Referring to FIG. 1, the turbine section 10 of a turbine engine includes a plurality of disks 12 provided on a rotor (not shown). The discs 12 are axially spaced along the rotor. A plurality of blades 14 are mounted on each disk 12 to form a row of blades 14. The blades 14 are circumferentially arrayed about each disk 12 and extend radially outward therefrom.
The rows of blades 14 alternate with rows of stationary airfoils or vanes 16. The vanes 16 are attached at one end to a vane carrier 18 and extend radially inward therefrom to a radially inner end, which can include an inner shroud 20. Additional structures can be attached to the inner shroud 20, including, for example, a u-shaped ring 22. Labyrinth seals 23 can be attached to the u-shaped ring 22 as well as portions of nearby rotor disks 12 to minimize leakage flow across the interface between them.
The u-shaped ring 22 defines in part a cavity 30. Coolant, such as air, is supplied to the cavity 30. The air is discharged from the cavity 30 to cool the u-ring 22. Such air is also be used to purge hot gases 28 ingested from a radially outer region 26 of the turbine 10 from a forward cavity 32 and an aft cavity 34 defined between the neighboring stationary and rotating structures.
Due to the large pressure differentials between the forward cavity 32 and the aft cavity 34, the forward cavity 32 requires a higher purge air pressure than the aft cavity 34 to prevent hot gas ingestion. However, the purge air for both cavities 32, 34 is supplied from the same source (the u-ring 22). As a result, inefficient distribution of the air occurs, as the majority of the air will naturally tend to the low pressure of the aft cavity 34 and will be able to do so because of the gap 38 between the u-ring 22 and the rotor disks 12. Such an inefficient arrangement keeps the demand for the air at a high level, which prevents the beneficial use of such air in other areas. In some cases, hot gas ingestion into the forward cavity 32 is a result of such inefficient distribution of the purge air.
One additional manner of minimizing has gas ingestion into either of the cavities 32, 34 is to provide a blade cover plate 24 with a single knife edge rim 26, which can create a tortuous path for impeding hot gas ingestion into the cavities 32, 34. However, this alone is an insufficient barrier to hot gas ingestion.
Thus, there is a need for a system and method that can control of rim cavity leakage flow distribution to reduce turbine rim cavity total purge air demand and/or to minimize the hot gas ingestion into the rim cavity.