US2675208A

US2675208A - Turbine rotor blade

Info

Publication number: US2675208A
Application number: US53846A
Authority: US
Inventors: Morton I Weinberg
Original assignee: Packard Motor Car Co
Current assignee: Packard Motor Car Co
Priority date: 1948-10-11
Filing date: 1948-10-11
Publication date: 1954-04-13
Anticipated expiration: 1971-04-13

Description

April 13, 1 4 M. l. WEINBERG TURBINE ROTOR BLADE Filed Oct. 11,, 1948 2 Sheets-Sheet 1 3 wk} IT I N VEZV TOR. [094M 19 fzzrz anf m, Ma, #4

M. WEINBERG TURBINE ROTOR BLADE April 13, 1954 2 Sheets-Sheet 2 Filed Oct. 11, 1948 III Patented Apr. 13, 1954 v UNITED STATES PATENT OFFICE 2,675,208 TURBINE ROTOR BLADE Mo ton I. Weinbe Y n i, Mich" assignor to Packard Motor Car COIIIBMIY; Det oit. M h" a corporation of Michigan Application October 11, 1948, Serial No. 53,846

1 claim, (Cl. 253 177) 2 The invention relates generally to turbine rotor The stresses occurring in each blade are due constructions and more particularly to blade not only to the centrifugal forces involved. but structure for gas turbines. also to the torsional efiects on the blade due The general object of the invention is to proto the force of the gases acting on the blade vide a rotor for a gas turbine, having blades 5 and the relative location of the crosseseotional which are capable of operating without danger center of gravity. fact, these stresses may of breakage due to the high operating speeds be more critical or more difiicult to meet than and the high temperature of the gases. th r s es due to the centrif al cti n. With More specifically, it is an object to provide a a hollowlblade having a rather thin wall, another novel blade structure in which undesired stresses form of stress occurs, particularly at the tip or are eliminated or at least minimized so that the outer end of the blade. Thus, unless the blade blade can, without breakage, withstand the operis properly designed, the portions of the two ating conditions to which it is subjected. side walls of the blade intermediate the front Another object is to provide a novel blade and rear edges may flex relative toeach other at structure facilitating manufacture at a reasonthe tip of the blade to cause what may be termed able cost, a breathing action. This,.of course, sets up A further object is to provide a novel blade s re s s n the m tal which a fiui fi hflsedfl for a gas turbine, in which the structure prohe stresses heretofore mentioned.

viding for elimination and minimization of un- A turbine blade of the character h rein desired stress results in a, shape which is hollow emplat d may be likened to a highly cambered and facilitates the passage of cooling air thereairfoil in which the maximum spar depth is through round well forward in the blade. so that prin- Other objects and advantages will become apcip e Of design of an airfoil may be applied parent from the following description taken in the t In applying such principles, the blade connection with the accompanying drawings, in in any t ansverse. section may be said to have which: a neutral axis, at any given cross section, about Figure 1 is an axial sectional view of a turbine which the compression and tension forces are rotor embodying the features of the invention balanced when the blade tends to bend as it and showing one of the blades thereof partially is l ad d and a shear center for any given neuin elevation. tral axis, which is defined as the point at which Fig. 2 is an enlarged view of the outer end a l ad applied normal to that axis will produce of one of the blades employed in the rotor shown 0 torsion in the section. The load in the presin Fig. 1. mt instance, of course, is a component of the Fig. 3 is a sectional view taken on the line force applied by combustion gases driving the f Fig 3 turbine. To prevent any torsional effects upon Fig is a sectional View taken on the line the blade, the center of gravity for such trans- 4-4 of Fig. 1. verse section should substantially coincide with Fig 5 is a Sectional View taken Substantially the shear center. With such an arrangement,

n th lin 5-5 of Fig. 1. the stresses due to the torsional effects will be In constructing a turbine rotor for a gas tureliminated.

