US 3011762 A
Description (OCR text may contain errors)
R. POUIT TURBINES AND IN PARTICULAR GAS TURBINES Dec. 5, 1961 4 Sheets-Sheet 1 Filed March 26, 1957 Dec. 5, 1961 R. POUlT 3,01
TURBINES AND IN PARTICULAR GAS TURBINES Filed March 26, 1957 4 Sheets-Sheet 2 4/ .nlllH III. j
INVENTOR ATTORNEYS Dec. 5, 1961 R. POUIT TURBINES AND IN PARTICULAR GAS TURBINES 4 Sheets-Sheet 3 Filed March 26, 1957 INVENT OR BY I ATTORNEY Dec. 5, 1961 R. POUIT 3,011,762
TURBINES AND IN PARTICULAR GAS TURBINES Filed March 26, 1957 4 Sheets-Sheet 4 Q35 42, I A, 11 a -6. T- i 57 i INVENTOR BY v ATTORNEYS United States Patent The present invention relates to turbines and in particular, but not exclusively, gas turbines.
The object of my invention is to provide a turbine in which the movable blades are capable of resisting high temperatures and have a good efliciency.
It has already been suggested to protect the leading edge of the movable blades of a turbine by shields cooled by means of air under pressure entering, at the root of said blades, between the leading edge of the blades and sa d shields, and to cause said cooling air to flow tangentially to the longitudinal sections of the blades through calibrated slots provided between the shields and the front walls of the blade bodies, so as thus to protect at least a portion of the walls of the movable blades by means of a laminar flow of air at relatively low temperature.
However up to the present time it has not been possible to ensure a sufficient stability of said laminar flow. My invention makes it possible to obtain the necessary stability of the laminar flow of air around the blades of the turbine rotor.
The turbine according to the invention is constructed in such a way that, on the one hand, means are provided to produce, at least along a portion of the surface of at least some of the movable blades of the turbine, a laminar flow of a gaseous fluid cooler than the power gas which serves principally to the drive of the turbine and that, on the other hand, these blades are disposed in such manner as to produce an acceleration of the power gas sufficient to stabilize the laminar flow of said fluid, means being further provided to prevent leaks between the rotor and the stator of the turbine.
The cooling fluid is generally constituted by air.
The leak preventing means are necessary in consequence of the high expansion of the power gases caused by their acceleration, which expansion would produce substantial leaks if said leaks were not reduced and possibly eliminated by said means.
Preferred embodiments of my invention will be hereinafter described with reference to the accompanying drawings, given merely by way of example and in which:
FIG. 1 is a sectional view of one movable blade of a turbine made according to my invention.
FIGS. 2 2 and 3 3 Show two modifications of the pneumatic means for preventing leaks between the rotor and the stator.
FIG. 3 shows in perspective the tips of the blades of FIG. 3
FIG. 4 is a longitudinal sectional view of a high pressure stage of a turbine made according to my invention.
FIGS. 5 and 6 show other embodiments of a turbine according to my invention with two modifications of the leak preventing means.
As shown by FIG. 1, I provide, at the front 'of the main body of a movable blade 1 of the turbine, a streamlined shield 2 advantage usly made of a thin rolled refractory metal such as nickel, the rear edges of said shield 2 forming, together with the body of blade 1, calibrated air blowing slots 3. Compressed air is fed under pressure through holes 4 provided in the rim of the turbine wheel, this air penetrating between the blade body 1 and the shield 2 so as to escape tangentially to the blade through calibrated slots 3.
By suitably choosing the pressure characteristics of ice said compressed air and also the dimensional characteristics of slots 3, I determine the rate of flow of air through slots 3 in such manner as to obtain a laminar flow of air at the outlet of said slot over some distance along the wall of the blade body 1.
In order to maintain a laminar flow along the convex face 1 of the blade body, supplementary air blowing slots are provided in this portion of the blade, for instance by providing in the blade body 1 radial channels 5 which open into the blade surface along the whole length thereof, to form slots 6 the width and direction of the flow of air through which are adjusted by plates such as 7.
