US3139264A - Canted vortex venturi - Google Patents

Description

CANTED VORTEX VENTURI 3 Sheets-Sheet 1 June 30, 1964 R. N. QUENNEVILLE ETAL Filed June 25, 1962 F IGJ I. I!!!" I III INVENTOPS ALDO A. PERACCH/O RAYMOND N. QUEfi/NEVILLE BY jVW W ATTORNEY June 30, 1964 R. N. QUENNEVILLE E TAL 3,139,264

CANTED VORTEX VENTURI Filed June 25, 1962 3 SheetsSheet 2 r-|c3-4 I [3 4z I Z l no-5 a /NVENTOR$ ALDO A.PERACCH/0 RAYMOND IV- QUENlVEV/LLE BY ATTORNEY June 30, 1964 R. N. QUENNEVILLE ETAL 3,139,254

CANTED VORTEX VENTURI 3 Sheets-Sheet 3 Filed June 25, 1962 QQM INVENTORS ALDO A. PERACCH/O RAYMOND N OUEZV/VE V/LLE BY flm/t/M M ATTORNEY United States Patent 3,139,264 CANTED VORTEX VENTURI Raymond N. Quenneville, Granby, and Aldo A. Peracchio,

Wapping, Conn., assignors to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed June 25, 1962, Ser. No. 204,823 7 Claims. (Cl. 253-65) This invention relates to fluid turbines and particularly to overspeed control mechanism for low specific speed, partial admission, turbines.

An object of this invention is mechanism which will automatically limit the overspeed of a partial admission axial flow turbine discharging exhaust gases from the plane of the turbine rotor at an acute angle having a tangential component.

A further object is a tapered normally choked exhaust conduit off-set from the turbine axis and canted at the same angle to the turbine axis as the path of the exhaust gases at normal turbine speed and receiving the gases over a minor sector of the conduit circumference at said circumference.

A still further object is an exhaust conduit choked at normal speed collecting exhaust gas discharged from a partial admission turbine with a swirling component about the turbine axis at normal speed and conducting said gas axially Without swirl along said conduit, but imparting a swirling motion to said gas in said conduit upon overspeed.

A still further object is a low specific speed partial admission gas turbine having a plurality of partial admission stations each having its respective exhaust conduits receiving axially, gas discharged from the turbine at normal speed, and imparting a swirling motion in said conduit to gas discharged at other speeds.

These and other objects will be apparent from the following specification and the accompanying drawings in which:

FIGURE 1 is a top-plan schematic view showing the canted exhaust nozzle and gas velocity vectors at normal or design speed;

FIGURE 2 is a partial view similar to FIGURE 1 showing the velocity vectors at overspeed;

FIGURE 3 is a side view of the turbine and exhaust conduit showing the discharge nozzle;

FIGURE 4 is an end View showing two nozzles and an adjusting mechanism;

FIGURE 5 is a detail showing the inlet nozzle; and

FIGURE 6 is a graph showing the eflect of the chokedvortex venturi.

In single stage axial flow turbines in which the activating fluid is directed at the turbine buckets at an angle having a large tangential component it is desirable to have the turbine peripheral speed approximately half of the velocity of the incoming gas so that the fluid leaving the turbine will have an absolute velocity which is substantially axial and without appreciable swirl. In a partial admission single stage axial flow turbine utilizing combustion gases the operating tip speeds of the turbine buckets are usually limited due to structural limitations of the turbine rotor and buckets to values well below one-half of the velocity of the incoming fluid and well below the zero swirl speed of the turbine. In order to usefully utilize the overspeed control of the Wood application Serial No. 804,188, filed April 6, 1959, noW Patent No. 3,073,114, issued January 15, 1963, the zero swirl speed must be at the operating or design speed. In a full admission turbine of low specific speed i.e. where the speed of the working fluid being admitted is considerably more than twice the operating tip speed of the rotor, this zero swirl speed at the operating and design speed can only be accomplished at the cost of efliciency.

