A gas turbine is described wherein the thermal stresses in the turbine rotor are reduced. The rotor includes a central disc with a peripheral rim, and a plurality of blades extending radially outward from the rim. To reduce thermal stresses, a duct arrangement is provided which selectively directs hot gases from the turbine combustor to the rim during the turbine start up. The hot gases from the combustor serve to heat the rim, and decrease the start up period necessary to bring the temperature profile of the rotor into the operating temperature range. After the start up period, the duct arrangement is then used to direct cool gases from the turbine compressor to the rim of the rotor in order to maintain a lower rotor equilibrium temperature

Heller, J. A.

English

NASA Technical Reports Server

4,117,669 
Oct. 3, 1978 
United States Patent [191 [111 
Heller WI 
[54] APPARATUS AND METHOD FOR 
REDUCING THERMAL STRESS IN A 
TURBINE ROTOR 
[75] Inventor: Jack A. Heller, Shaker Heights, Ohio 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. NO.: 776,029 
[22] Filed: Mar. 4,1977 
[51] Int. C I . 2  ............................ FO2C 7/26; FOlB 5/18 
[52] U.S. CI .  ................................... 60/39.14; 415/115; 
415/1 16 
[58] Field of Search ................. 60/39.14, 39.36, 39.37; 
415/115, 116, 117, 12; 416/95 
~561 References Cited 
U.S. PATENT DOCUMENTS 
1,164,091 12/1915 Herz .................................... 60/39.39 
2,685,421 8/1945 Klose .................................. 60/39.36 
2,977,760 4/1961 Soltav et al. ........................ 60/39.36 
3,267,676 8/1966 Sneeden .............................. 60/39.36 
3,316,714 5/1967 Smith et al. ......................... 60/39.36 
3,446,481 5/1969 Kydd .................................... 415/416 
3,975,901 EA976 Hollinger et al. .................... 415/115 
Primary Examiner-Louis J. Casaregola 
Attorney, Agent, or Firm-N. T. Musial; J. R. Manning; 
J. A. Mackin 
WI ABSTRACT 
A gas turbine is provided wherein the thermal stresses 
in the turbine rotor are reduced. The rotor includes a 
central disc with a peripheral rim, and a plurality of 
blades extending radially outwardly from the rim, and 
to reduce thermal stresses, a duct arrangement is pro- 
vided which selectively directs hot gases from the tur- 
bine combustor to the rim during the turbine start-up. 
The hot gases from the combustor serve to heat the rim, 
and thus decease the start-up period necessary to bring 
the temperature profile of the rotor into the operating 
temperature range. After the start-up period, the duct 
arrangement is then used to direct cool gases from the 
turbine compressor to the rim of the rotor in order to 
maintain a lower rotor equilibrium temperature. 
12 Clainis, 2 Drawing Figures 
COMBUSTOR 
62 
-64 
https://ntrs.nasa.gov/search.jsp?R=19790001886 2020-03-20T17:58:51+00:00Z
U.S. Patent oct. 3, 1978 Sheet 1 of 2 4,117,669 
62"4=lEfi44 COMBUSTOR i , i64 
COMPRESSOR 
I 
U.S. Patent oct. 3, 1978 Sheet 2 of 2 4,117,669 
TGAS 
LL 
0 
W u 
3 
I- 
W a. 
I- 
9 
E 
CRITICAL THERMAL 
STRESS REGION 
700 
HOT GAS IMPINGEMENT 
I 
400 
, .  . "  
TURBINE ROTOR RADIUS 
4,117,669 
1 2 
embodiment of the invention, there is provided a tur- 
bine comprising a combustor, and a rotor having a cen- 
tral disc with a peripheral rim, and a plurality of blades 
extending radially outwardly from the rim. The im- 
5 provement comprises a duct arrangement in fluid com- 
munication with the combustor which includes at least 
one injector that directs gases from the combustor at the 
rim. An aspect of the duct arrangement includes a valve 
APPARATUS AND METHOD FOR REDUCING 
THERMAL STRESS IN A TURBINE ROTOR 
ORIGIN OF THE INVENTION 
This invention was made by an employee of the 
United States Government and may be manufactured or 
used bv or for the Government without the Davment of 
. T  
any royalties thereon or therefor. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to gas turbine and, more partic- 
ularly, to an arrangement for reducing thermal stresses 
in turbine rotors. 
