CPC F02C 7/36 (2013.01) [F01D 15/12 (2013.01); F01L 15/12 (2013.01); F02C 3/113 (2013.01)] | 20 Claims |
1. A method of operating a gas turbine engine on an aircraft, the gas turbine engine comprising:
an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor;
a fan located upstream of the engine core, the fan comprising a plurality of fan blades; and
a gearbox that receives an input from the core shaft to drive the fan at a lower rotational speed than the core shaft, wherein
the method comprises operating the gas turbine engine to provide propulsion under cruise conditions such that a product of a jet velocity ratio RJ and a gear ratio of the gearbox is between 2.4 and 4.7,
the jet velocity ratio, RJ, is determined by the following formula:
where VB is the fully expanded first jet velocity, CB is a thrust coefficient of the bypass nozzle, VC is the fully expanded second jet velocity, CC is a thrust coefficient of the core exhaust nozzle, ηLPT is an isentropic efficiency of a lowest pressure turbine of the engine core and ηF is an isentropic efficiency of compression of air into the bypass duct by the fan, and
the bypass ratio is in the range 13 to 16.5, the bypass ratio being defined as defined as the ratio of the mass flow rate of the flow through the bypass duct to the mass flow rate of the flow through the core at the cruise conditions.
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