GB2111604A - Shell spar cooled airfoil using multiple spar cavities - Google Patents

Abstract

The airfoil (rotor or stator blade) comprises a hollow spar 12 partitioned into spanwise cavities 18a, 18b, 18c and an exterior shell 14 bonded to the spar. Substantially chordwise coolant passageways 16 are arranged between the shell and the spar to pass coolant from cavities designated as supply cavities 18a, 18c to cavities designated as exhaust cavities 18b; and the trailing edge 24 of the airfoil. The arrangement provides short, high velocity coolant passageways. <IMAGE>

Description

SPECIFICATION Shell spar cooled airfoil using multiple spar cavities The present invention relates generally to combustion turbine rotor and stator blades and vanes, and more particularly to an airfoil for a land-based combustion turbine rotor blade or vane having an improved arrangement for fluid cooling.

It is well established that improved operating efficiency and improved power output of a combustion turbine may be achieved through higher inlet operating temperatures. Inlet operating temperatures are limited, however, by the maximum temperature tolerable to the rotating turbine blades and stationary vanes. Also, as turbine blade and vane temperatures increase with increasing inlet gas temperature, the vulnerability of the blades to damage from the tension and stresses which normally accompany turbine operation also increases. Proper cooling of the blades and vanes permits an increase in inlet operating temperatures while keeping the turbine blade and vane temperatures below the maximum specified operating temperature for the material comprising the blade or vane.

There presently exist many arrangements for cooling a turbine blade or vane, including methods such as convection, film schemes, and transpiration schemes. Convention-cooled airfoils are preferable to film- and transpiration-cooled airfoils in many turbine applications because apertures in the airfoil surface can be avoided.

Surface apertures on the airfoils of turbines operating on heavy fuels may become blocked by deposits, rendering the airfoil cooling system ineffective. In most airfoil cooling arrangements, cooling air is drawn from a compressor section of the turbine and passed through independent channels within the turbine to reach the blades or vanes. In the case of turbine blades, cooling air drawn from the compressor section may typically pass through a channel along the turbine rotor to reach each of several turbine rotor discs. Each rotor disc may define a plurality of channels communicating cooling air to a plurality of blade roots secured within the periphery of each rotor disc. Cooling channels within each of the turbine blades communicate cooling air from the blade root throughout an airfoil portion of the blade.

Similar specialized arrangements typically communicate cooling air to the turbine stator vanes.

It is the goal of any turbine blade or vane cooling system to provide effective airfoil cooling while minimizing the cooling air flow required to accomplish this task. Air drawn from the compressor section for cooling purposes reduces the volume of air which eventually drives the turbine blades and thereby reduces the overall efficiency of the combustion turbine.

One technique for minimizing the cooling air flow is to utilize high cooling air velocity in the coolant passageways. High cooling air velocity, however, results in a high pressure loss per unit length of passageway. Because typical prior art convection-cooled airfoils are generally characterized by long coolant passageways and because the turbine supply pressure for the coolant passageways is limited by the turbine aerodynamic design, the coolant passageways of convection-cooled airfoils are typically limited to low cooling air velocities. Adequate cooling under a limited supply pressure is attained by increased coolant passageway cross-sectional area and increased cooling air flow.

The current trend toward increasing the inlet operating temperatures of combustion turbines has made it necessary to improve the cooling efficiency of cooled turbine blades and vanes. It appears, however, that prior art convection cooling arrangements for turbine blades and vanes do not adequately provide means for effectively increasing the efficiency of the airfoil cooling system.

The present invention provides a convection cooled airfoil arranged to overcome the coolant velocity limitation associated with prior art convection-cooled airfoils. In typical prior art combustion turbines which rely on convection cooling arrangements to cool the airfoils of rotor blades and stator vanes, the airfoil generally is provided with a plurality of long capillary coolant passageways arranged to cool substantially the entire exterior surface of the airfoil. For example, cooling air may be delivered through one or more passageways in a blade root to reach a plurality of spanwise capillary passageways extending to the blade tip, where the cooling air is exhausted.