2. Description of the Prior Art 
Present day gas turbines includes rotors characteristi- 
cally comprising a central disc or hub having a periph- 
eral rim and a plurality of blades extending radially 
outwardly from the rim. In general, the rotors are cast 
or forged as an integral unit and the blades are relatively 
small and thin in comparison with the central disc. Be- 
cause of this construction, a steep temperature gradient 
exists at the junction of the blades and the rim during 
turbine start-up because the relatively small thin blades 
reach an equilibrium temperature much faster than the 
rim. This steep temperature gradient produces local 
thermal stresses which can lead to a reduction in the 
useful life of the rotor. Another factor that adversely 
affects rotor life is the maximum allowable turbine inlet 
temperature, with higher, more efficient temperature 
shortening the life of the rotor. 
In order to reduce the effects of thermal stresses and 
therefore extend the useful life of such rotors, the rotors 
are designed with ultra-conservative, allowable stress 
limits. Such designs require relatively heavy rotors, and 
the use of such heavy rotors increases manufacturing 
costs and can also effect turbine operational efficiency. 
A number of patents deal with problems relating to 
turbine temperatures and employ heating and cooling 
techniques in attempting to solve these problems. For 
example, U.S. Pat. No. 966,588 (Parsons) discloses a 
technique of heating turbine parts wherein the turbine 
snindle is heated to maintain medetermined clearances. 
device for-regulating the flow of gases from the com- 
10 pressor to the rim during the start-up period. The hot 
gases are directed at the rim to reduce the steep thermal 
gradient, and thus the thermal stresses at the junction of 
the blades and the rim. 
As a further aspect of the invention, the turbine in- 
15 cludes a compressor and the duct arrangement includes 
a valve in fluid communication with the compressor. 
The valve regulates the flow of gases from the compres- 
sor so that after start-up is complete, the gases from the 
compressor are directed through the injector at the rim 
20 to reduce the operational equilibrium temperature of 
25 
30 
35 
40 
6.S. Pat. No. 3,903,691 (Szidlowski) discloses a tech- 45 
nique for avoiding the formation of thermal imbalance 
in turbine engines wherein compressed air is injected 
into the engine in proximity to the rotating parts as soon 
as the engine stops. 
arrangement for cooling the peripheral rim of a centrip- 
etal turbine wheel during operation so as to reduce the 
temperature range between operation and shut down. 
Also U.S. Pat. No. 3,286,461 (Johnson) discloses a tur- 
bine engine which is started by applying compressed air 55 
against the blade. Cooling is also provided during oper- 
ation. U.S. Pat. No. 3,588,265 (Berry) discloses a com- 
puter used in maintaining predetermined temperatures 
in a turbine. However, in summary these devices are not 
completely satisfactory for reducing thermal stresses in 60 
the rotor. 
Further, U.S. Pat. No. 2,919,103 (Schelp) discloses an 50 
SUMMARY OF THE INVENTION 
The present invention provides for a turbine that 
reduces the steep thermal gradients and thus thermal 65 
stresses in the rotor, and also reduces the operational 
equilibrium temperature of the rotor, both reductions 
extending rotor life. In accordance with a preferred 
the turbine. 
Additional features and advantages of the invention 
will be set forth in, or apparent from, the detailed de- 
scription of a preferred embodiment found hereinbe- 
low. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a cross-sectional side elevation of a turbine 
incorporating the invention; and 
FIG. 2 is a graph depicting the temperature profile 
along the radius of the rotor of the turbine shown in 
FIG. 1. 
DETAILED DESCRIPTION OF THE 
PREFERRED EMBODIMENTS 
With reference to FIG. 1, there is shown a preferred 
embodiment of the improved turbine of the invention, 
the turbine being generally denoted 10. The turbine 10 
includes a rotor 12 mounted on a shaft 14, shaft 14 being 
mounted for rotation by bearings 16 on support frame 
18. Turbine 10 further comprises a conventional com- 
bustor and a compressor, indicated schematically at 62 
and 64, respectively. 
Rotor 12 comprises a disc or hub 20, shown in FIG. 
1 in section along a diameter thereof, and also has a rim 
22, and a plurality of thin blades 24 extending outwardly 
from rim 22. In a preferred embodiment blades 24 are 
cast or forged integrally with disc 20. Each side of disc 
20 is recessed adjacent rim 22 to expose forward under- 
side 36 and aft underside 38 of rim 22. 
