US3032315A

US3032315A - Turbine blading

Info

Publication number: US3032315A
Application number: US528588A
Authority: US
Inventors: Birmann Rudolph
Original assignee: Laval Steam Turbine Co
Current assignee: De Laval Steam Turbine Co
Priority date: 1955-08-16
Filing date: 1955-08-16
Publication date: 1962-05-01
Anticipated expiration: 1979-05-01

Description

May 1, 1962 R. BIRMANN 3,032,315

TURBINE BLADING Filed Aug. 16, 1955 5 Sheets-Sheet l :agi 5kg) g I O l0 i Q'IS v l N N a v l Y lo i MIJ o p5 o gnk o' t I E INVENToR.

RUDOLPH BI RMANN ATTORNEYS R. BIRMANN TURBINE BLADING May 1, 1962 5 Sheets-Sheet 2 Filed Aug. 16, 1955 FIG. 3.

INVENTOR. l RUDOLPH BIRMANN ATTORNEYS May 1, 1962 R. BIRMANN 3,032,315

TURBINE BLADING Filed Aug. 16, 1955 3 Sheets-Sheet 3 FIG.5.

Izar

INVENToR. RUDOLPH BIRMANN ATTORNEYS 3,032,315 TURBINE BLADING Rudolph Birmann, Newtown, Pa., assigner to De Laval Steam Turbine Company, Trenton, NJ., a corporation of New Jersey Filed Aug. 16, 1955, Ser. No. 528,588 6 Claims. (Cl. 253-55) This invention relates to turbine blading and has particular reference to the blading for a turbine rotor operating at very high speeds and very high temperatures in a gas turbine.

For such rotors it has been quite generally accepted that the blading had to be substantially radial in order to withstand the great centrifugal stresses involved at high speeds and particularly at high temperatures when the material becomes substantially weakened. Centripetal turbine rotors were designed having radial blades throughout their extents and it was the practice to design the blades by establishing one of the ow lines, such as the mean or hub line, building the blade surface by passing radial lines through each point of the aforementioned mean or hub line. Such design necessarily results in a condition at the blade outlet such that the tangent of the outlet and angle is inversely proportional to the radius. Such variation of the outlet angle along the blade outlet edges results in serious losses.

In my application Serial No. 428,627, led May 10, 1954, now Patent No. 2,943,839, there is set forth a procedure for design of blading for elastic fluid devices resulting in blading of high efliciency which is particularly characterized by the maintenance throughout the passages defined by the blading of substantially vortex ow from the inlet to the outlet. Blading designed in accordance therewith is highly satisfactory from the point of'view of thermodynamic performance; but this blading involves certain non-radial portions which may lead to excessive bending stresses in operation at very high speeds.

In accordance with the present invention blading is provided suitable for use in centripetal turbines operatv ing at very high speeds and very high temperatures. In accordance with the invention the blading is essentially radial through the major portion of its extent in the direction of flow and is required to depart from radial condition only in the region of the outlet, where, however, the departure is of special nature as will appear hereafter. The result is that vortex flow occurs at the inlet and outlet with some deviations therefrom in the intermediate portions of the passages but nevertheless under conditions of satisfactorily high eiciency. In particular, it has been found desirable to so design the outlet edges of the blades that the outlet angle is nearly constant over the entire radial extent of the outlet edge rather than such that its tangent is inversely proportional to the radius as mentioned above for helicoidal blading. When the outlet angle is substantially constant there is substantially vortex ow at the outlet for blading of practical type as discussed hereafter. As a result of the design the axial extent of the non-radial condition is small. The relation between the outlet angle, the outlet annulus area and the cylindrical, or substantially cylindrical, inlet area provides the high degree of reaction necessary to eliminate the danger of ilow separation from the blade surface due to the abrupt local turning. A high leaving velocity results, but it is found that the now-stabilizing effect produced by a high degree of reaction oifsets the disadvantage of a high leaving velocity. Furthermore, the matter of constant outlet angle producing a vortex ow pattern has been found to result in good efficiency in association with an exhaust diffuser, the ow entering the diffuser 3,932,315 Patented May l, 1962 being stable and thus eliminating mixing losses. A diffuser is desirably provided at the turbine blade outlet for the purpose of transforming the high leaving velocity into pressure rise which results in lowering of the backpressure at the turbine outlet.

A further object of the invention is the provision of improved vibration damping means.

The general objects of the invention and other objects relating particularly to details of design will become apparent from the following description, read in conjunction with the accompanying drawings in which:

FIGURE 1 is an axial section through a turbocornpressor unit embodying in the turbine blading the matters of the present invention;

FIGURE 2 is an enlarged axial -sectional view of the inlet portion of the turbine;

FIGURE 3 is an elevation looking axially at the righthand side of FIGURE 2;

FIGURE 4 is a fragmentary elevation looking at the discharge end of the turbine rotor;

FIGURE 5 is a fragmentary axial section taken on the plane indicated at 5 5 in FIGURE 1; and

FIGURES 6, 7 and 8 are transverse sections through the blading taken on the respective planes indicated at 6 6, *7-'7, and S-S in FIGURE l.