In such a low specific speed turbine the ratio of the bucket speed to the gas velocity, U/C is in the neighborhood of .25-.30. An efficient zero swirl speed value of U/C is in the neighborhood of .4.45 for best efficiency. The present invention, being utilized in a partial admission turbine, permits the zero swirl U/C to be kept at its desired value of .4 to .45 for best efficiency and still retain the benefit of the speed limiting or control characteristics forming the subject matter of the Wood application.

In a partial admission turbine working fluid is admitted to only a portion of the rotor or to only a few of the buckets at one time. There may be but a single nozzle covering a few, such as three or four, buckets or there may be several nozzles, each covering a few buckets, but the sum of the nozzles covering much less than the full periphery of the turbine rotor. As shown schematically in the drawings the turbine may comprise a single rotor 10 mounted on a shaft 12 for rotation in a casing 14. The rotor has a plurality of buckets 16 on its periphery receiving working fluid through an entrance nozzle 18 directing the working fluid with a material tangential component into the space between the buckets 16 where its direction will be substantially reversed and will then be discharged from the buckets in a direction having a substantial tangential component with respect to the rotor. The working fluid may be a high temperature combustion gas generated in the chamber 20 and conducted to the entrance nozzle 18. As shown by the Vector diagram in connection with FIGURE 1 the gas discharged by the turbine buckets has a velocity W and the buckets have a speed U indicated by the vectors in FIG- URE 1. The combination of these two speeds results in an absolute velocity V of the gases leaving the turbine buckets which it is noted is in a direction having a material tangential or swirl component. In order to usefully utilize the Wood overspeed control it is necessary to deliver the exhaust gases into the converging or funnel shaped exhaust conduit without swirl at the operating or design speed of the turbine and out of the nozzle at sonic speed i.e. Mach 1 at that operating or normal speed of the turbine so as to have an exhaust conduit of circular cross section conducting gases axially without swirl to a choked discharge orifice at the discharge end of the conduit. Thus nozzle 30 is a choked nozzle when exhaust gas flow is at a speed of Mach 1 at the smallest diameter of nozzle 30.

Such a condition can be provided in a partial admis sion turbine of the type just described by canting the funnel-shaped exhaust nozzle at an acute angle to the plane of the rotor so that the centerline of the exhaust conduit will be substantially parallel to or have substantially the same tangial component as the gases being discharged from the turbine rotor. In such a construction the gases will then flow axially through the canted exhaust conduit.

In order to obtain the benefit of the Wood invention it is necessary to impart a swirl to the gases in the conduit upon overspeeding of the turbine. As shown somewhat exaggerated in FIGURE 2 as the turbine overspeeds and the vector U indicating rotor speed increases the absolute velocity V of the gases approaches a more nearly axial flow with respect to the turbine axis. However by placing the canted orifice'offset with respect to the axis 22 of the turbine so that the gases discharged from the rotor enter the exhaust conduit 28 at one edge 26 of the conduit the gases will enter at an angle to the axis 24 of the exhaust conduit and impart a swirl to the gases in the conduit. This swirl will materially augment the effect of the already choked nozzle 30 and will quickly build up a back pressure which will limit the turbine overspeed. As indicated in FIGURE 3 the exa haust conduit is offset radially with respect to the turbine axis 22 so that the gas receiving entrance or admission port 32 of the conduit 28 is between the center line 22 of the turbine and the center line 24 of the conduit and is a segment of the conduit defined by the overlapping of the axial projection of the circurnference of the rotor and a minor portion of the axial projection of the circumference of the large end of the exhaust conduit 28. The large end of the exhaust conduit 28 is blocked by the wall 34 except for the opening 32. The segment 32 has a circumferential extent along the periphery of the rotor to include all the buckets discharging the gases delivered by the nozzle 18. It should be noted that the gas will travel directly through the selected buckets and the remainder of the buckets will contain no Working fluid.

It will thus be seen that we have invented an exhaust conduit having a choked orifice and an axial flow at operating or normal speeds and a swirling fiow at overspeed in a partial admission low specific speed single stage turbine delivering gases with a swirling component at operating or normal speed.

