Apparatus for venting the rotor structure of a compressor of a gas turbine power plant

Method of apparatus for venting rotor parts of an axial flows compressor of a gas turbine power plant having an axial diffuser arranged behind the rotor and stator vanes at the last compressor stage. An annular chamber is formed downstream of the last rotor disk between adjacent rotor and stator parts and compressed air downstream of the diffuser is introduced into the chamber. The air in the chamber is divided into two individual streams, one of which is recycled to the compressor through an annular slot between the rotor and guide vanes at the last compressor stage and the other of which is discharged as a stream of leakage air into the secondary air system of the turbine.

FIELD OF THE INVENTION 
The invention relates to apparatus for venting the rotor structure of a 
compressor of a gas turbine power plant, particularly at the last stage of 
the compressor. 
DESCRIPTION OF PRIOR ART 
It has proven difficult to provide an effective venting concept which 
produces a considerable reduction of the temperature of secondary cooling 
air and thus also of the structural parts at the rear or downstream face 
of the rotor. 
Traditional venting constructions which, for example, have removed 
compressed air between the last rotor and stator stages for flow ono the 
root portions of the rotor have high temperature of the air as a result of 
the compressor temperature profile. Additionally, air friction between the 
rotating and stationary parts at the downstream face of the last rotor 
produces relatively extensive heating of the secondary or control air 
removed at the last compressor stage, which causes unnecessarily high 
temperature in the structural parts and leads to degrading of the desired 
optimization of the radial clearances between the rotor blades or vanes 
and the surrounding housing. 
A decisive disadvantage of the conventional solutions is that an increase 
in the life can be maintained in most cases only by increasing the 
thickness of the rotating parts or by the use of high strength materials. 
In an earlier proposal, additional venting of the inside of the rotor is 
obtained, for instance, by providing openings at the rear surface of the 
rotor. This has the great disadvantage that the vent temperature is 
extremely high as a result of heating of the secondary air and the 
required amount of air necessary to pass through the slot of the labyrinth 
main seal of the rotor arranged in front cannot be obtained to the desired 
extent, particularly during transient operation. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a venting apparatus which 
is of relatively simple construction and assures a comparatively low vent 
temperature, even in the case of sudden changes in load. 
A further object of the invention is to provide a venting apparatus and 
method which contributes to preservation of optimum vane clearance. 
The above objects are achieved in accordance with the invention by 
apparatus comprising: 
an annular chamber located in the vicinity of the last stage of the 
compressor and having an inlet for supply of a portion of the compressed 
air discharged from an axial diffuser downstream of the last stage; 
said annular chamber having one outlet for flow of a first portion of the 
compressed air supplied thereto as a discharge stream to a secondary air 
system of the turbine and a second outlet for flow of a second portion of 
the compressed air supplied to the chamber as a recycle stream to the 
compressor via an annular slot provided between the rotor and stator vanes 
of the last compressor stage; 
said apparatus including stationary and rotating portions between which 
said annular chamber is defined. 
In further accordance with the invention, a substantially quantitatively 
adjustable circulation of compressor outlet air can be provided by forming 
openings in the wall of a housing of the combustion chamber and utilizing 
the pressure rise in the region of the stator vanes at the last stage of 
the compressor and the adjacent diffuser. 
In accordance with the invention, the openings, preferably in simplified 
form as holes of large cross section, can be arranged at given locations 
in order to assure sufficient venting. The amount of air to be fed and 
thus the cross section of the holes can be established in accordance with 
the heat produced by air friction and be optimized by the temperature and 
strength requirements of the associated rotor parts.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to FIG. 1, therein is seen the last stage of an axial flow 
compressor of a gas turbine power plant. The compressor has stator vanes 1 
at the last stage which guide compressed air to an axial diffuser 2 from 
the rotor vanes 4 at the last compressor stage. The rotor vanes 4 are 
secured for rotation on the rotor disk 5 of the last stage. 
The invention is directed to the venting of the rotor by utilizing a 
portion of the stream 8 of compressed air which has passed through the 
last stage of the compressor and the diffuser 2. The portion of the stream 
8 which is utilized for venting is shown as stream 9. An annular chamber 
or space 11 is formed downstream of the rotor disk 5 between opposed rotor 
and stator parts and receives the stream 9 of compressed air. From the 
space 11, the stream 9 is divided essentially into two individual streams 
12 and 14. Stream 14 is recycled to the flow channel of the compressor via 
an annular slot 13 formed between the rotor vanes 4 and the stator vanes 1 
of the last compressor stage. The stream 12 is discharged as leakage air 
into the secondary air system of the turbine, for example, for turbine 
cooling purposes. 
