Current surface coolers are parasitic to the existing engine structure, and occupy surfaces that can also be used for acoustic treatment to control engine noise. As such the weight, volume and efficiency of the surface cooler are all of great importance. The design and installation of a compact and lightweight structural surface cooler in a core fairing structure will contribute positively to the efficiency of the power-plant by providing the necessary oil cooling at minimum overall weight and hence optimal fuel burn.
The project's aim is to develop and demonstrate an advanced structural surface cooler mounted in an appropriate core fairing composite structure. Currently surface coolers are an integral feature of advanced turbofan engine designs. They contribute to achieving the best engine performance by maintaining oil and fuel temperatures within defined limits and by virtue of their mounting on the inside of the fancase they obviate the need for additional ducting of air and a control valve to switch the air on/off. The lack of ducting and control valve leads to an overall cost and weight reduction. Oil and/or fuel is cooled by the passage of cool engine bypass air flow over the air washed surface of the heat exchanger.
Also it is envisaged that surface cooler/composite core fairing designs will evolve that employ novel structural design, advance manufacturing techniques, potentially novel materials and new concepts in utilising air washed surfaces on the engine. The structural integration of the metallic structural surface cooler to a composite core fairing type structure has been identified as an important area for success. The joint must allow a strong load path, handle dissimilar degrees of thermal displacement and provide sealing yet being light and durable. Therefore mounting of such a surface cooler in a composite core fairing structure will also be researched for future engines where composite air washed structures may be used.
Innovative heat exchangers for aero engines
EU-funded scientists are developing advanced surface coolers that are compact and lightweight to cool engine fuel and oil in aircraft. Potential applications include civil markets.
Air-to-oil heat exchangers are an integral feature of advanced turbofan engine designs. By maintaining oil and fuel temperatures within defined limits, the surface cooler contributes to achieving optimal engine performance. The passage of cool bypass flow over the air-washed surface of the heat exchanger cools oil and fuel.
However, current surface coolers are parasitic to the engine and also occupy surfaces that serve for abating engine noise. As such, their weight, volume and efficiency become critical issues.
In the EU-funded project 'Surface heat exchangers for aero-engines' (SHEFAE), scientists are designing and manufacturing a metallic surface cooler that will replace a part of the core fairing structure. Exploiting existing air-washed structures removes spatial constraints and helps to dissipate more heat. Furthermore, lightweight surface coolers mounted on the fairing result in increased power plant efficiency and reduced fuel consumption.
Use of composite materials for the fairing structure yields additional weight reductions. Research into composite materials, manufacturing techniques and surface cooler structural design includes challenges associated with thermal displacement, sealing and joining.
Once developed, the cooler will be installed and tested on a demonstrator engine, forming part of its heat management system. Project members have drafted the requirements for the structural surface cooler with respect to oil cooling, design point conditions, oil pressure drop and de-congealing. A preliminary and a critical design review are complete. Three newly developed test rigs will validate the component design.
The team has also drafted specifications for the mount composite structure (MCS) and investigated possible geometrical designs that were able to give good specific stiffness at low weight. Focus has been placed on fibre-reinforced composites and their manufacturing for the MCS. The team has conducted experimental tests on composite laminates to identify the main failure mechanisms and validate the newly developed models for composite bolted joints.
SHEFAE is contributing to the highly ambitious goals of the European Vision for Aviation 2050 for serving society and market needs. The project is also strengthening the link between European and Japanese research and technology partners and between European and Japanese industries.