| CPC F02K 3/115 (2013.01) [F02C 6/08 (2013.01); F02C 7/18 (2013.01)] | 20 Claims |

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1. A gas turbine engine defining a centerline, a radial direction, and a circumferential direction, the gas turbine engine comprising:
a turbomachine comprising a compressor section, a combustion section, a turbine section, and an exhaust section arranged in serial flow order, the exhaust section including a primary exhaust flowpath and a waste heat recovery flowpath parallel to the primary exhaust flowpath, the waste heat recovery flowpath comprising a substantially annular portion;
a rotor assembly incorporated into the turbomachine and operable at a blade passing frequency (f) greater than or equal to 300 hertz and less than or equal to 12,500 hertz during an operating condition; and
a heat exchanger positioned within the substantially annular portion of the waste heat recovery flowpath and extending substantially continuously along the circumferential direction;
wherein an effective transmission loss (ETL) for the heat exchanger positioned within the substantially annular portion is between 5 decibels and 1 decibels for the operating condition;
wherein the heat exchanger comprises a heat transfer section defining an acoustic length (Li), and wherein an Operational Acoustic Reduction Ratio (OARR) is greater than or equal to 0.75 to achieve the ETL at the operating condition, the OARR equal to:
![]() wherein aHot is representative of a speed of sound through a hot location of the gas turbine engine during the operating condition and is greater than or equal to 24,756 inches per second and less than or equal to 30,924 inches per second during the operating condition.
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