Midshaft rating for turbomachine engines
A turbomachine engine including an engine core including a high-pressure compressor, which has an exit stage having an exit stage diameter (D CORE ), a high-pressure turbine, and a combustion chamber in flow communication with the high-pressure compressor and the high-pressure turbine, a power turbine in flow communication with the high-pressure turbine, and a low-pressure shaft coupled to the power turbine and characterized by a midshaft rating (MSR) between two hundred (ft/sec) 1/2 and three hundred (ft/sec) 1/2 . The low-pressure shaft has a redline speed between fifty and two hundred fifty feet per second (ft/sec). The turbomachine engine is configured to operate up to the redline speed without passing through a critical speed associated with a first-order bending mode of the low-pressure shaft. The low-pressure shaft has a length (L MSR ) defined by an engine core length (L CORE ) given by: L CORE =[m (20+m) *n (10+n) ] (1/100) *D CORE +CIS.
1. A turbomachine engine comprising:
an engine core including a high-pressure compressor, which has an exit stage having an exit stage diameter (D CORE ), a high-pressure turbine, and a combustion chamber in flow communication with the high-pressure compressor and the high-pressure turbine;
a power turbine in flow communication with the high-pressure turbine; and
a low-pressure shaft coupled to the power turbine and characterized by a midshaft rating (MSR) between two hundred (ft/sec) 1/2 and three hundred (ft/sec) 1/2 ,
wherein the low-pressure shaft has a redline speed between fifty and two hundred fifty feet per second (ft/sec),
wherein the turbomachine engine is configured to operate up to the redline speed without passing through a critical speed associated with a first-order bending mode of the low-pressure shaft,
wherein the low-pressure shaft has a length (L MSR ) defined by an engine core length (L CORE ), and
wherein the engine core length (L CORE ) is given by:
L
CORE
=
[
m
(
20
+
m
)
*
n
(
10
+
n
)
]
(
1
100
)
*
D
CORE
+
CIS
,
where m is a number of stages of the high-pressure compressor, n is a number of stages of the high-pressure turbine, and CIS is a constant.
2. The turbomachine engine of claim 1 , wherein CIS is from twenty inches to thirty inches.
3. The turbomachine engine of claim 1 , wherein L CORE is from forty-three inches to eighty inches.
4. The turbomachine engine of claim 1 , wherein D CORE is from 13 inches to 41 inches.
5. The turbomachine engine of claim 1 , wherein the power turbine has four stages, five stages, or six stages.
6. The turbomachine engine of claim 1 , wherein n is one stage or two stages.
7. The turbomachine engine of claim 1 , wherein the power turbine comprises a ceramic matrix composite (CMC) material.
8. The turbomachine engine of claim 1 , wherein the length (L MSR ) is given by: L MSR =L IGB +L CORE +L AFT , where L IGB is a length forward of the core engine to the forward bearing and is from four inches to twelve inches and L AFT is a length from aft of the core engine to the aft bearing and is from two inches to twenty-four inches.
9. The turbomachine engine of claim 1 , wherein m is eight stages, nine stages, ten stages, or eleven stages.
10. The turbomachine engine of claim 9 , wherein m is nine stages.
11. The turbomachine engine of claim 1 , wherein the high-pressure turbine and the high-pressure compressor are connected to each other through a high-pressure shaft, and wherein the high-pressure shaft is characterized by a high-pressure shaft rating (HSR) given by:
HSR
=
10
-
6
*
N
2
r
/
l
*
D
CORE
*
(
L
CORE
D
CORE
)
2
,
where N2 r/l is a redline speed of the high-pressure shaft.
12. The turbomachine engine of claim 11 , wherein HSR is from 1.9 to 4.3.
13. The turbomachine engine of claim 11 , wherein N2 r/l is from 11000 RPM to 25000 RPM.
14. The turbomachine engine of claim 11 , wherein the high-pressure shaft is characterized by a second high-pressure shaft rating (HSR LP ) given by:
HSR
LP
=
10
-
6
*
N
1
r
/
l
*
D
CORE
*
(
L
CORE
D
CORE
)
2
,
where N1 r/l is a redline speed of the high-pressure shaft.
15. The turbomachine engine of claim 14 , wherein HSR LP is from 1.1 to 1.6.
16. The turbomachine engine of claim 1 , further including an electric machine coupled to the low-pressure shaft.
17. The turbomachine engine of claim 16 , wherein the electric machine is located aft of the power turbine.
18. The turbomachine engine of claim 1 , further comprising a primary fan driven by the power turbine through a gearbox assembly and a flex coupling that couples the gearbox assembly to the low-pressure shaft.
19. The turbomachine engine claim 18 , wherein the flex coupling is characterized by a decoupler moment stiffness in a range of 50 klb*in/rad to 200 klb*in/rad and a decoupler shear stiffness in a range of 100 klb/in to 500 klb/in.
20. A method of operating the turbomachine engine of claim 1 , the method comprising:
operating the turbomachine engine to generate an engine thrust wherein a linear speed of the low-pressure shaft does not exceed three hundred feet per second.