US2914241A

US2914241A - Means for adjusting the flow characteristics of fluid flow machines

Info

Publication number: US2914241A
Application number: US550123A
Authority: US
Inventors: Novak Richard August
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1955-11-30
Filing date: 1955-11-30
Publication date: 1959-11-24
Anticipated expiration: 1976-11-24

Description

JF, G .orA

Nov. 24, 1959 R A NOVAK 2 914,241

t n MEANS FOR ADJUSTING THE FLOW CHARACTERISTICS OF FLUID FLOW MACHINES Filed NOV. 50, 1955 Maisy/Mme@ IV//l//l/A United States Patent MEANS FOR ADJUSTING THE FLOW CHARAC-4 TERISTICS OF FLUID FLOW MACHINES Richard August Novak, Wyoming, Ohio, assignor to General Electric Company, a corporation of New York Application November 30, 1955, Serial No. 550,123 Claims. (Cl. 230-114) The present invention relates to means for adjusting the flow characteristics of lluid flow machines and more particularly to means for varying the ow characteristics of multi-staged compressors in accordance with rotational speed.

In present gas turbine engines ofthe type used in aircraft, the demand for increased thrust is conveniently met by providing a high pressure ratio compressor. Such engines are usually designed to function most eiciently in the upper portion of the speed range, so the shape of the compressor duct and the shape and incidence of the compressor blading are chosen for ecient operation at cruise or maximum power conditions. When a conventional high pressure compressor is designed under these conditions, it has been found that severe diiiiculties are encountered in operation over the lower portions of the speed range due to stalling of the blades in the inlet stages of the compressor. To alleviate this condition it becomes desirable to vary the flow characteristics of the compressor to correspond to the operating speed of the engine. This is accomplished by adjusting the angle of attack of the compressor blading in accordance with the design requirements of the various operating speeds, thus permitting eflicient operation of the compressor over the ilow speed range. In achieving the desired adjustment it is known to be beneficial to vary the orientation of the stator blades in the inlet stages and the usual practice is to adjust the entire blade. This practice has the disadvantage of changing the flow characteristics over the full length of the blade, whereas the most troublesome stalling conditions occur only at certain portions of the blade. In addition, this practice presents mechanical difiiculties due to the relatively large torques required to turn the blades plus the complicated blade mountings required.

The present invention comprehends adjusting the iiow characteristics over only that portion of the blade length where it is most important by provision of means for closing down the stator blades in the areas adjacent the outer casing only, and facilitating the use of the normal stator blade shroud construction.

An object of the present invention is the provision of means for adjusting the ow characteristics across the tips of compressor rotor blades in accordance with the design requirements of varying operating speeds.

Another object is the provision of means for adjusting the ilow characteristics across the tips of compressor rotor blades, said means requiring reduced torque to operate and permitting the use of normal stator shroud construction.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Figure 1 is an elevation view partly in section of the inlet stages of an axial llow compressor embodying the present invention;

ice

" on lines 2-2 of Figure 1;

Figure 3 is an elevation view partly in section of an axial ilow compressor embodying another embodiment of the present invention;

Figure 4 is a sectional view at an enlarged scale taken along lines 4-4 of Figure 3; and

Figure 5 is a sectional view of a modiication of the construction of Figures 1 and 2. y

Referring more particularly to Figure 1A of the drawing, the compressor construction shown includes an outer casing 11, an inner casing 12 and alternate rows of stator and

rotor blades

13 and 14 respectively. Each stage of stator blades is fitted with a circular shroud 15 atthe tips thereof. The shrouds provide support for the tips ofthe j stator blades and maintain the desired spacing between adjacent blades. A tab 16 ismounted closely adjacent to and downstream of each stator blade. Each tab is of right triangular construction and is pivotally mounted onthe outer casing and the shroud with its base adjacent theA outer casing and its apex adjacent the shroud, so that the leading edge of the tab is parallel with the trailing edge of the adjacent stator blade. The apex of the tab is connected to the shroud by means of pin 17 and the base of the tab is connected to the inner casing by means of the pin 1S which extends through the casing and is secured to crank arm 19.

As shown in Figure 2, each tab is mounted inline with ythe adjacent stator blade and is adapted for pivotal movement towards the pressure side of said blade to the dotted line position. n v

The conguration illustrated in Figure 3 includes an outer casing 21 and an inner casing 22 stator blades 23 and rotor blades 24. A shroud 25 is tted at the inner ends of the stator blades joining the tips thereof maintaining them in spaced relation. A triangular shaped tab 26 is mounted at the downstream edge of each stator blade and forms the trailing edge thereof. As in the embodiment of Figure l, the tab 26 is pivotally mounted on the inner casing andthe shroud by means of the pinf28 and 27 respectively. Crank arm 29 is connected to pin 23 at the outer surface of the outer casing.

As shown in Figure 4, the tab 26 forms the trailing edge of the stator blade 23 and is movable toward the pressure side thereof as indicated in the dotted line position.

