Turbine airfoil with an internal cooling system having trip strips with reduced pressure drop

A turbine airfoil usable in a turbine engine and having at least one cooling system with an efficient trip strip is disclosed At least a portion of the cooling system may include one or more cooling channels having one or more trip strips protruding from an inner surface forming the cooling channel. The trip strip may have improved operating characteristics including enhanced heat transfer capabilities and a substantial reduction in pressure drop typically associated with conventional trip strips In at least one embodiment, the trip strip may have a cross-sectional area with a first section of an upstream surface of the trip strip being positioned nonparallel and nonorthogonal to a surface forming the cooling system channel extending upstream from the at least one trip strip and a concave shaped downstream surface of the at least one trip strip that enables separated flow to reattach to the cooling fluid flow.

FIELD OF THE INVENTION

This invention is directed generally to turbine airfoils, and more particularly to hollow turbine airfoils having cooling channels for passing fluids, such as air, to cool the airfoils

BACKGROUND

Typically, gas turbine engines include a compressor for compressing air, a combustor for mixing the compressed air with fuel and igniting the mixture, and a turbine blade assembly for producing power. Combustors often operate at high temperatures that may exceed 2,500 degrees Fahrenheit Typical turbine combustor configurations expose turbine vane and blade assemblies to these high temperatures. As a result, turbine vanes and blades must be made of materials capable of withstanding such high temperatures. In addition, turbine vanes and blades often contain cooling systems for prolonging the life of the vanes and blades and reducing the likelihood of failure as a result of excessive temperatures

Typically, turbine blades are formed from an elongated portion forming a blade having one end configured to be coupled to a turbine blade carrier and an opposite end configured to form a blade tip. The blade is ordinarily composed of a leading edge, a trailing edge, a suction side, and a pressure side. The inner aspects of most turbine blades typically contain an intricate maze of cooling circuits forming a cooling system. The cooling circuits in the blades receive air from the compressor of the turbine engine and pass the air through the ends of the blade adapted to be coupled to the blade carrier. The cooling circuits often include multiple flow paths that are designed to maintain all aspects of the turbine blade at a relatively uniform temperature. At least some of the air passing through these cooling circuits is exhausted through orifices in the leading edge, trailing edge, suction side, and pressure side of the blade Cooling fluids pass over trip strips, which increase the heat transfer of the cooling system Most trip strips are formed from generally square or rectangular cross-sections, as shown inFIG. 1. Such configurations increase the cooling capacity of a cooling system but have inherent limitations, as shown by the loss regions5shown inFIG. 1. While advances have been made in the cooling systems in turbine blades, a need still exists for a turbine blade having increased cooling efficiency for dissipating heat and passing a sufficient amount of cooling air through the blade

SUMMARY OF THE INVENTION

A turbine airfoil usable in a turbine engine and having at least one cooling system with an efficient trip strip is disclosed. At least a portion of the cooling system may include one or more cooling channels having one or more trip strips protruding from an inner surface forming the cooling channel. The trip strip may have improved operating characteristics including enhanced heat transfer capabilities and a substantial reduction in pressure drop typically associated with conventional trip strips. In at least one embodiment, the trip strip may have a cross-sectional area with a first section of an upstream surface of the trip strip being positioned nonparallel and nonorthogonal to a surface forming the cooling system channel extending upstream from the at least one trip strip and a concave shaped downstream surface of the at least one trip strip that enables separated flow to reattach to the cooling fluid flow.

