JP3771596B2 - Turbine blade tip seal structure - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an internally cooled turbine blade of a gas turbine engine, and more particularly to a technique for preventing clogging and fouling of air holes at a blade tip used for blade tip sealing and blade cooling.
[0002]
[Prior art]
As is well known in the art of gas turbine engines, to improve engine performance, the clearance of the gap between the outer air seal and the turbine blade tip is minimized throughout the engine operating range. A great deal of effort has been made. For this purpose, what has been developed over the last few years is active clearance control and passive clearance control. Many of these inventions and concepts have met with some success, but the problem has become more difficult with increasing demands on engine and aircraft performance. These solutions are also compatible with some aircraft / engine types, i.e. general commercial airplanes, and are not suitable for military aircraft, especially those designed for combat.
[0003]
For example, it has already been demonstrated that active clearance control works well in engines designed for aircraft used solely for commercial purposes. An example of active clearance control that has made such commercial success is shown, for example, in US Pat. No. 4,069,662, filed Jan. 24, 1979, to the same applicant as the present application. Has been. This type of device blows air to the outer case of the engine that is approaching the turbine rotor at a predetermined time in the operating region so as to reduce the outer case, so that the outer air seal is connected to the turbine. Alternatively, the gap is reduced by approaching the blade tip of the compressor.
[0004]
Contrary to the design principles of active clearance control, passive clearance control uses a continuous method to achieve the desired clearance control. For example, in a certain apparatus, cooling air is continuously supplied to an external engine case close to the rotor blade, and the expansion rate of the external case that tends to become high temperature is limited to keep the clearance to a minimum. In short, active control requires a control system that controls the clearance by supplying hot or cold air or applying mechanical means in response to an input. Passive control does not require such a control system and is always in a static state.
[0005]
The present invention relates to a passive clearance control, and effectively controls a clearance between a tip of a turbine blade and an outer air seal by using discharge air used for internal cooling of the turbine blade. The present invention discloses a means for providing an aerodynamic seal to minimize the flow in the gap between the outer air seal and the blade tip. This reduces the flow of blades from the high pressure side to the low pressure side, improving the efficiency of the turbine. A discharge hole formed near the intersection of the tip of the turbine blade, specifically the pressure side surface of the blade and the tip, discharges a jet of cooling air toward the gap between the outer air seal and the blade tip. To do. In some applications, intersecting holes are used. One of the holes communicates with an internal cooling passage adjacent to the pressure side surface, and the other hole communicates with an internal cooling passage adjacent to the suction side surface. These holes intersect each other so as to affect the speed (momentum) and angle of the cooling air discharged from the slot formed by the two holes.
[0006]
The hole at the tip of the air-cooled turbine blade and the intersecting hole are conventionally known. For example, U.S. Pat. No. 4,540,339, filed on Sep. 10, 1985, and U.S. Pat. No. 5,062,768, issued on Nov. 5, 1991, respectively, are located at the tip of the turbine blade. An intersecting hole is disclosed. In one of them, the side wall surface at the tip in sliding contact is washed by the flow coming out of the discharge hole. In another example, the cross holes reduce the possibility of contamination and clogging of the holes. In these patents, these holes are not used for aerodynamic sealing, but there are known devices that have holes at the tip for aerodynamic sealing.
[0007]
[Problems to be solved by the invention]
As disclosed in the prior art, there is a concern that foreign matters, particularly foreign matters generated by sliding contact with the blade tip, move to the discharge hole at the blade tip and adversely affect the discharge flow coming out of the discharge hole . Recently, the blade tip is covered with an abrasive material, and particles come out of the abrasive by sliding contact with the blade tip. Therefore, the above problem becomes more serious. In other words, the possibility of clogging the discharge hole is clearly increased, which not only adversely affects the cooling effect of the cooling passage and the discharge flow, but also due to the clogging of the hole in the blade tip seal structure. It adversely affects the sealing performance and, in turn, reduces the efficiency of the turbine.
[0008]
An object of the present invention is to prevent clogging or clogging of a discharge hole located at the tip of an internally cooled axial flow turbine blade used in a gas turbine engine.
[0009]
[Means for Solving the Problems]
The sealing structure of the turbine blade according to the present invention is a tip sealing structure of an internally cooled turbine blade in a turbine rotor for a gas turbine engine.
