Turbine blade with triple pass serpentine cooling

A turbine rotor blade with a dual triple pass serpentine flow cooling circuit in which a first triple pass serpentine circuit flows along the pressure side wall and the second triple pass serpentine circuit flows along the suction side wall to provide near wall cooling to the two walls. The legs of the serpentine flow cooling circuits have slanted ribs that form diamond shaped mixing chambers such that a criss-cross flow path for the cooling air is formed. In one embodiment, the last leg of the first serpentine circuit provides cooling to the leading edge region with showerhead film holes while the last leg of the second serpentine provides cooling to the trailing edge region with a row of exit holes. In other embodiments, the two serpentine circuits flow in a forward or a rearward direction with two trailing edge cooling channels arranged in the trailing edge and with a separate leading edge cooling supply channel to provide cooling air form the leading edge region.

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CROSS-REFERENCE TO RELATED APPLICATIONS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a gas turbine engine, and more specifically to an air cooled turbine rotor blade in a gas turbine engine.

In a gas turbine engine, such as a large frame heavy-duty industrial gas turbine (IGT) engine, a hot gas stream generated in a combustor is passed through a turbine to produce mechanical work. The turbine includes one or more rows or stages of stator vanes and rotor blades that react with the hot gas stream in a progressively decreasing temperature. The efficiency of the turbine—and therefore the engine—can be increased by passing a higher temperature gas stream into the turbine. However, the turbine inlet temperature is limited to the material properties of the turbine, especially the first stage vanes and blades, and an amount of cooling capability for these first stage airfoils.

The first stage rotor blade and stator vanes are exposed to the highest gas stream temperatures, with the temperature gradually decreasing as the gas stream passes through the turbine stages. The first and second stage airfoils (blades and vanes) must be cooled by passing cooling air through internal cooling passages and discharging the cooling air through film cooling holes to provide a blanket layer of cooling air to protect the hot metal surface from the hot gas stream. In engines of the future, it is even anticipated that third stage airfoils will also require cooling such as to prevent erosion and limit creep.

In an industrial gas turbine (IGT) engine, the turbine is designed to withstand the highest turbine inlet temperature that can be operated while allowing for the turbine to run constantly under these conditions for long periods of time. Airfoil cooling is performed so that an airfoil mass average sectional metal temperature does not exceed a certain temperature in order to improve airfoil creep capability for a turbine rotor blade. Creep is when the blade stretches in length due to the high radial stress loads produced from the blade rotating while exposed to the high temperatures. As the metal temperature increases, the metal becomes weaker and can become over-stressed. The gap spacing between the blade tips and the outer shroud must be kept to a minimum to control blade tip leakage. When a blade creep occurs, the gap can become negative such that excessive rubbing will occur.

Prior art airfoil cooling makes use of a triple pass (3-pass) serpentine flow cooling circuit that includes a forward flowing triple pass serpentine circuit10and an aft flowing serpentine circuit20. The forward flowing triple pass serpentine circuit10includes a first leg11, a second leg12and a third leg13that is connected to the leading edge impingement channel or cavity15through a row of metering and impingement holes. The showerhead arrangement of film cooling holes (three film holes) and two gill holes (one of the P/S and another of the S/S) discharge film cooling air from the spent impingement cooling air in the L/E channel15. The forward flowing circuit10normally is designed in conjunction with leading edge backside impingement cooling plus a showerhead arrangement of film cooling holes with pressure side and suction side gill holes to provide cooling for the leading edge region of the blade.

The aft flowing serpentine flow circuit20is designed in conjunction with the airfoil trailing edge discharge cooling holes. This type of cooling flow circuit is called a dual triple pass serpentine “warm bridge” cooling design with three legs21-23and is shown inFIGS. 1 and 2. No film cooling holes are used along the middle section of the airfoil that discharges film cooling air from the serpentine flow cooling circuit. The “warm bridge” cooling circuit operates as follows. Cooling air flows into the forward flowing serpentine circuit10in a first leg11towards the blade tip, then turns into a second leg12and flows toward the root, and then flows into a third leg13toward the blade tip, where the third leg13is adjacent to the leading edge impingement cavity15so that cooling air is bled off through a row of metering and impingement holes to produce impingement cooling against the leading edge wall, in which the spent impingement cooling air then flows out through the showerhead film cooling holes. The aft end side of the blade is cooled with an aft flowing triple pass serpentine circuit20and flows through the three legs21-23in which the third leg23is located adjacent to the trailing edge region. The cooling air from the third leg23flows through trailing edge exit holes to cool the trailing edge region.