In at least one embodiment, a turbine airfoil may be formed from a generally elongated hollow airfoil formed from an outer wall, and having a leading edge, a trailing edge, a pressure side, a suction side, a root at a first end of the airfoil and a tip at a second end opposite to the first end, and a cooling system positioned within interior aspects of the generally elongated hollow airfoil. The cooling system may include one or more trip strips protruding from an inner surface defining a channel of the cooling system. The trip strip may be formed from a generally elongated body and the trip strip may have a cross-sectional area with at least a first section of an upstream surface of the trip strip being positioned nonparallel and nonorthogonal to a surface forming the cooling system channel extending upstream from the trip strip and a concave shaped downstream surface of the trip strip

A downstream surface of the trip strip may be formed from a concave surface forming generally a quarter circle. An upstreammost point of the downstream surface of the trip strip may be positioned upstream from an intersection of the downstream surface at a top surface of the trip strip An upstreammost point of the downstream surface of the trip strip may be positioned upstream from an intersection of the downstream surface and the inner surface defining the channel of the cooling system. The trip strip include a nonlinear top surface. In at least one embodiment, the nonlinear top surface has a convex shaped outer surface The nonlinear top surface have a leading edge that is positioned closer to the inner surface defining the channel of the cooling system than a trailing edge of the nonlinear top surface

The upstream surface of the trip strip may include a second section that is nonparallel and nonothogonal with the first section. The second section of the upstream surface may be positioned generally orthogonal to the surface forming the cooling system channel extending upstream from the trip strip. The second section of the upstream surface may be positioned generally orthogonal to a longitudinal axis of the channel of the cooling system in which the trip strip resides. The trip strip may have a consistent cross-sectional area throughout an entire length of the at least one trip strip

During use, cooling fluid is passed into the cooling system, including the cooling channel At least a portion of the cooling fluid contacts the trip strip In particular, at least a portion of the cooling fluid contacts the first section of the upstream surface, where the cooling fluid is directed upwardly at an angle that is nonparallel and nonorthogonal to the inner surface forming the cooling channel. The cooling fluid then strikes the second section of the upstream surface, which causes the cooling fluid to be directed at an even steeper angle away from the inner surface. The cooling fluid then flows past the second section and along the top surface. While passing the first section, the second section and the top surface, heat is being passed from the trip strip to the cooling fluid via convection The cooling fluid flows past the top surface and then a portion of the cooling fluids forms a circular flow of cooling fluids that flow against the concave downstream surface The formation of eddies on the downstream surface is mitigated by accommodating the primary vortex or eddie and ensuring higher velocity and thus higher heat transfer on the downstream surface as compared to the low velocity recirculation in conventional square or rectangle cross section trip strips. This uniquely shaped trip strip cross-sectional area creates higher internal convective cooling potential for the turbine blade cooling channel, thus generating a high rate of internal convective heat transfer and efficient overall cooling system performance. This performance equates to a reduction in cooling demand and better turbine engine performance. An advantage of the turbine airfoil cooling system is that the system is configured to cool cooling channels and because of its configuration is particularly well suited to cool cooling channels in industrial gas turbine engines.

Another advantage of the cooling system is that the configuration of the cross-sectional area of the trip strip reduces the amount of pressure drop typically associated with trip strips

DETAILED DESCRIPTION OF THE INVENTION

As shown inFIGS. 2-5, a turbine airfoil10usable in a turbine engine12and having at least one cooling system14with an efficient trip strip16is disclosed. At least a portion of the cooling system14may include one or more cooling channels18having one or more trip strips16protruding from an inner surface20forming the cooling channel18, as shown inFIGS. 3 and 4. The trip strip16may have improved operating characteristics including enhanced heat transfer capabilities and a substantial reduction in pressure drop typically associated with conventional trip strips. In at least one embodiment, as shown inFIG. 5, the trip strip16may have a cross-sectional area22with a first section24of an upstream surface26of the trip strip16being positioned nonparallel and nonorthogonal to a surface20forming the cooling system channel18extending upstream from the trip strip16and a concave shaped downstream surface28of the trip strip16that enables separated flow to reattach to the cooling fluid flow

In at least one embodiment, as shown inFIGS. 2 and 4, the turbine airfoil10may be formed from a generally elongated hollow airfoil30formed from an outer wall32, and having a leading edge34, a trailing edge36, a pressure side38, a suction side40, a root42at a first end44of the airfoil30and a tip46at a second end48opposite to the first end44, and a cooling system14positioned within interior aspects of the generally elongated hollow airfoil30The turbine airfoil10may include all of the these components or less than each of these components listed In addition, the turbine airfoil10may include fewer than each of these components.

