Cooling System For A Gas Turbine

Abstract

This invention comprises a system for cooling gas turbine rotor blades and discs. A coolant fluid enters a stationary portion of the turbine through a passage structure and then into an annular cavity. Opposite the stationary portion is a rotatable portion in which there is an annular row of apertures. In fluid communication with the apertures on the rotatable portion, is an axially extending annular passageway. Before the coolant enters the passageway, a tangential velocity is imparted on the coolant which is approximately equal to the tangential velocity of the passageway. The coolant flows through the passageway to a radially extending compartment in which is an annular series of radial vanes. A pressure rise occurs as the coolant is directed into further channels. The coolant flows to the blades and, in heat transfer relation, cools them.

Description

BACKGROUND OF THE INVENTION

This invention relates, generally, to an elastic fluid axial flow turbine and more particularly to a system for cooling fluid to the turbine rotor blades and discs.

In U.S. Pat. application Ser. No. 791,892 filed Jan. 17, 1969 by J. H. Borden and A. J. Scalzo, assigned to the present assignee, there is shown a sealed plate structure for directing the cooling fluid from the internal passages in the rotor to the root portions of the turbine rotor blades. This application constitutes an improvement over the aforementioned application by providing an arrangement for effectively directing the cooling air through the internal passages so as to maximize the heat transfer effectiveness of the coolant.

As gas turbines are required to operate with motive gases at higher temperatures for increased performance, there is greater demand to cool the rotor blades and it is desirable to so design a system to more effectively cool the blades.

SUMMARY

Generally, the present invention relates to an elastic fluid axial flow turbine and more particularly to a system for providing cooling fluid to gas turbine rotor blades and discs.

Hot motive gases derived from fuel combustion are diluted by secondary air to cool the gases to a temperature which the turbine parts and, more specifically, the rotor blades can withstand. By effectively cooling the blades, a minimal dilution of gases by the secondary air is required, thus minimizing the back work and increasing the useful work.

The pressurized cooling fluid enters the stationary portion of the turbine and flows through an internal passage structure. Opposite the stationary portion in a radially inward direction is a rotatable portion, said portions jointly defining an annular cavity, into which the passage structure opens. An annular series of apertures is on the rotatable portion in fluid communication with the cavity. On the rotatable portion is an axially elongated annular passageway, which is in fluid communication with the apertures.

An arrangement to impart a tangential velocity to the coolant before the coolant enters the passageway is provided in accordance with one of the main features of the invention.

In the first embodiment, the velocity inducing device comprises an annular series of tubular members, or swirl inducers, secured to the rotatable portion of the turbine. The axially elongated passageway opens into a radially elongated annular compartment in which is an annular series of radial vanes. As the coolant enters the compartment, the impartation of the tangential velocity by the swirl inducers increases the pressure rise as the coolant flows radially outward. The vanes direct the coolant into further channels with a minimum of pressure losses, the fluid then cooling the blades in heat transfer relation. In this manner, the turbine blades are more effectively cooled because the pressure losses in the cooling system are minimized.

The second embodiment is similar to the first except that the velocity inducing device comprises a ring having a plurality of nozzle passages, the ring being secured to the stationary portion of the turbine. The coolant is imparted with a tangential velocity which is approximately equal to the tangential velocity of the apertures before it enters the apertures. This results in an improved cooling system, because of an increased flow rate and a decrease in temperature losses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a longitudinal section of a portion of an axial flow gas turbine having a rotor blade cooling system formed in accordance with the principles of this invention;

FIG. 2 is an enlarged sectional view showing the cooling system shown in FIG. 1 in more detail;

FIG. 3 is a perspective view, partially in section, of a swirl inducer;

FIG. 4 is an enlarged view taken along line IV--IV in FIG. 2;

FIG. 5 is an enlarged fragmentary view taken along lines V--V in FIG. 2;

FIG. 6 is similar to FIG. 2, but showing another embodiment of the invention; and

FIG. 7 is an enlarged view taken along line VII--VII in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings in detail, and particularly to FIG. 1, there is shown a portion of an elastic fluid axial flow turbine 10. Only the upper half and a portion of the lower half of the turbine is shown since the lower half may be identical to the upper half. The turbine 10 comprises an outer casing 11 of generally tubular or annular shape, an inner casing 12 of annular shape encompassed by the outer casing 11, and a rotor structure 14 rotatably supported within the inner casing 12 in any suitable manner (not shown). The rotor structure 14 comprises an aggregate of rotor discs (only the first disc 16 and the second downstream disc 18 being shown), secured together by circumferentially disposed stay bolts 19 extending through the discs, only one stay bolt being shown. The discs 16 and 18, respectively, support a plurality of annular rows of blades 20 and 22 extending radially outward.

