Periodic Reporting for period 2 - C-ALM AOHE (Compact - Additive Layer Manufactured Air Oil Heat Exchanger)
Reporting period: 2020-11-01 to 2022-10-31
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.
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.
The first steps in the project were collaboration between Meggitt’s engineers and TWI’s ALM experts to fully understand the design freedom offered by ALM in order to harness the benefits in a novel design of AOHE. A number of varied novel AOHE concepts were then generated and evaluated, considering performance and manufacture cost, resulting in one being selected to be developed into a real AOHE design during this project. A mathematical thermal model was developed based on Meggitt’s long experience in heat exchanger technology, allowing the selected concept to be refined into a design to meet the Topic Manager’s specification. A patent application has been submitted for this design. The complex geometric design has been rigorously explored and several iterations of the fluid flow channels have been simulated using computational fluid dynamics (CFD), and validated by physical testing of subscale parts.
An AOHE concept demonstrator unit was designed to prove out the design’s thermal and structural performance. The build and test of this part provided evidence for achieving TRL4 and MCRL3, and performance data allowed full validation of the thermal modelling and CFD.
The aluminium alloy AlSi10Mg was selected as the material for the novel AOHE, since its material properties meet the project specification especially with regard to operating temperature. Following procurement the powder was fully characterised.
The development of appropriate L-PBF parameters to achieve the required density and geometry for thick and thin material sections was completed though a detailed manufacturing study. For the L-PBF method of additive manufacture, the precise set of laser parameters influences the mechanical properties of the material. A programme of material characterisation with over 150 test points has been undertaken to produce a comprehensive Materials Datasheet for AlSi10Mg, including data across the operating temperature range of the AOHE ina VHBR/UHBR engine application.
The complex geometry of the novel AOHE design is pushing the boundaries of the existing L-PBF technology requiring significant innovation in the laser scan strategy, exploiting TWI’s expertise in this area. Meeting this technical challenge has involved manufacture of iterations of subscale models of elements of the novel design concept for evaluation using XCT scanning and physical test.
A product concept for a single piece build complete AOHE including novel integrated headers has been designed. This combines the novel core with further ALM-enabled features to create a low weight unit. A prototype unit based on this product concept was designed, sized to be built within the build chamber of the ALM machine capability of the subcontractor. Trials to de-risk the build of complex sections were performed, addressing the localised stresses and feature formation.
Over the course of the project the manufacturing challenges of creating consistent repeatable large parts using L-PBF have become appreciated, requiring robust process control as well as fundamental design phase understanding. This knowledge will enable Meggitt to exploit the technology and the novel AOHE in future demonstrators and products.
An AOHE concept demonstrator unit was designed to prove out the design’s thermal and structural performance. The build and test of this part provided evidence for achieving TRL4 and MCRL3, and performance data allowed full validation of the thermal modelling and CFD.
The aluminium alloy AlSi10Mg was selected as the material for the novel AOHE, since its material properties meet the project specification especially with regard to operating temperature. Following procurement the powder was fully characterised.
The development of appropriate L-PBF parameters to achieve the required density and geometry for thick and thin material sections was completed though a detailed manufacturing study. For the L-PBF method of additive manufacture, the precise set of laser parameters influences the mechanical properties of the material. A programme of material characterisation with over 150 test points has been undertaken to produce a comprehensive Materials Datasheet for AlSi10Mg, including data across the operating temperature range of the AOHE ina VHBR/UHBR engine application.
The complex geometry of the novel AOHE design is pushing the boundaries of the existing L-PBF technology requiring significant innovation in the laser scan strategy, exploiting TWI’s expertise in this area. Meeting this technical challenge has involved manufacture of iterations of subscale models of elements of the novel design concept for evaluation using XCT scanning and physical test.
A product concept for a single piece build complete AOHE including novel integrated headers has been designed. This combines the novel core with further ALM-enabled features to create a low weight unit. A prototype unit based on this product concept was designed, sized to be built within the build chamber of the ALM machine capability of the subcontractor. Trials to de-risk the build of complex sections were performed, addressing the localised stresses and feature formation.
Over the course of the project the manufacturing challenges of creating consistent repeatable large parts using L-PBF have become appreciated, requiring robust process control as well as fundamental design phase understanding. This knowledge will enable Meggitt to exploit the technology and the novel AOHE in future demonstrators and products.
The novel AOHE is predicted to equal or exceed the performance attributes of the state of the art, with identified potential to improve in all areas with further development. A key benefit of the novel concept is the lightweight structure, resulting in a lighter unit for engine installation.