Gas turbine engine having a heat exchanger located in an annular duct

A gas turbine engine for an aeronautical vehicle, the 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, and a turbine section arranged in serial flow order;
• a steam system comprising a boiler heat exchanger in fluid communication with the turbine section at a location downstream of the turbine section;
• and
• a rotor assembly driven by 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 of the gas turbine engine, the turbomachine comprising a substantially annular duct relative to the centerline of the gas turbine engine, the rotor assembly being part of the turbine section of the turbomachine;
• wherein the boiler heat exchanger is positioned at a location within the substantially annular duct and extends substantially continuously along the circumferential direction;
• wherein an effective transmission loss (ETL) for the boiler heat exchanger positioned within the substantially annular duct is between 5 decibels and 1 decibels for the operating condition;
• wherein the boiler 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:
• (
• sin
• ⁢
• (
• 2
• ×
• π
• ×
• f
• a
• Hot
• ×
• L
• i
• )
• )
• 2
• wherein αHot is representative of a speed of sound through the location of the gas turbine engine at 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.