US3529903A - Nozzle blade structure - Google Patents

Description

United States Patent Oihce 3,529,903 NOZZLE BLADE STRUCTURE Augustine J. Scalzo, Philadelphia, and Andrew Zabrodsky, Boothwyn, Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 29, 1968, Ser. No. 780,057 Int. Cl. F01d 25 12 U.S. Cl. 415-115 5 Claims ABSTRACT F THE DISCLOSURE An improved nozzle blade structure for an axial flow gas turbine, or the like, comprising one or more blades arranged in an arcuate group and having a plenum chamber portion for admitting air or other coolant fluid to the blade in operation. The plenum chamber structure is an open channel of quadrilateral shape, with a pair of side walls and a contiguous bottom wall forming a U, and a pair of opposed end Walls formed integrally with the other walls and the blade, and the sixth wall or closure being provided by a cover plate of mating quadrilateral shape slidably received in encompassing rail members, which members are, in turn secured to the marginal portions of the side walls and the opposed end walls, by continuous leakproof weld joints.

BACKGROUND OF THE INVENTION The operating temperatures of gas turbines are constantly being increased to attain the present day goals of increase in operating efiiciency. Such increase in operating temperature is primarily being attained by introduction of cooling fluid, such as air, into the turbine hot components such as the rotor blades and blade roots, and the stationary nozzle blade structure.

One of the most effective, yet the most simple, ways of introducing coolant fluid into the turbine is by way of the stationary nozzle blades. Such nozzle blades are preferably formed in integral arcuate groups with inner and outer hollow shroud segments and hollow vane portions, and the coolant lluid is admitted to the outer shroud through a passage in a suitable securing means. Such an arrangement is disclosed in patent application 593,992, filed Nov. 14, 1966, now Pat. 3,427,000, in behalf of Augustine l. Scalzo (one of the present inventors) and assigned to the same assignee as this invention. Although in the above mentioned application, the nozzle blade segments are shown as having a plenum chamber defined f by integral enclosing outer hollow shroud portions, in actual practice Such as an arrangement is difficult to manufacture.

It has been proposed to form the hollow outer shroud portions (defining the coolant fluid plenum chamber) as an open channel structure with end walls, and welding a closure or cover plate to the channel structure. This arrangement is unsatisfactory since the large temperature gradients imposed thereon during operation greatly stress the structure and result in warping and distortion of the entire blade group.

A further proposal, to overcome the stress and warpage problem of the above proposal, resided in first forming the hollow outer shroud structure as an open channel -structure with end Walls, and providing a circumferential shoulder about the inner periphery of the open channel. The cover plate was then seated on the circumferential shoulder and retained in position by circumferential strips welded to the -channel structure. This arrangement induced high residual weld stresses that rotated the strips outwardly, destroying the slidable sealing and resulting in large uncontrolled air gaps around the periphery of the 3,529,903 Patented Sept. 22, 1970 cover plate with attendant excessive leakage of the coolant fluid.

The object of this invention is to provide an improved nozzle blade structure having a hollow outer shroud structure defining a plenum chamber for the coolant fluid, in which the outer shroud structure includes a cover plate that is slidably retained with a minimum of thermal stress and in which sealing of the cover plate against leakage of coolant lluid is assured.

BRIEF SUMMARY OF THE INVENTION In accordance with the invention, there is provided an improved, fluid cooled stationary nozzle blade structure for a hot elastic uid utilizing machine, such as an axial flow gas turbine. As well known in the art, the stationary nozzle blades for an axial flow gas turbine are formed as vanes of generally air-foil cross-section disposed in an annular array about the turbine rotor and disposed upstream of their associated rotary blades carried by the rotor. The nozzle blades are disposed in the hot motive gas passageway and are effective to direct the motive gas past the rotary blades to motivate the latter and drive the turbine rotor.

As motive gas temperatures higher than the nozzle blades, rotary blades and rotor can safely withstand, are employed, the stationary nozzle structure is maintained Within its safe operating temperature limits by directing pressurized coolant fluid therethrough. This pressurized coolant is preferably directed into the nozzle blade structure through the outer shroud structure in radially inwardly direction through the Vanes and then discharged into the motive gas stream.