Alternatively, cooling air may be delivered through one or more channels to the interior of a hollow airfoil from which the cooling air may, for example, pass through a plurality of apertures spanning the leading edge of the blade or vane to reach a plurality of chordwise capillary passageways spanning from the leading edge to the trailing edge of the airfoil. Both of the above arrangements provide adequate cooling under a limited range of airfoil operating temperatures.

Moreover, because the nature of the cooling arrangement relies on convection as opposed to transpiration or film to achieve the cooling effect, it is unnecessary to include apertures in the exterior surface of the airfoil, which apertures might become blocked by deposits and thereby render the airfoil cooling system ineffective.

The long spanwise or chordwise passageways associated with typical prior art convection-cooled airfoils limit cooling air velocity which in turn limits the efficiency and the effectiveness of the airfoil cooling system.

The present invention in its broad form comprsies a cooled, fluid-directing airfoil member for a combustion turbine, stator or rotor blade, said airfoil member having a leading edge, a trailing edge, and a tip portion, and comprising: a hollow, airfoil-shaped spar defining spaced concave and convex sides and having at least two span-wise cavities constituted by a supply cavity and an exhaust cavity; means for conveying to at least said supply cavity a supply of cooling air; means for venting from at least said exhaust cavity an exhaust of said cooling air which has been utilized to cool said airfoil member; a metallic shell substantially shrouding and bonded to said spaced convex and concave sides of the spar; and passageways extending substantially chordwise in spaces between said shell and said spar, said passageways arranged to communicate cooling air from said supply cavity to said exhaust cavity and through the trailing edge of said airfoil member.

In a preferred embodiment described herein, an airfoil for a combustion turbine rotor blade or stator vane having an improved structure for airfoil cooling comprises a hollow strut partitioned into at least three span-wise cavities and a metallic shell of one or more layers bonded to and enclosing the strut. The shell and the strut define therebetween substantially chordwise coolant passageways which conduct cooling air between adjacent cavities of the strut. Adjacent cavities are alternately designated supply cavities and exhaust cavities, supply cavities being arranged to receive a supply of cooling air from a compressor section of the turbine and exhaust cavities being arranged to vent cooling air to a turbine exhaust path.The arrangement of relatively short coolant passageways between adjacent cavities in the strut permits effective high velocity, convection cooling of the airfoil while minimizing the air flow utilized by the airfoil cooling system. As a result, turbine airfoils may be effectively cooled by convection without adversely affecting overall combustion turbine operating efficiency.

A more detailed understanding of the invention may be had from the following description of a preferred embodiment, given by way of example and to be studied in conjunction with the accompanying drawings wherein: Figure 1 depicts in cross-section an airfoil for a combustion turbine rotor blade or vane structured according to an embodiment of the invention; Figure 2 depicts in cross-section the wall of the airfoil shown in Figure 1; Figure 3 shows a combustion turbine rotor blade and air flow patterns therein; Figure 4 depicts in elevation a combustion turbine stator vane arranged using the principles of the invention; Figure 5 depicts in elevation an alternative embodiment of the stator vane depicted in Figure 4; and Figure 6 depicts a sectional view of a second alternative embodiment of the stator vane of Figure 4.

Figure 1 depicts in cross-section an airfoil from a land-based combustion turbine arranged using the principles of the invention. The airfoil 10 comprises a frame-like, airfoil-shaped strut, or spar, 12 to which is bonded one or more layers of sheet metal to form a shell 14 which encloses the spar 12. Coolant passageways 16, arranged as further described below, are formed.by the conjunction of the spar 12 and the shell 14. The passageways 1 6 may be defined by channels in the shell 14, as shown in Figure 2, or channels in the spar 12 (not shown), or a combination of both (not shown).

The spar 1 2 defines a plurality of cavities 1 8.

