Patent Application
20050244264
The present invention relates to a trailing edge air cooling configuration for a turbine nozzle, and particularly relates to a hybrid convective channel and pin cooling configuration for the trailing edge portion of a gas turbine nozzle vane.
Gas turbine nozzle cooling is typically achieved by locating impingement inserts within the airfoil cavities, e.g., two or more cavities of the first stage nozzle of a gas turbine. The pressure and suction sides of the vane are thus impingement cooled. The post-impingement cooling air is then either discharged through film holes along the airfoil surface to provide an insulating barrier of cooler air between the hot gas stream and the airfoil or sent to an additional circuit to convectively cool the airfoil trailing edge. The additional trailing edge circuit is required due to geometric limitations of the vane, i.e., there is insufficient space within the airfoil cavity to extend the aft impingement insert to the trailing edge. Furthermore, three-dimensional advanced airfoil nozzle vanes have a high degree of bowing and twist. This lengthens the trailing edge region where impingement cooling using inserts is not mechanically practical.
Various trailing edge air cooling circuits have been proposed and utilized in the past. Certain circuits use pins extending between the opposite sides of the airfoil for receiving the post-impingement cooling flow for cooling the trailing edge portion. Pin cooling, however, is associated with a substantial pressure drop and is practical over very short distances. Turbulative convective channel designs have also been employed, resulting in a lower pressure drop. However, those designs often achieve insufficient cooling efficiency to meet cooling performance requirements for the nozzle vane. There are also examples of pin cooling and convective channel cooling circuits coexisting in the same design. However, there has developed a need for even further cooling efficiencies, particularly for nozzle vanes having a high degree of bowing and twist in enhanced three-dimensional aerodynamic designs which will meet the cooling requirements for these advanced aerodynamic designs.
In accordance with a preferred aspect of the present invention, post-impingement cooling air is directed to a trailing edge portion cooling circuit wherein the air first passes through turbulated convective cooling channels and into a plenum. Film cooling holes are arranged on the pressure side of the vane for receiving post-impingement cooling air from the plenum for film cooling. The convective channels upstream of the plenum provide a pressure drop sufficiently low to maintain the required pressure in the plenum to drive the flow through the film cooling holes. The balance of the post-impingement cooling air then passes about rows of pins which then cools the region of the trailing edge portion with the relatively higher external heat load as compared with the heat load adjacent the upstream convective cooling channels. The greater pressure drop associated with the post-impingement air flowing about the cooling pins is tolerated because the remaining coolant is then discharged through trailing edge apertures on the pressure side where the dump pressures are lower. Consequently, an optimal cooling arrangement is provided to satisfy unique cooling and performance requirements of the trailing edge portion of a nozzle vane having a high degree of bowing and twist in an advanced aerodynamic design.
In a preferred embodiment according to the present invention, there is provided an air-cooled nozzle for disposition in the hot gas path of a turbine comprising inner and outer platforms with an airfoil extending therebetween, the airfoil having opposite pressure and suction sides and an air-cooled trailing edge region having a trailing edge; a plurality of ribs in the trailing edge region extending between the opposite sides and spaced one from the other in a generally radial direction between the platforms defining a plurality of generally axially extending radially spaced flow channels for directing cooling air generally axially toward the trailing edge; a plurality of pins extending between the opposite sides of the airfoil at locations spaced axially downstream from the ribs and spaced radially from one another for impingement by the cooling air exiting the channels; and exit apertures adjacent the trailing edge spaced radially from one another opening through the pressure side for flowing air received from about the pins to cool the trailing edge and for discharge into the hot gas path of the turbine.
In a further preferred embodiment according to the present invention, there is provided air-cooled nozzle for disposition in the hot gas path of a turbine comprising inner and outer platforms with an airfoil extending therebetween, the airfoil having opposite pressure and suction sides and an air-cooled trailing edge region having a trailing edge; a plurality of ribs in the trailing edge region extending between the opposite sides and spaced one from the other in a generally radial direction between the platforms defining a plurality of generally axially extending radially spaced flow channels for directing cooling air generally axially toward said trailing edge; a plurality of pins extending between the opposite sides of the airfoil at locations spaced axially downstream from the ribs and spaced radially from one another for impingement by the cooling air exiting the channels; and a plenum located generally axially between the ribs and the pins, and a plurality of film cooling holes in the pressure side of the airfoil in communication with the plenum, whereby cooling air is enabled for flow through the holes and internally within the trailing edge region about the pins.
Referring now to the drawings, particularly to
The vane 16 has pressure and suction sides 26 and 28, respectively, as best illustrated in
Referring to
Also in communication with the plenum 34 is a generally radially spaced row of film cooling holes 38 which open through the pressure side only of the airfoil 16. Thus, the air from the plenum 34 in part flows through the film cooling holes 38 to film cool the trailing edge region on the pressure side of the vane while the remaining portion of the cooling air in plenum 34 flows about the rows of pins 36 for cooling augmentation along the pressure and suction sides of the trailing edge region. Downstream of the pins 36 are a plurality of generally radially spaced ribs 40 defining therebetween generally axially extending flow paths 42 for receiving the cooling air exiting from the rows of pins 36. Consequently, the opposite sides of the vane are cooled convectively with the air exiting from the channels 42 through exit apertures 44 along the pressure side of the vane.
With the trailing edge cooling configuration as described, it will be appreciated that the post-impingement cooling air flows in the channels 30 between the ribs 32 whereby the opposite sides of the airfoil 16 are convectively cooled. The cooling air exiting from between the ribs 32 flows into the plenum 34. The plenum feeds the row of film cooling holes 38 on the pressure side for film cooling of the pressure side of the airfoil. Thus, with the channels 30 providing relatively low pressure drop, sufficient air pressure is maintained within the plenum to drive the cooling air through the film cooling holes 38. The remaining portion of the cooling air flows about the pins 36 for pin cooling of the opposite sides of the airfoil. The pins cool the opposite sides of the airfoil in the region with the relatively higher external heat load than the external heat load in the area of the upstream convective channels 30. While the arrangement of the pins provide a significant pressure drop, this pressure drop can be tolerated since the coolant air flow is then discharged through trailing edge slots where the pressures are much lower. The flow of cooling air in channels 42 between ribs 40 also convectively cools the opposite sides of the vane directly adjacent the trailing edge. In the foregoing manner, the trailing edge cooling configuration hereof satisfies the cooling requirements of an advanced three-dimensional aerodynamic nozzle vane having significant bow and twist where impingement cooling is not practical in light of the axial extent of the trailing edge region of the airfoil.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