FIGURE 1 shows the general assembly of the type of turbocompressor unit to which the invention is particularly applicable, such a unit, for example, forming part of a gas turbine power plant or being used for the turbocharging of an internal combustion engine. A shaft 2,

mounted in suitable bearings, supports in overhung` fashion by a flange 4 an assembly of rotor hub sections designated 6, 8, 12 and 14 secured together and to the shaft by tie-bolts 16.-

The compressor hub'section 16 is provided with compressor blading 18, the compressor being of mixed ow type and arranged to deliver air in usual fashion through a diffuser to the point of use, i.e., to a combustion chamber or to an engine for turbocharging purposes.

The turbine comprises, as shown, the three

hub sections

8, 12 and 14 and the elements carried thereby. The

hub section 8 is provided with a side plate or disc 1t) which separates the compressor and turbine units and provides a wall for portions of the turbine gas passages. The disc 1t) is slightly conical at its outer portion where it engages the blades Zit carried by hub section 12, this design providing an axial component of deflection of the disc under the action of centrifugal forces which pressesv the disc against the edges of blades 20. This insures.

contact under all conditions of operation to effect vibration damping and still permit differential expansion. The

second and

third hub sections

12 and 14 carry the blades.

constituted lby the portions 2G and 22. The invention is particularly directed to the blading at 20 and 22. This may provide a suitable number of blades, and in the specific form disclosed the turbine comprises eighteen equally spaced blades.

`The split turbine construction shown and described is particularly useful for relatively large turbine wheels, for example, eight or more inches in diameter, wherein vibration and thermal stresses constitute a substantial problem. In smaller turbine wheels where such problem is not serious the entire turbine wheel may be formed as a single piece, i.e., the three sections described may be precision cast as a single unit. However, the inlet and outlet blade portions 2t) and 22, though unitary, involve special design considerations and will be separately described, with the understanding that they may be either physically separate or merely parts of single blades.

Referring rst to the inlet portions 2t) of the blades carried by the hub element 12, it will be noted that each blade is centered about an axial plane, each blade generally tapering from its base towards its tip as will be clear from FIGURE 3. For maximum strength the outermost portions of the blades should have a uniform thickness radially inward to the point where the centrifugal stresses reach the maximum permitted by that thickness. From this point inwardly the maximum stresses are kept constant by the employment of a suitable hyperbolic blade prole. The trough 26 at the hub between the blades is shaped to suit continuity requirements of the gas passages.

The disc l engages the left-hand edges 30 ofthe blades as viewed in FIGURE 2 to provide a passage wall on one side of the flow, the other being provided by the housing along the outer blade edges 3l. In the arrangement illustrated the gas is received without a substantial axial component of ow, and the outermost edges 32 of the blades accordingly extend parallel to the axis. The inflowing gas is, of course, provided with a high velocity circumferential component of flow which may be provided by nozzles located radially outwardly of the edges 32, or, even more desirably, by virtue of free rotation in an annular chamber which is not interrupted in the vicinity of the blades by any guide vanes. In such case the approaching iiow will have substantially vortex motion at theentrance to the turbine passages defined by the blades 2t), the axial edges 32 receiving the flow properly in such case at normal speeds of operation. The inlet blading as described accordingly receives the flow desirably under vortex conditions. In accordance with what has been described in my application referred to above the vortex conditions should desirably be maintained to the outlet. For the strict attainment of this result the intermediate portions of the blading would have to depart somewhat from radial condition; but analysisv will show that if the blade portions 20 are radial, as described, the departure from vortex flow will not be su'iciently serious to affect substantially the efficiency of operation. In accordance with the present invention, vortex flow exists at the inlet portions of the passages formed by blades 26, then the ow pattern changes within the passages to another flow pattern, and then, as will appear, again changes to vortex ow at the passage outlets.

Referring now particularly to FIGURES 1 and 4 to 8, these show the outlet portions 22 of the blades supported by the hub section I4. The inlet edges 38 of these blade portions are shaped in radial section to conform precisely with the radial sections of the inlet portions of the blades and are circumferentially aligned therewith by means of the tie bolts 16, the flow guiding surfaces being smooth continuations of the surfaces of the inlet blade portions. In the assembly of the several sections a dellectable spring washer 39 is desirably located between the

hub portions

12 and 14 of the two rotor portions which are drawn tightly together. However, in most cases the hub portions 12 and I4 may be integral with each other, with the

blade portions

20 and 22 also integral with each other.

