Turbofan engine having a low-pressure turbine
A turbofan engine having a low-pressure turbine that has at last four stages, at least one of the four stages having a transonic airfoil cascade is provided.
1 . A turbofan engine comprising:
a low-pressure turbine having at least four stages, at least one of the four stages having a transonic airfoil cascade,
wherein the last downstream airfoil cascade is a transonic airfoil cascade and at least one of the airfoil cascades upstream from the downstream airfoil cascades is not transonic.
2 . The turbofan engine as recited in claim 1 wherein the transonic airfoil cascade is a transonic vane cascade.
3 . The turbofan engine as recited in claim 1 wherein the transonic airfoil cascade is a transonic blade cascade.
4 . The turbofan engine as recited in claim 1 wherein a transonic airfoil of the transonic airfoil cascade has a suction side surface including a linear portion having a linear profile when viewed in a sectional plane of the airfoil.
5 . The turbofan engine as recited in claim 4 wherein the linear profile in the sectional plane of the airfoil extends over at least 10% of an axial width of the transonic airfoil.
6 . The turbofan engine as recited in claim 4 wherein the linear profile in the sectional plane of the airfoil extends radially over at least 10% of a radial length of the transonic airfoil.
7 . The turbofan engine as recited in claim 4 wherein the linear profile has a curvature when viewed in the sectional plane of the airfoil, the curvature deviating from a linear shape by at most 5%.
8 . The turbofan engine as recited in claim 4 wherein the linear portion in the sectional plane of the airfoil is located immediately adjacent a trailing edge radius or a trailing edge curvature of the transonic airfoil.
9 . The turbofan engine as recited in claim 4 wherein a plurality of transonic airfoil cascades each have a respective transonic airfoil having a respective linear portion, wherein a respective total area of the respective linear portion increases from each of the plurality of airfoil cascades to a next airfoil cascade of the plurality of airfoil cascades in the downstream direction.
10 . The turbofan engine as recited in claim 1 wherein at least two of the stages have a respective transonic airfoil cascade.
11 . The turbofan engine as recited in claim 1 wherein at least three of the stages have a respective transonic airfoil cascade.
12 . The turbofan engine as recited in claim 1 wherein at least four of the stages have a respective transonic airfoil cascade.
13 . The turbofan engine as recited in claim 1 wherein the low-pressure turbine has exactly four stages.
14 . The turbofan engine as recited in claim 1 wherein the turbofan engine is a geared turbofan engine having a fan and a gearbox, and wherein during operation, the fan rotates at a lower speed than the low-pressure turbine due to a gear reduction.
15 . The turbofan engine as recited in claim 1 wherein at least one of the immediately adjacent upstream airfoil cascades to the last downstream airfoil cascade has a respective transonic airfoil cascade.
16 . The turbofan engine as recited in claim 1 wherein only the last downstream airfoil cascade has the transonic airfoil cascades.
17 . The turbofan engine as recited in claim 1 wherein an airfoil of the transonic airfoil cascade is an uncooled airfoil.
18 . A method for operating the low-pressure turbine in the turbofan engine as recited in claim 1 , the method comprising flowing a transonic flow through the transonic airfoil cascade.
19 . A turbofan engine comprising:
a low-pressure turbine having at least four stages, at least one of the four stages having a transonic airfoil cascade,
a transonic airfoil of the transonic airfoil cascade having a suction side surface including a linear portion having a linear profile when viewed in a sectional plane of the airfoil,
the linear profile in the sectional plane of the airfoil extending radially over at least 10% of a radial length of the transonic airfoil.
20 . A turbofan engine comprising:
a low-pressure turbine having at least four stages, at least one of the four stages having a transonic airfoil cascade,
a transonic airfoil of the transonic airfoil cascade having a suction side surface including a linear portion having a linear profile when viewed in a sectional plane of the airfoil,
the linear profile having a curvature when viewed in the sectional plane of the airfoil, the curvature deviating from a linear shape by at most 5%.
21 . A turbofan engine comprising:
a low-pressure turbine having at least four stages, at least one of the four stages having a transonic airfoil cascade,
a transonic airfoil of the transonic airfoil cascade having a suction side surface including a linear portion having a linear profile when viewed in a sectional plane of the airfoil,
a plurality of transonic airfoil cascades each having a respective transonic airfoil having a respective linear portion, wherein a respective total area of the respective linear portion increases from each of the plurality of airfoil cascades to a next airfoil cascade of the plurality of airfoil cascades in the downstream direction.