The stream 9 of compressed air is diverted from the stream 8 which is 
discharged at the outlet of the diffuser 2 and the stream 9 flows through 
outer and inner double walls 3', 3" of a combustion chamber housing 3, 
into the annular space 11. The outer wall 3' has openings 17 for the flow 
of the compressed air thereinto and inner wall 3" has openings 10, 10' for 
flow of the compressed air into space 11. The walls 3', 3" enclose an 
annular channel which is disposed between space 11 and the discharge 
region of the compressed air 8 downstream of diffuser 2. The compressed 
air at the compressor outlet passes through the stator vanes 1 and the 
adjoining diffuser 2 and after flowing from inner wall 3" the compressed 
air is guided by guide devices 18 into the annular space 11 where it 
undergoes the division into the individual streams 12 and 14. 
The guide devices 18 face respective openings 10' to guide the stream of 
air flowing therefrom, the guide devices 18 being formed as angle plates 
having one leg 18' extending in the axial direction below the unit 
compressed of the guide vanes 1 and diffuser 2 and a second leg 18" 
extending radially into space 11 and secured by leg 18' in parallel, 
spaced relation opposite a radial portion of inner wall 3" which contains 
the respective openings 10'. 
As seen in FIG. 1, the annular space 11 to be vented is circumferentially 
bounded at the outside by the guide vanes 1, the guide device 18 and the 
diffuser 2, at the rear by the double wall 3 of the combustion chamber 
housing, at the inside by a conical portion 6 of the rotor shaft and at 
the front by the rotor disk 5. The rotor disk 5 is connected by attachment 
bolts 15 to the rotor structure 16 which carries the rotor blades of the 
upstream stages. The air present in the annular space 11 undergoes 
additional heating due to air friction. The magnitude of the air friction 
is a function of a number of factors, such as speed of rotation of the 
rotor, the radial position of space 11, the surrounding pressure, the air 
temperature and, in particular, surface features on disk 5 such as, its 
smoothness, the rotating bolts 15, etc. The rotating bolts 15 which are 
required for attachment to the rotor structure 16 produce increased heat 
within the annular space 11. In order to keep the heating of the air as 
small as possible, the annular space 11 must be sufficiently ventilated. 
The pressure within the annular space 11 is adapted by the annular slot 13 
to the pressure between the rotor vanes 4 and the stator vanes 1. 
By the arrangement in space and size of the openings 10, 10' in wall 3" and 
of the openings 17 in wall 3', sufficient venting of the annular space 11 
with compressed air 9 taken from the compressor outlet can be achieved as 
a result of the increase in pressure of the air flow 7 between the 
entrance to the stator vanes 1 and the air flow 8 at the exit of the 
diffuser 2. 
The optimal mixing or utilization of the amount of compressed air 9 can be 
effected within the annular space 11 by the locally directed influence of 
the air flow by the stationary guide devices 18 which are fastened to the 
combustion chamber housing 3. Furthermore, the guide devices 18 result in 
a definite reduction of the heat transmission from the outside through the 
inner wall of the guide vanes 1. 
The individual stream 14, which is recycled through the annular slot 13 to 
the primary air stream in the compressor between the rotor blades 4 and 
the axial guide vanes 1 of the last compressor stage, experiences rapid 
acceleration to the speed of the primary air stream within guide vanes 1 
and diffuser 2 by the suction produced by the primary air flow. 
The arrangement and size of the openings 17, which serve essentially for 
the supply of venting air to the high-pressure turbine, are so selected to 
insure a sufficient mixing of the primary air stream and a reduction in 
the compressor temperature profile and hence a minimal vent inlet 
temperature. 
The spacing 19 and the diameter 20 of the openings 10' (shown as holes in 
FIG. 2) depend on the required amount of venting. Furthermore, the radial 
position of the axis of openings 10' should correspond as far as possible 
with the radial position of maximum air friction, i.e. at the level of 
bolts 15. 