Plates 7 are advantageously fixed to the blades at points located upstream of slots 6, whereby, even if the flow is already turbulent upstream of slots 6 and if consequently the blade body is not very well insulated thermally from the power gases, plates 7 form a shield between the blade body and the hot gases so as to slow down the passage of heat from said gases to said blade to such a degree that the heat transmitted to the blade body at this place may be absorbed by the air circulating in channels 5. For this purpose, as shown by the drawing, the cooling surface of channels 5 may advantageously be increased by providing ribs or corrugations 8 therein.
In order to achieve a sufficient stability of the laminar flow, the torque'to be applied to the rotor is, at least partly, obtained by the reaction of the power gases as they leave the turbine wheel, this result being obtained in the known manner which consists in giving a convergent shape to at least the leading portions of the passages through which the power gases circulate between the blades, the convergence continuing at least up to a throat approximately at 1' in the trailing area of the blades, whereby said gases undergo an acceleration and a partial expansion in said passages.
The advantages, Well known from the point of view of efiiciency, of reaction turbines can however be effective only if there are no substantial leaks between the tips of the blade and the stator. For this purpose, of course, the radial clearance between said blade tips and the stator should be very small. This condition can be complied with only if the radial expansion of-the blades is itself reduced to a minimum and therefore if the temperature of said blades is kept at relatively low value.
In addition to the reduction of the radial clearance bet-ween the tips of the blades and the rotor, which is made possible by the relatively low temperature of the movable blades, I further make use of the action of an auxiliary fluid to prevent leaks past the blade tips.
Thus, in the embodiments shown by FIGS. 1 to 4, at least a portion of the air under pressure that is used for partly cooling the turbine blades serves to create a peripheral countercurrent flowing in a direction opposed to that of the stream of power gases in the intervals between the blades. I
For this purpose, the rear portions of the bladesare constituted by hollow bodies 9 made of a thin rolled refractory metallic alloy. Air pressure at low temperature is made to flow through said hollow bodies 9. This air is introduced, for instance as shown on FIG.. 2, through holes 10 provided in the rim 26. of the turbine wheels;
Preferably, as shown by PEG. 1, I assemble shields 2, plates 7 and hollow parts 9 on the one hand with the blade body 1 through pins 29 which lock extensions of said elements 2, 7, 9 in slots 31, and on the other hand with the rim 26'of the turbinewheel through flat parts 32 bent at right angles from said pieces 2, 7, 9 and fixed in any suitable manner, for instance by riveting, on said rim 26. I may use, to constitute thebodies of said'blades,
'-relatively cheap non refractory materials and possibly light alloys, for instance aluminum, which are particularly well adapted for casting under pressure or sintering, so as to obtain at low price rotors of low inertia capable of turning at high speed.
Peripheral leaks may be prevented in different ways, as shown by FIGS. 2 and 3.
In the construction of FIGS. 2 and 2 I provide in stator 11 a toroidal chamber partly filled with a ring 12 advantageously made of graphite and constituted by several adjoining elements assembled in juxtaposition by means of screws such as 13. The intervals 14 between ring 12 and the tips of blades 1 may be very small since, in case of too great an expansion of blades 1, said blades can cut their way through the graphite material without serious consequences.
Between the body of the stator and ring 12 there is provided an annular space 15 which establishes a communication between the upstream and the downstream sides of blades 1. I
The operation of this device is as follows:
The power gases passing through space 14 and which constitute the gaseous leaks are driven by the ejection of cooling air from hollow bodies 9 so as to follow a trajectory between ring 12 and the wall of the chamber provided in the stator, as indicated by the arrows. At the rear, ring 12 is tangent to the resultant of the velocity of the gases passing through the leak passage 14 and the velocity of ejection of air from channels 9. The
a gaseous mixture thus formed flows around rin 12 through passages 15 and is returned to the upstream side of blades 1 where it is driven by the main current of gases into the spaces provided between the turbine blades, where it expands together with the power fluid.
"It should be noted that the cooling air that is expelled through channels 9 must drive along with it not only the gases which have passed through leak spaces 14 between the stator and the tips of blades 1, but also the stationary gases located at the level and on the sides of spaces 14 between blades 1, this portion of the gas that is not expanded constituting the most important portion of the leak. Therefore, as shown by FIG. 2 the outlet of conduits 9 is given a flaring shape so as to send jets in all directions which cross one another between blades 1 and drive toward spaces 15 and toward the upstream side of the blades the power fluid which has not expanded between blades 1, thus returning this fluid into the main flow which is to pass through passages 20.
