Abstract

The integrated design of a variable cycle engine (VCE) and an aircraft thermal management system (TMS) is investigated. The integrated system is designed using the multiple design point (MDP) approach in order to achieve required performance metrics at points other than the cycle design condition. The VCE architecture under investigation is a three-stream design where the third-stream is split off after the fan, exhausting through a separate third-stream nozzle. The primary air stream passes through a low-pressure compressor before splitting into an inner bypass stream and a core stream. The inner bypass and core streams mix aft of the low-pressure turbine and exhaust through a core nozzle. The variable cycle engine utilizes multiple variable geometry components: variable compressor inlet guide vanes (IGVs), a variable area bypass injector (VABI) at the inner bypass / core stream mixing plane, and variable throats in the two exhaust nozzles. The TMS architecture modeled is an open-loop air cycle system (ACS) that uses air bled from the high-pressure compressor as the working medium. The bleed air passes through heat exchangers (located in the engine third stream) before and after passing through a supercharging compressor, and is then expanded through two turbines to reach the low temperatures required to absorb heat from the aircraft cooling system. The effect of integrating the TMS into the engine design loop is investigated. In addition, a comparison is made to prior studies, where the same TMS architecture was connected to a low-bypass ratio turbofan engine, with the heat exchangers placed in either a ram-air stream or the engine bypass stream. The comparison shows that the variable cycle engine is able to improve heat dissipation capability versus a ram-air cooled system, while eliminating the airframe integration impact that comes with a separate ram-air stream. Lastly, the impact of modulating the variable geometry features on overall cooling capability is investigated. Results are presented for individual operating points as well as at the aircraft mission level.

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