BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a turbine wheel of gas turbines.

2. Description of the Related Art

A gas turbine generally includes: a compressor that compresses air to generate compressed air; a combustor that mixes the compressed air from the compressor with fuel and combusts the mixture to generate a combustion gas; and a turbine that obtains shaft power by the combustion gas from the combustor. The turbine includes a turbine rotor that converts the kinetic energy of the combustion gas into rotational power. The turbine rotor is formed by axially stacking disc-like turbine wheels having a plurality of turbine rotor blades that are arrayed over the entire circumference of outer peripheral portions of the turbine wheels.

As one of structures for connecting a turbine wheel and turbine rotor blades, there is one referred to as a dovetail structure. In this connecting structure, blade root sections (dovetails) of turbine rotor blades are axially inserted into slots (mating grooves) provided at an outer peripheral portion of a turbine wheel to be connected to the turbine wheel. The slots of the turbine wheel extend in a direction approximately parallel to a rotor axial direction And are formed into a shape that is complementary to the blade root sections of the turbine rotor blades. In this connecting structure, the turbine rotor blades are fixed to the turbine wheel by the engagement between recesses and projections of the blade root sections of the turbine rotor blades and complementary recesses and projections on the wall surfaces of the slots of the turbine wheel due to the action of the radially outward centrifugal force on the turbine rotor blades along with the rotation of the turbine rotor.

Although the turbine rotor blades are inhibited from moving in the rotor radial direction in this connecting structure, the turbine rotor blades are allowed to move in the rotor axial direction Along the slots of the turbine wheel. In view of this, there is one that uses a fixation wire in order to inhibit the turbine rotor blades from moving in the rotor axis direction (see JP-2011-21605-A, for example).

JP-2011-21605-A discloses that a first lockwire slot (groove) that is closed at its radially outer end and opens at its radially inner end is formed on one axial side of each of a plurality of radially projecting portions defining dovetail slots of a turbine wheel. In addition, second lockwire slots (groove) are defined by lock tabs provided on one side, in the axial direction, of dovetails (blade root sections) of a plurality of turbine rotor blades. When the plurality of first lockwire slots of the turbine wheel and the second lockwire slots of the plurality of turbine rotor blades align with each other, an annular retention slot is formed to extend over the entire circumference of an outer peripheral portion of the turbine wheel. Arranging a lockwire (fixation wire) in the annular retention slot inhibits the turbine rotor blades from moving along the dovetail slots.

Meanwhile, since a gas turbine obtains shaft power for a turbine rotor from a high-temperature and high-pressure combustion gas, it is necessary to cool each part of the turbine rotor such as turbine wheels or turbine rotor blades by cooling air, and to suppress a temperature increase in each part. In the gas turbine, generally, compressed air bled from a compressor is used as the cooling air. In this case, increasing the flow rate of the cooling air means increasing the flow rate of the compressed air bled from the compressor. Accordingly, if the flow rate of the cooling air is increased, the flow rate of the combustion gas to drive the turbine rotor decreases by a corresponding amount, and thus the overall efficiency of the gas turbine deteriorates.

One of the effective means for attaining high efficiency of a gas turbine is to reduce cooling air for cooling each part of a turbine rotor. In this case, the ambient temperature in a wheel space formed in front and rear of a turbine wheel in the rotor axis direction increases. In view of this, it has been proposed to change the material of a turbine wheel to a Ni based alloy that is more heat-resistant than conventionally used 12 Cr steels. It should be noted however that there is a concern over occurrences of cracks resulting from residual tensile stresses if parts formed of a Ni based alloy material are used in a high-temperature environment in a state in which they are receiving the residual tensile stresses.

In the technique described in JP-2011-21605-A, both sides, in the circumferential direction, of the dovetails (blade root sections) of the turbine rotor blades are processed into concave-convex shapes, and thereby concave-convex portions are also formed on both sides, in the circumferential direction, of the lock tabs of the turbine rotor blades. In addition, both sides, in the circumferential direction, of the radially projecting portions defining the dovetail slots are processed into concave-convex shapes, and thereby concave-convex portions are also formed on both sides, in the circumferential direction, of protruding portions (lock tabs) that are provided on one axial side of the radially projecting portions and defines the first lockwire slots of the turbine wheel. Accordingly, the circumferentially concave-convex portions of the lock tabs of the turbine wheel and the circumferentially concave-convex portions of the lock tabs of the turbine rotor blades have shapes that are complementary to each other, and engage with each other.