The normal swirl at normal or design speed of the gases leaving the buckets of a single stage turbine or the last stage of a multi-stage turbine is transformed by the canted exhaust conduit into an axial flow of the gases through the conduit and any change in the direction of flow of the gases leaving the buckets such as is occasioned by overspeed is transformed into a swirling motion in the exhaust conduit. Thus, by canting the exhaust conduit and its choked nozzle at such an angle as to have the absolute velocity of the gas leaving the turbine at the operating speed line up with the conduit axis, the zero swirl point of the exhaust gases in the conduit has been moved to the operating speed, and it is thus possible to utilize the overspeed control of the com bination of the swirling gases and the choked orifice without sacrificing turbine efficiency. The greater the overspeed, the greater the swirl, and the greater the vortex venturi back pressurizing process.

While the above-described structure will operate satisfactorily for a single set of design conditions, the structure may be adapted to operate satisfactorily at different design conditions by making the exhaust conduit adjustable both with respect to the angle at which the exhaust conduit is canted and with respect to the position of the exhaust conduit and particularly the exhaust conduit inlet 32 circumferentially around the circumference of the turbine with respect to the turbine gas inlet 18. The exhaust conduit including the nozzle 30 may be pivotally mounted upon a base 36 which may be integral with the turbine casing 14- or may be a separate member secured to the casing 14. The mating surfaces 38 between the conduit 28 and the base 36 may be formed as a fiat disc having an axis 40 about which the conduit 23 may be swung to change the angle of the axis 24 of the conduit with respect to the plane of the rotor. The conduit 28 may be secured to the base 36 in any suitable manner such as by bolt 42. The nozzle may thus be adjusted to provide an axial flow for different angles of absolute velocity of the exhaust gases. It may also be desirable to move the entire nozzle with respect to the periphery of the rotor in order to line up the entrance 32 of the exhaust conduit with the position in the turbine at which the rotor blades 16 discharge the working fluid. This may be accomplished by securing the base 36 to the discharge side of the casing 14 and providing clamping bolts 44 adjustably securing the portion 14 of the casing to the remainder 46 of the turbine casing carrying the nozzle 18 to permit some circumferential movement of the base 36 with respect to the nozzle 18 as the base 36 is made integral with the casing 14 the entire exhaust side of the turbine including the entire end plate of the casing 14 is made adjustable relative to the remainder of the turbine around the d turbine axis 22 so as to provide circumferential adjustment of the exhaust nozzle 28 carried by the base 36, with respect to the entrance nozzle 18.

The graph of FIGURE 6 plots torque in foot pounds against speed in revolutions per minute for a partial admission turbine in which the temperature of the gas orworking fluid was 2050 R. and the average nozzle.

pressure was 208 pounds per square inch and the output was from a gear reduction of about 18 to l. The line 6% of the graph shows the performance or calibration of the turbine when discharging free. The line 62 represents the performance of the turbine with the canted vortex venturi from which is will be seen that the performance of the turbine at its design speed is' substantially the same as its calibration but that at a very small increase in speed above the design point results in a very drastic and rapid reduction in the torque of the turbine and thus provides a very effective overspeed limiting mechanism.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from its spirit and that various changes can be made which would come within the scope of the invention which is limited only by the appended claims.

We claim:

1. In a partial admission, low specific speed, single stage turbine, a funnel shaped exhaust nozzle arranged at an angle to the turbine axis, at the turbine periphery and having an axis substantially parallel to the flow path of the turbine discharge gases, at normal speed, receiv-.

2. In a partial admission, low specific speed, single stage axial flow turbine in which exhaust gases are discharged over a limited sector of the turbine periphery at one tangential angle at normal speed and at a different tangential angle at overspeed, a funnel shaped exhaust nozzle choked at normal speed receiving said gases over a minor sector of its nozzle circumference at the large end of said funnel, said nozzle having an axis parallel with said gas flow at normal speed to provide non-swirlproducing gas flow in said nozzle, said different tangential angle of discharge providing a swirl-producing direction of flow in said nozzle. v

3. In a partial admission turbine having a tapered exhaust conduit, a rotor discharging gases at normal speed at an acute tangential angle with respect to the plane of said rotor and at a different angle at overspeed into the large end of said conduit and at sonic speed out of the small end of the conduit to provide a choked small end at normal speed, the center line of said exhaust conduit positioned outside of the periphery of said rotor substantially parallel to the flow path of said discharging gases at normal speed, said conduit receiving said gases over a minor peripheral portion of, and along one side of, said conduit to conduct said gases axially substantially without swirl to said choked small end at normal speed, and with a swirl at overspeed.

