Gas turbine engine

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 and comprising a plurality of primary fan blades;
• an outer nacelle surrounding the primary fan;
• a secondary fan located downstream of the primary fan within the inlet duct;
• and
• a plurality of outlet guide vanes disposed aft of the primary fan;
• a blade effective acoustic length (BEAL) defined as:
• BEAL
• =
• 2
• ⁢
• c
• 2
• S
• ⁡
• (
• 1
• -
• r
• ⁢
• r
• )
• ⁢
• N
• b
• ⁢
• c
• ⁢
• os
• ⁢
• (
• γ
• )
• wherein c is a chord length of a primary fan blade of the plurality of primary fan blades, S is a span of the primary fan blade, rr is a radius ratio of the primary fan, γ is a stagger angle of the primary fan blade, and Nb is a number of the plurality of primary fan blades;
• an inlet-to-nacelle (ITN) ratio between 0.23 and 0.35;
• and
• an acoustic spacing ratio (ASR) between 1.5 and 16.0, wherein the acoustic spacing ratio is defined as:
• ASR
• =
• 1
• (
• N
• ⁢
• v
• N
• ⁢
• b
• )
• ·
• A
• ⁢
• s
• B
• ⁢
• E
• ⁢
• A
• ⁢
• L
• wherein As is the acoustic spacing and Nv is a number of the plurality of outlet guide vanes,
• wherein the gas turbine engine defines a thrust to power airflow ratio between 3.5 and 100 and a core bypass ratio between 0.1 and 10,
• wherein the thrust to power airflow ratio is a ratio of an airflow through a bypass passage over the turbomachine plus an airflow through the fan duct to an airflow through the core duct,
• wherein the core bypass ratio is a ratio of the airflow through the fan duct to the airflow through the core duct, and
• wherein the ITN ratio is a ratio of an inlet length to a maximum diameter of the outer nacelle.