bine, difficulties are encountered by th designer The breathing action Of the side walls of the of such a rotor because of peeds blade at. the can be Substantially which Such raters went? and because f the by rigidly tying them together, preferably high temperatures to which the blades thereof throughout the radial length of the blade, the are subjected. The temperature of the metal in tie being PmVid-ed eferably at adjacent the the blades, of course, may be held materially point of maximum breathing Such attachment lower than that of the gases'by making the blades between the two Walls at that point is i e hollow and conducting a stream of cooling fluid, by a tion in the nature of a Web which lsuch as air, through each blade, Even t such ously necessitates the use of material affecting an arrangement, the temperature of the blade location of the center of gravity in any becomes fairly high so that the strength of the transverse Section metal is substantially reduced from that obtain- The present invention contemplates a blade able at lower temperatures. This fact, coupled Qmbodying the furegol'ng principles, and in Figswith the excessive speeds at which the blades 31- an fiz f the draw there are shown transen rate. renders the design of such blades diff;- vers e tion f the b d at vary n radial distances from the axis of rotation of the rotor.

In Fig. 5, which is a transverse sectional view of the blade intermediate its ends, I have shown what may be termed a typical section, to illustrate the foregoing principles. Thus, dash-anddot line It in Fig. 5 may be said to be the neutral axis of the section of the blade illustrated therein. The point II indicates the shear center of this section, which, by definition, is the point about which the load applied normal to the axis I will produce no torsion in the section. The distribution of metal in the section is such that the center of gravity for the section lies substantially at the point II. Thus, there will be no torsional eifect acting on the blade, about the point it, to produce undesired stresses in the blade.

The section shown in Fig. also illustrates the manner in which stresses due to the breathing action of the side walls of the blade are eliminated. Thus, it will be noted, the blade comprises a pair of spaced side walls I2 and I3.

These walls are interconnected at the front and rear edges of the blade but will undergo a breathing action relative to each other, particularly at the tip of the blade, unless they are rigidly tied together intermediate the front and rear edges. For this purpose, an intermediate rib I4 is provided, which is illustrated as being integral with the wall I2 and is welded to the wall I3. The rib I4 extends throughout the radial length of the blade so that the two walls I2 and I3 are thus held in fixed relation to each other, not only at the front and rear edges of the blade but intermediate such edges. By this means, substantially no breathing action between the walls takes place, and the stresses occurring because of any breathing action are thereby eliminated.

A blade having the foregoing characteristics may be readily manufactured in what may be termed a two-part construction. One of such parts, which may be termed the body member, comprises the wall I2 with the rib I4 integrally formed therewith. A rib or ridge I5 may also be formed integrally with the wall I2 at the front edge of the blade, while a similar rib It may be formed at the rear edge of the wall I2. The outer or tip end of this part has an end wall portion I'I, while the inner end is provided with a wall portion I8. This one part comprising i the wall I2 and the ribs may be readily formed either by a casting process or a forging process, either of which may be broadly defined as hot forming. The wall I2 in the present instance constitutes, as will be obvious, the low-pressure or rear face of the blade.

The opposite or high-pressure face of the blade, formed by the wall I3, is provided by the other part of the two-part construction and, in the present instance, comprises a camber plate I3 made of sheet metal. The camber plate I3 thus may be punched from a sheet and is then curved to fit against the ribs I4, I5 and I6 and bridges the spaces therebetween. To rigidly secure the camber plate to the ribs and make it an integral part thereof, the ribs and camber plate are welded together throughout their area of contact. The camber plate is also welded at its ends to the wall portions I1 and I8. After such welding, the front and rear edges of the plate I3 may be rounded to conform to the desired rounding of the edges of the ribs I5 and It. The welding of the plate I3 to the intermediate rib I4, as heretofore mentioned, ties the two walls I2 and I3 together to prevent the breathing action.

Thus, the wall portion I8 of the blade is J ture.

