Gas Turbine Engine with Third Stream

A method of operating a gas turbine engine, the method comprising:

• operating the gas turbine engine at a rated speed, wherein operating the gas turbine engine at the rated speed comprises operating the gas turbine engine to define a thrust to power airflow ratio between 3.5 and 100 and a core bypass ratio between 0.1 and 5, wherein the thrust to power airflow ratio is a ratio of an airflow through a bypass passage over a turbomachine of the gas turbine engine plus an airflow through a fan duct to an airflow through a core duct, and wherein the core bypass ratio is a ratio of the airflow through the fan duct to the airflow through the core duct;
• separating a stream of air between a first fan stream flowing toward an upper fan duct inlet and an inner stream flowing toward a lower fan duct inlet and the core inlet;
• and
• separating the inner stream into a second fan stream flowing into the lower fan duct inlet and a core stream flowing into the core inlet.

A gas turbine engine comprising:

• a turbomachine comprising a compressor section, a combustion section, and a turbine section arranged in serial flow order, the turbomachine defining an engine inlet to an inlet duct, a fan duct inlet to a fan duct, and a core inlet to a core duct;
• a primary fan driven by the turbomachine;
• a secondary fan located downstream of the primary fan within the inlet duct;
• a core cowl;
• and
• a booster located downstream of the secondary fan and comprising a booster rotor blade and a booster cowl, the booster cowl located outward of the booster rotor blade and within the fan duct at the fan duct inlet, the booster cowl separating an upstream portion of the fan duct into an upper fan duct having an upper fan duct inlet and a lower fan duct having a lower fan duct inlet, the upper fan duct inlet and lower fan duct inlet collectively forming the fan duct inlet, the booster including a midspan shroud coupled to the booster rotor blade.