An alternative prior art cooling design to that ofFIGS. 1 and 2utilizes the dual triple pass serpentine flow circuits for a high operating gas temperature and is shown inFIGS. 3 and 4. TheFIGS. 3 and 4blade cooling circuit is called a “cold bridge” cooling design. In this “cold bridge” cooling circuit, the leading edge airfoil is cooled with a self-contained flow circuit31. The airfoil mid-chord section is cooled with a triple pass serpentine flow circuit32. The trailing edge region is cooled with a triple-pass forward flowing serpentine cooling circuit33that continues toward the mid-chord triple pass serpentine flow circuit32. However, the aft flow circuit is flowing in a forward direction instead of the aftward direction as in the “warm bridge” design ofFIGS. 1 and 2. Again, the aft flowing serpentine flow circuit is designed in conjunction with the airfoil trailing edge discharge cooling holes.FIG. 4shows a flow diagram for this “cold bridge” cooling circuit which has two forward flowing triple pass serpentine flow circuits32and33plus a leading edge cooling air supply channel31separate from the triple pass serpentine flow circuits that is used for cooling the leading edge region and discharging the film cooling air through the showerhead holes.

In both of these prior art blade serpentine flow cooling circuits, the internal cavities are constructed with internal ribs that extend across the channels and connect the airfoil pressure side and suction side walls. In most cases, the internal cooling cavities are at a low aspect ratio which is subject to high rotational effect on the cooling side heat transfer coefficient. In addition, the low aspect ratio cavity yields a very low internal cooling side convective area ratio to the airfoil hot gas external surface.

BRIEF SUMMARY OF THE INVENTION

A turbine blade for a gas turbine engine, especially for a large frame heavy-duty industrial gas turbine engine, with a multiple layer serpentine flow cooling circuit that optimizes the airfoil mass average sectional metal temperature to improve airfoil creep capability for the blade cooling design.

In a first embodiment, the blade includes a triple-pass forward flowing serpentine flow cooling circuit located on the pressure side wall that includes a leading edge impingement cavity connected to the third leg, and an aft flowing triple-pass serpentine flow cooling circuit located on the suction side wall that includes the third leg located along the trailing edge region to supply cooling air to trailing edge exit holes. The channels or legs of the serpentine circuits are formed with an arrangement of slanted ribs that form a criss-cross flow path for the cooling air.

In a second embodiment, the blade includes a separate leading edge cooling supply channels with a leading edge impingement cavity supplied by metering holes and connected to a showerhead arrangement of film cooling holes with gill holes. The pressure side wall is cooled by a triple-pass forward flowing serpentine circuit and the suction side wall is cooled by a separate triple-pass serpentine flow circuit, where both triple-pass serpentine circuits have first legs located along the trailing edge region and discharge cooling air out through the pressure side wall and the trailing edge of the blade. The serpentine flow channels also include slanted ribs that form a criss-cross flow path for the cooling air.

A third embodiment is similar to the second embodiment except that the two triple-pass serpentine circuits are aft flowing with the third legs located along the trailing edge region and discharging the cooling air out through the pressure side wall and the trailing edge of the blade. As in the other two embodiments, the serpentine channels are formed with an arrangement of slanted ribs that form a criss-cross flow path for the cooling air.

DETAILED DESCRIPTION OF THE INVENTION

The dual triple pass (3-pass) serpentine flow cooling circuit for the turbine rotor blade of the present invention is shown inFIG. 5for the first embodiment. The blade includes a first triple pass serpentine flow cooling circuit30that flows in a forward direction towards the leading edge and a second triple pass serpentine flow cooling circuit40that flows in a rearward (aftward) direction towards the trailing edge. The channels of the two serpentine flow circuits are formed by an arrangement of slanted robs on the P/S and S/S walls of each channel in which the two sets of slanted ribs form a criss-cross flow path for the cooling air.

The first serpentine circuit30includes a first leg31located adjacent to the trailing edge region and along the pressure side wall and a second leg32also along the pressure side wall. The third leg33is located adjacent to the leading edge region but extends from the pressure side wall to the suction side wall.

A showerhead arrangement of film cooling holes26along with gill holes27on the pressure side wall and suction side wall are all connected to a leading edge impingement channel28to discharge layers of film cooling air onto the external surface of the leading edge region. A row of metering and impingement holes29connect the third leg33to the impingement channel28.

The second triple pass serpentine circuit40includes a first leg41adjacent to the leading edge region and along the suction side wall, a second leg42also along the suction side wall and a third leg43located in the trailing edge region of the airfoil that extends across both walls of the airfoil. A row of trailing edge exit cooling holes46are connected to the third leg43.

