58942 - Design and Analysis of an Aircraft Thermal Management System Linked to a Low-Bypass Ratio Turbofan Engine 

The design of an aircraft thermal management system (TMS) that is capable of rejecting heat loads into the bypass stream of a typical low-bypass ratio turbofan engine, or a ram-air stream, is investigated. The TMS consists of two primary sub-systems: an air cycle system (ACS) and a vapor cycle system (VCS). The ACS, which is similar to the typical air cycle machines (ACMs) used on current aircraft, both military and commercial, supercharges compressor bleed air and uses heat exchangers in the engine bypass stream or a ram air stream to cool the engine bleed air prior to expanding it to low temperatures suitable for heat rejection. The VCS uses engine fuel flow as a heat sink to absorb a portion of the demanded heat load from the aircraft. In this study, a simple low-bypass ratio afterburning turbofan engine was modeled in NPSS to provide boundary conditions to the TMS system throughout the flight envelope of a typical military fighter aircraft. The engine was sized to produce sea level static (SLS) thrust roughly equivalent to that of an F-35-class engine. Various aircraft heat loads, including environmental control system (ECS) loads, avionics cooling loads, and other miscellaneous loads were modeled, and the ability of the TMS system to reject these loads was analyzed. The architecture and modeling of the TMS is described in detail, and the load dissipation capability of the TMS was investigated at typical mission points, along with the impact of ACS engine bleeds on engine thrust and fuel consumption. A comparison is made between the cooling capabilities of the ram-air stream versus the engine bypass stream, along with the benefits and drawbacks of each cooling stream. It is observed that the maximum load dissipation capability of the TMS is tied to the temperature and amount of cooling stream flow, as well as the amount of engine bleed flow. These results demonstrate the advantage that adaptive, variable cycle engines (VCEs) may have for future military aircraft designs, and may be used to improve potential future TMS/engine integration. Eventually, an architecture similar to the one proposed here may be used in the development of an integrated propulsion, power, and thermal management system (IPPTMS) for a variable cycle engine.