Patent Application
20100226789
This invention is directed generally to turbine blades, and more particularly to cooling systems in hollow turbine blades.
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 blade assemblies to these high temperatures. As a result, turbine blades must be made of materials capable of withstanding such high temperatures. In addition, turbine blades often contain cooling systems for prolonging the life of the blades and reducing the likelihood of failure as a result of excessive temperatures.
Typically, turbine blades are formed from a root portion at one end and an elongated portion forming a blade that extends outwardly from a platform coupled to the root portion at an opposite end of the turbine blade. The blade is ordinarily composed of a tip opposite the root section, a leading edge, and a trailing edge. The inner aspects of most turbine blades typically contain an intricate maze of cooling channels forming a cooling system. The cooling channels in the blades receive air from the compressor of the turbine engine and pass the air through the blade. The cooling channels often include multiple flow paths that are designed to maintain all aspects of the turbine blade at a relatively uniform temperature. However, centrifugal forces and air flow at boundary layers often prevent some areas of the turbine blade from being adequately cooled, which results in the formation of localized hot spots. Localized hot spots, depending on their location, can reduce the useful life of a turbine blade and can damage a turbine blade to an extent necessitating replacement of the blade. Often times, localized hot spots form in the tip section of turbine blades. Thus, a need exists for removing excessive heat in the tip section of turbine blades.
This invention relates to a turbine blade cooling system for turbine blades used in turbine engines. In particular, the turbine blade cooling system includes a cavity positioned between two or more walls forming a housing of the turbine blade. The cooling system may be formed from first and second cooling channels positioned in internal aspects of the blade and in communication with first and second tip cooling channels, respectively. The first and second tip cooling channels provide cooling to the tip aspects of the turbine blade to prevent temperature overages and blade damage.
The turbine blade may be formed from a generally elongated blade having a leading edge, a trailing edge, a tip wall at a first end, a root coupled to the blade at an end generally opposite the first end for supporting the blade and for coupling the blade to a disc, and at least one cavity forming a cooling system in the blade. The cooling system may be formed from first and second cooling channels extending throughout internal aspects of the generally elongated blade, wherein the first cooling channel extends throughout a first section between the leading edge and a midchord region and the second cooling channel extends throughout a second section between the midchord region and the trailing edge. A first tip cooling channel may be in communication with the first cooling channel and may extend along the tip from proximate to the leading edge to a position proximate to the trailing edge. A second tip cooling channel may be in communication with the second cooling channel, positioned at least partially radially inward of the first tip cooling channel and may extend generally along the tip from about the midchord region to a position proximate to the trailing edge.
In one embodiment, the first and second cooling channels may be counterflow serpentine cooling channels. The first cooling channel may be a counterflow serpentine cooling channel flowing from the midchord region towards the leading edge and may include an inlet positioned proximate to the root and an outlet at the tip that is in communication with the first tip cooling channel. The second cooling channel may be a counterflow serpentine cooling channel flowing from the trailing edge towards the midchord region and may include an inlet proximate to the root and an outlet at the tip that is in communication with the second tip cooling channel. The first and second cooling channels may include trip strips or pin fins, or both.
The first tip cooling channel may include a first suction side cooling channel that extends from the leading edge to the trailing edge generally along the suction side of the airfoil and a first pressure side cooling channel that extends from the leading edge to the trailing edge generally along the pressure side of the airfoil. The first suction side and pressure side cooling channels may include a plurality of micro pin fins. A plurality of orifices may extend between the first suction side cooling channel and the suction side, and a plurality of orifices may extend between the first pressure side cooling channel and the pressure side. In one embodiment, the first suction side cooling channel and the first pressure side cooling channel may merge at the trailing edge to form a single channel.
The second tip cooling channel may have a cross-sectional area at the inlet that is greater than a cross-sectional area at the trailing edge. The second tip cooling channel may also include a plurality of micro pin fins and a plurality of orifices extending between the second tip cooling channel and the suction side. The second tip cooling channel may also include a plurality of orifices extending between the second tip cooling channel and the pressure side. The orifices proximate to the suction side may be offset chordwise from the orifices on the pressure side.
An advantage of this invention is that the turbine blade cooling system presents a unique turbine blade tip section peripheral cooling system in conjunction with the cooling supply serpentine flow circuitry for the turbine airfoil cooling that greatly increase serpentine flow channel performance, which results in the reduction of airfoil metal temperature as well as reduction of cooling flow requirements and improved turbine efficiency.
Another advantage of this invention is that the tip cooling system can be used in a blade cooling design to optimize the Mach number of the serpentine channel and for use with industrial turbine engines that have thick or low conductivity TBC with reduced cooling flow.