Cooperatively associated with the rotor blades to form stages for motive fluid expansion is an equal number of annular rows of stationary blades 23 and 25, supported within the inner casing 12.

The rotor blades 20 and 22 are substantially similar to each other although there is a gradual increase in height in each stage from left to right. The blades 20 and 22 are of the unshrouded type with a vane portion 28 directed radially outward, a base portion 29, and a root portion 30 suitably secured to the discs 16 and 18.

Similarly, the stationary blades 23 and 25 are substantially similar to each other although gradually increasing in height in each stage from left to right. Each of the blades 23 and 25 has a vane portion 32 directed radially inward, a base portion 33, and an inner shroud portion 34.

Hot motive fluid, such as pressurized combustion gas is generated in a plurality of circumferentially disposed combustion chambers 36 (only one being shown). The chambers 36 have corresponding transition members 37, where the downstream ends of the members form arcuate outlets 38. Together the outlets 38 form an annular outlet to direct the motive gases to the first blade row 23. The gases flow past the stationary blades 23 and 25 and the rotor blades 20 and 22 as shown by the arrows from left to right, with resulting expansion of the fluid to rotate the rotor structure 14 about its longitudinal axis R--R'.

The combustion chambers 36 are disposed in an annular high pressure plenum chamber 40 and pressurized air is directed into the combustion chambers to mix with the fuel (not shown) to form a combustible mixture which is burned to provide the hot motive fluid.

Secured to the rotor structure 14 by the stay bolts 19 is a rotatable cylindrical torque tube 42 and a hollow tubular shaft member 43, the torque tube and the shaft being disposed in driving relation with each other such as by bolts 44. The shaft 43 is in turn drivingly connected to the rotor of an air compressor (not shown) so that the compressor and turbine rotors rotate together, , the turbine 10 driving the compressor, as well known in the art.

Encompassing the torque tube 42 and the shaft 43 is a stationary, circumferential inner liner 45 forming the radially inner wall of the plenum chamber 40.

A ring manifold 47 secured to the outer casing 11 has one or more outlet pipes 48 (only one of which is shown in FIG. 1) extending radially inward, which are connected to the stationary liner 45. Disposed in the liner 45 are annular labyrinth seals 46 employed, as well known in the art, to minimize fluid leakage.

In accordance with the invention, and as best seen in FIG. 2, a tubular fairing member 49 is disposed in encompassing relation with the torque tube 42. The fairing member 49 has a disc shaped flange portion 50 extending radially outward and is connected at its periphery to the disc 16 by a ring seal 52. As shown, the rotatable portion of the turbine comprises the rotor structure 14, the torque tube 42, the shaft 43, and the fairing member 49.

The pipe 48 extends into the stationary liner 45 and exits into an annular cavity 56, jointly formed by the liner 45, the annular labyrinth seals 46, and the fairing member 49.

The tubular portion of the fairing member 49 forms a wall of the cavity 56 and is provided with an annular series of radial apertures 58 in fluid communication with the cavity. The fairing member 49 and the torque tube 42 are in spaced relation and define an axially elongated annular passageway 60 in fluid communication with the apertures 58.

Referring to FIG. 4, it can be seen that an annular series of swirl inducers 62, three of which are shown, are radially disposed in the fairing member 49. The swirl inducers 62, are in fluid communication with the apertures 58 and the passageway 60.