A wing that is exposed to the working fluid of the gas turbine engine and has a tip surface, a leading edge, a trailing edge, and a pressure side surface;
An annular shroud supported concentrically on the outer periphery of the wing and forming a gap with the tip surface;
An internal passage formed inside the wing and into which cooling air is introduced;
A jet of cooling air is formed from the internal passage toward the gap at a predetermined angle that is formed to extend to the blade tip surface at a position close to the pressure side surface and is inclined toward the pressure side surface. A discharge hole that seals the gap and blocks the gap to prevent the working medium fluid from flowing into the gap;
In order to prevent clogging of the discharge hole, the pressure side surface is formed only on the pressure side surface side of the discharge hole so as to communicate with the discharge hole, and has a width substantially equal to the width of the discharge hole. With cavities,
The pressure-side surface side of the discharge hole opens to the pressure-side surface through the cavity, and the back wall surface of the discharge hole on the side opposite to the cavity extends to the blade tip surface at the predetermined angle. It is characterized by that.
[0011]
That is, a feature of the present invention is that the above-described turbine blade is provided with a cavity adjacent to the discharge hole used for the tip seal, and the discharge hole, the cavity, and the blade shape maintain a predetermined relationship with each other. It is in.
[0012]
The foregoing and other features of the present invention will become more apparent from the following description and accompanying drawings.
[0013]
The present application is related to US Patent Application No. 07 / 236,094 “Clearance Control for the Turbine of Gas Turbine Engine” filed on August 24, 1988. Yes.
[0014]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As will be apparent from the following description, an object of the present invention is to prevent clogging of a tip seal of an axial-flow turbine blade that is air-cooled and a tip hole used for cooling the blade. Although the tip hole has many shapes, an object of the present invention is to prevent clogging of these holes, and is limited by the shape and position of the hole shown here within the scope of the invention. It is not a thing.
[0015]
As known by those skilled in the art, an axial turbine is constructed by supporting a number of turbine blades on a turbine rotor disk and is driven by hot gases generated in the combustion chamber of a gas turbine engine. It is like that. In general, the energy extracted by the turbine drives the compressor of the engine and generates thrust. Since the turbine is closest to the combustion chamber and is the hottest of all the engine components, as has been a problem in the early commercialization of turbines, means to cool the turbine blades are conventionally used . Turbine blade cooling is well known and necessary to understand the present invention. The most cooling mechanism for turbine blades is generally provided with a longitudinal passage inside the blade, and pressurized cooling air used for shower head cooling, film cooling, and the like is supplied by the passage.
[0016]
An embodiment of the present invention will be described with reference to FIGS. Reference numeral 10 denotes one of the turbine blades. The turbine blade 10 has a mounting base 12, a platform part 14, and a wing part 16. In general, high-pressure air introduced from a compressor (not shown) is supplied from the bottom surface of the mounting base 12 to the inside of the blade 10, and a large number of air discharges configured as shower head cooling holes and film cooling holes (not shown). It is discharged to the gas flow path through the hole. Since the present invention mainly relates to the tip seal and the cooling hole, only the blade part which is the main part will be described. Other known arrangements are disclosed in US Pat. No. 4,257,737, “Cooled Rotor Blade”, patented on March 24, 1981, and US Pat. No. 4,753,575 “Airfoil with Nested Cooling Channels”. Both patents belong to the same applicant as the present application. The wing portion 16 includes a pressure side surface 18, a leading edge 20, a trailing edge 22, a tip surface 32 that faces the outer peripheral side of the turbine, and a suction side surface 24 that is a surface opposite to the pressure side surface 18. Composed.
[0017]
As shown in FIGS. 2 and 3, a plurality of spaced holes or slots 30 are formed at the tip of the blade 10 along the chord direction from the leading edge 20 to the trailing edge 22. Conventionally, these holes extend from the internal cooling passage 52 toward the tip of the blade, and the terminal ends open in a flush state on the tip surface 32. In the present invention, a cavity 36 is formed in the tip surface 32 adjacent to the hole 30 under predetermined critical dimensions and constraints. Since the configuration of all the cavities 36 and the reference for the holes 30 of the cavities 36 are constant, for convenience, one of the holes 30 and the cavities 36 will be described as an example.