According to the modification of FIGS, 3 and 3 I provide in the stator an annular recess 1'6 closed on the side of the stator by wall 17 and on the side of the rotor, between the blades 1 thereof, by partitions 18 extending between the hollow trailing portions 9 of the blades (see FIG. 3 Said chamber'l'6 is fed with air under pressure through-radial conduits 9 which distributesaid air on the one hand through spaces 14 toward the upstream side of the turbine wheel, thus pushing back the gas tending to leak through said spaces 14, on the otherhand between blades 1, toward the passages 20 existing beair and gases can pass.
In all cases, the cooling air that is used to prevent power gases from leaking past the turbine wheel is always conveyed, together with said gas leaks, toward the upstream tween said blades and through which the main flow of side of the turbine wheel, so that it is possible to recuperare, in the form of expansion work, most of the work spent'for compressing the air that has been used both to prevent gas leaks and also to cool'down the hollow frontan d. intermediate portions "of the blades and to the .j cooling of the rear portions thereof. The compressed air used for these two purposes and also to prevent gas leaks must be at a pressure higher than the total pressure (i.e. both thestatic and dynamic pressures) of the power gases so that it can acquire by expansion a velocity at least equal to the velocity of flow of the power fluid, account being taken of the fact that this air is at a temperature lower than that of the power gases.
The compressed air that is used may be obtained from an external source. It may also be produced by an auxiliary compressor mechanically driven by the turbine. Preferably, this air is collected'from one or several compression elements existing in the power plant for feeding the combustion chambers. For this purpose, and according to the construction illustrated by FIG. 4, if it is supposed that it is desired to feed compressed air, for cooling and preventing gas leaks, to the turbine stage at their highest pressure and temperature, compressed air is collected from the last compression stage 21 through conduits 22 leading to a manifold 23 in which the hollow shaft 24 rotates. This compressed air enters the hollow inside of shaft 24 and flows out therefrom through radial channels 25 provided in arms 27 so as to enter the turbine blades 1 through orifices 10 provided in the rim 26 of the turbine blade.
The compressed air collected from the high pressure compressor 21 may advantageous be cooled down by cooling ribs 28, before it is reintroduced into the rotor. By its circulation through centrifugal channels 25, it is given a supplementary pressure and velocity which make it possible to use it efiiciently in blades 1.
In the construction illustrated by FIGS. 5 and 6, the movable blade system is constituted, as above, by blades 1 having, at their rear parts, hollow bodies 9 through which cooling air is fed to orifices 33 provided in an annular sleeve 34 toward an annular recess 16 provided in stator 11 in a manner analogous to what is shown in FIG. 3 This recess 16 of suitable shape conveys the air from orifices 33 toward the upstream side of turbine blades 1. A flange 35 carried by said sleeve 34 is provided with an annular groove 38 divided into two communicating adjacent portions by a flange 39 fixed to stator 11. This annular groove 38 is advantageously provided with fins 471 extending in radial planes. When the turbine is running at normal working speed, I inject into groove 38, through a conduit 40, a liquid such as oil intended to form, under the effect of the centrifugal force, a hydraulic joint which acts as a packing between the'rotor and the stator of the turbine. 'Fins 47 cause said liquid to rotate together with the stator.
If itis supposed that the pressure of the power gases upstream of blades 1 is 5 kg./sq. cm. and that the pressure of the cooling air introduced through; conduits 9 is 7 kg./sq. cm., the static height of an oil column balancing the pressure of 7 kg./sq. cm., could be about meters (the acceleration of gravity being g.=9.81) If the peripheral speed of the blade system 1 is supposed to be 250 meters per second, the contn'fugal acceleration at a distance from the rotation axis equal to 0.175 111. could be that is-to say 257,000. Its value is equal to 36,500 times the acceleration of gravity. It follows that the difference of oil level in the two respective adjacent portions of groove 38 to balance the pressure of 7 kg./sq. cm. is only 90,000 assoc fi and stator 11) is sent to the upstream side of the set of blades 1 so as to mix with the hot power gases and to expand together therewith, whereby an important portion of the energy spent to compress this air is recovered in the intervals between the turbine blades.
