Patent Grant
6994514
1. Field of the Invention
The present invention relates to a gas turbine which is preferably used for a power plant or the like, and in particular, a turbine blade equipped with a cooling structure.
2. Description of Related Art
To improve heat efficiency of an industrial gas turbine used for a power plant or the like, it is effective that the temperature of a combustion gas (fluid) for operation at an inlet of the turbine is increased. However, since the heat resistance performance of each of the members which are exposed to the combustion gas, such as moving blades, stationary blades, and turbine blades, is limited by the physical characteristics of the materials used in the members, the temperature of the inlet of the turbine cannot be simply increased.
To solve the above problem, since the turbine blades are cooled by a cooling medium such as cooling air or the like, and simultaneously, the temperature of the inlet of the turbine is increased, the heat resistance performance of the turbine blades is maintained to improve the heat efficiency.
Examples of cooling methods for the turbine blade include a convection cooling method and an impingement cooling method in which the cooling medium passes through the inside of the turbine blade, and a film cooling method in which the cooling medium is injected to the outside surface of the turbine blade to form a film of the cooling medium.
Furthermore, a structure of a conventional moving blade (turbine blade) is explained below with reference to
As shown in
As shown in
Moving blades 51 are arranged in a path of the combustion gas which blows out from a combustor (not shown). The path is composed of a wall surface of platform 55 and an inner wall surface (not shown) of a casing which forms the exterior of the turbine. The casing is a separating ring.
When the gas turbine is started, a high temperature gas collides against moving blade 51, resulting in the heat expansion of moving blade 51. The stationary blades of course also undergo heat expansion. However, since the casing does not make direct contact with high temperature gas, the casing undergoes heat expansion more slowly than these moving and stationary blades. Therefore, the casing cannot undergo heat expansion in response to the heat expansion of each blade. In this condition, since moving blades 51 and the like are rotated together with a rotation axis in the casing, the top portion TP of moving blade 51 may be abraded by making contact with the inner wall surface of the casing. This phenomenon is called “tip rubbing” and occurs because the top portion TP of moving blade 51 and the inner wall surface of the casing are closely formed so as to prevent pressure leakage from a space between the top portion TP and the inner wall surface.
Since tip squealers 54a and 54b, which are provided as the portions to be abraded or for holding pressure have a sufficient height h2, if tip rubbing is generated, the height h2 sufficiently corresponds to the portion to be abraded.
However, if such a relatively large concaving formed by tip squealers 54a and 54b is provided at the top portion TP of moving blade 51 which has a high temperature, disadvantages are generated in many respects. For example, since the top portion TP is separated from the surface to be cooled, it is difficult to cool the top portion TP. Therefore, the durability of the top portion TP with respect to the operating the turbine may be decreased by burnout of the top portion TP and the further generation of cracking.
To solve the above problems, the top portion TP of moving blade 51 has a structure as shown in
Each of holes 56 and 57 communicates with cavity R in moving blade 51, and cooling medium inflowing into moving blade 51 is taken up from upstream opening portions 56b and 57b of holes 56 and 57 and is blown out from downstream opening portions 56a and 57a. As a result, the cooling medium blown out from the opening portions cools the top portion TP, blade surfaces 52 and 53, and the inner wall surfaces, which face the blade surfaces, of the casing.
Upstream opening portions 56b and 57b and downstream opening portions 56a and 57a are holes having the same cross-sectional area about 1 mm in diameter, and are generally formed by electric discharge machining, laser beam machining, or the like.
According to the above constitution, since the cooling medium blown out from holes 56 and 57 is used to cool the top portion TP and the like, the thermal stress of tip squealer 54 is relaxed and is prevented from burning out and cracking. Furthermore, since the height of tip squealer 54 is lower than the height of tip squealer 54b shown in
However, in moving blade 51 as a conventional turbine blade, when tip rubbing is generated on the top portion TP, the periphery of each of holes 56 and 57 of the cooling medium is abraded, resulting in a problem wherein these holes 56 and 57 are covered. This is because the member of the top portion TP is deformed by abrasion and burrs, for example, remain at the periphery of each of holes 56 and 57 in the deformed member.
The condition after the generation of tip rubbing is explained below with reference to
When attempting to make the cooling medium in the cavity R of moving blade 51 flow to holes 56′ and 57′ from upstream opening portions 56b and 57b, since downstream opening portions 56a′ and 57a′ are covered, a sufficient amount of cooling medium cannot be blown out to the top portion TP for cooling. If cooling of the top portion TP is not normally carried out, problems arise in that burnout and cracking are generated on the top portion TP and that the durability of the turbine is decreased.
