TECHNICAL FIELD

The present invention relates to a turbine blade and a gas turbine.

Priority is claimed on Japanese Patent Application No. 2017-031767, filed Feb. 23, 2017, the content of which is incorporated herein by reference.

BACKGROUND ART

For example, as a turbine blade of a gas turbine, one having a shroud at a blade end portion is known (see, for example, Patent Literature 1). In particular, in long blades of a final stage of the turbine, contact surfaces of the shrouds of the respective adjacent turbine blades come into contact with each other to suppress vibration occurring at the time of high-speed rotation. Further, fins extending in a circumferential direction are provided on outer circumferential surfaces of the shrouds. This prevents the combustion gas for driving the turbine from flowing out from a clearance formed between an inner circumferential surface of a casing and the outer circumferential surfaces of the shrouds.

CITATION LIST

Patent Literature

Patent Literature 1

Japanese Unexamined Patent Application, First Publication No. 2005-207294

SUMMARY OF INVENTION

Technical Problem

Incidentally, with the increases in output and performance of recent gas turbines, in particular, the blades of the final stage of the turbine are being made longer. In order to reduce a flow velocity of an exhaust gas discharged from the turbine as much as possible and to increase turbine efficiency, it is effective to extend a blade length of the blades of the final stage and to increase a contact area.

On the other hand, as blades become longer in this way, since a centrifugal force acting on the shrouds also increases, in particular, the stress of root portions of the shrouds against the blade bodies considerably increases. In contrast, for example, a method of enhancing rigidity by enlarging a fillet when welding a blade body and a shroud is known. However, since the fillet protrudes in a main flow passage of the combustion gas, the work of the combustion gas is hindered, which causes a decrease in efficiency.

Here, for the turbine blades described in Patent Literature 1, a configuration in which the stress is reduced by providing reinforcing ribs in a region from the contact surfaces of the shrouds to leading edges of the blade bodies and regions from the contact surfaces to trailing edge of the blade bodies is disclosed. However, in the turbine blades, existing regions of the reinforcing ribs are not sufficient, and it is not possible to properly cope with the occurring stress.

The present invention has been made in view of such circumstances, and an object thereof is to provide a turbine blade and a gas turbine capable of resisting the stress occurring in a shroud, while suppressing a decrease in efficiency.

Solution to Problem

A turbine blade according to a first aspect of the present invention includes a blade body in which a suction side facing one side in a circumferential direction and a pressure side facing the other side in the circumferential direction are connected at a leading edge and a trailing edge and which extends in a radial direction; and a shroud provided at a tip which is a radially outer end portion of the blade body, in which the shroud includes a shroud body which has an outer circumferential surface facing radially outward, a front end surface extending to both sides in the circumferential direction with a leading edge side of the blade body as a reference point, a rear end surface extending to both sides in the circumferential direction with a trailing edge side of the blade body as a reference point, and a contact surface provided on both sides in the circumferential direction, and a reinforcing portion which protrudes from the outer circumferential surface and extends over the front end surface and the rear end surface.

According to the turbine blade of the above configuration, the reinforcing portion is formed over the front end surface and the rear end surface of the shroud body. Thus, the reinforcing portion is over the entire region between the leading edge and the trailing edge of the blade body. For this reason, rigidity can be secured in the entire region of the root portion of the shroud with respect to the blade body. In addition, since the reinforcing portion is provided on the outer circumferential surface of the shroud, it does not affect the main flow passage of a combustion gas.

In the aforementioned turbine blade, the front end surface may have a first front end surface extending from the reference point of the leading edge side to the one side in the circumferential direction, and a second front end surface extending to intersect the first front end surface from the reference point of the leading edge side toward the other side in the circumferential direction, the rear end surface may have a first rear end surface extending from the reference point of the trailing edge side to the one side in the circumferential direction, and a second rear end surface extending to intersect the first rear end surface from the reference point of the trailing edge side toward the other side in the circumferential direction, and the reinforcing portion may have a first reinforcing rib extending over the first front end surface and the first rear end surface.

Since the first reinforcing rib is formed on one side in the circumferential direction, that is, on the suction side of the blade body, especially when the stress on the suction side of the blade body in the shroud increases, it is possible to cope with the stress by an increase in the rigidity due to the first reinforcing rib.

