US3033519A - Turbine nozzle vane construction - Google Patents

Description

May 8, 1962 E. w. RADTKE 3,033,519

TURBINE NOZZLE VANE CONSTRUCTION Filed Sept. 12, 1958 f l/VVEN TOR Z EDWARD W RADTKE A 7'7'ORNEY r M". n

United States Patent TURBINE NOZZLE VANE CONSTRUCTION Edward W. Radtke, Bloomfield, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Sept. 12, 1958, Ser. No. 760,582 1 (Ilaim. (Cl. 25352) This invention relates to turbomachinery and more particularly to the nozzle vane arrangement immediately upstream of the turbine.

In turbines which are intended to drive a compressor or the like where the speed or load on the turbine must be controlled, the nozzles leading to the turbine buckets may beof variable geometry. These variable geometry nozzle passages can be provided by means of a plurality of vanes which are pivotable so as to alter the configuration of the passages therebetween. With these pivoted vanes it is necessary to adequately seal the free ends of the vanes so as to avoid leakage of air around the tips of the vanes.

It is therefore an object of this invention to provide a sealing arrangement for pivoted nozzle vanes whereby just the right amount of sealing force is provided thus avoiding excessive friction and excessively high torque necessary for pivoting the vanes.

These and other objects of this invention will become readily apparent from the following detailed description of the drawing in which:

FIG. 1 is a side elevation of a turbine-compressor arrangement with portions partly broken away to show the turbine nozzle vane arrangement;

FIG. 2 is an enlarged detailed partial cross section of the nozzle vane arrangement and its sealing mechanism;

FIG. 3 is a partial cross section taken along the line 33 of FIG. 2; and

FIG. 4 is a partial cross section taken along the line 44 of FIG. 1.

Referring to FIG. 1 a turbine casing is shown which houses turbine blades or buckets 12. The blades or buckets 12 are connected to a suitable shaft for driving a compressor housed within the casing 14 or other load. Air under pressure enters the toroid or volute 16 where it is ducted through an annular passage 18. The flow then moves radially inwardly toward the axis of turbine rotation past a plurality of nozzle vanes 20. The nozzle vanes 20 are peripherally spaced about the turbine buckets 12 and each includes a pivot shaft 22 which lies su stantially parallel to the axis of rotation of the turbine.

As seen in FIGS. 2 and 3, each of the turbine blades 26 is arranged such that a nozzle passage is for-med between adjacent blades. By rotating each of the vanes 2% about their pivot shaft 22 the geometry of the passage 24 therebetween can be varied to provide suitable flow into the turbine blades. Thus, the driving force on the turbine can be controlled in accordance with any desired schedule.

As seen in FIGS. 2 and 4, each of the nozzle vanes 20 and the pivot shaft 22 includes a spline 26 which has mounted thereon a gear segment 28. Each of the gear segments 28 is operatively connected to a ring gear 30 so that upon rotation of the ring gear 30 all of the nozzle vanes 20 will be simultaneously pivoted about their shafts 22 thereby varying the geometry of each of the nozzle passages 24 therebetween.

As best seen at the top of FIG. 1, one of the vanes 20 has a master pivot shaft 34 suitably connected by a yoke 36 to an actuating piston rod 38. The piston rod 38 may be controlled by mechanism such as shown in US. Patent No. 2,752,858 to Berges, or US. Patent No. 2,651,492 to Feilden. Motion of the rod 38 rotates the master pivot 34 which through the ring gear 30' rotates all the remaining segmental gears 28 and the respective vanes.

