Turbine airfoil with multiple near wall compartment cooling

The present invention is a turbine airfoil such as a rotor blade with a cooling circuit that provides convective cooling to the airfoil main body, and impingement cooling and film cooling to the outer wall of the airfoil in order to maximize the cooling while minimizing the amount of cooling air used. The blade main body includes walls of such thickness to provide sufficient structural strength to support the airfoil assembly. The blade main body includes a rib that separates a first or forward cooling air supply channel from a spent air collector cavity. Another rib separates the spent air collector cavity from a second or mid-chord cooling air supply channel. A leading edge cooling supply cavity is connected to the forward supply channel through metering and impingement holes. Film cooling holes forming a well known showerhead arrangement provides film cooling for the leading edge of the blade.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to fluid reaction surfaces, and more specifically to turbine airfoils with cooling circuits.

In a gas turbine engine, especially in an industrial gas turbine engine, compressed air is delivered to a combustor and burned with a fuel to produce an extremely hot gas flow. The hot gas flow is passed through a multiple stage turbine to extract mechanical energy. The engine efficiency can be increased by increasing the temperature of the hot gas flow entering the turbine. One of the major problems with the design of gas turbine engines is forming the first stage stator vanes and rotor blades from materials that can withstand the extreme high temperature of the hot gas flow. In order to overcome the limitations due to the material properties, complex internal cooling circuits have been proposed to provide high levels of cooling for these airfoils while minimizing the amount of cooling air used. Since the pressurized cooling air is typically diverted from the compressor of the engine, which is compressed air that is not used to perform work, using less air from the compressor for cooling will also increase the engine efficiency.

Prior Art turbine airfoils near wall cooling utilized in an airfoil main body is constructed with radial flow channels plus re-supply holes in conjunction with film discharge cooling holes. As a result of this cooling construction approach, span-wise and chord-wise cooling flow control due to airfoil external hot gas temperature and pressure variation is difficult to achieve. In addition, single radial channel flow is not the best method of utilizing cooling air, resulting in a low convective cooling effectiveness. U.S. Pat. No. 5,660,524 issued to Lee et al on Aug. 26, 1997 and entitled AIRFOIL BLADE HAVING A SERPENTINE COOLING CIRCUIT AND IMPINGEMENT COOLING discloses a turbine airfoil blade with generally longitudinally extending coolant passageways (#40, 42, and 44 in this patent) with first and second impingement chambers (#53 and 60 in this patent) located on the pressure side and the suction side of the blade adjacent to the coolant passageway. The two impingement chambers also extend along the entire span-wise direction of the blade from the root to the blade tip. One problem with this design is that the blade may have hot spots along the span-wise direction. Because the impingement chamber is one long passage, some areas of the blade along the span-wise direction may be under-cooled while others may be over-cooled.

U.S. Pat. No. 6,773,230 B2 issued to Bather et al on Aug. 10, 2004 and entitled AIR COOLED AEROFOIL discloses a turbine airfoil with a central cooling air supply channel and a series of cooling wall cavities spaced along the airfoil wall and connected to the cooling air supply channel by impingement holes. The impingement cavities can be separated into a plurality of compartments spaced along the airfoil span-wise direction in order to increase the efficiency of such a cooling arrangement (see column 3, line 42 of this patent). In the Bather et al patent, the source of cooling air supply is only connected to the central cavity (#34 in this patent), and this central cavity is in direct fluid communication with the film cooling holes that provide cooling for the leading edge showerhead arrangement. Also, the impingement cooling air passes into the second cavity (#26 in this patent) which is located downstream from the first or supply cooling air cavity. Therefore, a series flow is formed that passes from the first cooling air supply cavity34, into the impingement cavities24and28, into the second cavity26, and then into a trailing edge cavity26and out through exit cooling holes44in the trailing edge of the airfoil. This is a long flow path for the cooling air, which results in lower efficiency because the cooling air heats up before reaching the middle and trailing edge portions of the airfoil.

It is an object of the present invention to provide a turbine airfoil with a near wall cooling arrangement for a turbine airfoil main body region that will greatly reduce the airfoil main body metal temperature and thus reduce the cooling flow requirement and improve the turbine efficiency.

It is another object of the present invention to provide for a turbine airfoil in which the airfoil is cooled by a cooling air circuit that uses convection in series with impingement cooling and film cooling to maximize the heat transfer coefficient while minimizing the amount of cooling air used.