The energy difference between compression and expansion of the cooling air, being small, makes it possible to cool adequately the blades of the rotor and the flange thereof. Furthermore, since any air loss due to the annular clearance between the rotor and the stator is avoided, it is possible to obtain a high degree of reaction in the convergent passages between the movable blade and to stabilize, by the increase of velocity that results therefrom, the laminar flow of the fluid in the vicinity of the wall of the blades, and also the laminar flow of the insulating air layer interposed between the wall of said blades and the power fluid.
It should be noted that the liquid level difference between the two adjoining chambers of groove 38 must be higher as the speed of rotation of the turbine blades is lower. It follows that, during the starting period, a hydraulic joint of the dimensions above mentioned would have no efliciency whatever and the liquid would be driven by the air under pressure escaping between the walls of groove 38 and those of flange 39. This is why the liquid of the hydraulic joint is introduced into said groove only when the turbine is rotating at a relatively high speed.
During the starting period, the air loss at the joint between the rotor and the stator is limited by providing, between annular space 16 and groove 38, successive expansion chambers such as 42 and 42 acting in bathe-like fashion, so as to form eddies which dissipate the kinetic energy, said eddies opposing a direct flow of the fluid.
According to another modification illustrated by FIG. 6, if it is supposed thatthe cooling air is introduced into the conduits 9 of blades 1 through an axial channel 43 provided in shaft 44, and that air penetrates into channel 43 from a chamber 45, I may introduced the liquid which is to constitute the hydraulic joint into the cooling air itself, by injection of the atomized liquid (this liquid being preferably water in this case) into chamber 45 through injectors 46. The droplets of atomized water carried along by the compressed air which they cool down separate from said air in the first expansion chamber 42, the radius of which is smaller than that of groove 38. In said chamber 42 I advantageously dispose blades such as 47 and the external bottom of said chamber 42 is connected with groove 38 through conduits 48 through which flows the liquid separated in chamber 38 which is filled with said liquid. As long as a suflicient speed of the rotor is not reached, water is carried along by the leaking air escaping through groove 38 and it is only when the speed increases to a given value that water, accumulating in said chamber 38, constitutes a hydraulic joint as above described. For speeds higher than this value, the injection of water may be stopped.
It should be noted here that the hydraulic joints shown in FIGS. 5 and 6 may also be applied to steam turbines working on the reaction principle and where it is advantageous to eliminate steam losses by preventing leaks between the rotor blade tips and the stator. In this case, the hydraulic joints are preferably fed from the condensation water which is obtained at the last low pressure stage.
Of course, my invention is not limited to the above described embodiments and in particular, in the case of a gas turbine, the combustion chambers where fuel is burnt with air under pressure might be constituted by the power chambers of hot gas generators, for instance of the free piston type.
In a general manner, while I have, in the above description, disclosed what I deem to be practical and efiicient embodiments of my invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.
What I claim is:
1. A gas turbine which comprises in combination, a stator and a rotor, said rotor including a turbine wheel, a multiplicity of turbine blades radially fixed to the rim of said wheel, a source of compressed air substantially at ordinary temperature, means for blowing air from said source along at least a portion of the surface of each of said blades to form a laminar flow of cooling air thereon, said blades being arranged so that the passages between them are convergent in the direction of flow of the power gases flowing between them to produce an acceleration of said power gases suflicient to stabilize said fluid laminar flow, the trailing edges of said blades being provided with radial conduits leading to the tips of said blades, means for feeding air from said source to said radial conduits, the inner wall of said stator being provided, opposite the tips of said blades, with an annular recess shaped to cause at least most of the air streams that flow out from said radial conduits at the tips of said blades to be deflected toward the upstream side of said blades.
2. In a turbine as claimed in claim 1, at least one streamlined shield extending around the leading edge of each of said blade bodies at a distance therefrom, said shield being made of thin rolled refractory metal, and means for blowing air under pressure into the space between said shield and said blade body, the rear edges of said shield forming, with the side fans of said blade body, slots running along the span of said blade body and through which said air escapes tangentially to said body to form a laminar flow air stream along said body.
3. A turbine according to claim 2, further including a rearward extension rigid with each of said shields, each of said blade bodies being provided with a slot located in the front portion thereof to accommodate said extension, and means fitting in said last mentioned slot for locking said extension therein.
