Objectives
The Compact - Additive Layer Manufactured Air Oil Heat Exchanger (C-ALM AOHE) project will design, develop, manufacture and test a compact air-oil heat exchanger for next generation geared VHBR/UHBR turbofan engines. It will deliver a fully validated air-oil heat exchanger to TRL6, MCRL4 and MRL6 with a heat load of 80kW and a dry weight of significantly less than 10kg that can directly flow into follow on flight demonstrator and NPI programmes.
Context
Advanced, high efficiency thermal management is an enabling technology for the next generation of VHBR/UHBR (Very- and Ultra-High Bypass Ratio) aero engines. These new engine architectures will incorporate a power gearbox to drive the fan, generating additional heat load, and will improve specific heat consumption, reducing the fuel available as a heat sink. C-ALM AOHE will deliver the step-change air-oil heat exchanger technology required to manage the thermal load of VHBR/UHBR engines with the over-arching goal of the project being to position Europe to be the world‘s number one in the technology and sales of gas turbine aero engine air-oil heat exchangers; a market segment that is forecast to be worth more than €1.5 bn over the next twenty years, with a higher growth rate than average for aerospace.
Approach
ALM opens up the heat exchanger design space by enabling the manufacture of complex structures that could not previously be built with any conventional manufacturing process. However, it is critical that these new complex structures are developed to not only have step change thermal, pressure loss and air side mass flow performance; but also must have the mechanical integrity to meet all life requirements and the requisite unit cost and through life cycle costs to make sound business cases for both supplier and customer.
The ALM technology selected for this project is laser powder bed fusion (L-PBF). L-PBF ALM technology is not currently proven to MCRL4 for the manufacture of aerospace ALM components thus this capability will be developed during the project.
The C-ALM AOHE project will focus on aluminium alloy as the material for the manufacture of the design based on the requirements related to heat transfer, mass efficiency, cost and a maximum surrounding air temperature of 220 °C.
Conclusions
The work of this project has resulted in a novel concept for an additively manufactured Air Oil Heat Exchanger of lighter weight than the state of the art, and gravimetric heat transfer of the core matrix is 1.3 times greater than the State of the Art. It is a one-piece design and features novel AM-enabled heat transfer surfaces and integrated headers. While designed to meet the requirements for an UHBR engine, the design is scalable to suit other engine applications.
The work has explored the interaction of design and manufacturing method, and pushed the boundaries of the laser powder bed fusion technique to create leak tight thin walls. Material characterisation campaigns have provided mechanical property data specific to the method of manufacture, to be used in the design and structural analysis.
Demonstrator units were manufactured and tested to prove the heat exchange core concept and guide design improvements as the core was integrated into a full product concept. A prototype was designed and manufactured, but was not able to undergo performance testing within the project timeframe. Meggitt will continue to take this to TRL6 and MCRL4 and exploit the technology.