Figure 1 depicts the preferred embodiment of the invention, having three cavities 18a, b, c. The fore cavity 18a and the aft cavity 1 sic are utilized as supply cavities. The supply cavities are pressurized by a flow of cooling air from a compressor section of the turbine. Cooling air within the supply cavities is delivered to a plurality of generally chordwise coolant passageways through a plurality of apertures in the spar 12. The apertures are arranged in one or more dual columns 30, 36, 38 spanning the length of the airfoil 10.

Each aperture in the spar 12 of the supply cavities 18a, c delivers a flow of coolant air to one or more passageways 1 6 which terminate at either an aperture in the spar 12 within an exhaust cavity 1 8b or at the trailing edge 24 of the airfoil.

Hence, the exhaust cavity 1 8b receives a flow of cooling air directed through passageways 1 6 .from the supply cavities and vents this cooling air through an opening at the blade tip.

In the embodiment of the invention depicted in Figure 1, there are six distinct paths which the cooling air may follow through the passageways 1 6. For example, cooling air which enters an aperture of the column of apertures depicted at reference character 30a, passes through a passageway which chordwise traverses the leading edge of the airfoil 10 and exists through a corresponding aperture of the column of apertures depicted by reference character 32a.Similarly, coolant air which enters an aperture of column 30b of supply cavity 18a chordwise traverses a passageway 1 6 along the convex side of the airfoil 10 to exit through a corresponding aperture of column 34a into exhaust cavity 18b. The other four potential cooling air flow paths originate in the aft supply cavity 1 sic at one of the four columns of apertures depicted by reference characters 36a, 36b, 38a, and 38b. These four potential paths terminate in the exhaust cavity 1 8b at column 34b, at the trailing edge 24 of the airfoil 10, in the exhaust cavity at 32b, and at the trailing edge of the airfoil 10, respectively. Figure 3 provides an overview of the cavity and air flow arrangement in a combustion turbine rotor blade structured according to the principles of the invention.

The multiple cavity arrangement of the airfoil 10 provides a convection-cooled airfoil not subject to the severe cooling velocity limitations associated with the long coolant passageways of typical prior art convection-cooled airfoils. The present invention utilizes a plurality of cavities to direct the flow of cooling air through a plurality of short passageways at increased velocity to convectively cool substantially the entire exterior surface of the airfoil 10. The air flow utilized is thereby reduced and the efficiency of overall turbine operation is improved.

Although the embodiment disclosed herein utilizes generally chordwise coolant passageways between apertures in the spar 12, it is envisioned that the passageways may be arranged in any combination of chordwise and spanwise pattern so as to maximize the efficient convective cooling of the airfoil 10. It should also be evident from the description herein that the airfoil 10 may be structured with any odd number of cavities greater than the three cavities depicted in Figure 1.

Increasing the number of cavities utilized correspondingly shortens the length of coolant passageways which communicate cooling air from one cavity to an adjacent cavity. For hotter applications, therefore, it may be appropriate to utilize more than three cavities. For embodiments utilizing five, seven or more cavities, the fore and aft cavities should preferably be maintained as supply cavities with succeeding adjacent cavities therebetween alternately functioning as exhaust and supply cavities.

Figure 4 shows in section a combustion turbine stator vane 50 structured to cooperate with the rotor blade constructed using the principles of the invention. Typically, the stator vane 50 is supported within the turbine casing (not shown) between an inner arcuate shroud 52 and an outer arcuate shroud 54. In the preferred embodiment, cooling air 51 is delivered to the fore and aft supply cavities 18a, 18e by coolant supply channels (not shown) at the outer shroud 54, which channels are in flow communication with the compressor section (not shown) of the combustion turbine. Cooling air is vented from the exhaust cavity 18b through an exhaust port 58 connected to a low pressure point downstream.

Although not shown in Figure 4, cooling air may also be exhausted through the trailing edge of the vane 50, consistent with the structure described according to Figure 1.