The swirl inducer 62, as best shown in FIG. 3, is of tubular shape, having an exit portion 63 where part of the tubular wall is removed so that an orifice 64 is formed. A middle portion 65 has a reduced outside diameter and an entrance portion 67 has an outside diameter which is further reduced. The swirl inducer 62 has a concave inner wall 69. The entrance and middle portions 67 and 65 frictionally engage cooperating recesses 68 in the fairing member 49 so that upon rotation the swirl inducers 62 are prevented from moving radially outwardly due to the centrifugal force. Other means may be used to prevent the swirl inducers 62 from dislodging from the fairing member 49 without departing from the invention.

The axially elongated passageway 60 exits into a radially elongated annular compartment 70, as shown in FIG. 2, defined by the flange 50 and the disc 16. An annular series of vanes 71 is interposed between the flange 50 and the disc 16. The vanes 71 may be fastened to the flange 50 or the disc 16 but, as shown are secured to the flange. In fluid communication with the compartment 70, are radially extending openings 74 which open into an annular continuous coolant chamber 75 adjacent the blade roots 30, as explained in the aforementioned Borden and Scalzo application. The colling system may be used to cool only the root portions 30 of the rotor blades 20 or the entire blades 20.

The purpose of this system is to effectively cool the rotor blades. Although the theory of operation of the cooling system is complex, the following explanation describes the operation according to present scientific thought. The heat transfer effectiveness of the coolant is dependent on the coolant temperature and the quantity of coolant flow. By either decreasing the temperature or increasing the flow, there is a corresponding increase in heat removed. The first embodiment improves the cooling effectiveness by minimizing pressure losses and producing a pressure rise.

The coolant, which may be air extracted from a compressor, can be treated to provide specified environmental conditions. More specifically, the air may be cooled, filtered, and metered to control flow (none of which are shown) before entering the ring manifold 47. As the coolant flows from the outlet pipes 48, filling the annular cavity 46, there is a pressure differential between the cavity 56 and the axial passageway 60 forcing the air to enter the apertures 58.

In FIG. 5, a vectorial analysis is shown of the velocity components of a single particle of coolant entering a swirl inducer 62. The particle forced into the swirl inducer 62 is struck by the concave wall 69 of the swirl inducer, which rotating at the seam angular velocity .omega. as the rotor structure 14. The swirl inducer 62 serves two functions. The first is to impart an axial velocity component V.sub.AS to the coolant particle. This, when added to the smaller axial velocity component V.sub.AP, due to the pressure differential, forms the total axial velocity V.sub.A which enables the particle to flow in a downstream axial direction along passageway 60. The second function is to impart a tangential velocity component V.sub.T on the particle approximately equal to the tangential velocity of the passageway 60. This enables the coolant particle, when it reaches the radial compartment 70, to obtain in increase in pressure as it is projected radially outwardly due to the centrifugal force.

To be most effective, the orifice 64 is preferably oriented so that the resultant velocity V.sub.R is at an angle .theta. with the axis of rotation R--R' of the rotor structure .theta. can be determined experimentally depending on the variables such as the size and shape of the orifice 64 and the radius of curvature of the swirl inducer 62. It is not necessary that the swirl inducer 62 be a tube as shown but may for example be a straight sheet oriented at the angle .theta..

To effect the pressure rise in the radial compartment 70, the vanes 71 rotate with the same angular velocity .omega. as the rotor and function as a centrifugal pump. As the air comes in contact with the rotating vanes 71, the air is discharged at a higher pressure as a function of its increasing radial distance form the axis of rotation R--R'.

If the actual motion of the coolant were of the free vortex type, the coolant would enter the rotating vanes with a velocity different than the vane rotation resulting in an inefficient utilization of the centrifugal pump. However, since the coolant has the same tangential velocity V.sub.T as the entrance portion of the vanes 71, so that there is no relative velocity between the coolant and the vanes 71, the coolant will rotate with the vanes with virtually no bouncing effect. This is known as the rigid body type of motion. It can be shown that pressure rise through the radial compartment 70 with the vanes 71 is proportional to the square of the tangential velocity of the air particle at a fixed radial distance. Therefore, the importance of maximizing the tangential velocity becomes readily apparent.

