness through using more fuel efficient jet engines.

The cost of air travel is dominated by fuel costs, so the fuel efficiency improvements will support reduction in ticket costs. The aero-engine industry is committed to developing technology to reduce engine fuel burn so that
modern engines can replace older, less efficient engines.

The environment will benefit from reduced CO2 emissions from improved jet engines. Estimates of the benefits from the theoretical performance of transpiration cooling show that, for a certain class of turbofan, the engine efficiency gain from the potential reduction in coolant is estimated as capable of reducing CO2 emissions by over 180,000kg per engine per year.

Pupils and students inspired by the research will seek careers in aerospace and engineering. Jet engines and hypersonic vehicles are naturally inspiring to many pupils, students and the wider public. This will ensure that this exciting and world leading research enables us to advocate engineering and STEM subjects at outreach and public engagement activities. If successful, we envisage that the research will culminate in a flight demonstration of the transpiration cooling technology both in jet engines research (through Rolls-Royce) and in a rocket test (through DSTL).

Development of transpiration cooling has direct impact in future capabilities for the UK defence. This can be applied to improve performance and reliability of high speed missile interceptors and to understand capability of external weapon system. The new numerical approaches can not only be applied in simulating the cooling, but also as a basis for ablation modelling.

Other UK industry will gain from recruiting the students and postdoctoral researchers who work on this research. The research and engineering skills acquired by postgraduates and postdoctoral researchers will read across well into other fields of mechanical engineering.