Completely surrounding rotor 12 is a shroud 26 that 
is spaced apart from, and secured to, support frame 18 
by a plurality of fixed hollow stator blades 28. Shroud 
26 is also secured to an internal support member 30 of 
turbine 10 by a plurality of fixed hollow stator blades 
32. A generally annular passageway 34 is defined be- 
tween shroud 26 and support frame 18, passageway 34 
serving to direct the main hot gas flow generated by 
combustor 62 (as indicated by arrows in FIG. 1) toward 
blades 24. In accordance with the invention, a duct 
arrangement, generally denoted 40, is provided for 
diverting hot, high pressure gases, bled from combustor 
62 to the rim 22 of rotor 12. The duct arrangement 40 
includes a first duct 42, through which hot, high pres- 
sure gases are bled from combustor 62 to a first flow 
control valve 44. In a preferred embodiment, the first 
flow control valve 44 includes either a passive, heat- 
actuated, bi-metallic valve operator, or a time delay 
3 
device, for regulating the flow of hot gases through 
valve 44. A second duct 46 is connected to the outlet of 
flow control valve 44 and is, in turn, connected to a 
flow splitter 48. Flow splitter 48 divides the flow of 
gases, providing hot gases to a third duct 50 and a 
fourth duct 52. The third duct 50 extends through the 
hollow central portion of one of the stator blades 28 and 
through a hollow portion of support frame 18, as illus- 
trated, and communicates with a forward bleed flow 
7,669 
4 
proach can be realized in the resulting extension of the 
maximum operable life of the rotor. 
Referring to FIG. 2, a graph is shown wherein the 
turbine rotor radius is indicated on the abscissa, and the 
5 temperature of the rotor during start-up is indicated on 
the ordinate. In particular, on the abscissa, two radii are 
indicated, R, indicating the radius to rim 22 and R, indi- 
cating the radius to the end of blade 24. These radii are 
clearly indicated on a section of rotor 12 depicted 
injector 54. Injector 54 is mounted on support frame 18 10 below and parallel to the abscissa. A critical thermal 
and positioned so as to direct hot gases toward the stress region is indicated on the graph which generally 
forward underside 36 of rim 22, as indicated by the corresponds to the width of rim 22. The solid line of the 
arrow in FIG. 1. Similarly, duct 52 extends through the graph of FIG. 2 indicates the temperature profile along 
hollow central portion of one of the stator blades 32 and rotor 12 during the start-up of a prior art turbine. The 
through a hollow portion of internal support member 15 dotted line of the graph of FIG. 2 indicates the tempera- 
30, and communicates with an aft bleed flow injector ture profile of the improved turbine of the invention 
56. Injector 56 is mounted in internal support member with hot gases impinging on rim 22. It will be seen that 
30 and positioned so as to direct hot gases toward aft in the thermal stress region the improved turbine has a 
underside 38 of rim 22, as indicated by the arrow in more gently sloping temperature profile, and conse- 
FIG. 5. 20 quently less thermal stress, than is evidenced by the 
As stated hereinabove, in accordance with a further more drastically downwardly sloping temperature pro- 
aspect of the invention, cool gases from the compressor file of the prior art turbine. This results in an increase in 
64 are directed to the rim 22 to lower the operating the useful operating life of the turbine rotor. 
temperatures of the rotor after start-up. To this end, It is noted that the invention, although of general 
duct arrangement 40 further includes a second flow 25 application, is particularly applicable to gas turbines 
control valve 58 in fluid communication with second employed in vehicles since the number of cold starts of 
duct 46 and a fifth duct 60 providing fluid communica- these turbines is very large when compared with air- 
tion between second flow control valve 58 and com- craft turbines or stationary power turbines. 
pressor 64 of turbine 10. Valve 58 regulates the flow of Although the present invention has been described 
gases bled from compressor 64 and prevents hot, high 30 relative to exemplary embodiments thereof, modifica- 
pressure gases from entering duct 60, and thus from tions and variations can be effected in these embodi- 
entering compressor 64. ments without departing from the scope and spirit of the 
The operation of the improved turbine of the inven- invention. 
tion will now be considered. Turbine combustor 62 is I claim: 
fired up, and hot, high pressure gases are directed 35 1. In a turbine comprising a combustor, a rotor hav- 
through annular passageway 34 to impinge on blades 24 ing a central disc with a peripheral rim, a plurality of 
and thereby cause rotation of rotor 12. As blades 24 are blades extending radially outwardly from said rim, and 
thin, they quickly reach an equilibrium temperature. a flow path for a main flow of hot gases from the com- 
Simultaneous with the passage of hot gases through bustor to the turbine rotor, the improvement compris- 
annular passageway 34, first flow control valve 44 is 40 ing: a duct arrangement bypassing said flow path and in 
opened and hot gases are bled from combustor 62 fluid communication with said combustor for directing 
through duct arrangement 40 to forward bleed flow hot gases from said combustor to the under side of the 
injector 54 and aft bleed flow injector 56. Injectors 54 rim of the rotor during turbine start up. 