As the coolant particle moves radially outward with rigid body motion, it will have a tangential velocity equal to the tangential velocity of the channels 77 when it reaches the same radial distance as the channels. Correspondingly, as it reaches the same radial distance as the openings 74, it will have approximately the same tangential velocity as the openings. Therefore, the relative velocity between the coolant and channels will be approximately zero so that any entrances losses will be minimized. If desired, air may be directed to an annular series of channels 77 or axial holes in the disc 16 to cool downstream disc 18 (FIG. 1) and blades 22. This colling system then provides a more effective way of cooling the blade roots and the discs.

SECOND EMBODIMENT

The second embodiment as shown in FIG. 6 is similar to the cooling system in FIGS. 1 and 2 but differs in the following manner. The outlet pipes 78 enter into an annular inlet channel 79. At the exit portion 80 of the channel 79 is a circumferential ring 82 forming a part of the stationary portion of the turbine. The ring 82 is secured in circumferential liner 83. The liner 83 has annular recesses 84 and the ring 82 has radial lips 85, the lips and recessed cooperating to secure the ring to the liner. Other fastening means may be used without departing from the invention. A plurality of annular labyrinth seals 85a are disposed in the liner 83. Forming a part of the rotatable portion of the turbine, is a tubular fairing member 86. The ring 82, the seals 85a, and the fairing member 86 jointly define an annular cavity 87. An annular series of radial apertures 88 is on the fairing member 86 in communication with the cavity 87. The apertures 88 are in fluid communication with an axially elongated annular passageway 89.

Referring to FIG. 7 which is a sectional view taken along line VII--VII in FIG. 6, it can be seen that the ring 82 comprises an annular series of internal holes or nozzle passages 90 of which a quadrant is shown. The nozzle passage 90 consists of a larger diameter inlet portion 91 and a smaller diameter exit portion 92. The two nozzle portions 91 and 92 are concentric around the common centerline L--L'.

The nozzle passages 90 are equally spaced in a circumferential direction and are inclined at an angle .phi., where .phi. is the angle made by the intersection of the centerline L--L' of the nozzle passage 90 with the tangent T--T' of the annular cavity 87 at the nozzle exit 92. The series of nozzle passages 90 will all be inclined with the cavity 87 at approximately the same angle .phi.. The angle .phi. is designed to impart a tangential velocity on the coolant which is approximately equal to the tangential velocity of the apertures 88.

The advantages of the second embodiment are that a greater amount of air can be supplied to the blades at lower temperatures. This embodiment may be more desirable when the whole blade is to be cooled rather than just the root portion.

Since the nozzle passages 90 insure that the air entering the cavity 87 will be approximately the same tangential velocity as the apertures 88 rotating on the fairing member 86, there will be no relative velocity between them. The ability to pass air flow through a given aperture is measured by a coefficient of discharge. This discharge coefficient is much greater in the second embodiment, where the coolant entering the apertures is moving at about the same speed as the apertures, rather than the system shown in the first embodiment where the coolant has no pretangential velocity component. Therefore, this increased entrance condition enables a greater flow of air to pass through the apertures 88.

The second advantage of using the nozzle structure is that there will be approximately zero relative velocity between the coolant particles and rotating apertures 88, friction will be minimized and there will be only a slight temperature rise in the coolant.

With this colling scheme, there is a small pressure loss to the total system because of the pressure drop across the nozzles 90, this drop being necessary to accelerate the coolant. This pressure drop can be compensated for, except when using compressor discharge by properly locating the extraction point for removal of compressor air form the cycle.

Although more than one embodiment has been shown it is intended that all the matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

What we claim is:

1. In an axial flow elastic fluid utilizing machine comprising a stationary portion and a rotatable portion,

means to supply cooling fluid to said stationary portion,

said rotatable portion including a rotor structure,

said rotor structure comprising a disc extending radially outward from said rotor,

a corresponding annular row of blades in said disc,

an annular cavity between said rotatable and stationary portions, said cavity being in communication with said cooling fluid supply means,

an annular series of apertures on said rotatable portion,

said cavity providing for substantial uniformity of flow of said cooling fluid from said cavity into said rotatable apertures,

a passageway in said rotatable portion in fluid communication with said apertures,

means to impart a tangential velocity to said cooling fluid before it enters said passageway,

and means to direct said fluid from said passageway to said rotor blades to cool the same.

