Patent Application
20050265841
1. Technical Field
This invention applies to gas turbine rotor blades in general, and to cooled gas turbine rotor blades in particular.
2. Background Information
Turbine sections within an axial flow turbine engine include rotor assemblies that include a disc and a number of rotor blades. The disk includes a plurality of recesses circumferentially disposed around the disk for receiving the blades. Each blade includes a root, a hollow airfoil, and a platform. The root includes conduits through which cooling air may enter the blade and pass through into a cavity within the hollow airfoil. The blade roots and recesses are shaped (e.g., a fir tree configuration) to mate with one another to retain the blades to the disk. The mating geometries create a predetermined gap between the base of each recess and the base of the blade root. The gap enables cooling air to enter the recess and pass into the blade root.
Airflow pressure differences propel cooling air into and out of the rotor blade. Relatively high pressure cooling air is typically bled off of a compressor section. The energy imparted to that air enables the requisite cooling, but does so at a cost since that energy is no longer available to create thrust within the engine. Hence, it is desirable to minimize the amount of energy that is necessary to provide cooling within a rotor blade.
The gas path pressure external to a rotor blade airfoil is highest at the leading edge region during operation of the blade. In many turbine applications, airfoils are typically backflow margin limited at the leading edge of the airfoil. The term “backflow margin” refers to the ratio of internal pressure to external pressure. To ensure hot gases from the external gas path do not flow into an airfoil, it is necessary to maintain a particular predetermined backflow margin that accounts for expected internal and external pressure variations. Hence, it is desirable to minimize pressure drops within the airfoil to the extent possible, particularly with respect to passages providing airflow to cool the leading edge.
It is known to use conduits within a blade root having a bellmouth inlet; i.e., an inlet that is flared on the leading edge (“forward”) side, suction side, pressure side, and the trailing edge (“aft”) side. A disadvantage of this approach is that the bellmouth inlet decreases the size of the root material that extends between the suction side and pressure side, between adjacent conduits. During operation, the blade root is highly loaded between the suction and pressure sides. Decreasing the cross-sectional area of root material between the suction and pressure sides undesirably decreases the ability of the root to handle the load.
What is needed is a rotor blade that requires less energy to be adequately cooled relative to prior art rotor blades, one that requires less energy for cooling by reducing pressure losses within the rotor blade relative to prior art rotor blades, and one that can adequately handle the attachment loading within the root.
According to the present invention, a rotor blade is provided having a hollow airfoil and a root. The hollow airfoil has a cavity and one or more cooling apertures. The root is attached to the airfoil, and has a leading edge conduit, at least one mid-body conduit, and a trailing edge conduit. The conduits are operable to permit cooling airflow through the root and into the cavity. Each conduit has a centerline. The leading edge conduit includes an inlet having a forward side, a suction side, and a pressure side that diverge from the centerline of the leading edge conduit, and an aft side. Each of the mid-body conduits includes an inlet having a suction side and a pressure side that diverge from the centerline of the mid-body conduit, and an aft side and a forward side. The trailing edge conduit includes an inlet having a suction side and a pressure side that diverge from the centerline of the trailing edge conduit, and a forward side and an aft side.
One of the advantages of the present rotor blade is that airflow pressure losses within the blade root are decreased relative to many prior art blade root configurations of which we are aware.
Another advantage of the present invention is that airflow pressure losses are achieved without compromising blade root load capability. Prior art root conduits having bellmouth inlets decreased the pressure loss for cooling air entering the root conduits, but did so at the expense of blade root load capability. The present invention provides the advantageous flow characteristics without appreciably negatively affecting the blade root load capability.
These and other objects, features and advantages of the present invention will become apparent in light of the detailed description of the best mode embodiment thereof, as illustrated in the accompanying drawings.
Referring to
Referring to
The root 20 has a leading edge conduit 42, at least one mid-body conduit 44, and a trailing edge conduit 46. The conduits 42, 44, 46 are operable to permit airflow through the root 20 and into the cavity 40. Each conduit 42, 44, 46 has a centerline 58,74,88.
Referring to
The leading edge conduit 42 is in fluid communication with one or more leading edge passages 62 disposed within the cavity 40, adjacent the leading edge 32 of the airfoil 22. The leading edge conduit 42 provides the primary path into the leading edge passage(s) 62 for cooling air, and therefore the airfoil leading edge 32 is primarily cooled by the cooling air that enters the airfoil 22 through the leading edge conduit 42.
The mid-body conduit(s) 44 includes an inlet 64 having a suction side 66, a pressure side 68, an aft side 70, and a forward side 72. The suction and pressure sides 66, 68 each diverge from the centerline 74 of the mid-body conduit 44. In some embodiments, the aft and forward sides 70, 72 are substantially parallel to the centerline 74 of the mid-body conduit 44 (
The mid-body conduit(s) 44 is in fluid communication with one or more mid-body passages 76 disposed within the cavity 40. The mid-body conduit 44 provides the primary path into the mid-body passages 76 for cooling air, and therefore the airfoil 22 mid-body region is primarily cooled by the cooling air that enters the airfoil 22 through the mid-body conduit 44.
The trailing edge conduit 46 includes an inlet 78 having an aft side 80, a forward side 82, a suction side 84, and a pressure side 86. The suction and pressure sides 84, 86 each diverge from the centerline 88 of the trailing edge conduit 46. In some embodiments, the aft and forward sides 80, 82 are substantially parallel to the centerline 88 of the trailing edge conduit 46 (e.g.,
The trailing edge conduit 46 is in fluid communication with one or more passages 90 disposed within the cavity 40, adjacent the trailing edge 34 of the airfoil 22. The trailing edge conduit 46 provides the primary path into the passages 90 for cooling air. Consequently, the trailing edge 34 is primarily cooled by cooling air that enters the airfoil 22 through the trailing edge conduit 46.
Referring to
Cooling air 93 that travels past the leading edge conduit 42 encounters the one or more mid-body conduits 44. The divergent suction and pressure sides 66, 68 open the inlet 64 to facilitate cooling airflow entry from the sides, and to decrease the pressure drop for cooling airflow turning into the inlet 46 from the sides. In the embodiment that includes a mid-body conduit inlet 64 with a divergent forward side 72, the inlet 64 forward side 72 facilitates the transition of cooling airflow into the mid-body conduit 44 as described above. Both embodiments of the forward side 72 do not decrease the cross-sectional area of the root portion 96 disposed between the leading edge conduit 42 and the mid-body conduit 44. Consequently, the blade root load capability is not negatively affected, as would be the case if the leading edge and mid-body conduit inlets 48, 64 flared toward one another.
Cooling air 95 that travels past the mid-body conduit 44 encounters the trailing edge conduit inlet 78. The divergent suction and pressure sides 84, 86 open the inlet to facilitate cooling airflow entry from the sides, and to decrease the pressure drop for cooling airflow turning into the inlet 78 from the sides. In the embodiment that includes a trailing edge conduit inlet 78 with a divergent forward side 82, the inlet forward side 82 facilitates the transition of cooling airflow into the trailing edge conduit 46 as described above. Both embodiments of the trailing edge conduit forward side 82 do not decrease the cross-sectional area of the root portion 98 extending between the mid-body conduit 44 and the trailing edge conduit 46. Consequently, the blade root load capability is not negatively affected, as would be the case if mid-body and trailing edge conduit inlets 64, 78 flared toward one another.
Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and the scope of the invention.