Figure 5 depicts in elevation an alternative embodiment of a combustion turbine stator vane 70 structured on the same lines as the embodiment of Figure 4. In this embodiment, cooling air 71 is supplied to the fore 18a and aft 1 sic cavities of the vane 70 in the same manner as that for the vane 50 of Figure 4. Cooling air is vented, however, through an exhaust aperture 72 in the inner shroud 52. The exhaust aperture 72 is positioned downstream of a static seal 74, which seals the space upsteam of the vane 70 from the space downstream so that exhausted coolant air flows into the exhaust path of hot motive gases driving the turbine.

Figure 6 shows a cross-sectional view of a second alternative embodiment of a combustion turbine stator vane 80 structured according to the principles of the invention. The vane 80 differs from prior embodiments in the manner of venting exhaust cooling air from the exhaust cavity 1 8b.

The vane 80 includes cooling air exhaust apertures 82 through the shell 14 and the spar 1 2 arranged to vent cooling air on the convex side of the vane 80. Experimentation has revealed that there is little propensity for surface apertures on the convex side of the blade to become blocked, even during heavy oil fuel operation. The preferred arrangement of the apertures 82 is in dual, spanwise columns as shown in Figure 6; however, any arrangement providing adequate exhaust flow may be utilized.

Claims (13)

1. A cooled, fluid-directing airfoil member for a combustion turbine, stator or rotor blade, said airfoil member having a leading edge, a trailing edge, and a tip portion, and comprising: a hollow, airfoil-shaped spar defining spaced concave and convex sides and having at least two span-wise cavities constituted by a supply cavity and an exhaust cavity; means for conveying to at least said supply cavity a supply of cooling air; means for venting from at least said exhaust cavity an exhaust of said cooling air which has been utilized to cool said airfoil member; a metallic shell substantially shrouding and bonded to said spaced convex and concave sides of the spar; and passageways extending substantially chordwise in spaces between said shell and said spar, said passageways arranged to communicate cooling air from said suppty cavity to said exhaust cavity and through the trailing edge of said airfoil member.

2. A cooled, fluid-directing airfoil member as in claim 1 wherein said spar defines at least three spanwise cavities.

3. A cooled, fluid-directing airfoil member according to claim 2 wherein the spanwise cavities of said spar are defined by at least two spanwise partitions attaching and extending generally normal to the sides of said spar.

4. A cooled, fluid-directing airfoil member according to claim 2 wherein said spar is in the fom of a strut having an odd number of cavities.

5. A cooled, fluid-directing airfoil member according to claim 4 wherein the cavities of said spar nearest to the leading edge and the trailing edge of said member are supply cavities and succeeding adjacent cavities therebetween are exhaust cavities and supply cavities alternately.

6. A cooled, fluid-directing airfoil member according to claim 5 wherein at least some of the passageways defined by said shell and said spar connect each of the supply cavities to an adjacent exhaust cavity.

7. A cooled, fluid-directing airfoil member according to claim 6 wherein at least some of the passageways defined by said shell and said spar extend spanwise and chordwise between supply cavities and exhaust cavities.

8. A cooled, fluid-directing airfoil member according to claim 6 wherein the passageways defined by said shell and said spar are formed of channels in said shell.

9. A cooled, fluid-directing airfoil member according to claim 6 wherein the passageways defined by said shell and said spar are formed of channels in said spar.

10. A cooled, fluid-directing airfoil member according to claim 6 wherein the passageways defined by said shell and said spar are formed of a combination of channels in said shell and channels in said spar.

11. A cooled fluid-directing airfoil member according to claim 6 wherein said shell comprises at least one layer of sheet metal.

12. A cooled, fluid-directing airfoil member according to claim 6 wherein said venting means comprises an opening at the tip portion of said airfoil member conveying cooling air from said exhaust cavities to the exterior of said airfoil member.

13. A cooled, fluid-directing airfoil member according to claim 6 wherein said venting means comprises a plurality of apertures through said spar and said shell on the convex side of said spar.