TECHNICAL FIELD

The present invention relates generally to a gas turbine engine, and more specifically to a turbine stator vane with an insert and a flexible or compliant seal.

BACKGROUND

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.

Turbine stator vanes are often cooled using impingement cooling inserts because the stator vanes do not rotate and thus an insert can be used. High thermal stress occurs in first and even second stage stator vanes, and thus an insert would undergo relatively high movement within the cavity of the airfoil. A flexible seal can be used to maintain a seal even under these relatively large displacements between the insert and the airfoil. However, too much relative movement between the insert and the airfoil cavity would affect the seal performance. SUMMARY

A turbine stator vane with an impingement cooling insert, with a flexible seal used to provide for a seal between the insert and the cavity of the airfoil, and where seal slots include bumper surfaces to limit a range of relative movement between the insert and the airfoil cavity so that the flexible seal continues to maintain a good seal.

In one embodiment, an airfoil includes a rib forming a forward impingement cavity and an aft impingement cavity each having an impingement cooling insert located therein. Each insert and cavity includes a forward seal slot and an aft seal slot with a flexible seal secured therein. Each seal slot includes a chordwise movement bumper and a sideways movement bumper with a gap to allow for a range of movement of the insert within the cavity while the flexible seal still maintains a seal. The flexible seal is X-shaped with four contact points on the seal slots so that a relatively large but limited movement between the insert and the cavity can occur.

Another embodiment of the present invention includes a double impingement cooling insert having a pressure side surface and a suction side surface that forms a cooling air supply cavity, and where an arrangement of cross-over tubes connect return air holes on the pressure side of the insert to impingement holes on the suction side of the insert. Cooling air supplied to the supply cavity thus flows out through pressure side impingement holes to impinge on the pressure side surface of the airfoil, then flows through return air holes that are connected to the cross-over tubes. The cross-over tubes are connected to impingement cooling holes on the suction side of the insert for impingement cooling of the suction side wall of the airfoil. With the cross-over tubes, the impingement cooling holes can be made as close together as possible depending on the diameter of the cross-over tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic view of a top section of a stator vane airfoil with two inserts secured inside with four flexible seals of the present invention;

Figure 2 shows a schematic view of a top section of a forward insert and an aft insert each with two flexible seals of the present invention;

Figure 3 shows a cross section top view of an airfoil wall and a forward insert with a flexible seal secured within slots having bumper surfaces of the present invention;

Figure 4 shows a cross section top view of an airfoil wall and an aft insert with a flexible seal secured within slots having bumper surfaces of the present invention; and

Figure 5 shows a cross section top view of an airfoil wall with the forward insert and the aft insert secured within slots having bumper surfaces of the present invention. DETAILED DESCRIPTION

The present invention is a turbine stator vane, such as a large frame industrial engine turbine stator vane, with impingement cooling inserts secured within the airfoil and sealed using a flexible or compliant seal, where the seal slots have bumper surfaces between the insert and the airfoil inner wall that limit relative movement of the seal slots so that the flexible seal maintains an adequate seal between the two surfaces. The flexible seal used in the present invention is disclosed in U.S. Pat. No. 8,556,578, issued on October 15, 2013, to Memmen et al., which entire patent is incorporated herein by reference. The flexible seal allows for a proper seal to be maintained between seal slots formed in the airfoil wall and the insert that will allow a large relative displacement where the prior art seals will not keep a seal. One major feature missing from the Memmen patent is structure to limit the relative movements of the seal slots for a single flexible seal. The present invention solves this problem.

Figure 1 shows an embodiment of a stator vane with an airfoil 11 having a forward cavity with a forward impingement cooling insert 12 and an aft cavity with an aft impingement cooling insert 13. Each impingement insert produces a sequential impingement or series of impingement of the airfoil walls. In this embodiment, impingement cooling occurs on the pressure side wall 9 and then on the suction side wall 10. The cooling air pressure will be higher on the pressure side wall 9 than on the suction side wall 10, and thus seals are required to seal the pressure side impingement cavity from the suction side impingement cavity. In one embodiment, the forward impingement cooling insert 12 includes a forward flexible seal 14A and an aft flexible seal 14B. The aft impingement insert 13 also includes a forward flexible seal 14C and an aft flexible seal 14D as seen in Figure 1.

