US2862686A - Hollow vane with internal vibration dampener - Google Patents

Description

1958 K. M. BARTLETT HOLLOW mm mm INTERNAL VIBRATION DAMPENER Filed Au 19. 1954 fiYVEfiZUfi KENA/Efl/M 34572 EN" all v United States. Patfltc) I 2,862,685 HOLLOW VANE WITH INTERNAL VIBRATION DAMPENER Kenneth Bartlett, Lyndliiirst, Ohio, assignor to Thompson Products, Inc., Cleveland, Ghio, a corporation of Ohio Application August-19, 1954, Serial No.'4 5tl, 9 2 Claims. (01. 253- 77 stress; resistance becomes particularly acute in the case of turbine buckets designed'so'as to provide a' hollow cavity centrally of the vane portion.

Closely allied to the problem of adequate stress resistanceis the problem of vibration. While problems of vibration are present in substantially all types of turbine .-buckets, it appearsthat the problem is particularly troublesome in 'the case of the hollow buckets. Continued subjection of the bucket to the conditions of vibration existing in the turbine engines is very likely to produce a failure due not so much to the prolonged stresses in tension or in compression but rather to continuedflexing. Apparently, this repeated flexing of the metal walls of the fluid directing member causes a failure by fatigue of the metal. This failure frequently manifests itself as a series of cracks or fissures along the airfoil surfaces of the vane as well as splits along the leading and trailing' edges of the vanel'on'g before the vane would normally be subject to buckling or bending due' to prolonged presence in the hot corrosive atmosphere of the engine; These cracks and splits are particularly troublesome because in many cases, turbine buckets arelfabricated .from a base metal which has good hot strength properties butpoor resistance to oxidative corrosion, so thatfa thin, firmly bonded coating of metal, metalloids, ceramics .or combinations of these materials are applied to the base metal to provide adequate resistance to the corrosive atmosphere. Once the outer coating has been cracked, however, by the effects of this vibratiomthe body metal is left open to severe attack by the high temperature oxidizing gases present in the gas stream passing the'turbine bucket.

In order to increase the strength ofjhollowfluid directing members of the type described, some turbinegbucket designs have made use of ribs or agrid-like. reinforcing network within the hollow interior of ,the vane... .While this expedient frequently serves to reinforce thevane against premature buckling due to thenormal stresses encountered in the operation of the turbine engine, the provisionof such ribs'or networks has not always .been effective to eliminate or even decrease the vibrational" effects. Indeed, in some designs of reinforcing ribs and along the line IV- IV of Figure 2;

* 2,8 36 Pa s? 13%.25195 Z or substantially decrease the. harmful efiects on, the vane due to the previously discussed-vibrational problem. The provision of such means is the principal object of the present invention..

Another object of the present invention is to rovide animproved hollow fluid-directing memberflwith s elfaligning.. reinforcing means, which not onlyags to strengthen, the member against buckling tendencies, but also provides an effective vibration dampening to the ifiernlieL, w

I A still further object ;of the, invention istoprovi improved turbine bucket having a hollow 'vane se' on with automatically positionable reinforcing means and vilira t'ion dampening means. a p

Otherahd further objectsof this invention will.,be apparent .to those skilled in the art from the following detailed description of the annexed sheet (of. drawings which, by way of preferred embodiment, illustrate two examples of the present invention. I

In the drawings: I U

Figure l is a schematic view,.with parts in elevation, illustrating the manner in which a seriesof turbine buckets "are normally secured to the turbine wheel; f Figure; 2 is a plan view, on an enlarged scale of, a single turbine bucket locked in position on the periphery of thewheel';

; Figure 3''.' a'cr 'ciss-sectional view taken substantially along the line. III-:III of Figure 2; b

Figure 4. is a cross-'ectional .view taken substantially FigureiSis a cross-sectional viewof a turbine employing a somewhat modified form of the invention;

. and

and apIurality of turbine buckets 11 disp osedin spaced relation about the peripheryof the turbine wheel..- ten of the buckts ll may include a-firtreef root porno .12

which is received in wedged engagement, in complementary shaped notches formed in theperipherj of the turbine wheel. Immediately above. the. root porno" 1 2, the turbine buck'et ay have a'n angular b'ase'portion 13 (Figure 2) and an airfoil s'ection.14. The latter. consists grid networks, the vibration problem appears to be greater than it is without the reinforcing means present.

As a result, the need still remains for a practical, relatively inexpensive means for strengthening hollow fluid directing members to provide adequate resistance against the normal, more or less constant stresses encountered in the operation of the turbine engine, and also to eliminate "face of 'the bucket is'provided by introducing a se es of two ,arcuately shapedsidewalls lfi and. I7, merge along a. smoothly c'tmtcnlre'dv leading edge 18,a'nd a'trailing',edge1'9'. e

The interiorv structure of the turbine bucket best illustrated in Figures 3 and 4 of the drawings. seen in these two drawings, the sidewallslfi and, 117 converge upwardly from the, baseto provide an internal void or cavity 21 whose breadth decreases toward the top. edge ofthe turbinebilckeh e An; automatically positionable reinforcing means ,to prevent buckling of the hollow turbine.bucket,,1 and .to dampen vibrations which could cause cracks in the of wedge elements,fwhich may take the form of a series offdiscr'ete balls 22 into the cavity 21. ,Theballs 22 jrrayf beintroduced into the cavity. 21 through; an, opening .23 afterwhi'chTthe.latter aybe sealed by welding or 'bl'aii ti ga The balls ZZ nia yconsist of any suitable material, but preferably should be relatively resistant to oxidation, and should have a reasonable amount of hot strength. Chromium coated steel balls of the type used in ball bearings, or balls of ceramic composition are both suitable in most instances for this use. The diameter of the balls 22 should be intermediate the two extreme thicknesses of the cavity 'tions intermediate the ends of said side 21, i. e. intermediate the thickness of the cavity at the base, and at the top surface of the vane. The balls 22 are thus freely movable within the base of the cavity 21 when the balls are first inserted therein, but as the turbine wheel is rotated and centrifugal force acts upon the balls, they are thrown outwardly and become wedged or at least firmly engaged with the vane walls 16 and 17 in a position intermediate the ends of the vane portion 14, as illustrated by the dotted line showings in Figures 3 and 4.