In view of the above problems, an object of the present invention is the provision of a turbine blade and a gas turbine thereof which can be stably driven by cooling the turbine blade accurately without closing the holes for cooling, which are formed on the top portion of the turbine blade, due to tip rubbing or the like.
In order to solve the above problems, the following structures are adopted in the present invention.
The first aspect of the present invention is the provision of a turbine blade arranged in a flow path, wherein plural holes are provided at a top portion of the turbine blade for blowing out cooling medium to an outside surface, and wherein the cross-sectional area of a hole provided at a downstream opening portion is larger than the cross-sectional area of a hole provided at an upstream opening portion.
Plural holes for cooling the outside surface of the turbine blade are provided on the top portion which is a tip portion of the turbine blade. The cooling medium flows from the inside of the turbine blade toward the outside of the top portion and is blown out from the holes.
The diameter of the section area of the hole provided at the upstream side and that of the hole provided at the downstream side differ from each other. The hole provided at the downstream opening portion at which the cooling medium is blown out to the outside of the turbine blade has a larger cross-sectional area than the hole provided at the upstream opening portion at which the cooling medium flows into each hole.
Therefore, the cooling medium inflows from the upstream opening portion having a relatively small diameter and blows out from the downstream opening portion having a relatively large diameter.
Furthermore, even if tip rubbing is generated, the cooling medium is always blown out to the outside of the top portion without closing the downstream opening portion.
Therefore, a turbine blade having high durability can be provided by preventing the burnout of the top portion, generation of cracking, and the like.
In the turbine blade according to the first aspect of the present invention, each hole may have a tapered shape.
Holes provided at the downstream opening portion have a larger cross-sectional area than holes provided at the upstream opening portion in the flow direction of the cooling medium. The variation in the diameter of each hole provided at the upstream opening portion and the diameter of each hole provided at the downstream opening portion is connected by a tapered portion, and as a result, the cross-sectional area of the hole at the upstream opening portion is gradually enlarged to the cross-sectional area of the hole at the downstream opening portion to form each hole. The cooling medium is blown out from each hole having a tapered shape to cool the turbine blade and the like. The cooling medium is smoothly passed through the holes toward the top portion.
When the hole is formed in a tapered shape, for example, even if the hole is partly covered with burrs or the like due to abrasion of the top portion, since the cross-sectional area of the hole is larger than that of the upstream opening portion, it is unlikely for the partly-covered hole to become smaller than the upstream opening portion in cross-sectional area from the condition of the generation of burrs.
Furthermore, if the angle of the tapered shape is increased, the angle between the wall surface and the end surface of the top portion has a gentle slope. As a result, the generation of burrs can be prevented, and the clogging of the holes is prevented, thereby cooling the turbine blade.
In the turbine blade according to the first aspect of the present invention, each hole may have a step portion having two or more steps which have different cross-sectional areas.
The hole provided at the downstream opening portion has a larger cross-sectional area than the hole provided at the upstream opening portion in the flow direction of the cooling medium. The variation in the cross-sectional area (diameter) of each hole provided at the upstream opening portion and the cross-sectional area (diameter) of each hole provided at the downstream opening portion is connected by the step portion. The cooling medium is blown out from each hole having the step portion to cool the turbine blade and the like.
If the top portion of the turbine blade is abraded and the holes are partly covered by burrs or the like, the cross-sectional area of the holes for the height of the portion which is estimated to be abraded should be preferably formed. As a result, even if the downstream opening portion is gradually abraded, a downstream opening portion having a large cross-sectional area can be ensured. In addition, clogging of the holes due to the generation of burrs or the like by tip rubbing is prevented, thereby ensuring the holes will be open.
In the turbine blade according to the first aspect of the present invention, the downstream opening portion of each hole may be formed so as to flare in a direction opposite to the relative moving direction of a wall surface facing the top portion.
The top portion of the turbine blade is provided close to the wall surface which it faces and moves relative to the top portion. If the wall surface and the top portion make contact with each other during relative movement, the top portion in which the holes are formed is gradually abraded. As the top portion is abraded, burrs or the like are generated in the holes due to tip rubbing or the like along the relative moving direction of the wall surface. However, since the downstream opening portion, which is formed larger than the upstream opening portion in cross-sectional area, is formed so as to flare toward the relative moving direction of the wall surface, burrs or the like are prevented from directly covering the downstream opening portion. That is, the cooling medium blowing out from the holes can be blown out without being blocked by burrs or the like even if burrs or the like are generated. Furthermore, if each hole has a tapered shape, since the portion on which the burrs are generated is smoothly formed, the effect of the burrs on the holes is remarkably decreased.