The cooling system14may include one or more trip strips16protruding from an inner surface20defining a channel18of the cooling system14The trip strip16may be formed from a generally elongated body50. The trip strip16, as shown inFIG. 5, may have a cross-sectional area with at least a first section24of an upstream surface26of the trip strip16being positioned nonparallel and nonorthogonal to a surface20forming the cooling system channel18extending upstream from the trip strip16and a concave shaped downstream surface28of the trip strip16. The downstream surface28of the trip strip16may be formed from a concave surface forming generally a quarter circle. In other embodiments, the downstream surface28is not limited to being a quarter circle but may be formed from other sized partial circles as well, such as, but not limited to, between 1/16 of a circle and ½ of a circle. An upstreammost point52of the downstream surface28of the trip strip16may be positioned upstream from an intersection54of the downstream surface28at a top surface56of the trip strip16The upstreammost point52of the downstream surface28of the trip strip16may be positioned upstream from the intersection58of the downstream surface28and the inner surface20defining the channel18of the cooling system14,

In at least one embodiment, the trip strip16may include a nonlinear top surface56. The nonlinear top surface56may have a convex shaped outer surface

The nonlinear top surface56may have a leading edge60that is positioned closer to the inner surface20defining the channel18of the cooling system14than a trailing edge62of the nonlinear top surface56.

The upstream surface26of the trip strip16may include a second section64that is nonparallel and nonothogonal with the first section24. The second section64of the upstream surface26may be positioned generally orthogonal to the surface20forming the cooling system channel18extending upstream from the trip strip16The second section64of the upstream surface26may be positioned generally orthogonal to a longitudinal axis66of the channel18of the cooling system14in which the trip strip16resides.

In at least one embodiment, the trip strip16may have a consistent cross-sectional area throughout an entire length of the trip strip16. In another embodiment, the shape of the cross-sectional area of the trip strip16may vary throughout its length, especially when the trip strip16is nonorthogonal to the flow of cooling fluids over the trip strip16, such as when the trip strip16is nonorthogonal to a longitudinal axis of the cooling channel18The trip strip16may extend from a first sidewall68to a second sidewall70forming the cooling channel18. In another embodiment, the trip strip16may extend between the first and second sidewalls68,70but only contact one of the sidewalls68,70or stop short of contacting either sidewalls68,70. In yet another embodiment, the trip strip16may be positioned generally orthogonal to the longitudinal axis66of the cooling channel18The trip strip16may also be positioned nonparallel and nonorthogonal to the longitudinal axis66of the cooling channel18The height, e, of the trip strip16can change as a function of the relative distance between upstream and downstream trip strips16, the pitch p. A consistent p/e ratio may be maintained for a cooling channel18or the p/e ratio may be varied along a portion of or along an entire length of the cooling channel18.

During use, cooling fluid is passed into the cooling system14, including the cooling channel18. At least a portion of the cooling fluid contacts the trip strip16. In particular, at least a portion of the cooling fluid contacts the first section24of the upstream surface26, where the cooling fluid is directed upwardly at an angle that is nonparallel and nonorthogonal to the inner surface26forming the cooling channel18. The cooling fluid then strikes the second section64of the upstream surface26, which causes the cooling fluid to be directed at an even steeper angle away from the inner surface26The cooling fluid then flows past the second section64and along the top surface56. While passing the first section24, the second section64and the top surface56, heat is being passed from the trip strip16to the cooling fluid via convection. The cooling fluid flows past the top surface56and then a portion of the cooling fluids forms a circular flow of cooling fluids that flow against the concave downstream surface28The flow of cooling fluids flows against the concave downstream surface28without formation of any eddies which would reduce the heat transfer and therefore negatively affect the heat transfer efficiency of the trip strip16.

This uniquely shaped trip strip cross-sectional area creates higher internal convective cooling potential for the turbine blade cooling channel18, thus generating a high rate of internal convective heat transfer and efficient overall cooling system performance. This performance equates to a reduction in cooling demand and better turbine engine performance.