Turbine nozzle and axial-flow turbine including same
A turbine nozzle includes a plurality of blades arranged so as to form a tapered flow passage between each two adjacent blades. A suction surface of each blade includes a curved surface, and a throat of the flow passage is formed between the curved surface of one blade and a trailing edge of the other blade of the two adjacent blades at a throat position. An upstream end of the curved surface is positioned upstream of the throat position, and a downstream end of the curved surface is positioned downstream of the throat position.
1. A turbine nozzle comprising a plurality of blades arranged so as to form a tapered flow passage between each two adjacent blades,
wherein a suction surface of each blade includes a curved surface, and a throat of the flow passage is formed between the curved surface of one blade and a trailing edge of the other blade of the two adjacent blades at a throat position:
wherein an upstream end of the curved surface is positioned upstream of the throat position, and a downstream end of the curved surface is positioned downstream of the throat position,
wherein the suction surface of each blade includes a flat surface extending flat from the downstream end of the curved surface to a trailing edge of the blade, and
wherein when L is a dimensionless axial chord length which is a ratio of a length from a leading edge of the blade in an axial direction to a length from the leading edge to the trailing edge of the blade in the axial direction, and AR(L) is a ratio of a flow passage area of the flow passage at a dimensionless axial chord length of L to a flow passage area of the flow passage at a dimensionless axial chord length of 1.0, the following expression is satisfied:
AR
(
1.0
)
-
AR
(
0.98
)
1.0
-
0.98
≧
0.5
.
2. The turbine nozzle according to claim 1 ,
wherein a suction-side deflection angle between the flat surface and a tangent plane to the curved surface at the throat position is equal to or less than 10°.
3. The turbine nozzle according to claim 1 ,
wherein a trailing-edge included angle between two tangent planes at contact points of a trailing edge incircle with a pressure surface and the suction surface of the blade is equal to or greater than 3°, the trailing edge incircle being an incircle of minimum area touching the pressure surface and the suction surface.
4. The turbine nozzle according to claim 1 ,
wherein the suction surface of each blade includes a second concave surface concavely curved between a leading edge and the throat position.
5. The turbine nozzle according to claim 4 ,
wherein each blade includes a hub-side edge and a tip-side edge on both edges in a blade height direction, and
wherein the second concave surface has a depth decreasing from the hub-side edge toward a first boundary position away from the hub-side edge at a distance of 20% of a blade height in a direction from the hub-side edge toward the tip-side edge, between the first boundary position and the hub-side edge.
6. The turbine nozzle according to claim 4 ,
wherein each blade includes a hub-side edge and a tip-side edge on both edges in a blade height direction, and
wherein the second concave surface has a depth increasing from a second boundary position away from the hub-side edge at a distance of 50% of a blade height in a direction from the hub-side edge toward the tip-side edge, toward the tip-side edge, between the second boundary position and the tip-side edge.
7. An axial-flow turbine comprising the turbine nozzle according to claim 1 .