The stationary nozzle structure is divided into a plurality of arcuate groups of vanes, each group having common inner and outer arcuate shroud segments, and the groups are disposed in end-to-end relation to form the annular array, mentioned previously.

The outer shroud segments are of open U or channel shape with integral opposed end walls and having a circumferential shoulder about the inner periphery of the opening. An arcuate cover plate conforming to the shape of the opening is slidably received in peripheral rail members having inwardly facing slots to accommodate and hold captive the cover plate, and the rail members are inserted in the opening in abutment with the shoulders and welded about their periphery to wallls of the outer shroud segments to form a plenum chamber.

The cover plate is of slightly less Width and breadth than the width and breadth of the slots, so that it is free to expand in operation without stressing and/or distorting the structure, thereby retaining its sliding seal characteristics, and obviating the possibility of leakage of the coolant fluid in operation.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an axial sectional view of a portion of an axial ow gas turbine having a stationary nozzle structure in accordance with the invention;

FIG. 2 is an enlarged sectional view of the nozzle structure shown in FIG. 1;

FIG. 3 is a plan of the nozzle structure; and

FIG. 4 is a radial sectional view of one of the arcuate nozzle groups, taken on line IV-IV of FIG. 2.

PREFERRED EMBODIMENT Referring to the drawing in detail, in FIG. 1 there is shown a portion of an axial flow gas turbine 10. Only the upper half of the turbine is shown, since the lower half is identical to the upper half. The turbine 10 comprises an outer casing 11 of generally tubular or annular shape, an inner casing 12 of annular shape encompassed by the outer casing 11, and a rotor 14 rotatably supported within the inner casing 12 in any suitable manner and having at least one annular row or array of blades 16.

Cooperatively associated with the rotor blades 16 to form a motive fluid expansion stage is an annular row of stationary nozzle blades 18 supported within the casing 12.

The stationary blades 18 are provided with a radially inwardly extending vane portion 19 of air-foil shape, a base portion 20 and an outer shroud portion 22 abutting the annular inner surface portion 23 of an annular groove 24 formed in the inner casing 12.

The inner casing 12 is suitably secured to the outer casing 11 by an annular fiange 26 and jointly therewlth defines an annular air space 27.

The stationary blades 18 are of hollow form, with the outer shroud portion 22 of box-like form and defining an arcuately shaped plenum chamber 28, and the base portion 20 of box-like form and defining an arcuately shaped plenum chamber 29. The chambers 28 and 29 are disposed in fluid communication with each other by passages 31 formed in the vane portions 19, and the vane port1ons 19 are provided with a radial series of outlet orices 32 in their trailing edge portions.

The blades 18 are preferably formed in arcuate groups 34 (as best shown in FIGS. 3 and 4) with a plurality of the vane portions 19 connected in parallel flow communication with the common outer and inner plenum chambers 28 and 29. As illustrated, the arcuate group extends through a central angle of hence the annular row of stationary blades would include eight such groups disposed end-to-end, as well known in the art (example: 8X45=360).

The blade groups 34 are held in the groove 24 by a tubular fitting 35 threadedly received in the inner casing 12 and having a cylindrical portion 36 extending through a mating opening 37 in the outer plenum chamber 28. The fitting 35 has a central bore 38 extending therethrough providing a -uid communication between the intercasing space 27 and the plenum chamber 28, and a tube or pipe 39 received in the outer casing 11 provides pressurized coolant fluid, such as pressurized air from any suitable source (not shown) to the space 27, during operation.

The structure thus far described has been previously proposed and is more fully shown and described in the Scalzo patent application 595,992, previously mentioned. As explained therein, in operation, hot motive fluid, such as pressurized combustion gas generated in a suitable fuel combustion chamber (not shown), is directed through an inlet passageway 41 past the stationary blades 18 and rotor Iblades 16, in the direction indicated by the arrow 41a, with resulting expansion of the motive fluid to rotate the rotor 14.

Since the motive gases employed are hotter than the blades can safely withstand, pressurized coolant air is continuously provided to the stationary blades 18, as previously described, to maintain them within safe temperature limits and then ejected through the outlet orifices 32 into the stream of hot motive fluid.