A leading edge region of the airfoil is the region in which the impingement channel28and the third leg33is located. The mid-airfoil region is the region in which the first and second legs (31,32,41,42) of both triple pass serpentine circuits30and40are located. The trailing edge region is where the third leg43is located.

FIG. 6shows a flow diagram for the first embodiment dual triple pass serpentine circuit ofFIG. 5. Cooling air supplied to the first leg31of the forward flowing first serpentine circuit flows along the pressure side wall and then into the second leg32along the pressure side wall to provide near wall cooling to the pressure side wall in this region of the airfoil. The cooling air then flows into the third leg33to provide cooling for both pressure side and suction side walls and then through the row of metering holes29and into the impingement channel28to produce impingement cooling on the backside surface of the leading edge wall of the airfoil. The spent impingement cooling air then flows out through the rows of film cooling holes and gill holes arranged around the leading edge region. The third leg33also includes at least one tip hole to discharge some of the cooling air out through the blade tip as represented by the arrow inFIG. 6.

FIG. 6also shows cooling air supplied to the first leg41of the second serpentine circuit40that flows up and along the suction side wall to provide near wall cooling to this section, and then into the second leg42along the suction side wall, and then into the third leg43to provide near wall cooling to both side walls along this trailing edge region. From the third leg43, the cooling air is discharged through the row of trailing edge exit cooling holes46to provide cooling to the trailing edge region. The third leg43also includes a tip hole to discharge some of the cooling air through the blade tip in this region as represented by the arrow inFIG. 6.

A second embodiment of the dual triple pass serpentine flow cooling circuit is shown inFIG. 7in which tow forward flowing serpentine circuits are used. A first forward flowing serpentine circuit30is located along the pressure side wall and the second forward flowing serpentine40is located along the suction side wall. Both serpentine30and40include three legs31-33and41-43that are adjacent to one another and of the same chordwise length. All of the legs31-33and41-43include slanted ribs on both side walls of the channels that form a criss-cross flow path for the cooling air. In the second embodiment ofFIG. 7, the leading edge region is cooled with a separate cooling circuit that includes a leading edge region cooling supply channel24connected by a row of metering and impingement holes29to a leading edge impingement channel28that is then connected to the showerhead film cooling holes25and gill holes26. The leading edge region cooling circuit and the two triple-pass serpentine flow cooling circuits30and40are separate cooling circuits that are not connected to one another. One or more rows of film cooling air can be located on the PS or the S/S walls to discharge cooling air from a channel of the serpentine flow circuit to provide a layer of film cooling air to needed surfaces of the blade.

In the second embodiment ofFIG. 7, the row of trailing edge exit holes46is connected to the first leg41of the second serpentine40circuit located along the suction side wall. A row of pressure side film cooling holes is located along the trailing edge region and is connected to the first leg31of the first serpentine30located along the pressure side wall. A row of film cooling holes is located on the pressure side wall and is connected to the third leg33of the first serpentine circuit30. A row of film cooling holes is located on the suction side wall and is connected to the third leg43of the second serpentine circuit40.

A flow diagram of the cooling circuit ofFIG. 7is shown inFIG. 8and operates as follows. Cooling air is supplied to both serpentines30and40through the first legs31and41and flows upward toward the blade tip to cool the respective wall of the airfoil in this region. Some of the cooling air in the first leg31flows through the row of film cooling holes along the pressure side wall. Some of the cooling air in the first leg41flows through the trailing edge exit holes46to provide cooling for the trailing edge. Cooling air from the first leg31turns and flows into the second leg32to provide impingement cooling to the tip floor, and then flows into the third leg33where most of the cooling air flows through the film cooling holes on the pressure side wall with the remaining cooling air flowing through the tip cooling hole to provide cooling to the blade tip. The cooling air from the first leg41turns into the second leg and provide impingement cooling to the tip floor. The cooling air then flows into the third leg43where most is discharged through the film cooling holes on the suction side wall. The remaining cooling air flows through the tip hole to provide cooling to the blade tip.