BRIEF SUMMARY OF THE INVENTION

A turbine airfoil with a multiple near wall cooled compartments in conjunction with multi-hole impingement cooling construction for the airfoil main body. A forward cooling air supply channel supplies cooling air to impingement holes on the suction side and the pressure side of the cooling supply channel. Cooling air is supplied to three cooling supply channels in the airfoil. A forward cooling supply channel supplies cooling air through impingement holes on the suction side of the airfoil in which the impingement cooling air collects before discharging out film cooling holes on the suction side. A mid-chord cooling air supply channel supplies cooling air to a suction side cavity compartment through impingement holes. Both the forward and mid-chord cooling supply channels supply cooling air through impingement holes on the pressure side into a common impingement cavity compartment along the pressure side. Spaced between the forward and mid-chord cooling supply channels is a spent air collector cavity in which the impingement air from the common pressure side impingement cavity compartment and the mid-chord suction side impingement cavity compartment is collected, this collected spent air then discharged through film cooling holes on the suction side upstream from the gage point. A leading edge cooling air supply cavity is connected to the forward cooling air supply channel through metering holes, and discharges cooling air onto the leading edge through the showerhead film cooling holes. A separate cooling air supply channel is located in the trailing edge region, and supplies cooling air through impingement holes on the pressure side and suction side into impingement cavity compartments on the pressure side and suction side. The two trailing edge impingement cavity compartment then discharge the cooling air through exit holes spaced along the trailing edge.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a turbine airfoil such as a rotor blade with a cooling circuit that provides convective cooling to the airfoil main body, and impingement cooling and film cooling to the outer wall of the airfoil in order to maximize the cooling while minimizing the amount of cooling air used.FIG. 1shows the blade10of the present invention in a cross section view. The blade10includes a blade main body11having the general shape of the airfoil with a leading edge and a trailing edge, and a pressure side and a suction side. The blade main body includes walls of such thickness to provide sufficient structural strength to support the airfoil assembly10. The blade main body11includes a rib12that separates a first or forward cooling air supply channel15from a spent air collector cavity31. Another rib separates the spent air collector cavity31from a second or mid-chord cooling air supply channel16. A third rib13separates the second or mid-chord channel16from a third or trailing edge cooling air supply channel17. A leading edge cooling supply cavity18is connected to the forward supply channel15through metering and impingement holes41. Film cooling holes22forming a well known showerhead arrangement provides film cooling for the leading edge of the blade.

Impingement channels are arranged along the blade main body on both sides of the blade to form impingement channels for near wall cooling of an outer wall19of the blade. A TBC or thermal barrier coating21is applied over the outer wall19. a suction side impingement channel24is formed between the blade main body11and the outer wall19and includes a plurality of impingement holes23connecting the forward cooling supply channel15to the suction side impingement channel24.

A pressure side impingement channel27is located on the pressure side of the blade main body11and is connected to the forward cooling supply channel15by a plurality of metering and impingement holes23, the second or mid-chord cooling supply channel16is connected to a suction side impingement channel28on the suction side through metering and impingement holes43, and is connected to the pressure side impingement channel27through metering and impingement holes43, the pressure side impingement channel27is common to both the forward and mid-chord cooling supply channels15and16for the pressure side of the blade main body11.

Impingement air flowing into the suction side impingement channel28adjacent to the mid-chord cooling air supply channel16is directed into the spent air collector cavity31through a metering hole29. Impingement air flowing into the common pressure side impingement channel27common to the forward and mid-chord cooling air supply channels15and16is directed into the spent air collector cavity31through a metering hole32. The cooling air from the spent air collector cavity31is discharged through film cooling holes33on the suction side of the blade just upstream from the gage point.

The cooling air supply channel17on the trailing edge region passes cooling air through metering and impingement holes53into a pressure side impingement channel35and a suction side impingement channel34. The cooling air in the two impingement channels34and35then flows out a channel exit hole36and into a collector channel37and out through trailing edge exit holes38spaced along the trailing edge of the blade.

As seen inFIG. 2, the impingement channels spaced along the blade main body on both sides are segmented or compartments along the span-wise direction of the blade.FIG. 2shows a front view of the pressure side impingement channel27common to both of the forward and mid-chord cooling air supply channels15and16. The impingement channel27is shown with the three metering and impingement holes23connected to the forward supply channel15, the metering hole32leading into the spent air collector cavity31, and the four holes43connected to the second supply channel16. Three compartments are shown inFIG. 2, each connected to the common cooling air supply channel through its own metering and impingement holes. Cooling air supplied through the trailing edge supply channel17is discharged out through the exit holes38.

FIG. 3shows a front view of a cross section of the trailing edge region of the blade with the pressure side impingement channel35extending along the blade toward the exit holes38. Horizontal ribs also separate the impingement channels35along the span-wise direction of the blade. Each separated impingement channel35is connected to the trailing edge supply channel17through metering and impingement holes53. Each impingement channel35is connected to a plurality of the exit holes38. Two are shown inFIG. 3, but three could also be used for each channel35.