The particular form of the ribs I4, I5 and I6 in their relation to the walls I2 and I3 pro vides a center of gravity for any transverse section, such as illustrated in Fig. 5, which is located at the shear center'for such section. Stresses due to torsional effects are thereby substantially eliminated, so that the centrifugal stresses are the only ones which, with this construction, remain of material magnitude. Provision for such centrifugal stresses, however, may be made by increasing the strength of the blade toward its inner end. Thus, as is noted by a comparison of Figs. 3, 4 and 5, the ribs 14, I5 and I5 are of greater depth near the inner end of each blade than at the outer end, providing a blade of tapering thickness. The thickness of the wall I2 is also increased toward the inner end of the blade so that the centrifugal stresses can well be sustained without danger of breakage of the blade. The camber plate I3, since it is made from sheet metal, is preferably of uniform thicl ness throughout its radial length.

In Figs. 1, 2 and 3, the manner in which the blade is attached to a rotor has been indicated. formed on a base 20 of generally rectangular shape. The base 20 is provided with a plurality of spaced tangs 2| adapted to interfit with similar tangs 22 formed on the periphery of the rotor of the turbine, indicated at 23. The two outer tangs on the base 20, indicated at 24 (see Figs. 1 and 3) are preferably segmental in form and of such size that they abut the corresponding tangs of the adjacent blades. The base 20 is also of such I size that it abuts the bases of adjoining blades,

so that the bases 20 and tangs 24 provide a complete rim about the rotor 23. The tangs 2i and 24 on the base 20 are secured to the tangs 22 on the rotor 23 by means of a pin 25 extending therethrough, as illustrated in Fig. 1.

It is contemplated, of course, that with a hollow construction for the blade, cooling air will be passed through the blade to keep the metal of the blade at sufficiently low operating tempera- The rotor 23, in the present instance, is provided with an air-receiving chamber 39 in its central or hub portion, from which extend a plurality of radial air passages 3 I. In the present instance, the passages 3I are in a staggered relation to each other to provide a sufficient number of such passages without weakening the rotor. The passages 3I extend outwardly to discharge air against and between the tangs 2! and 22. The tangs 2|, as will be noted in Fig. 3, are of less peripheral width than the base 20, so that there is space for the air to circulate about the tangs.

The rib I4 extending throughout the length oi the blade proper divides the interior of the blade into two passages, indicated at 32 and 33 in Fig. 3. These passages are adapted to receive the air, which circulates about the tangs, by means of a pair of apertures 34 (see Fig. 3) bored through the base 20 and each generally aligned with one of the spaces between a pair of tangs it The tangs 22 on the rotor 23 are of less radial depth than such space, so that air is free to circulate over the outer end of the tangs 22 and pass outwardly through the apertures 34 into the

respective passages

32 and 33. The air then passes outwardly through the blade and is discharged or vented at the outer end thereof through a pair of notches 35 cut in the outer end of the camber plate I3. By the separation of the interior of the blade into the two

separate passages

32 and 33, a definite flow of air is provided, both in the front edge portion of the blade and in the rear edge portion, so that the edge portions of the blade formed by the ribs I5 and I6 will be adequately cooled.

It has been noted that, in gas turbines, the hot combustion gases have an abrading effect on the metal of the blades, such effect being concentrated chiefly at the leading or front edge of the blade. With the present construction, the rib or ridge I5 provides a heavy wall section at the point of great abrasion, so that the structure will not be materially weakened by the abrasion.

I claim:

A hollow turbine blade having the form of a highly caznbered twisted air foil of varying crosssection in which the maximum spar depth is well forward in the blade, said blade having a rear wall and a forward wall, a thickened leading edge and a relatively thin trailing edge, a longitudinally continuous generally centrally disposed stiffening rib integrally formed with said rear wall and engaging said forward wall, each of said cross sections having a neutral axis, a, shear center located at a point along said axis, and the mass of said blade and rib being so disposed that the center of gravity of any such cross section is located in said axis at said shear center whereby substantially no torsional effects are produced upon the blade and the stresses inherent in such effects are thus substantially eliminated.

References Cited in the file of this patent UNITED STATES PATENTS