In accordance with the invention, the outer shroud portion 22 of the blade group 34 is formed with a U or channel shape in cross section, as seen in FIG. 2, and comprises a central bottom Wall 43, a pair of side walls 44, and a pair of opposed end walls 46 (FIGS. 3 and 4). The walls v43, 44 and 46 define an outer peripheral opening 48 of arcuate shape for the plenum chamber 28 and are integral with the vane portions 19 and the base portions 20, and may be formed by any suitable method, as by casting.

The inner marginal portions of the side walls 44 and 46 that form the opening 48 are formed with inwardly extending peripheral shoulder portions 50` and 51. Upon the shoulders S0, 51 there is a rail structure comprising side rails 54 and end rails 56, nested therein and secured 4 to the side walls 44 and the end walls 46, respectively, by a continuous weld joint 57.

The side and end rails are provided with longitudinal slots 58 and 59', respectively, disposed in end-to-end registry with each other and hold a cover plate 60 captive therein.

The rails are preferably of rectangular cross section and are linearly shaped to conform to the size and shape of the opening 48. It will be noted that, in the example, the opening 48 to the plenum chamber is of quadrilateral shape, more particularly a parallelogram. The end rails 56 are rectilinear to conform to the shape of the associated shoulders 51, while the side rail members 54 are of arcuate longitudinal shape to conform to the arcuate longitudinal shape of the shoulders 51. The cover plate 60, in a like manner, is of parallelogram shape, curved to an arcuate longitudinal cross-sectional shape to slidably fit in the associated slots S8, 59.

The cover plate 60 is of substantially the same thickness as the width of the slots to prevent leakage of coolant fluid therepast in operation and is fitted in the slots with a small end clearance space C peripheral in nature, so that during operation as the cover plate 60 expands lengthwise and breadthwise due to the high operational temperatures, it can do so freely without stressing the adjacent structure, and/ or without buckling or distorting.

Since the cover plate 6i) is closely, yet slidably, received in the peripheral rail structure slots and, since the side and end rails are welded to the neighboring walls 44 and 46 with the continuous weld connection 57, a good leakage restricting arrangement is provided, so that the pressurized coolant is prevented from leaking around the cover.

While the invention has been shown in one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof.

We claim as our invention:

1. A nozzle blade structure for a hot elastic fluid utilizing machine, comprising a vane portion of generally air foil cross-section,

a base portion connected to one end of said vane portion, and

a plenum chamber structure connected to the opposite end of said vane portion,

said chamber structure having wall structure integral with said vane portion,

said wall structure having peripheral marginal portions defining an open ended cavity,

said marginal portions being formed with shoulders,

a cover plate having the same shape as the open end of the cavity,

a rail structure supported by said shoulders about its periphery, said rail structure having a slot disposed in its inner periphery and facing inwardly,

said cover plate having its peripheral marginal portions slidably received in said slot and held captive therein,

means including an aperture in said plate to admit pressurized coolant uid to said plenum chamber, and

means including passage structure in said vane portion disposed in communication with said plenum chamber for directing coolant fluid from said chamber through said vane portion to cool the latter.

2. The structure recited in claim 1, wherein the rail structure is integrally connected about its outer periphery to the marginal wall portions by a continuous weld connection in a susbtantially fluid flow restricting manner.

3. The structure recited in claim 1, wherein the marginal portions of the cover plate define a clearance space with the end of the slot to permit relative thermal expansion and contraction to occur without interference.

4. The structure recited in claim 1 and further including a second vane portion of generally air foil cross-section integrally connected to the plenum chamber and the base portion, and

means including second passage structure in said second vane portion disposed in communication with the plenum chamber for directing a portion of the c001- ant fluid from the plenum chamber through said second vane portion to cool the latter.

5. The structure recited in claim 4, wherein the plenum chamber structure is quadrilateral in crosssection and of arcuate shape in longitudinal section,

the rail structure includes a pair of rectilinear cross rails and a pair of arcuate longitudinal rails, and

the cover plate is of arcuate longitudinal cross-section.

References Cited UNITED STATES PATENTS Scalzo 415-115 Kercher 415-115 Waugh et al. 415-115 Allen et al 4l5e-115 Payne et al 415-115 Rainbow et al 415*1l5 U.S. Cl. XLR.

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