At its inlet edge 38 the blade portion 22 is radial. Beyond this the central surface on which the physical blade may be regarded as centered starts deviating approximately helicoidally from an axial plane with gradually increasing helix angle and with the maintenance of approximately radial elements through its initial region. However, there is then departure from the radial condition as will beapparent from the following.

The discharge edge 46B of the blade portion 22 is designed to provide a constant outlet angle which, depending upon the required operating conditions may vary, typically, from about 2 to about 35. The variations of crosssectional widths of the blade portion with radius are then determined in accordance with conventional stress analysis to provide allowable stresses for the intended conditions of operation, this procedure resulting in considerable taper ofthe blades from the hub to the periphery. The resultI is the establishment of the profiles at the inlet edge 38 (where the inlet angle is and at the outlet edge 40, when the outlet angle is of the constant value chosen. Between 38 and 40 the profiles' at different radii are then faired in tentatively, giving, approximately, sections such as appear in FIGURES 6, 7 and 8. tmay be noted that, to the extent of the procedure so far described, only the region at the inlet 38 is fixed but that, consistent with maintenance of constant outlet angle the outlet edge section at various radii could lie quite arbitrarily about the rotor axis, i.e. they could be shifted angularly about this axis arbitrarily and the profiles between inlet and outlet at the various radii could be correspondingly shifted while maintaining the proper variation of cross-section with radius.

In accordance with the invention, shifting of the outlet edge sections, with shifting of profiles at the various radii to correspond, is now carried out so that the centers of gravity of the Various sections' are brought into radial alignment. The end result will be clear from FIGURES 6, 7 and 8. The centers of gravity of the sections Shown, respectively, in FIGURES 8, 7 and 6 at at 42, 44 and 46 and these are in radial alignment. The centers of the inlet edges of these sections at 48, Si) and 52 are, of course, in radial alignment, this following from the premise of merging condition of the inlet portion of each blade portion 22 with its corresponding inlet blade portion Ztl.

As will be evident, due to the arcuate shapes of the profiles, their centers of gravity will not generally, except in the region of the hub, lie within the sections, with the result that sections of the blade portions by radial planes will not be radial but will depart from radial condition as indicated in FIGURES 5. However, each outlet blade portion will oder great resistance to deiiection under centrifugal stresses since (a), viewing a section at any radius as a rigid unit, centrifugal stresses would tend to lineup radially the centers of gravity of the sections and this is achieved initially in the design as stated, and (b) each section in itself has an arch-like shape so that the stresses tending to deflect any off-radial portion to a radial position would be similar to those tending to collapse an arch and would be resisted in arch-like fashion. Each blade portion as a whole is thus highly rigid despite the fact that individual sections by radial planes may depart considerably from radial shape.

It may be noted that while radial alignment of centers of gravity of the sections may theoretically give maximum resistance to deflection, this may be only approximately achieved consistently with the attainment of a blade portion highly resistant to deilection. For example, considering that along the inlet edge 33 the blade portion is radial, with no tendency there towards deflection under centrifugal stress, the centers of gravity considered forv alignment may be only those of some arbitrary portions of the blade sections nearer the discharge edge 4t), where thc circumferentially measured blade thicknesses are less. Such considerations would particularly arise in the design of blading in which blade portions 2d and 22 were integral, and wherein consideration of alignment of centers of gravity would be confined to the portion of each blade where local deviations from the radial condition would be material.

As mentioned above, the maintenance of substantial constancy of the outlet angle at the discharge edge of cach blade approximately gives rise to the attainment of vortex ilow at the blade outlet if the u/c i.e, the ratio of the peripheral velocity of the turbine blades at the inlet to the theoretical spouting Velocity of the driving gases, of theV turbine is in the vicinity of 0.6 to 0.7 and if the reaction, i.e., the division of the total heat drop between the nozzles and blades, is properly made. The necessary reaction usually is obtained with the range .of blade angles specified above, and with the area ratio specified below. A lower u/c would be desirable from the point of View of lowering the tip speed for a given heat drop and thereby reducing stresses, but it results in poor efficiency. A u/c higher than 0.7 usually cannot be provided because of stress considerations;v It, there; fore, happens that the above useful range of u/'es coincides with vortex ow under conditions of an approximately constant exit angle along the radial extent of the exit edge. v l p For optimum results 4it is desirable that the'inlet and cutl'et areas of the turbine should be properly related tothe substantially constant outlet angle. lf the cylindrical inlet area is designated A1 (this area being the axial length of inlet edge 32 multiplied by the circumference at the radius of this edge), the outlet annulus area is designated A2 (this area being that swept by the discharge edge 40), and the outlet angle is designated [32, the relationship should be:

wherein k is no smaller than about 1.0 and no larger than about 2.0, .Bz varying from about 22 to about 35" as stated above.

