Operation Strategies for An Engine-Integrated Thermal Management System in Fighter Aircraft

Abstract

Managing the rising thermal loads of modern military aircraft has become increasingly difficult as avionics, sensors, and power electronics grow in power. This demands advanced Thermal Management Systems (TMS) that combine multiple heat sinks while maximizing cooling capacity and efficiency. Although reverse Brayton cycle (RBC) TMS architectures are well established, effective operation strategies under off-design mission and environmental conditions remain limited.

This paper examines an engine-integrated TMS using a closed RBC that rejects heat to the engine bypass stream. Several off-design operation strategies are evaluated to determine an approach that enhances operating range and overall efficiency. The strategies include varying turbo component shaft speed, adjusting fluid inventory, and introducing bypass flows around either the cooling turbine or the bypass-duct heat exchanger.

Results show that shaft speed variation provides the largest cooling capacity. To maintain adequate surge margin at low loads, it must be combined with a cooling turbine bypass. In terms of efficiency, measured by coefficient of performance (COP), shaft speed adjustment is most effective at low and high loads, while fluid-inventory changes are more beneficial at medium loads. A load-dependent combined and concurrent use of both strategies therefore offers the best balance between wide operating capability and minimized drive power. These results highlight the significant performance gains enabled by optimized TMS operation.