ACOC-TH: Acoustic and thermal instrumentation, tests and modelling of engine surface coolers in representative aerodynamic conditions

The ACOC-TH project was funded by CleanSky.

New turbofan engine designs for greater efficiency are creating challenges for engine oil cooling. With financial support from the EU, ATM evaluated new air-cooled oil cooler (ACOC) heat exchanger concepts within the scope of the project ACOC-TH. ACOCs, also known as engine surface coolers, are commonly employed to cool oil for recyclation in the oil circuit of an aircraft engine.

Thermal performance is increased by adding longitudinal fins to increase surface area for exchange, but this can compromise aerodynamic performance. In light of this, in the fram of ACOC-TH mathematical mathematical descriptions of ACOC thermal behaviour were developed. New concepts testing in a transonic wind tunnel and in a surface ACOC test bed to maximise their aero-thermal performance. Mathematical descriptions of heat transfer in the case of ACOCs require knowledge of heat characteristics in places where measurement is not always possible. This imposes the necessity of solving a so-called inverse problem, for which a solution is not guaranteed to exist as it is in a direct problem.

Such problems can also be unstable to perturbations in input data. During the first 18 months of the ACO-TH project, researchers developed an inverse heat conduction method (IHCM) to estimate the heat flux distribution using infrared thermography temperature measurements. The new IHCM is robust to noisy data inputs and provides a solution to the 3D heat transfer problem with an average uncertainty below 20 %. Scientists also designed and utilised a wind tunnel test setup enabling optical access and measurements for advanced heat transfer analysis.

Optical access on one complete fin was not possible. However, the team successfully employed the new IHCM to assess the 3D heat transfer process.
Finally, they manufactured a surface ACOC test setup dedicated to conducting aero-thermal comparisons of various promising technologies by modifying parameters on the air or oil side.ACOC-TH has established the required mathematical and experimental testing tools to evaluate ACOC technologies for tomorrow’s eco-friendly turbofan engines.

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The projects achievements have resulted into following publications: