Experimental and numerical investigation on cooling ducts for thermal management of fuel cell based aero engines

Abstract

Effective thermal management is crucial for the development of future electrified aircraft propulsion systems. One of the critical phases is the take-off phase posing particularly high demands on cooling systems. In addition, the aerodynamic drag during cruise flight has to be kept to a minimum. This study introduces a novel experimental thermal management system (TMS) test stand with a modular air duct, designed specifically to investigate different configurations of air supply and heat exchangers in fuel cell-based electrified propulsion systems. Given the versatility in nacelle-integrated electrified propulsion architectures, this approach offers high flexibility in design and integration of TMS. This includes aspects such as the location, orientation and geometry of an air-cooled heat exchanger (HEX), as well as inlet and outlet configurations. Moreover, the optimization of the uniform flow guidance of the duct flow within the nacelle and the integration of additional fans to ensure airflow in critical conditions can be studied. Various system components, including particle separators, grids and filters, can be incorporated to examine their thermal behavior within a controlled experimental environment, facilitating a fundamental understanding of their interactions. The TMS experimental setup, depicted in Figure 1, consists of air inlet, several modular air ducts with a cross-sectional area of 20 cm x 20 cm emulating nacelle-integrated flow guidance. Test sections for HEX, fans, adapters and to integrate sensors allow the study of heat and fluid flow dynamics. Module segments are designed to be both extendable and interchangeable according to the engine and aircraft requirements. They are made from acrylic glass to enable optical measurements of fluid flow, while additional short modules facilitate probe-based measurements. A thermostat unit is used as main heat source, delivering up to 6 kW of heating power and temperature range from -20°C to 200 °C. The study measures the heat flux and pressure losses within these systems and includes thorough fluid flow analysis. Furthermore, the experimental data serves as a valuable resource for validating numerical models of cooling ducts, enhancing the accuracy and reliability of future design iterations. For that purpose, the agreement between Large Eddy Simulations and the experimental findings is discussed.