The showing of Figure 5 is a modification of the construction of Figures 1 and 2, wherein a tab 31 is mounted downstream of and between adjacent stator blades 32 and 33. The tab is pivotally mounted on the outer casing and the shroud and is not positioned in line with the stator blades, but instead is laterally offset from the stator blade 32.

In the operation of the present invention the tabs are rotated to close down the compressor by deilecting the ilow of working uid through the rotor blade stages adjacent the outer casing. When the compressor is operated at speeds less than the designed speed, the axial velocity lof the working uid adjacent the inner casing is reduced more sharply than that adjacent the outer casing,

thus creating an energy gradient extending diagonally downstream between the inner casing and outer casing. This energy gradient increases as the llow of tiuid progresses from one stage of rotor blades to another causing an increase in ow adjacent the outer casing and a decrease in flow next to the inner casing until the axial velocity of ow adjacent the inner casing approaches zero, at which point stall occurs. To prevent the development of these stall conditions the present invention returns the energy gradient to a radial position between the inner casing and the outer casing. This is accomplished by movement of the tabs, causing a transfer of energy from `the outer casing to.the inner casing so that the energy gradient is sharply decreased and is returned to a radial position. When the 'tabs are moved towards the pressure side of the adjacent blades, the ow of working fltid is 'dee'ted or turned such that the ratio Vof its 'rotational velocity to its axial velocity is increased adjacent the outer easing. In addition, a portion of the o`W of working uid is displaced inwardly by the tabs so that the axial velocity is increased adjacent the inner casing. The stall generating conditions characterized by the diiic'erence in axial velocities adjacent the inner and outer casings are thus o'vercor'ne.

The tabs in a single stage may be operated simultaneously b'y means of the crank arms I9 and 29 as a function of compressor speed. The amount of turning in 'a single stage will vary with operating speed and if desired the anount of 'tlriing' may be varied from stage testage for a single speed.

lThe tabV constructions' illustrated -in "Figures 2, 4 and 5 all operate in a similar mann/er to cause a vtransfer of energy from lthe oter easing 'to the inner casing and reduce the diiferent'i'al hetween'theaxial velocities of working' tluid adjacent the o'uf'er' and inner casings. The tab arrangement of Figure 2 isV slightly more efticient in turning the working duid -since the space between the stator blade and the tab acts as a vboundary layer bleed duct to draw olf the suction side boundary layer air. In addition, the construction of Figures 2 and 5 permits the use of conventional stator blades.

While particular embodiments of lthe invention have been illustrated and described it will be obvious to those skilled in the art vthat various changes and modifications may be made without Vdeparting from the invention and it is intended to cover inthe appended claims all such changes and modifications that come within the true spirit and scope of the invention.

What is claimed is:

1. In a multi stage compressor 'including' an inner casing, an outer casing and alternate stages of stator and rotor blading, at least one stage of stator blades being shrouded the improvement Consisting of longitudinally tapered tab pivotally mounted between the shroud and outer 'casing downstream of ea'ch stator blade, each of said tabs extending over the full length of the adjacent stator blade and having a larger chord at the outer casing than'at the inner casing. o

2. In a multi stage compressor including an inner casing, an outer casing and alternate stages of stator and rotor blading, the improvement consisting of an air foil shaped tab extending between the inner and outer casings downstream of each stator blade and pivotally mounted on at least the outer casing, the leading edge of each tab being parallel with the trailing edge of the adjacent stator blade, and the trailing edge of each tab diverging from the leading edge thereof from the inner casing to the outer casing.

3. In a multi stage compressor including an inner casing, an outer casing and alternate stages of stator and rotor blading, atleast one stage of stator blades being shrouded the improvement consisting of an air foil shaped tab pivotally mounted between the shroud and outer casing immediately downstream fof -each stator blade, the leading edge of'each tab being parallel with the trailing edge of the adjacent stator blade, and the trailing edge of each tab diverging from the leading edge thereof from the inner casing to the outer casing, each tab being pivoted at its leading edge, and the trailing edge of the tab tapering yfrom a very smalllchord at the inner casing to a relatively large chord at the outer casing.

4. In a multi stage compressor as defined in claim 2, wherein each tab is positioned-in line with the adjacent stator blade.

5. In a multi stage compressor as dened in claim 1, wherein each tab is offset laterally from the adjacent stator blade.

References Cited in the leof this patent UNITED STATES PATENTS 1,544,288 Van'Ormer e June 30, 1925 1,622,930 Von Karman et al Mar. 29, 1927 2,314,572 ChitZ Mar. 23, 1943 2,337,861 Adamtchlk Dec. 28, 1943 2,412,365 Sollinger Dec. l10, 1946 2,606,713 Bauger Aug. 12, 1952 v2,648,390 De Lagabbe Aug. l1, 1953 2,689,680 Lovesey Sept. 21, 1954