In accordance with FIG. 3, the annular space can be divided by a seal 22, 
23 into an outer part 11' which communicates with the annular slot 13 and 
an inner part 11" from which air is discharged as stream 12 to the 
secondary air system of the turbine. The compressed air 9 coming from the 
compressor outlet flows, via openings 10' arranged at the level of the 
guide devices 18 secured to the inner wall 3", into outer part 11' and 
then at reduced pressure and quantity through the seal 22, 23, into the 
inner part 11". 
Referring further to FIG. 3, the seal is composed of stationary part 23 and 
rotating part 22, and is disposed radially inwards of the axial leg or 
section 18' of the guide devices 18 and axially spaced from the radially 
protruding leg or section 18" of the guide plates 18. The stationary part 
23 of the seal can be secured integrally with the support for the axial 
section 18'. 
The utilization of the seal 22, 23 in the embodiment in FIG. 3 makes it 
possible to reduce the pressure in the inner part 11" of the annular space 
which results in a reduction of compressive force on the outer surface of 
the conical portion 6 of the rotor shaft and consequent axial thrust on 
the rotor shaft. In the outer part 11' of the annular space, the air is at 
a higher pressure and venting can take place effectively, particularly in 
view of the relatively pronounced heating of the secondary air in part 11' 
of the annular space. 
In view of the above, it is also advantageous, as seen in FIG. 3, for the 
openings 10' to be arranged substantially at the level of the maximum air 
friction developed in the outer part 11' of the annular space, over the 
circumference of the combustion chamber housing 3 on the radially outer 
section of the combustion chamber wall. 
In accordance with the embodiment in FIG. 4, the compressed air 9 coming 
from the compressor outlet is fed through the openings 10 of the 
combustion chamber housing 3 directly to the inner part 11' of the annular 
space and is mixed thereat with leakage air 24 which flows, at reduced 
pressure, past labyrinth seal 22', 23' from the flow channel of the 
compressor. A mixture of air 25', produced from streams 9 and 24, flows in 
a direction opposite the direction of the main flow 7 within the 
compressor towards the root portions of the rotor disks which are close to 
the axis of rotation of the rotor. As a result of this mixing operation, 
an optimal temperature level is obtained and the heating effect due to air 
friction produced on the leakage air 24 no longer has any detrimental 
consequences. 
In the embodiment of FIG. 4, therefore, there is obtained, in addition to 
air supply to the inner space of the rotor which is independent of the 
behavior of the slot of the labyrinth seal 22', 23' arranged upstream of 
space 11', a decisive lowering of the inlet temperature of the vent air 
because of the formation of the mixed air stream 25'. The magnitude of the 
reduction in the vent air temperature is determined essentially by the 
quantity of compressed air 9 supplied to space 11'. However, since an 
increase in pressure is developed within the annular space 11' due to the 
openings 10, the axial thrust on the rotor is increased which could lead 
to a limit in the supplied amount of compressed air 9. 
In a further advantageous arrangement in the embodiment of FIG. 4, the 
rotating part 22' of the labyrinth seal, constituted as the rotor main 
seal, can be a part of a disk 5' of the compressor which is arranged 
behind the last rotor disk 5. 
A seal support R at the outer circumferential region of the rotating part 
22' serves as a spacer between the rotor disk 5 and the supporting disk 
5'. The stationary part 23' of the labyrinth seal is radially inwards of 
the axial guide vanes 1 and the axial diffuser 2 and is secured to a 
radial portion of the combustion chamber housing 3. 
The possibly detrimental effect due to the increase in axial thrust caused 
by pressurization in space 11' in the embodiment of FIG. 4, can be 
completely circumvented by the embodiment shown in FIG. 5. Herein the 
outer part 11' of the annular space is arranged between a front section of 
the seal support R, serving as a spacer between disks 5 and 5' and the 
stationary part 23 of the seal on one side and end surfaces on the rotor 
disk 5 proximate the root regions of the vanes 4 on the other side. The 
outer part 11' of the annular space is in communication with a channel 30 
located below the unit composed of guide vanes 1 and diffuser 2 to conduct 
compressed air 9 taken from the compressor outlet to outer part 11'. A 
portion of the compressed air 9 discharged at the outlet of the diffuser 2 
flows through openings 10' in housing 3 of the combustion chamber 3 at the 
level of the channel 30. The outer part 11' of the annular space is also 
in communication via slot-shaped inlet openings 26, with an outer 
intermediate space 27 between the rotor disk 5 and the rotating part 22 of 
the labyrinth seal which is integral with supporting disk 5'. The space 27 
is vented via the supporting disk 5' and rotor disk 5, as will be 
explained later. Similar parts of FIGS. 4 and 5 are affected by this and 
the following description applies to both figures. 