In the aforementioned turbine blade, the shroud may include a first fillet portion which is formed at a portion on which the suction side of the blade body and the inner circumferential surface of the shroud body are connected, and which extends to form a curved surface shape from the pressure side of the blade body to the inner circumferential surface of the shroud body, and the first reinforcing rib may be disposed to overlap the first fillet portion in the circumferential direction across the shroud body.

A centrifugal force acts on the shroud body radially outward with the rotation of the turbine blade. However, as the turbine blade is made longer for the purpose of improving the operation efficiency of the gas turbine, since the centrifugal force acting on the shroud body also increases, it is necessary to take countermeasures. In the past, measures such as enhancing the strength by increasing the fillet portion formed at the connection portion between the blade body and the shroud body have also been taken. However, increasing the fillet portion is not preferable because a cross-sectional area of the combustion gas main flow passage inside the shroud is reduced, which interferes with the purpose of lengthening the turbine blade.

The first fillet portion extending to form a curved surface shape from the suction side of the blade body to the inner circumferential surface of the shroud body is formed at a portion of the turbine blade on which the suction side of the blade body and the inner circumferential surface of the shroud body are connected, and the first reinforcing rib overlaps the first fillet portion in the circumferential direction across the shroud body. Thus, even if the centrifugal force acting on the shroud body increases with the increase in length of the turbine blade, the influence of the centrifugal force on the shroud body can be reduced without reducing the cross-sectional area of the gas main flow passage. That is, since the rigidity of the shroud on the suction side of the blade body increases, even if the stress on the suction side of the blade body in the shroud increases, the deformation of the shroud body can be suppressed.

In the aforementioned turbine blade, the reinforcing portion may further include a second reinforcing rib extending over the second front end surface and the second rear end surface.

Since the second reinforcing rib is formed on the other side in the circumferential direction, that is, on the pressure side of the blade body, particularly when the stress on the pressure side of the blade body in the shroud increases, it is possible to cope with the stress by the increase in the rigidity due to the second reinforcing rib. That is, since the first reinforcing rib is on the suction side of the blade body and the second reinforcing rib is on the pressure side, it is possible to form a high rigidity region from the leading edge to the trailing edge of the blade body on both sides of the blade body.

In the aforementioned turbine blade, the front end surface may have a first front end surface extending from the reference point of the leading edge side to the one side in the circumferential direction, and a second front end surface extending to intersect the first front end surface from the reference point of the leading edge side toward the other side in the circumferential direction, the rear end surface may have a first rear end surface extending from the reference point of the trailing edge side to the one side in the circumferential direction, and a second rear end surface extending to intersect the first rear end surface from the reference point of the trailing edge side toward the other side in the circumferential direction, and the reinforcing portion may have a second reinforcing rib extending over the second front end surface and the second rear end surface.

In the aforementioned turbine blade, the shroud may include a second fillet portion which is formed at a portion on which the suction side of the blade body and the inner circumferential surface of the shroud body are connected, and which extends to form a curved surface shape from the pressure side of the blade body to the inner circumferential surface of the shroud body, and the second reinforcing rib may be disposed to overlap the second fillet portion in the circumferential direction across the shroud body.

In the turbine blade, the second fillet portion extending to form a curved surface shape from the pressure side of the blade body to the inner circumferential surface of the shroud body is formed at a portion of the turbine blade on which the pressure side of the blade body and the inner circumferential surface of the shroud body are connected, and the second reinforcing rib overlaps the second fillet portion in the circumferential direction across the shroud body. Thus, even if the centrifugal force acting on the shroud body increases with the increase in length of the turbine blade, the influence of the centrifugal force on the shroud body can be reduced without reducing the cross-sectional area of the gas main flow passage. That is, since the rigidity of the shroud on the pressure side of the blade body increases, even if the stress on the pressure side of the blade body in the shroud increases, deformation of the shroud body can be suppressed.

A gas turbine according to a second aspect of the present invention includes a compressor which compresses air to generate high-pressure air; a combustor which combusts the high-pressure air to generate a combustion gas; and a turbine which includes a plurality of blade stages in which a plurality of blades are arranged in a circumferential direction and is driven by the combustion gas, wherein the blades of a last blade stage among the plurality of blade stages are turbine blades according to any one of the aforementioned aspects.

This can increase the rigidity of the shroud in the final stage of the turbine.

Advantageous Effects of Invention

According to the turbine blade and the gas turbine of the present invention, it is possible to resist the stress occurring in the shroud, while suppressing the decrease in efficiency.