It will be evident from the foregoing that blades are provided which are nearly radial throughout their entire extents and with minor departure at the exit only (with provision for maximum rigidity there), providing for entrance of how under vortex conditions and discharge of flow under substantially vortex conditions with deviations which are rather slight through intermediate portions of the blades. Reaction conditions are involved in the region of the outlets from the blades, but, as mentioned above, while this results in increased discharge velocity a diffuser following the turbine effects the transformation of the added velocity into a pressure rise, the overall situation actually providing a balancing of desirable aspects over undesirable aspects to provide a high eiliciency arrangement. As a result a highly eifective turbine is provided which by reason of the blade structure is capable of operating under very high speed and very high temperature conditions.

It will be evident that variations in details of the shown embodiment of the invention may be provided without departing from its scope as dened in the following claims.

What is claimed is:

1. A centripetal turbine rotor comprising a hub, blades carried thereby, said blades having edges extending outwardly, and a member providing a cone-shaped ilexible disc separate from and engaging said edges at its radially outer face and arranged to deect to exert axial forces on said edges when subjected to centrifugal stresses.

2. A centripetal turbine rotor comprising a hub and blades carried thereby, each of the blades having an inlet edge extending axially to receive gas flow having a substantial radially inward component, the region of the blade immediately beyond said edge in the direction of gas ow being substantially radial, said blade having an exit edge with the region of the blade preceding the exit edge deviating, in its radial cross-section, from radial condition and having throughout its radial extent a substantially constant discharge angle, the two said regions of the blade being smoothly connected by a region which is substantially helicoidal.

3. A centripetal turbine rotor comprising a hub and blades carried thereby, each of the blades having an inlet edge extending axially to receive gas ow having a substantial radially inward component, the region of the blade immediately beyond said edge in the direction of gas ow conforming substantially to an axial plane, said blade having an exit edge with the region of the blade preceding the exit edge deviating, in its radial cross-section, from radial condition and having throughout its radial extent a substantially constant discharge angle, the two said regions 7o of the blade being smoothly connected by a region which is substantially helicoidal.

6 4. A centripetal turbine rotor comprising a hub and blades carried thereby, each o the blades having an inlet 'edge extending axially to receive gas How having asuba stantial radially inward component, the region ofthe blade immediately beyond said edge in the direction of gas llow being substantially radial, said blade having an exit edge with the region of the blade preceding the exit edge deviating, in its radial cross-section, from radia condition and having throughout its radial extent a substantially constant discharge angle, the' two said regions of the blade being smoothly connected by a region which is substantially helicoidal, the centers of gravity of sections through the second of said regions preceding the exit edge, taken by parallel planes normal to the lirst of said regions of the same blades, being approximately 1n radial alignment.

5. A centripetal turbine rotor comprising a hub and blades carried thereby, each of the blades having an inlet edge extending axially to receive gas ow having a substantial radially inward component, the region of the blade immediately beyond said edge in the direction of gas ow being substantially radial, said blade having an exit edge with the region of the blade preceding the exit edge deviating, in its radial cross-section, from radial condition and having throughout its radial extent a substantially constant discharge angle, the two said regions of the blade being smoothly connected by a region which is substantially helicoidal, the centers of gravity of seetions through the second of said regions preceding the exit edge, taken by parallel planes normal to the rst of said regions of the same blade, being approximately in radial alignment, with at least some of said centers of gravity lying outside their corresponding sections.

6. A centripetal turbine comprising a rotor anda housing therefor, said rotor comprising a hub and blades carried thereby, each of the blades having an inlet edge extending axially to receive gas ow having a substantial radially inward component, the region of the blade imi mediately beyond said edge in the direction of gas flow being substantially radial, said blade having an exit edge with the region of the blade preceding the exit edge dcviating, in its radial cross-section, from radial condition and having throughout its radial extent a substantially constant discharge angle within the range from about 22 to about 35, the two said regions of the blade being smoothly connected by a region which is substantially helicoidal, said turbine satisfying the relation in which A1 is the cylindrical inlet area of the blades, A2 is the annulus outlet area therefrom, 132 is said discharge angle, and k is a constant ranging from about 1.0 to about 2.0.

References Cited in the file of this patent UNITED STATES PATENTS 2,261,463 Garve Nov. 4, 1941 2,399,852 Campbell et al. May 7, 1946 2,465,671 Van Millingen et al. Mar. 29, 1949 2,484,554 Concordia et al. Oct. 11, 1949 2,646,210 Kohlmann et al. July 21, 1953 2,648,491 Wood Aug. 11, 1953 2,668,006 Larrecq Feb. 2, 1954 2,709,567 Wood May 31, 1955 2,792,197 Wood May 14, 1957 2,859,933 Whitaker Nov. 11, 1958 FOREIGN PATENTS 628,697 Great Britain Sept. 2, 1949 892,691 France Jan. 13, 1944