4. A turbine according to claim 1, further including a hollow body made of a refractory metal fixed to each of said blade main bodies to form the trailing edge portions thereof, the interiors of the hollow bodies constituting said radial conduits.
5.-A turbine according to claim 1 further including a hollow body made of a refractory metal fixed to each of said blade main bodies to form the trailing edge portions thereof, the interiors of the hollow bodies constituting said radial conduits, a frontward extension rigid with said hollow body, said blade main body being provided in the rear portion thereof with a slot accommodating said extension, and means for locking said last mentioned extension in said slot.
6. A turbine according to claim 1 in which the downstream face of each of said blade bodies is provided with a supplementary air blowing slot and a plate fixed on said face of said blade body so as partly to close said slot.
7. A turbine according to claim 1 in which the outlets of said radial air conduits are shaped to send a portion of the air flowing through said conduits toward the spaces between the tips of said blades.
8. A turbine according to claim 1 further including, in said annular recess, an annular member the inner surface of which is close to the tips of said blades as they pass along said member, the outer face of said annular member forming, with the bottom of said annular recess, a curved passage for the flow of air from the tips of the blades in the upstream direction.
9. A turbine according to claim 8 in which said annular member is made of graphite.
10. In a turbine as claimed in claim 1, a ring-shaped flange rigid with the downstream ends of the tips of said blades, said flange being spaced from said stator, said ringshaped flange beingprovided with an annular groove having its opening turned inwardly toward the axis of said wheel, said stator including, rigid with the downstream end thereof, an annular extension passing around said first mentioned flange to form an annular flange, substantially located in a plane at right angles to said axis, extending into said grooves so as to form with the inner wall thereof an annular space of U-shaped section by a plane passing through said axis, and means for feeding a liquid into said space to form a hydraulic joint.
11. A turbine according to claim 10 in which said liquid is oil.
12. A turbine according to claim 10 in which said liquid is water. 7
13. A turbine according to claim 10 further including, in said space, fins substantially located in planes passing through said axis.
14. in a turbine as claimed in claim 1, a ring-shaped flange rigid with the downstream ends of the tips of said blades, said flange being spaced from said stator, said ring-shaped flange being provided with an annular groove having its opening turned inwardly toward the axis of said Wheel, said stator including, rigid with the downstream end thereof, an annular extension passing around said first mentioned flange to form an annular flange, substantially located in a plane at right angles to said axis, extending into said grooves so as to form with the inner wall thereof an annular space of U-shaped section by a plane passing through said axis, and means for feeding a liquid into said space to form a hydraulic joint, the annular space between said 'first mentioned flange and saidstator being in communication with said annular recess in the inner wall of said stator opposite the tips of said blades.
. 15. A turbine according to claim 14 in which the communication between said annular space and said annular recess forms at least one annular expansion chamber'with battles for the formation of eddies.
16. A turbine according tov claim 14 in which the communication between said annular space and said annular recess forms at least one annular expansion chamber with baffles for the formation of eddies, said chamber being at a distance from said axis smaller than the distance from said axis to the bottom of said U-shaped section annular space, said first mentioned flange being provided with condu'itsffor connecting said chamber with said U-shaped section annular space.
17. A turbine according to claim 16 further including, in said annular expansion chamber, fins located in planes passing through said axis.
18. A turbine according to claim 14 in which said liquid feeding means are arranged to inject water into the air streams flowing through said radial conduits.
19. A turbine according to claim 1 further including partitions extending across the spaces between the trailing edge portions of the tips of said blades.
References Cited in the file of this patent UNITED STATES PATENTS 1,255,650 Samuelson Feb. 5, 1918 2,378,372 Whittle June 12, 1945 2,399,009 Doran .Apr. 23, 1946 2,598,176 Johnstone May 27, 1952 2,622,843 Williams Dec. 23, 1952 2,649,278 Stalker .Aug. 18, 1953 2,685,429 Auyer Aug. 3, 1954 I FOREIGN PATENTS 10,179 Great Britain of 1912 221,408 Switzerland Aug. 17, 1942 313,128 Germany June 25, 1919 668,434 Great Britain Mar. 19, 1952 679,530 Great Britain Sept. 17, 1952