2. The machine according to claim 1 wherein said velocity means comprise an annular series of swirl inducers,

said swirl inducers having entrance portions and exit portions,

said entrance portions being in fluid communication with the annular cavity,

said exit portions being in fluid communication with the passageway,

said swirl inducers having orifices in said exit portions, and

said orifices being oriented to impart a tangential velocity component to the fluid which is substantially equal to the tangential velocity component of the passageway.

3. The machine according to claim 1 wherein the velocity means comprises a circumferential ring,

said ring forming part of the stationary portion and comprising an annular series of nozzle passages,

said nozzle passages oriented to impart a tangential velocity component to the coolant which is approximately equal to the tangential velocity component of the apertures.

4. The structure according to claim 1 wherein the velocity imparting means is arranged in a manner to impart a velocity component in the direction of rotation of the rotatable portion.

5. In an axial flow elastic fluid utilizing machine comprising a stationary portion and a rotatable portion,

means to supply cooling fluid to said machine,

said rotatable portion including a rotor structure,

said rotor structure comprising a disc extending radially outward from said rotor,

a corresponding annular row of blades in said disc,

an annular cavity between said rotatable and stationary portions,

an annular series of apertures on said rotatable portion,

a passageway in said rotatable portion in fluid communication with said apertures,

means to impart a tangential velocity to said cooling fluid before it enters said passageway,

means to direct a fluid from said passageway to said rotor blades,

said velocity means comprising an annular series of swirl inducers,

said swirl inducers having entrance portions, middle portions and exit portions,

recesses in the rotatable portion between the apertures and the passageway,

said entrance and middle portions cooperating with said recesses to secure said swirl inducers to the rotatable portion,

said orifices in said exit portions being oriented so that the resultant velocity of the fluid which flows through said swirl inducers is at an angle with the axis of rotation of the rotor structure.

6. The machine according to claim 5 wherein the means to direct the fluid from the passageway to the rotor blades comprises

an annular fairing member,

said member having a flange portion extending radially outward,

said flange portion and the first rotor disc being arranged in spaced relation to form a radial compartment,

an annular series of vanes extending radially outward relative to the axis of rotation of the rotor in said compartment,

said vanes being secured to the rotatable portion,

a plurality of radially extending openings in the disc,

said openings being in fluid communication with the root portions of the rotor blades,

said vanes directing the cooling fluid into said radial openings to that the tangential velocity of the fluid in the compartment at the point of entry into the openings is approximately equal to the tangential velocity of the openings.

7. The machine according to claim 5 wherein the rotatable portion further comprises a cylindrical torque tube and a tubular fairing member,

said torque tube and fairing member jointly defining an axially elongated passageway,

a disc-shaped flange portion of said fairing member extending radially outward,

said flange portion and the disc defining a radially elongated compartment,

the means to direct the fluid from the passageway to the rotor blades comprising said radial compartment, and annular series of radial openings in the disc in fluid communication with the rotor blades.

8. The machine according to claim 7 and further including a second disc downstream of the first disc, wherein the first disc has a series of channels in fluid communication with the downstream disc and rotor blades.

9. In an axial flow elastic fluid utilizing machine comprising a stationary portion and a rotatable portion,

said rotatable portion including a rotor structure,

said rotor structure comprising a disc extending radially outward from said rotor,

a corresponding annular row of blades in said disc,

an annular cavity between said rotatable and stationary portions,

an annular series of apertures on said rotatable portion,

a passageway in said rotatable portion in fluid communication with said apertures,

means to impart a tangential velocity to a cooling fluid before it enters said passageway,

means to direct said fluid from said passageway to said rotor blades,

a circumferential liner in the stationary member,

a circumferential ring,

said ring comprising an annular series of nozzle passages,

annular recesses in said liner,

annular lips on said ring,

said recesses and lips cooperating to secure said ring into said liner.

10. The machine according to claim 9 wherein said nozzle passages are substantially equally spaced in a circumferential direction

said passages comprising concentric larger diameter inlet portions and smaller diameter outlet portions,

and said passages being oriented so that the coolant will leave the nozzle passages at an angle with the tangent of the annular cavity at the nozzle exits.