Impingement insert assembly for gas turbine nozzle vanes and corresponding manufacturing method

0001The invention relates to the provision of metering plates together with impingement inserts for use in gas turbine nozzles.

0002Gas turbine nozzles typically use impingement inserts inside of the nozzle to cool the airfoil walls. If the nozzle has a multiple circuit cooling system then there may be unbalanced cooling flow to the different circuits of the nozzle.

0003To overcome the problem described in the prior art, metering plates are used with or without impingement inserts to balance cooling flow to the different circuits of the nozzle. In one embodiment of the invention, a metering plate with a single metering hole is used.

0004In a second and preferred embodiment of the invention, a metering plate is used with multiple holes to overcome potential flow disruption which can be caused by a single metering hole. More specifically, when using only one metering hole in a metering plate a flow disruption occurs that produces a variable static pressure distribution in the area just below the metering plate. This variability in static pressure distribution relative to the rest of the impingement insert can cause variable impingement pressure ratios across impingement holes leading to back-flow issues and/or reduce cooling effectiveness. This flow field disruption is produced by the Vena Contracta of the orifice. Using several metering holes instead of just one significantly reduces the static pressure variation downstream of the metering plate.

0005The invention will now be described in greater detail, by way of example, with reference to the drawings, in which:- <ul id="ul0001" list-style="none"><li>FIGURE 1 shows a typical impingement insert combined with a multiple hole metering plate at the flow inlet.</li><li>Figure 2 shows the assembled insert and metering plate being inserted into a nozzle assembly.</li><li>Figure 3 schematically shows in cross section the nozzle assembly of Figure 2 and depicts a multiple circuit cooling system within the nozzle assembly.</li></ul>

0006The invention involves a metering plate having one or more holes, combined with or without an associated impingement insert, installed in a gas turbine nozzle for equalizing the balance of cooling flow to different circuits of a nozzle. Multiple holes in the metering plate are preferably used for reducing static pressure variation in the area near the exit of the metering plate.

0007As shown in Figure 1, metering plate 10 is attached to the inlet portion of a nozzle impingement insert 12. Metering plate 10 can be attached either on top of the insert after assembly in the nozzle or as part of the insert at the extreme entrance interface prior to installation.

0008In the preferred embodiment, metering plate 10 has multiple holes 14 so as to reduce the static pressure variation caused by the Vena Contracta effect produced by flow through a single metering hole. Thus, a multiple hole metering plate achieves the desired impingement flow through impingement holes near the exit of the metering plate. The actual pattern of the metering holes is specific to the characteristics and physical parameters of the nozzle.

0009Figure 2 shows an assembled insert and metering plate 20 being inserted into nozzle assembly 22. Nozzle assembly 22 includes airfoil 24 and impingement plate assemblies 26 located at either end of airfoil 24. Alternatively, an insert 12 can be assembled into nozzle 22 and, subsequently, metering plate 14 can be attached to the top of insert 12.

0010Figure 3 shows the flow paths through a nozzle assembly having a multiple circuit cooling system. In Figure 3, airflow through the nozzle assembly 22 is shown by the arrows. In particular, at the top of nozzle assembly 22, inlet air flows into the nozzle assembly as shown by the arrow traversing the nozzle outer sidewall. The airflow continues within the nozzle assembly through pre-impingement plate assembly 26, through pre-impingement plate 28 with respect to cavities 1 and 6, and downward through cavities 1, 6 and 7. As it exits these cavities, the airflow in cavity 1 passes through another pre-impingement plate 28 at the exit end of the cavity while the airflow in cavities 6 and 7 does not exit through pre-impingement plate 28.

0011Arrows 30, shown in Figure 3 with an oval around their base, depict airflow that has passed through a metering plate. Thus, as shown in Figure 3, airflow in cavities 1, 6 and 7 has passed through respective metering plates. Cavity 7, however, is shown not to include pre-impingement plate 28 and, accordingly, the inlet air passes directly through a metering plate into the cavity. Similarly, cavities 1, 6 and 7 may or may not include pre-impingement plates, metering plates and/or inserts depending on the cooling needs of those portions of the nozzle assembly.

0012The use of metering plates in cavities 1, 6 and 7 serves to spread or apportion the inlet airflow between these cavities. After traversing cavities 1, 6 and 7 the airflow enters cavities 2-5 after passing through metering plates at their inlets, as depicted by arrows 30 in Figure 3. The metering plates in cavities 2-5 are also provided to spread or apportion the airflow between these cavities. Depending upon the physical characteristics of the nozzle assembly, particular cavities may or may not require pre-impingement plates, metering plates and/or impingement inserts. For example, cavity 5 may or may not need to be provided with a pre-impingement plate, metering plate and/or impingement insert. More particularly, suitable metering plates provided to cavities 2-4 may obviate the need for a metering plate in cavity 5 (not shown).

0013As further shown in Figure 3, the cooling air exits the nozzle assembly through pre-impingement plate 28 and the nozzle outer sidewall after traversing cavities 2-5. As described above, the airflow in cavity 7 does not pass through pre-impingement plate 28, but does pass through a metering plate, and cavity 5 may or may not require a pre-impingement plate, an impingement insert and/or metering plate. In practice, achieving the desired airflow within the nozzle assembly and/or the impingement flow through impingement holes near the exit of the metering plate can be arrived at by either iteration on analytical models or via testing actual hardware. The metering hole plate serves two basic purposes, namely, metering the airflow down the cavity and impinging airflow on the sidewall to the airfoil.