Figure 2 shows a top section of the forward insert 12 and the aft insert 13 with each insert having two flexible seals 14A-D. Cross-over tubes 27 connect the pressure side impingement cavity to the suction side impingement cavity. The aft insert 13 will also include these cross-over tubes. Cooling air is supplied to the interior each insert and then flows out through an arrangement of impingement cooling holes 29 on the pressure side to impinge against a backside surface of the pressure side wall of the airfoil 11. The spent impingement cooling air then flows through the cross-over tubes 27 and then through impingement cooling holes to impinge on the backside surface of the suction side wall of the airfoil 1 1.

Use of the cross-over tubes 27 in the insert allows for a lightweight double impingement insert to be formed. Also, using the cross-over tubes 27 will allow for the impingement cooling holes on both the pressure side and the suction side of the insert to be closely spaced. This limitation in how close the impingement holes can be located will depend on the diameter of the cross-over tubes 27. The multiple impingement insert with cross-over tubes 27 can also be manufactured using one of the additive manufacturing processes such as direct metal sintering, electron beam welding, or other 3D metal printing processes to produce a one-piece insert with the cross-over tubes. The impingement holes 29 can also be formed from the metal additive manufacturing process which will further reduce cost of manufacturing because EDM drilling of the holes is quite expensive.

Figure 3 shows a cross section top view of the forward insert 12 with a forward seal slot between the leading edge surface of the airfoil 1 1 and a forward side of the forward insert 12. An airfoil slot portion 16 is formed in the airfoil 11 and an insert slot portion 17 is formed in the insert 12, with the flexible seal 14A being located within the slot formed by the first 16 and second 17 slot portions. Because the cooled insert is at a much lower temperature than the airfoil during a steady state operation of the vane in an engine, the airfoil slot portion 16 and the insert slot portion 17 will have a great movement relative to each other. Too much of a relative movement will cause the flexible seal to leak. Therefore, the present invention includes structure to limit the relative movement of the slots. In Figure 3, two bumper surfaces (a first bumper surface 18A on the insert 12 and a corresponding second bumper surface 18B on the airfoil 1 1) will limit a sideways movement, while two bumper surfaces (a first bumper surface 19A on the insert 12 and a corresponding second bumper surface 19B on the airfoil 1 1 ) will limit a chordwise movement. Any space formed between bumper surfaces will depend on the flexibility of the seal 14.

Figure 4 shows a flexible seal 14D secured within a slot between an aft side of the aft insert 13 and airfoil 1 1. Bumper surfaces 21 A, 21B formed on the insert 13 and the airfoil 1 1, respectively, will limit sideways movement while bumpers 22A, 22B formed on the insert 13 and the airfoil 1 1, respectively, will limit a chordwise movement between seal slot portions. In the Figure 4 embodiment, the seal slot in the airfoil extends from a pressure side wall of the airfoil 1 1. A slot 15 for discharge of film cooling air is show along the pressure side wall of the airfoil 1 1.

Figure 5 shows a rib 28 formed between the forward cavity and the aft cavity of the airfoil in which the forward insert 12 and the aft insert 13 are sealed with a flexible seal 14B and 14C, respectively. The forward insert 12 includes bumper surfaces 23 A, 23B formed on the insert 12 and the airfoil 11 , respectively, to limit a sideways movement and bumper surfaces 24A, 24B formed on the insert 12 and the airfoil 1 1, respectively, to limit a chordwise movement. Similar structure is formed for the aft insert 13. Bumper surfaces 25 A, 25B formed on the insert 13 and the airfoil 1 1 , respectively, limit sideways movement while bumper surfaces 26A, 26B formed on the insert 13 and the airfoil 1 1, respectively, limit a chordwise movement. Figure 5 also shows a discharge slot 15 on the suction side wall of the airfoil 1 1. As seen in Figures 3 and 5, each seal slot has two bumper surfaces to limit sideways movement and two bumper surfaces to limit chordwise movement. In Figure 4, two bumper surfaces 22A, 22B are formed to limit chordwise movement. To limit sideways movement, the suction side wall 10 of the airfoil 1 1 includes a circular shaped bumper 21B (and the aft insert 13 includes bumper 21 A) while the pressure side wall 9 has a flat bumper surface 22B like the other seals of the airfoil. This structure is due to the seal slots being formed upstream from the trailing edge and without a rib extending across the airfoil from the pressure side wall to the suction side wall.

The flexible seal 14 must maintain a seal between slots that have a large relative movement in order to prevent high pressure cooling air from crossing over the seal into the lower pressure cooling air and thus disrupt the series of impingement cooling from the pressure side to the suction side of the airfoil.