The plurality of balls in seated engagementbetween the WallS 16 and 17 provides effective reinforcing bridges or struts to prevent buckling of the walls, while at the same time serving as a vibration dampener to a substantially greater extent than the solid, continuous reinforcing networks previously employed in hollow turbine buckets.

An important feature of this invention is the automatic positioning of the balls during operation of the turbine wheel. Thus, as the vanes expand under heat of operation, the centrifugal force of operation will move the balls if necessary to maintain a tight fit or if the balls expand more than the vanes, they may be squeezed to shift toward the root ends of the vanes against the centrifugal force action. This centrifugal force thereby serves as a cushion load applyingmedium on the balls. After operation of the turbine wheel and cessation of the centrifugal force load on'the balls, the wheel will cool and the balls may be free to drop to the root ends of the vanes. The freed balls will not exert any load on the vane walls and the walls will be free of stress when idle. Then, upon the next operation of the wheels, the balls will again come into firm contact with the vane walls.

A somewhat modified form of the invention is illus trated in, Figures 5 and 6 of the drawings. This form of the invention employs two series of balls 26 and 27, the balls 26 each having the same diameter, and the balls 27 likewise being of the same diameter but having a diameter larger than that of the balls 26. It will thus be seen that when the balls 26 and 27 are subjected to centrifugal force by the rotation of the turbine bucket, the balls 26, by virtue of their smaller diameters, will become firmly engaged between the walls 16 and 17 at a higher level than are the balls 27. Thus, by selection of the diameters of the wedge elements, a series of reinforcing members can be provided for the hollow turbine bucket at various levels.

The reinforcing meansv of the present invention has the further advantage that the discrete wedge elements do not completely cut ofi" the flow of air through the hollow interior of the vane, so that if desired, air can be fed to the rotating bucket from the rotor of the turbine during its operation, to assist in cooling the bucket.

It will be evident that various modifications can be made in the described structure without departing from the scope of the present invention.

I claim as my invention:

1. In a hollow fluid directing member having a base portion arranged for attachment to a wheel, a pair of integral, continuousside wall portions extending upwardly from said base portion in spaced relation, and providing a tapering cavity in the interior of said fluid directing member, and a plurality of balls disposed in freely movable relation in said cavity, said cavity having a chordwise dimension sufiicient to receive said balls, each of said balls having a diameter permitting each of said balls to become firmly engaged between said side wall porwall portions upon rotation of said fluid directing member.

2. A turbine bucket comprising a root portion arranged to be received in tight engagement in a turbine wheel, an airfoil portion comprising two arcuately shaped opposed walls merging in continuous, integral opposed leading and trailing edges, said opposed walls being spaced from each other and converging toward each other upwardly from said root portion to provide an internal void of decreasing breadth upwardly from said root portion, and a plurality of freely movable wedge means disposed in said internal void, said void having a chord-wise dimension sutficient to receive said wedge means said wedge means being proportioned to be received in wedged engagement between said walls when said wedge means are subjected to centrifugal force. I

3. A turbine bucket comprising a root portion arranged to be received in tight engagement in a turbine Wheel, an airfoil portion comprising two arcuately shaped opposed walls merging in continuous, integral opposed leading and trailing edges, said opposed walls being spaced from each other and converging toward each other upwardly from said root portion to provide an internal void of decreasing breadth upwardly from said root portion, and a plurality of discrete balls disposed freely at the base of said void, each of said balls having a diameter suflicient to cause said balls to become wedged between said walls when said balls are subjected to centrifugal action.

4. A turbine bucket comprising a root portion arranged to be received in tight'engagement in a turbine wheel, an airfoil portion comprising two arcuately shaped opposed walls merging in continuous, integral opposed leading and trailing edges, said opposed walls being spaced from each other and converging toward each other upwardly from said root portion to provide an internal void of decreasing breadth upwardly from said root portion, and a plurality of balls of diflering diameters contained within said void, each of said balls having a diameter suflicient to cause said balls to become wedged between said walls at diflerent levels when said balls are subjected to centrifugal force.

5; In a hollow fluid directing member, a root portion arranged for attachment to a wheel, integral side wall portions extending upwardly from said root portion to provide a continuous air foil periphery including spaced fluid directing walls merging at the chordal edges into smooth leading and trailing edges, said fluid directing walls being spaced to provide an internal void therebetween of decreasing breadth from said root upwardly in the span-wise dimension of said member, and at least one wedge member received freely at the base of said void and having a dimension suflicient to cause said wedge member to be received in wedged engagement between the walls defining said void upon movement of said wedge member in thespan-wise direction of said member.

References Cited in the file of this patent UNITED STATES PATENTS 1,856,820 Robinson May 3, 1932 2,144,428 -Martin Jan. 17,. 1939 2,155,052 Byland Apr.,' 18, 1939 2,349,187 Meyer May 16, 1944 2,405,283. Birmann Aug. 6, 1946 2,447,628 Baker Aug. 24, 1948 2,462,961 Harker Mar. 1, 1949 2,646,920 Butcher July 28, 1953 2,689,107 Odegaard Sept. 14, 1954 2,771,240 Gurin Nov. 20, 1956

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