A third embodiment is shown inFIG. 9and includes two aft flowing triple pass serpentine circuits50and60with the first serpentine circuit50located along the pressure side wall and the second serpentine circuit60located along the suction side wall. The first legs51and61are located adjacent to the leading edge region with the second legs52and62and the third legs53and63occupying the remaining portions of the airfoil and ending at the trailing edge region. The row of trailing edge exit holes26is connected to the third leg63of the second serpentine circuit60. The row of film cooling holes on the pressure side wall is connected to the third leg53of the first serpentine circuit50. As in theFIGS. 6 and 7embodiment, theFIG. 9embodiment includes a separate cooling circuit for the leading edge region with a leading edge cooling supply channel24connected by a row of metering holes29to the leading edge impingement channel28that is then connected to the showerhead arrangement of film cooling holes25and gill holes26along the pressure side and suction side walls. Both of the third legs53and63are connected to tip cooling holes to discharge cooling air through the tip floor. All of the legs51-53and61-63of the two serpentine flow circuits are formed by an arrangement of slanted robs on the P/S and S/S walls of each channel in which the two sets of slanted ribs form a criss-cross flow path for the cooling air.

In each of the three embodiments ofFIGS. 5,7, and9, the airfoil is cooled with a leading edge impingement channel28, a leading edge cooling air supply channel (labeled33inFIG. 5), two cooling channels (31and32inFIG. 5) located along the pressure side wall and extending along the mid-airfoil section, two cooling channels (41and42inFIG. 5) located along the suction side wall and extending along the mid-airfoil section, and either a single trailing edge cooling channel (43inFIG. 5) or two cooling channels (31and41inFIGS. 7 and 9). A row of exit holes46connected to one of the channels is used in each of the three embodiments. Each different embodiment ofFIGS. 5,7and9passes the cooling air through these commonly positioned channels in a different path. For example, the leading edge cooling air channel33inFIG. 5is the third leg of the forward flowing serpentine circuit along the pressure side wall. In theFIGS. 7 and 9embodiments, the same cooling channel is a separate cooling air supply channel from the dual triple pass serpentine circuits. InFIG. 5, the trailing edge cooling channel means is a single channel43that extends across both pressure and suction side walls, while inFIGS. 7 and 9the trailing edge cooling channel means is formed by the two channels31and41or53and63that together extend across the pressure and suction side walls.

FIG. 13shows a side view of one of the channels of the serpentine flow circuits used in the various embodiments of the present invention. The channel is formed between two ribs that extend from a P/S wall to a S/S wall of the airfoil and includes a first row of slanted ribs75that are slanted toward the L/E and a second row of slanted ribs76that are slanted toward the T/E of the blade. The first row of slanted ribs is located on one side of the channel while the second row of slanted ribs76is located on the opposite wall of the channel. The first row of slanted ribs75form a first row of slanted passages formed between adjacent ribs, while the second row of slanted ribs76form a second row of slanted passages. Cooling air flows along these slanted passages and mixes within the diamond shaped mixing chambers74formed by the slanted ribs to produce a criss-cross flow for the cooling air that produces an improved heat transfer coefficient that the cited prior art. The slanted ribs75and76can be formed in the blade during the investment casting process that forms the blade and the internal cooling circuits. The slanted ribs are offset at around45degrees but could be at a different angle.

FIG. 11shows a first embodiment of the slanted ribs and slanted passages formed within the cooling channels. The slanted ribs from both sides of the channel extend about half way such that they abut each other. The slanted passages71and72have an elliptical cross sectional shape as seen inFIG. 11in which the slanted ribs have concave shaped sides. However, the ribs and the resulting passages can have other configurations.

FIG. 12shows a second embodiment of the slanted ribs and slanted passages formed within the cooling channels. The slanted ribs extend beyond the half way point to form the slanted channels81and82. The diamond shaped mixing chambers74are also formed by the slanted ribs81and82of theFIG. 12embodiment.

The three embodiments of the dual triple pass serpentine flow cooling circuit of the present invention will maximize the airfoil rotational effects on the internal heat transfer coefficient. Manufacturability can be enhanced due to the high aspect ratio cavity geometry. This design achieves a better airfoil internal cooling heat transfer coefficient for a given cooling air supply pressure and flow level. The channels of the two serpentine flow circuits are formed by an arrangement of slanted robs on the P/S and S/S walls of each channel in which the two sets of slanted ribs form a criss-cross flow path for the cooling air. The blade with the cooling circuits of the present invention will maximize the airfoil rotational effects on the internal heat transfer coefficient to achieve a better airfoil internal cooling heat transfer coefficient for a given cooling air supply pressure and flow level. For these serpentine flow cooling circuits, the criss-cross flow paths formed within the channels incorporated into the high aspect ration cooling channels with further increase the internal cooling performance and conduct heat from the airfoil external walls to the serpentine flow channels to achieve a more thermally balanced cooling design. A lower airfoil mass average sectional metal temperature and a higher stress rupture life are produced. The criss-cross flow channels within the serpentine cooling circuits for both sides of the airfoil will yield a multiple layer cooling formation.