4. In a partial admission turbine a rotor, discharging exhaust gases at an acute tangential angle to the plane of the rotor, at normal speed, an exhaust conduit choked at normal speed, offset radially from the center line of the turbine so that'the axial projection of the circumference of the rotor and the axial projection of the circumference of the conduit intersect and overlap and having an admission port consisting of a segment of the conduit defined by a minor portion of the circumference of the conduit and the portion of the circumference of the turbine rotor overlapping said conduit and including the discharge section of the turbine corresponding to the partial admission area, said conduit arranged at an acute tangential angle to the plane of turbine rotor corresponding to the flow path of its exhaust gases at normal speed and discharging exhaust gases axially substantially without swirl along one side of said conduit at normal rotor speeds and a swirl-producing direction at other than normal speed.

5. In a low specific speed partial admission turbine exhausting working fluid at normal speed with a tangential component and having a plurality of separate partial admission sections, a rotor, a separate exhaust conduit having an exit orifice choked at normal turbine speed for each section, each said conduit offset radially from the turbine axis and arranged at an angle to the plane of said rotor corresponding to the angle of discharge of the turbine working fluid at normal speed, the entrance portion of said conduit being blocked ofl except for an admission port comprising a minor section adjacent the circumference of said conduit corresponding to said corresponding turbine partial admission section said fluid having a non-swirl-producing direction of flow parallel to the axis of said conduit at normal speed and a swirl-producing direction of flow at other than normal speed.

6. In a partial admission turbine, having a rotor, means directing an angular discharge from said rotor at normal speed into a non-swirling axial flow discharge in an exhaust conduit and utilizing a change in angle of discharge from said rotor at overspeed to produce swirl in said conduit and limit overspeed comprising an exhaust conduit whose greatest diameter is less than the rotor diameter and having a discharge receiving segment comprising only a minor portion of the conduit periphery and corresponding to a discharge sector of said rotor, said conduit axis offset from said sector and arranged at an angle to said rotor substantially equal to the angle of said discharge at normal speed, the exit of said conduit being sized to provide a substantially choked orifice at normal speed.

7. In combination with a partial admission turbine, a choked exhaust conduit having an axis arranged at an acute angle to the plane of rotation of said turbine and having an entrance end receiving exhaust gases from said turbine over only a minor sector of the periphery of said conduit entrance, said gases having a non-swirl-producing direction of flow parallel to the axis of said conduit at normal speed and a swirl-producing direction of flow at other than normal speed.

References Cited in the file of this patent UNITED STATES PATENTS 3,073,114 Wood Jan. 15, 1963 FOREIGN PATENTS 200,731 Australia Jan. 27, 1956 20,603 Great Britain of 1891

Claims (1)

1. IN A PARTIAL ADMISSION, LOW SPECIFIC SPEED, SINGLE STAGE TURBINE, A FUNNEL SHAPED EXHAUST NOZZLE ARRANGED AT AN ANGLE TO THE TURBINE AXIS, AT THE TURBINE PERIPHERY AND HAVING AN AXIS SUBSTANTIALLY PARALLEL TO THE FLOW PATH OF THE TURBINE DISCHARGE GASES, AT NORMAL SPEED, RECEIVING THE GASES DISCHARGED FROM SAID TURBINE OVER A MINOR SECTOR OF THE PERIPHERY OF THE LARGE END OF SAID FUNNEL IN A NON-SWIRL-PRODUCING DIRECTION, SAID NOZZLE BEING CHOKED AT THE SMALL END AT NORMAL SPEED, SAID GASES BEING DISCHARGED INTO THE LARGE END OF SAID FUNNEL AT THE PERIPHERY OF SAID FUNNEL AT AN ANGLE TO SAID FUNNEL AXIS AT OVERSPEED TO PRODUCE A SWIRL IN SAID FUNNEL AND LIMIT THE OVERSPEED.

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