[0018]
As shown in FIG. 3, the cavity 36 is formed from the edge of the pressure side surface 18 toward the suction side surface 26 and reaches the back wall surface 40 of the hole 30. In the direction from the leading edge 20 toward the trailing edge 22, each cavity 36 extends over substantially the entire width of the hole 30. There are other restrictions on the formation of the cavity 36. As one of them, the discharge air flow from the hole 30, that is, the jet flow 42 must be considered. The holes 30 are arranged such that the outer edge 44 is included within the boundary defined by the gap 48 and the extension of the pressure side surface 18 when viewed from a lateral plane through the air jet 42. In addition, although the air jet 42 is illustrated in a straight line, in reality, the jetted air hits the outer air seal 50. The depth of cavity 36 (indicated by reference letter A) is preferably, but not limited to, at least 75% of the thickness of slot 30 (indicated by reference letter B).
[0019]
It is important that the back wall surface 40 of the hole 30 extends radially and reaches the blade tip surface 32. In order to increase turbine efficiency and maximize engine performance, the angle between the back wall 40 and the tip surface 32 (indicated by the letter C) should maximize the aerodynamic seal. Selected.
[0020]
The angle C is designed to maximize the engine performance. As an advantage of the present invention, the optimum angle C is larger than the conventional angle without the cavity 36. . What is important is that on the trailing edge 22 side, the angle C inevitably increases in order to ensure the intersection of the hole 30 and the internal cooling passage 52, that is, the communication between the two. As described above, by obtaining a large optimum angle C, it is possible to obtain more excellent performance at the trailing edge 22 side. The internal cooling passage 52 is a source of pressurized cooling air, but the allowable limit of the distance from the pressure side surface 18 to the internal cooling passage 52 in the portion on the trailing edge 22 side is relaxed.
[0021]
The reason why the optimum angle C is higher for each hole 30 of the present invention will be understood in the following description. First, since the pressure surface of the air jet 42 is exposed to the pressure side surface 18 of the wing 16 having a high static pressure, additional air flow on the wing surface is drawn by the jet 42 and accelerated. Is done. The air merges well with each other even at larger angles, thus allowing the optimum angle to be larger.
[0022]
Secondly, the cavity 36 'as shown in FIG. 4 increases the above-described effect, resulting in an even greater optimum angle C. Even in this case, the air merges sufficiently well. However, in the case of FIG. 4, since the additionally flowing air becomes air in the gas flow path having a temperature higher than that of the jet air, there is a restriction in terms of heat resistance of the surface 56 ′.
[0023]
Third, when the blade 10 is in sliding contact with the outer air seal 50 (see FIG. 3), a thin flash of material is generated and the blade 10 is covered. Here, according to the present invention, instead of this “burr” blocking the jet 42, the substantial angle C of the jet 42 is acted to be directed to a lower effective angle, and a more optimal angle is obtained. C can be approached.
[0024]
In the present invention, the angle of the surface 56 with respect to the hole 30 may be increased as in the surface 56 'shown in FIG. In the embodiment of FIG. 4, the dimensions of each part may be the same as in the above-described embodiment. However, the depth of the cavity 36 ′ is measured by the depth from the intersection D between the cavity 36 ′ and the hole 30 to the plane parallel to the tip surface 32. That is, the depth indicated by the arrow E in FIG. 4 is the depth of the cavity 36 '. In FIG. 4, the same reference numerals as those in FIG. 3 denote the same elements.
[0025]
The cavities 36 (FIG. 3) and 36 ′ (FIG. 4) are formed by an appropriate electric discharge machine (EDM) used for general drilling operations. In order to obtain the predetermined dimensions and shapes of these cavities, the electrode bars of the EDM machine are formed in a well-known manner into shapes corresponding to the cavities. In recent designs, a slot as shown is usually used as the hole 30, and the terms “hole” and “slot” are synonymous. However, in conventional designs, in order to obtain the desired performance results, the slot is small on the pressure side surface 18 despite being about 0.050 inches long and 0.012 inches wide. It is necessary to penetrate the tip surface 32 completely in a very close position. This is difficult to manufacture and therefore causes manufacturing problems. The present invention can alleviate this problem.