The intermediate space 27 supplies air to air chambers 28, 35 formed 
respectively in axial spacers 31, 32, 33 and 34 of the rotor disks. The 
spacers define annular inner and outer intermediate spaces 27, 36 and 37, 
38. The air chambers 38, 35 receive an air mixture 25' in FIG. 4 or 
removal air 25 in FIG. 5 respectively from the inner part 11' of the 
annular space in FIG. 4 or from the outer intermediate space 27 in FIG. 5. 
Furthermore, the air mixture 25' in FIG. 4 is fed, via openings 26' in the 
supporting disk 5' to the air chamber 28 and then to the air chamber 35 
via the openings 26' in rotor disk 5. In FIG. 5, the removal air 25 flows 
via openings 29 in axial spacer 31 into the air chamber 28 and then into 
air chamber 35 via openings 26' in disk 5. The air chambers 28, 35 in both 
FIGS. 4 and 5 are in communications via inner openings 30, 40 in the axial 
spacers 32, 34, with the inner intermediate spaces 36, 38 for venting the 
compression air against the root portions of the disks. 
The decisive advantage of shifting the inlet openings 26 in FIG. 5 radially 
outwards is that the feeding of the vented or control air can take place 
substantially independently of the heating of the secondary air by air 
friction and the influence of the slot of the labyrinth seal. Furthermore, 
an additional decrease in the temperature of the removal air 25 used for 
the venting can be obtained by the construction of the flow path of the 
compressed air and therefore of the type of guidance of the compressed air 
9 into the outer part 11' of the annular space. 
The size of the openings 26 as well as the maximum slot length, the maximum 
depth of recess, the radii and the circumferential distribution or maximum 
number of slots are based on strength requirements. The maximum cross 
section of the resultant opening determines the greatest possible amount 
of removal air 25 and the pressures in the annular intermediate spaces 27, 
36 and in the air chambers, for example air chamber 28, within the rotor. 
Within the outer annular intermediate space 27, the quantity of the 
inwardly flowing removal air 25 effects a cooling of the sealing disk 22, 
which is heated from the outside by air friction. The removal air 25 flows 
through the openings 29, which preferably are boreholes, into the air 
chambers 28 disposed radially inwards thereof. The removal air 25 is then 
divided in the manner already described. 
This construction of the venting apparatus makes it possible for the rotor 
disks to achieve an optimum reduction of temperature at the root portions 
or hubs thereof to the level of the temperature of the rims of the disks, 
thereby avoiding heat transfer which enables optimization of the radial 
clearance between the rotor vanes and the stator housing for all loads 
during uniform and transient operations. 
Another advantage of the formation of the annular intermediate spaces 27, 
36 as shown in FIG. 5 is that, due to the smaller change in pressure, the 
tap or bypass pressure for venting can be correspondingly low or a 
sufficiently high pressure difference can be present at the inlet openings 
26. Within the air chambers 28 which are separated from each other in the 
circumferential direction by radial webs 100 (FIG. 5), a circumferential 
speed can be imparted to the air stream 25 in connection with the 
aforementioned inlet and outlet openings 29, 39 which belong to each of 
said vapoarted air chambers 28. 
Due to the enforced circumferential flow, there is produced within the air 
chambers 28 a smaller change in pressure than takes place comparatively in 
the outer and inner intermediate spaces 27, 36 due to the equilibration of 
the velocity of the air and the free flow which takes place. 
Furthermore, in FIG. 5, the openings 10' are located at a radial position 
which corresponds essentially to the radial position of the maximum air 
friction which is developed locally in the outer part 11' of the annular 
space, as has already been explained. 
As can furthermore be noted in FIGS. 4 and 5, the rotor disks 5 can be 
supported by one another by conventional rotor spaces rings 41 arranged in 
the outer circumferential region. 
The invention is particularly suitable for axial-flow gas turbine jet 
engines of aircraft, but, of course, is not so limited. 
Although the invention has been described in relation to specific 
embodiments thereof, it will become apparent to those skilled in the art 
that numerous modifications and variations thereto can be made within the 
scope and spirit of the attached claims.