Compressor
A compressor is provided that can avoid fretting damage to improve fatigue strength reliability. The present invention is characterized in that a portion on the circumferential outside and radial outside of a radial outside contact end portion 9a with a dovetail portion 4a is removed from a wheel 7. Specifically, the wheel 7 is formed with a groove portion 10 in an area that is located on the circumferential outside of the radial outside contact end portion 9a of a blade securing portion 15 with the dovetail portion 4a and that includes a radial outside of the contact end portion 9a. Rigidity on the wheel side of the contact end portion 9a between the dovetail portion 4a and the wheel 7 is reduced to reduce the occurrence of stress, thereby avoiding the lowering of fatigue life reliability resulting from fretting.
1. Field of the Invention
The present invention relates to a blade-implanting structure for a compressor that is a constituent element of a gas turbine.
2. Description of the Related Art
Gas turbines generally have a compressor to compress and deliver air to a combustor. The compressor is internally provided with a compressor rotor rotating around a central axis of a gas turbine. In the compressor, an implanting portion of a rotor blade is fixedly fitted into a circumferential groove portion provided on a rotor wheel. Incidentally, a conventional technique relating to the rotor blade securing structure is described in e.g. JP-63-273000-A.
SUMMARY OF THE INVENTIONWhile the gas turbine operates, the rotor blade of the gas turbine compressor is subjected to centrifugal force caused by its own weight and to a large pressure load on its high-pressure side. In addition, vibration stress acts on the dovetail portion of the blade due to the exciting force caused by irregular pressure variations that occur during start-up. As a result, fatigue damage may result.
Conventionally, the surface on which the dovetail portion of the blade receives load wholly bears such load. However, high stress occurs at a contact end portion between the blade-load-receiving surface and the wheel-load-receiving surface of a wheel. Since such a contact end portion suffers fretting damage resulting from abrasion in addition to high stress, reliability in fatigue strength is likely to lower.
In view of the above, it is desirable to apply to an actual machine a blade-groove structure capable of providing higher reliability.
It is an object of the present invention to provide a compressor that can reduce stress occurring at a contact end portion between a blade and a wheel to suppress lowering of fatigue strength reliability resulting from fretting.
To achieve the above object, the compressor according to the present invention is characterized in that a portion on the circumferential outside and radial outside of a contact end portion with a blade is removed from a wheel.
More specifically, the compressor includes a rotor blade secured to an outer circumferential side of a wheel and a stator blade secured to an inner circumferential side of a casing incorporating the wheel. The rotor blade includes a blade portion, a platform portion joined to a root side of the blade portion and having planes parallel to a centrifugal-force load direction of the blade portion, and a dovetail portion which merges with the platform portion, is located radially inward of the platform portion and is increased in width outwardly from the parallel planes of the platform portion. The dovetail portion is fixedly inserted into a blade securing groove formed on the outer circumferential side of the wheel. In addition, the wheel is formed with a groove portion or a hollow portion in an area that is located on a circumferential outside of a radial outside contact end portion of the blade securing groove with the dovetail portion and that includes a radial outside of the radial outside contact end portion.
With the blade groove structure described above, rigidity of the wheel side at a position close to the contact end portion between the wheel and the blade is reduced to reduce the occurrence of stress. Thus, the lowering of fatigue life reliability resulting from fretting can be avoided.
The present invention can provide the compressor that can reduce stress occurring at the contact end portion between the wheel and the blade to suppress the lowering of fatigue strength reliability resulting from fretting.
Preferred embodiments of the present invention will hereinafter be described with reference to the drawings.
To eliminate such disadvantages, the present invention is devised such that a wheel 7 is formed with a groove portion or a hollow portion formed in an area that is located on a circumferential outside (a widthwise outside of a platform portion 4b) of a radial outside contact end portion 9a of a blade securing groove 15 with a dovetail portion 4a and that includes a radial outside of the contact end portion 9a. The specific examples thereof are described below.
Embodiment 1A second embodiment of the present invention is shown in
A third embodiment of the present invention is shown in
A fourth embodiment of the present invention is described in
In the embodiments described above, it is believed that the deformation of the contact end portion 9a of the wheel can achieve a reduction in stress. It is desirable, therefore, that the groove and the hollow portion (the hole) be located radially above the contact surface. However, it is necessary to appropriately set the size and position of the groove portion or the hollow portion taking into consideration the load conditions of an actual machine, the strength of material to be applied and the like.
Methods of increasing the fatigue strength of the area having reduced rigidity include application of compressive residual stress by shot peening or water jet peening and surface modification by friction stir.
Claims
1. A compressor comprising:
- a rotor blade secured to an outer circumferential side of a wheel; and
- a stator blade secured to an inner circumferential side of a casing incorporating the wheel;
- wherein the rotor blade includes:
- a blade portion;
- a platform portion joined to a root side of the blade portion and having planes parallel to a centrifugal-force load direction of the blade portion; and
- a dovetail portion which merges with the platform portion, is located radially inward of the platform portion and is increased in width outwardly from the parallel planes of the platform portion, the dovetail portion being fixedly inserted into a blade securing groove formed on the outer circumferential side of the wheel, and
- wherein the wheel is formed with a groove portion or a hollow portion in an area that is located on a circumferential outside of a radial outside contact end portion of the blade securing groove with the dovetail portion and that includes a radial outside of the radial outside contact end portion.
2. The compressor according to claim 1,
- wherein the wheel is formed with the groove portion or the hollow portion in an area including a circumferential inside of a radial inside contact end portion of the blade securing groove with the dovetail portion.
3. The compressor according to claim 1,
- wherein the groove portion is formed by a first straight-line part extending circumferentially outward from the radial outside contact end portion, a second straight-line part extending radially outward, and a curved part connecting the first and second straight-line parts together.
4. The compressor according to claim 1,
- wherein the groove portion is formed such that a distance from the parallel plane of the platform portion is gradually increased as the groove portion goes toward the radial outside from the radial outside contact end portion.
5. The compressor according to claim 1,
- wherein the groove portion or the hollow portion is subjected to compressive residual stress by shot peening.
6. The compressor according to claim 1,
- wherein the groove portion or the hollow portion has a surface subjected to surface modification by friction stir.
Type: Application
Filed: May 30, 2013
Publication Date: Dec 5, 2013
Inventor: Kota NAGANO (Hitachinaka)
Application Number: 13/905,326