In such a configuration, at the time of assembly or disassembly of the turbine rotor blades onto or from the turbine wheel, part of the turbine rotor blades come into contact with the circumferentially protruding portions of the lock tabs of the turbine wheel in some cases. This may cause residual tensile stresses at base portions of the lock tabs. Accordingly, when a Ni based alloy is applied to the turbine wheel with a configuration like the one described in JP-2011-21605-A, there is a concern over occurrences of cracks in the turbine wheel resulting from residual tensile stresses caused by the interference of the turbine rotor blades with the lock tabs of the turbine wheel at the time of assembly or disassembly of the turbine rotor blades.

In addition, the lockwire (fixation wire) is retained in the annular retention slot formed by the first lockwire slots of the turbine wheel and the second lockwire slots of the turbine rotor blades. The lockwire is pressed against the bottom of the annular retention slot due to the action of the centrifugal force when the turbine rotor is rotated at high speed. In order to ensure the durability of the lockwire, it is necessary to suppress local occurrences of excessive stresses on the lockwire when the lockwire is retained in the first and second lockwire slots.

The present invention has been made in order to overcome the problems described above, and an object of the present invention is to provide a turbine wheel that can suppress occurrences of residual tensile stresses due to contact with turbine rotor blades at the time of assembly or disassembly while suppressing local occurrences of excessive stresses on a fixation wire at the time of the rotation of a turbine rotor.

SUMMARY OF THE INVENTION

The present application includes a plurality of means for overcoming the problems described above, and one example thereof is a turbine wheel that is rotatable around a central axis, and is connectable, at an outer peripheral portion, with a plurality of turbine rotor blades each including a blade root section and a blade-side tab section, the blade root section having a plurality of tiers of concave-convex blade-side neck portions and blade-side hook portions in a radial direction, the plurality of tiers of blade-side neck portions and blade-side hook portions being formed on both sides of the blade root section in a circumferential direction, the blade-side tab section being provided on one side of the blade root section in an axial direction and forming a first groove opened toward both sides in the circumferential direction and toward a radially inward side. The turbine wheel includes: a plurality of attachment sections that are arranged at the outer peripheral portion at intervals in the circumferential direction, and form a plurality of slots into which the blade root sections are inserted in the axial direction to engage with the plurality of slots; and a plurality of wheel-side tab sections provided on one side of the plurality of attachment sections in the axial direction, each of the plurality of wheel-side tab sections forming a second groove opened toward both sides in the circumferential direction and toward the radially inward side. Each of the plurality of attachment sections has a plurality of tiers of wheel-side hook portions and a plurality of tiers of wheel-side neck portions on both sides of the attachment section in the circumferential direction, the plurality of tiers of wheel-side hook portions and the plurality of tiers of wheel-side neck portions being formed to respectively engage with the blade-side neck portions and the blade-side hook portions of the blade root section. The plurality of wheel-side tab sections are formed such that, together with the blade-side tab sections of the plurality of turbine rotor blades, the plurality of wheel-side tab sections form a wire groove for retaining an annular fixation wire to inhibit the plurality of turbine rotor blades from moving along the slots. Each of the plurality of wheel-side tab sections is formed such that a bottom surface of the second groove is continuous with bottom surfaces of first grooves that are adjacent on both sides in the circumferential direction. An outline shape of each wheel-side tab section when seen in the axial direction is formed such that the outline shape matches a shape in which a portion of a particular shape is replaced with straight portions along predetermined straight lines. The particular shape is part of an outline shape of each attachment section when seen in the axial direction, and includes an range from a radially outer end, toward the radially inward side, to at least a wheel-side hook portion adjacent, on the radially inward side, to the bottom surface of the second groove. The portion being at least on the radially inward side of the bottom surface of the second groove and being on an outer side, in the circumferential direction, of the predetermined straight lines. Each of the predetermined straight lines passes through the central axis and a point in a range along the particular shape from an intersection with the bottom surface of the second groove to a peak of wheel-side hook portion adjacent, on the radially inward side, to the bottom surface of the second groove.

According to the present invention, an annular fixation wire is pressed almost uniformly against continuous bottom surfaces of first grooves and the second grooves due to the action of the centrifugal force at the time of the rotation of a turbine rotor. Accordingly, it is possible to prevent local occurrences of excessive stresses on the fixation wire. In addition, the outline shape of the wheel-side tab section when seen in the axial direction is such that at least part of projecting portions are removed from a wheel-side tab section of a conventional turbine wheel. Accordingly, it is possible to inhibit the wheel-side tab section from getting caught by a blade root section or a blade-side tab section of a turbine rotor blade when the turbine rotor blade is assembled onto or disassembled from the turbine wheel. Accordingly, occurrences of residual tensile stresses on the turbine wheel due to contact between turbine rotor blades and the wheel-side tab sections can be suppressed.

Problems, configurations and advantages other than those described above become apparent from the following explanation of embodiments.