In very small turbine compressor units, as for example for aircraft air conditioning assemblies, the actuating force for pivoting the nozzle vanes must be at a minimum. However, at the same time it is necessary that a good seal be provided at the free ends of the nozzle vanes 20 so that there will be a minimum amount of leakage around the ends of the blades. Such leakage reduces the performance of the machine. In order to provide an adequate seal for the free ends of the nozzle vanes 20, an annular pressure plate 40 (see FIGS. 1 and 2) is provided which engages, the outer free ends of all of the nozzle vanes 20. The pressure plate 40 fits into an annular recess 42 and also includes inner and outer sealing rings 44 and 46 which engage the inner and outer walls of the annular recess 42. A light spring 48 may be provided to provide a nominal pressure for holding the plate 40 against the outer ends of the nozzle vanes 20. However, when there is a flow of air through the nozzle passages 24 formed by the vanes 20, there is a negative pressure gradient or distribution pattern in a downstream direction through the passage 24 which gradient is due both to the shape of the nozzle and the pressure drop existing between the inlet and the outlet of the turbine.

In any event, when there is flow there will be a pressure gradient. Since there exists along the flow path a pressure gradient or pressure distribution, it is immaterial that the nozzles are pivoted because the new passageway will also exhibit a pressure gradient or distribution along its flow path. This pressure tends to push the plate 40 away from the outer ends of the nozzle vanes 20. In order to insure proper seating of the pressure plate against the ends of the vanes 20, one or more pressure taps 50 are provided in the pressure plate 40 so that a predetermined air pressure will be established behind the pressure plate 40. Since there is a pressure drop in a downstream or cho-rdwise direction past the vanes 20, the location of the taps 50 along this flow path is chosen so that the pressure at this location, established behind the pressure plate 40 provides a total force greater than the total force tending to push the plate 40 away from the vanes 20. The net force is just sutficient to insure an adequate sealing engagement of the pressure plate 40 with the ends of the vanes 20. In this manner the friction caused by the pressure plate engaging the vanes 20 is not excessive yet the force is sufiicient to insure adequate sealing throughout the operating range of the turbine.

In reality, the point at which the pressure is picked oif and fed behind the pressure plate is a compromise condition which will exert a force on the plate to give substantially its optimum operating range. Thus, it can be seen that the force of the plate pressing against the nozzles will differ for every position of the nozzles, i.e., from its full open to its full closed position.

As a result of this invention a very simple yet highly efficient sealing mechanism has been provided which insures positive sealing of the ends of turbine nozzle vanes while avoiding excessive torque requirements.

Although only one embodiment of this invention has been illustrated and described herein, it will be apparent that various changes may be made in the construction and arrangement of the various parts without departing from the scope of the novel concept.

What it is desired by Letters Patent is:

In a radial entry turbomachine having a rotor having an axis, blades disposed about the periphery of said axis carried by said rotor, a plurality of vanes surrounding said blades and forming a plurality of radial entry nozzle passages for directing fluid under pressure against said blades for driving said rotor, said passages having a shaft which induces a negative pressure gradient in the flow therethrough, said vanes having their spans running parallel to said axis, a pivot shaft carried by one spanwise end of each of said vanes and being parallel to the span, means for rotating said shafts and varying the geometry of said nozzle passages, an annular plate having one side engaging the other spanwise ends of said vanes and having a sealing engagement therewith to define one end wall of said nozzle passages, said plate being in a plane transverse to said axis, a channel having radially inner and outer walls and receiving said plate, said plate and channel forming a substantially closed chamber on the other side of said plate, seal means carried adjacent the inner and outer peripheral edges of said plate and engaging the walls of said chamber, and means for conducting fluid under pressure from at least one of said nozzle passages into said chamber to create a force on the other side of said plate to provide a sealing engagement between said one side of said plate and said vanes, including a duct leading to one of said nozzle passages and terminating at a point between the leading and trailing edge of the adjacent respective vane, said duct terminating at a point located along the flow in said nozzle passage wherein the average pressure of said fluid will provide a total force on said other side of said plate which is slightly in excess of that necessary to maintain a sealing engagement between the plate and the adjacent vane during flow through the nozzle passages.

References Cited in the file of this patent UNITED STATES PATENTS 2,651,496 Buckland et a1. Sept. 8, 1953 2,733,853 Trumpler Feb. 7, 1956 2,770,943- Beale NOV. 20, 1956 2,976,013 Hunter Mar. 21, 1961 FOREIGN PATENTS 88,257 Sweden Jan. 5. 1937

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