and 56 cause the hot gases to impinge on rim 22, and, in 2. A turbine in accordance with claim 1 wherein said 
particular, on the forward and aft underside portions 36 45 duct arrangement includes a flow control valve for 
and 38. This flow of hot gases continues for the duration regulating the flow of hot gases from the combustor. 
of the start-up transient period, (which is on the order of 3. A turbine in accordance with claim 2 and including 
15 to 20 seconds in the preferred embodiment), until rim temperature responsive means for actuating said flow 
22 and the peripheral portion of disc 20 reach an equilib- control valve. 
rium, steady-state temperature. As noted hereinabove, 50 4. A turbine in accordance with claim 3 wherein said 
first flow control valve 44 can comprise either a heat flow control valve includes a bimetallic member. 
actuated valve operator or a time delay device and is 5. A turbine in accordance with claim 1 wherein a 
designed to completely shut off the flow of hot bleed peripheral portion of each side of said central disc adja- 
gases from combustor 62 once this equilibrium tempera- cent said peripheral rim is recessed to expose forward 
ture is reached. 55 and aft undersides of said rim, and wherein said duct 
Subsequent to the initial start-up period, and after arrangement includes a plurality of injectors for direct- 
valve 44 has shut off the flow of hot gases to rim 22, ing hot gases toward said undersides of said rim. 
cooling air from the compressor 64 is directed through 6. A turbine in accordance with claim 1 wherein said 
second valve 58 to injectors 54 and 56 and thus to rim central disc is tapered along radii extending from the 
22. This cooling air produces a rim operating equilib- 60 center of said central disc, said peripheral rim extending 
rium temperature of from 75 to 100" F lower than the orthogonally outwardly from the radii of said central 
rim operating equilibrium temperature of a correspond- disc and said peripheral rim having a forward underside 
ing prior art turbine. With the rim at a lower equilib- and an aft underside, said duct arrangement including a 
rium temperature, the maximum allowable turbine inlet plurality of injectors for directing hot gases toward said 
temperature (the temperature of the main flow of hot 65 undersides of said rim. 
gases that impinges on the blades) can be increased. 7. A turbine in accordance with claim 2 wherein said 
Alternatively, if the maximum allowable turbine inlet duct arrangement includes a flow splitter located down- 
temperature is not increased, the benefit of this ap- stream from, and in fluid communication with, said flow 
5 
4,117,669 
6 
control valve for dividing the flow of hot gases from 
said control valve into a first duct directed at the for- 
ward underside of Said rim and into a second duct di- 
rected at the aft underside of said rim. 
with a peripheral rim and a plurality of blades extending 
radially outwardly from said rim, the turbine further 
including a combustor and a flow path for a main flow 
of hot gases from the combustor to the turbine rotor, 
8. A turbine in accordance with claim 2 further in- 5 said method comprising the steps of: 
eluding a shroud and a structure for supporting said bleeding hot gases from the combustor of the turbine 
rotor, said shroud being spaced apart from said support- 
ing structure by a plurality of hollow stator blades, said 
shroud and said supporting structure defining therebe- 
tween an annular passageway adapted to receive a main 10 
flow Of hot gases from said Of the 
duct arrangement extending through the hollow por- 
tion of said hollow stator blades. 
9. A turbine in accordance with claim 2 further in- 
cluding a compressor, said duct arrangement including 15 
a further flow control valve, in fluid communication 
with said compressor, for controlling bleeding of cool- 
ing gases from said compressor to cool the underside of 
said rim. 
rotor of a turbine, said rotor comprising a central disc 
in bypass relation to said flow path, and 
said rotor during turbine start-up. 
directing the hot gases at the underside of the rim of 
ll. A method in accordance with claim wherein 
the flow of hot gases from the combustor is terminated 
after the rim of the rotor has reached a steady-state 
temperature. 
l1 wherein 
said turbine further includes a compressor, and the 
method further comprises the step of bleeding cooling 
gases from the compressor and directing the cooling 
gases at the rim of the rotor after the flow of hot gases 
a 
12* A method in accordance with 
10. A method for reducing the thermal stress in a 20 from the combustor is terminated. * * * * *  
25 
30 
35 
40 
45 
50 
55 
60 
65 


Apparatus and method for reducing thermal stress in a turbine rotor

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