[0026]
The present invention has the following advantages.
[0027]
1. The material that is rubbed during sliding contact with the tip of the blade 10 minimizes the possibility of clogging the hole 30 at the tip of the blade 10. Thereby, the sealing action and cooling action by the hole 30 are maintained.
[0028]
2. By reducing the adverse effect of the position of the hole 30 on the pressure side surface 18 of the wing 16 on the performance, the productivity of the hole 30 at the tip is improved.
[0029]
3. In a portion where the angle C (FIG. 3) becomes large due to space limitations, the sealing performance of the blade 10 tip is improved.
[0030]
4). When the tip surface of the blade 10 is covered with an abrasive that causes a problem of blocking the hole 30, the shape of the hole at the tip is made more suitable for the seal.
[0031]
The present invention is not limited to the above-described embodiments, and various modifications can be made.
[0032]
【The invention's effect】
As is clear from the above description, according to the present invention, the cavity leading to the pressure side surface of the blade is provided adjacent to the discharge hole for ejecting cooling air for cooling and tip sealing. Clogging of the discharge hole due to the sliding contact is reliably prevented, and cooling air is ejected toward the pressure side surface, thereby improving the sealing performance. Further, the angle of the discharge hole can be increased, and the performance on the trailing edge side where the thickness of the wing portion is reduced is improved.
[Brief description of the drawings]
FIG. 1 is a perspective view of a turbine blade of a gas turbine engine according to the present invention.
FIG. 2 is a plan view of a tip of a blade illustrated in FIG.
3 is a partial cross-sectional view taken along line 3-3 in FIG.
FIG. 4 is a partial cross-sectional view illustrating another embodiment of the present invention.
FIG. 5 is a plan view of the entire turbine.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Turbine blade 12 ... Mounting base 14 ... Platform part 16 ... Blade | wing part 18 ... Pressure side surface 20 ... Leading edge 22 ... Trailing edge 24 ... Suction side surface 30 ... Hole 32 ... Tip surface 36 ... Cavity 36 '... Cavity 40 ... back wall 42 ... jet 50 ... outer air seal 52 ... internal cooling passage 56 '... surface

Claims (7)

In a tip seal structure of an internally cooled turbine blade in a turbine rotor for a gas turbine engine,
A wing that is exposed to the working fluid of the gas turbine engine and has a tip surface, a leading edge, a trailing edge, and a pressure side surface;
An annular shroud supported concentrically on the outer periphery of the wing and forming a gap with the tip surface;
An internal passage formed inside the wing and into which cooling air is introduced;
A jet of cooling air is directed from the internal passage toward the gap at a predetermined angle that is formed to extend to the blade tip surface at a position close to the pressure side surface and is inclined toward the pressure side surface. A discharge hole that seals the gap and blocks the gap so as to prevent the working medium fluid from flowing into the gap;
To prevent clogging of the discharge hole, the formed only on the pressure side surface of the discharge hole and the discharge hole and the pressure side surface so as to communicate, and has a width substantially equal to the width of the discharge hole With cavities,
The pressure-side surface side of the discharge hole opens to the pressure-side surface through the cavity, and the back wall surface of the discharge hole on the side opposite to the cavity extends to the blade tip surface at the predetermined angle. A tip sealing structure for a turbine blade, characterized in that   The turbine rotor has a plurality of blade portions arranged at appropriate intervals in the circumferential direction, and the shroud forms an annular gap between the tip surface of the blade portions. The tip seal structure according to claim 1.   The tip seal structure according to claim 1, wherein a plurality of cavities are arranged in a state of being separated from each other along the pressure side surface extending from the leading edge to the trailing edge. The tip seal structure according to claim 3, wherein the cavity has a deep portion adjacent to the pressure side surface and a shallow portion adjacent to the discharge hole . The tip seal structure according to claim 1, wherein the discharge hole is a slot.   The tip seal structure of claim 5, wherein the depth of the cavity substantially corresponds to at least 75 percent of the thickness of the slot. 5. The tip according to claim 4, wherein the discharge hole is a slot, and a cavity depth measured near an intersection where the cavity and the slot intersect substantially corresponds to at least 75 percent of the slot. Seal structure.

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