In the turbine blade according to the first aspect of the present invention, a protrusion portion may be provided on at least one shoulder in which an outside surface of the protrusion portion elongates along the outside surface of the turbine blade and an inside wall of the protrusion portion protrudes from the top portion, and the holes may be provided along the inside wall of the protrusion portion.
On the top portion of the turbine blade, the protrusion portion is formed so as to elongate along the outside surface of the turbine blade and the holes through which the cooling medium is blown out are formed along the inside wall of the protrusion portion. Even if the protrusion portion is abraded by tip rubbing or the like to produce burrs or the like, since the holes are provided perpendicular to the inside wall of the protrusion portion, the holes are ensured without being blocked by the burrs or the like.
These holes are formed from the upstream opening portion toward the end surface of the top portion. When an upper portion of each hole provided at the protrusion portion is covered by burrs or the like, the hole becomes as if it is provided at the inside wall of the protrusion portion, in other words, the hole can be approximately perpendicular to the longitudinal direction of the turbine blade. Therefore, the cooling medium is accurately blown to the top portion for effective cooling, and burnout of the top portion and the generation of cracking are prevented to provide a turbine blade having improved durability.
The second aspect of the present invention is the provision of a gas turbine equipped with a compressor for compressing air, a combustor for generating high-temperature and high-pressure fluid, and a turbine for generating engine torque by converting energy of the fluid into mechanical work, wherein the turbine blade according to the above aspect is provided in the turbine.
The turbine blade is equipped with plural holes for blowing out the cooling medium, in which a downstream opening portion and an upstream opening portion are formed in each hole so that the downstream opening portion has a larger cross-sectional area than the upstream opening portion. The turbine blade is equipped in the turbine of the gas turbine.
Therefore, since the holes provided at the top portion of the turbine blade are not covered even if burrs are generated by tip rubbing, the cooling medium for cooling the turbine blade is blown out from the holes. Then, by adopting a turbine blade which includes an outside surface and a top portion to be cooled, the heat resistance property of the turbine blade is maintained while the temperature of the inlet of the turbine is increased to a high temperature, and the gas turbine can be driven. Furthermore, the cooling property of the turbine blade is maintained from the initial operation, thereby providing a gas turbine having reliability, durability, and simple maintenance.
An embodiment according to the present invention is explained with reference to the figures.
Compressor 10 compresses a large amount of air therein. In gas turbine 1, generally, a part of the power of turbine 30 obtained by rotational shaft 2 is used as power for compressor 10 (compressor input).
Combustor 20 carries out combustion after mixing the compressed air in compressor 10 and fuel to send a combustion gas (fluid) to path 32 which is connected to turbine 30.
Turbine 30 is equipped with rotational shaft 2 which extends from, at least, compressor 10 in casing 31 which forms the exterior of gas turbine 1, and plural moving blades 34 and stationary blades 33 (both are called “turbine blades”).
Moving blades 34 are fixed around rotational shaft 2, and rotate rotational shaft 2 due to the pressure of the combustion gas flowing along the axial direction of rotational shaft 2.
Furthermore, stationary blades 33 are fixed around a separating ring which composes an inside wall of casing 31, and are used in order to change the direction, pressure, and speed of the flow in casing 31. At the top portion of stationary blade 33, shaft sealing mechanism 33a is provided at the top portion of stationary blade 33 to close the space between rotational shaft 2 and the top portion of stationary blade 33.
These moving blades 34 and stationary blades 33 are alternately provided in a path of the combustion gas formed between rotational shaft 2 and the inside wall surface of casing 31. The combustion gas generated in combustor 20 is introduced into path 32 and expands, and the expanded combustion gas is blown to these blades to generate power by converting thermal energy of the combustion gas into rotational energy of mechanical work. The power is used as power for compressor 10 as described above, and in general, the power is used as power for a generator of an electric power plant.
Next, a structure of the top portion, which is a tip portion of moving blade 34 shown by reference symbol A of
Holes 38 and 39 are formed toward different directions, each connects cavity R inside moving blade 34 and the end surface of the top portion. The cooling medium flowing in cavity R is taken up from upstream opening portions 38b and 39b of holes 38 and 39, passes through paths T1 and T2 having tapered shapes, is introduced into downstream opening portions 38a and 39a connected to paths T1 and T2, which have a larger cross-sectional area than upstream opening portions 38b and 39b, and is blown out the outside of moving blade 34.