Operation of the cooling flow circuit of the blade10in the present invention will now be described with respect toFIG. 1. Cooling air, typically from the engine compressor, is supplied to the three separate cooling supply channels15,16, and17through passages formed in the blade root. Cooling air in the forward supply channel15flows through the pressure side holes23and into the pressure side impingement channel27to provide impingement cooling to the outer blade wall19on the pressure side. Cooling air also flows through the suction side holes23and into the suction side impingement channel24to provide impingement cooling to the suction side outer wall19. The impingement cooling air collected in the suction side impingement channel24then flows out the film cooling holes26located at the upstream end of the channel24to provide film cooling to the outer surface of the outer wall19or the TBC21if applied. Cooling air from the forward supply channel15also flows through the metering holes18and into the leading edge supply cavity18, and then through the showerhead film cooling holes22to provide film cooling for the blade leading edge.

The second or mid-chord cooling air supply channel16delivers cooling air to the suction side impingement channel28through the holes42for impingement cooling of the suction side outer wall19in this section of the blade. Impingement cooling air collected in the channel28is then directed through the metering hole29and into the spent air collector cavity31. The mid-chord supply channel16also directs cooling air into the common pressure side impingement channel27spaced along the pressure side between the forward and mid-chord supply channels15and16through the holes43. Cooling air collected in the common pressure side impingement channel27is collected and directed through the metering hole32into the spent air collector cavity31. The cooling air collected in the collector cavity31is then discharged out through the film cooling hole33located on the suction side wall upstream of the gage point to provide film cooling for the suction side outer wall19or TBC21is applied.

The trailing edge cooling supply channel17passes cooling air through the holes53and into the suction side impingement channel34and the pressure side impingement channel35to provide impingement cooling to that section of the blade on the pressure side and suction side. The impingement cooling air is then collected in the trailing edge collector cavity37and discharged through the exit holes38spaced along the trailing edge to provide convection cooling in the trailing edge region.

The airfoil leading edge is cooled with a single row of backside span-wise impingement holes. The cooling air is supplied through the leading edge cooling supply cavity15and impinges onto the backside of the leading edge wall to provide backside impingement convective cooling prior to discharging through the leading edge showerheads22to provide film cooling for the blade leading edge region. In the forward section of the blade suction side surface, the multi-hole impingement cooling air is supplied through the airfoil leading edge supply cavity15, impinges onto the backside of the airfoil forward surface, and the spent cooling air flows forward and is then discharged onto the airfoil suction side surface to provide film cooling. The mid-chord section of the suction side surface, downstream of the gage point, a counter flow similar to the forward section cooling is utilized. The spent cooling air is discharged into the mid-chord collecting cavity31prior to discharging onto the suction surface upstream of the gage point. For the pressure side cooling, a parallel flow is used for the forward section while a counter flow is used for the aft section. The spent air is discharged into the cooling air collector cavity31through a row of metering holes32. The use of the cooling air collector cavity31also for the collection of the spent cooling air from the airfoil pressure surface and downstream of the airfoil suction surface and discharge the spent cooling air upstream of the airfoil gage point as well as transporting the pressure side spent cooling air to provide film cooling for the airfoil suction side surface. The airfoil trailing edge cooling, aft flowing multi-impingement is used for both of the pressure and suction sides. The spent cooling air discharges through a row of trailing edge exit slots38for the cooling of the trailing edge corner prior to exit from the airfoil.

From the use of the separate impingement compartments spaced along the span-wise direction of the blade, and with the separate metering and impingement holes and separate cooling air supply channels, the cooling flow amount and pressure can be individually controlled to provide the desired amount of impingement cooling and film cooling to the particular area of the blade. This allows for certain hot regions or areas of the blade to be properly cooled without sending too much cooling air to areas that do not need the cooling. Also, by providing for the film cooling holes26and33on the suction side of the blade in combination with the common impingement channel27on the pressure side of the blade, adequate film cooling is provided for on the suction side of the blade while enough cooling through impingement and convection is performed on the cooler pressure side. Maximum cooling of the blade main body and the outer blade wall is accomplished while using a minimal amount of cooling air. Therefore, turbine efficiency is increased.

An improvement over the Bather et al patent described above for the airfoil main body near wall cooling can be achieved by the cooling circuit of the present invention which includes the multiple near wall compartments in conjunction with multi-hole impingement cooling for the airfoil main body. The multi-hole impingement cooling design of the present invention is constructed at inline formation within each chord-wise compartment. Individual compartments are designed based on the airfoil gas side pressure distribution in both the chord-wise and span-wise directions. In addition, each individual compartment can be designed based on the airfoil local external heat load to achieve a desired local metal temperature. These individual chord-wise compartments are constructed in an inline array along the airfoil main body wall. With this unique cooling construction approach, the maximum usage of cooling air for a given airfoil inlet gas temperature and pressure profile is achieved. In addition, the entire airfoil utilizes the multi-hole impingement cooling technique for the backside convective cooling as well as flow metering purpose and the spent cooling air is discharged onto the airfoil surface at the high heat load region where film cooling is most desired. The combination effects of multi-hole impingement cooling plus film cooling yields a very high cooling effectiveness and uniform wall temperature for the airfoil main body wall.