Gas turbine engine transfer efficiency
A gas turbine engine for an aircraft includes an engine core including a first, lower pressure, turbine, a first compressor, and a first core shaft connecting the first turbine to the first compressor; and a second, higher pressure, turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor, and a fan located upstream of the engine core and including a plurality of fan blades extending from a hub. A low pressure turbine temperature change is defined as: the first turbine entrance temperature the first turbine exit temperature . A fan tip temperature rise is defined as: the fan tip rotor exit temperature the fan rotor entry temperature . A turbine to fan tip temperature change ratio of: the low pressure turbine temperature change the fan tip temperature rise is in the range from 1.46 to 2.0.
1. A method of operating a gas turbine engine on an aircraft, the gas turbine engine comprising:
an engine core comprising a first turbine, a first compressor, and a first core shaft connecting the first turbine to the first compressor; and a second turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor, the second turbine being a higher pressure turbine than the first turbine and the second compressor being a higher pressure compressor than the first compressor, wherein a first turbine entrance temperature is defined as an average temperature of airflow at the entrance to the first turbine at cruise conditions and a first turbine exit temperature is defined as an average temperature of airflow at the exit from the first turbine at cruise conditions, and a low pressure turbine temperature change is defined as:
the
first
turbine
entrance
temperature
the
first
turbine
exit
temperature
,
the engine core further comprising an annular splitter at which flow is divided between a core flow that flows through the engine core, and a bypass flow that flows along a bypass duct, wherein stagnation streamlines around the circumference of the engine, stagnating on a leading edge of the annular splitter, form a streamsurface forming a radially inner boundary of a streamtube that contains all of the bypass flow;
a fan located upstream of the engine core, the fan comprising a plurality of fan blades extending from a hub, each fan blade having a leading edge and a trailing edge, each fan blade having a radially outer portion lying within the streamtube that contains the bypass flow, and wherein a fan rotor entry temperature is defined as an average temperature of airflow across the leading edge of each fan blade at cruise conditions and a fan tip rotor exit temperature is defined as an average temperature of airflow across the radially outer portion of each fan blade at the trailing edge at cruise conditions and a fan tip temperature rise is defined as:
the
fan
tip
rotor
exit
temperature
the
fan
rotor
entry
temperature
,
and wherein a turbine to fan tip temperature change ratio of:
the
low
pressure
turbine
temperature
change
the
fan
tip
temperature
rise
rise is in the range from 1.46 to 2.0.
2. The method of claim 1 , wherein the turbine to fan tip temperature change ratio is in the range from 1.5 to 1.8.
3. The method of claim 1 , wherein the fan tip temperature rise is in the range from 1.05 to 1.1.
4. The method of claim 1 , wherein the low pressure turbine temperature change is in the range from 1.6 to 1.85.
5. The gas turbine engine according to claim 1 , wherein the engine comprises more than two turbines and wherein a highest pressure turbine of the engine is selected as the second turbine and a lowest pressure turbine of the engine is selected as the first turbine.
6. The method according to claim 1 , wherein a specific thrust of the engine at cruise conditions, defined as net engine thrust divided by mass flow rate through the engine, is in the range from 50 to 100 Nkg −1 s.
7. The method according to claim 1 , wherein a quasi-non-dimensional mass flow rate Q is defined as:
Q
=
W
T
0
P
0
.
A
f
a
n
.
where:
W is mass flow rate through the fan in Kg/s;
T 0 is average stagnation temperature of the air at the fan face in Kelvin;
P 0 is average stagnation pressure of the air at the fan face in Pa;
A fan is the area of the fan face in m 2 ;
and has a value in the range from 0.025 to 0.038 Kgs −1 N −1 K 1/2 at cruise conditions.
8. The method according to claim 7 , wherein Q takes a value less than or equal to 0.035 Kgs −1 N −1 K 1/2 at cruise conditions.
9. The method according to claim 1 , wherein a fan tip loading at cruise conditions is defined as dH/U tip 2 , where dH is an enthalpy rise across the fan and U tip is the velocity of the fan tip is in the range from 0.25 to 0.4.
10. The method according to claim 1 , wherein cruise conditions means the conditions at mid-cruise of the aircraft to which the engine is attached.
11. The method according to claim 1 , wherein a forward speed of the gas turbine engine at the cruise conditions is in the range of from Mn 0.75 to Mn 0.85.
12. The method according to claim 1 , wherein the cruise conditions correspond to atmospheric conditions defined by the International Standard Atmosphere at an altitude of 11582 m and a forward Mach Number of 0.8.
13. The method according to claim 1 , wherein the cruise conditions correspond to atmospheric conditions defined by the International Standard Atmosphere at an altitude of 10668 m and a forward Mach Number of 0.85.
14. The method according to claim 1 , wherein the cruise conditions correspond to atmospheric conditions at an altitude that is in the range of from 10500 m to 11600 m.
15. The method according to claim 1 , wherein an Overall Pressure Ratio (OPR) at cruise is greater than 40 and lower than 80.
16. The method of claim 1 , wherein:
(i) the fan tip radius is in the range from 110 cm to 150 cm; or
(ii) the fan tip radius is in the range from 155 cm to 200 cm.
17. The method according to claim 1 , further comprising a gearbox that receives an input from the first core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the first core shaft, and wherein, optionally, the gearbox has a gear ratio in the range of from 3.2 to 5.
18. The method according to claim 1 , wherein the first turbine has four or more rotor stages.