In this embodiment, the diameter of each of upstream opening portions 38b and 39b is about 0.8 to 1.0 mm, and the diameter of each of downstream opening portions 38a and 39a is about 2 to 3 mm. Holes 38 and 39 are shown as holes each having a cylindrical shape in
When moving blade 34 rotates in the direction of rotation so as to move left to right in the figure, the top portion TP of moving blade 34 may make contact with the inside wall surface of casing 31 (refer to
The heat expansion of casing 31 is slower than that of moving blade 34. Moving blade 34 undergoes heat expansion before casing 31 and makes contact with casing 31 which undergoes slow heat expansion. The phenomenon is remarkably generated during the warm-up and starting of gas turbine 1. The wall surface facing the top portion TP is the inside wall surface of casing 31 and moves relative to the actual movement of moving blade 34.
When the top portion TP contacts the inside wall surface of casing 31, the top portion TP is gradually abraded. This is called rubbing.
When rubbing is generated at the top portion TP, tip squealer 37 is abraded as shown in
However, since holes 38 and 39, which are formed at the top portion TP in the present embodiment, are formed into tapered shapes having cross-sectional areas of two or three times the diameter of the upstream opening portions 38b and 39b, holes 38 and 39 are not covered by burrs B. Therefore, the cooling medium in cavity R is easily blown out from each of holes 38 and 39, and the cooling medium blown out flows from the high pressure side to the low pressure side to cool the top portion TP, tip squealer 37, blade surfaces 35 and 36, the inside wall surface of casing 31 which faces the top portion TP, and the like.
According to the above embodiment of moving blade 34, even if rubbing is generated, holes 38 and 39 blowing out the cooling medium are not covered, and moving blade 34 is accurately and continuously cooled. Simultaneously, since the heat load of tip squealer 37 and top portion TP is decreased, defects such as burnout and cracking are prevented so as to allow stable driving of gas turbine 1.
A modified example of the present embodiment may have the following structure.
Holes 38 and 39 connecting cavity R of moving blade 34 and the end surface of the top portion are enlarged in their cross-sectional areas from upstream opening portions 38b and 39b each having a narrow diameter of about 1 mm along the tapered shapes T1 and T2. If moving blade 34 is regarded as being in a stationary state, the enlarged direction of the cross-sectional area is off to the right side of the figure. The direction is opposite to the relative moving direction of the inside wall surface of casing 2 which faces moving blade 34. The center of each of downstream opening portions 38a and 39a is eccentrically provided so as to flare toward the opposite direction of the relative moving direction of the inside wall surface of casing 2, in comparison with the center of upstream opening portions 38b and 39b.
According to the eccentricity of downstream opening portions 38a and 39a, the angle between the end surface of the top portion and the wall surface of each of tapered shapes T1 and T2 respectively is decreased.
Therefore, even if burrs are generated, covering of holes 38 and 39 becomes difficult. Furthermore, since the portions at which burrs are generated have a gentle angle, the generation of burrs is decreased.
Next, holes 38 and 39 having step portions are explained with reference to
Holes 38 and 39 having step portions S1 and S2 are explained with reference to
Accordingly, downstream opening portions 38a and 39a can be formed with a two to three times larger cross-sectional area than upstream opening portions 38b and 39b to prevent clogging of holes 38 and 39 by the generation of burrs. Furthermore, since step portions S1 and S2 are formed, holes 38 and 39 are easily formed by electric discharge machining, machining, or the like.
Furthermore, holes 38 and 39 having step portions S1 and S2 which are eccentrically provided are explained with reference to
Holes 38 and 39 connecting cavity R of moving blade 34 and the end surface of the top portion are enlarged in their cross-sectional areas from upstream opening portions 38b and 39b each having a narrow diameter of about 1 mm by step portions Sa1 and Sa2. If moving blade 34 is regarded as being in a stationary state, the enlarged direction of the cross-sectional area is off to the right side of the figure. The direction is opposite to the relative moving direction of the inside wall surface of casing 2 which faces moving blade 34. The center of each of downstream opening portions 38a and 39a is eccentrically provided so as to flare toward the relative moving direction of the inside wall surface of casing 2, in comparison with the center of upstream opening portions 38b and 39b.
Accordingly, downstream opening portions 38a and 39a can be formed with a two to three times larger cross-sectional area than upstream opening portions 38b and 39b to effectively prevent clogging of holes 38 and 39 by the generation of burrs. Furthermore, since step portions Sa1 and Sa2 are formed, holes 38 and 39 are easily formed by electric discharge machining, machining, or the like.
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