Yet another advantage of this invention is that the dual serpentine cooling channels increase the Mach number in the last legs of the cooling channels, which increase the through flow velocity of the cooling fluids and increase the cooling side internal heat transfer coefficient.
Another advantage of this invention is that the forward flowing cooling channels in cooperation with the tip cooling channels, maximize the cooling fluid potential, the use of the tip cooling channels and tailor the airfoil external heat load.
Still another advantage of this invention is that the cooling fluids are used as internal cooling fluids and then to form external protective film layers.
These and other embodiments are described in more detail below.
The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the presently disclosed invention and, together with the description, disclose the principles of the invention.
As shown in
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In at least one embodiment, as shown in
The first cooling channel 18 may include pin fins 62 extending between an internal surface of a wall forming a pressure side 64 and an internal surface of a wall forming a suction side 66 opposite to the pressure side 64. The pin fins 62 may be positioned in the midpoint of the channel created by the first cooling channel 18 or in other appropriate positions. The pin fins 62 may have any appropriately shaped cross-sectional area. In one embodiment, the pin fins 62 may have generally cylindrically shaped cross-sections. The first cooling channel 18 may also include trip strips 68 protruding from the internal walls forming the pressure side 64 or suction side 66, or both. The trip strips 68 may protrude generally orthogonally from the internal surface a sufficient distance to create turbulence in the fluid flow to increase the cooling efficiency. The trip strips 68 may also be positioned nonparallel and nonothrogonal relative to the direction of fluid flow.
The second cooling channel 20 may include an inlet 70 proximate to the root 36. The second cooling channel 20 may have a counterflow configuration such that the inlet 70 is positioned closer to the trailing edge 30 than an outlet 72. The second cooling channel 20 may extend throughout a second section 86 between the trailing edge 30 and a midchord region 42. The second cooling channel 20 may extend from an inlet radially outwardly toward the tip 32. A first turn 74 may couple a first pass 76 directed radially outwardly with a second pass 78 directed radially inwardly. A second turn 80 may couple the second pass 78 with a third pass 82 directed radially outward that is in communication with the outlet 72. The second turn 80 may be formed from a cover plate 84 at the radially inwardmost portion of the root 36 and adjacent ribs 60.
The second cooling channel 20 may include pin fins 62 extending between the internal surface forming the pressure side 64 and the internal surface forming the suction side 66. The pin fins 62 may be positioned in the midpoint of the channel created by the second cooling channel 20 or in other appropriate positions. The pin fins 62 may be configured as discussed in regards to the first cooling channel 18. The second cooling channel 20 may also include trip strips 68 protruding from the internal walls forming the pressure side 64 or suction side 66, or both. The trip strips 68 may protrude generally orthogonally from the internal surface a sufficient distance to create turbulence in the fluid flow to increase the cooling efficiency. The trip strips 68 may also be positioned nonparallel and nonothrogonal relative to the direction of fluid flow.
The first tip cooling channel 22, as shown in
The second tip cooling channel 24 may have a cross-sectional area at the inlet 96 that is greater than a cross-sectional area at the trailing edge 30, as shown in
During operation, cooling fluids, which may be, but are not limited to, air, flow into the cooling system 10 from a cooling supply system upstream of the root 36 in the cooling system. The cooling fluids flow into the inlets 44 and 70 and into the first and second cooling channels 18, 20, respectively. The flow of the cooling fluids is generally back and forth from the root 36 to the tip 32 and generally from a direction from the trailing edge 30 toward the leading edge 28, which is referred to as counterflow. Such counterflow allows the cooling fluids to be preheated in areas of low thermal stress and be used in areas of high thermal stress after being preheated to prevent the formation of large thermal gradients, which can cause blade damage. The cooling fluids may flow past pin fins 62 and trip strips 68, which increase the thermal efficiency of the cooling system 10. The cooling fluids may be exhausted into the first and second tip cooling channels 22, 24.
In operation, the majority of the tip section cooling fluids are not discharged from the turbine first and second serpentine cooling channels 18, 20 when the fluids reach the outlets 46, 72. As a result, the majority of the tip cooling air is channeled through the serpentine flow channels 18, 20 to enhance the serpentine flow channels 18, 20 internal through flow Mach number, which equates to a higher internal heat transfer coefficient for the channels 18, 20, and greatly increases the internal cooling performance of the serpentine cooling channels 18, 20.
The cooling fluids may then be exhausted into the first and second tip cooling channels 22, 24. The cooling fluids may flow through the channels 22, 24 and impinge on the micro pin fins 92 positioned therein. The channels 22, 24 run generally along the backside of the squealer tip 32, thereby providing backside cooling to the tip 32. The cooling fluids may be exhausted through orifices 94 to enhance formation of and to supplement a film cooling fluid layer. Cooling fluids may also be exhausted through orifices in the trailing edge 30.
The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of this invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of this invention.
