WO2016068855A1

WO2016068855A1 - Active turbine blade tip clearance control system for turbine engines

Info

Publication number: WO2016068855A1
Application number: PCT/US2014/062490
Authority: WO
Inventors: Robert T. Brooks; Ernie B. CAMPBELL; Jose L. RODRIGUEZ
Original assignee: Siemens Aktiengesellschaft
Priority date: 2014-10-28
Filing date: 2014-10-28
Publication date: 2016-05-06

Abstract

An active turbine blade tip clearance control system (10) for increasing efficiency of a turbine engine (12) by reducing the clearance between a tip (14) of a turbine airfoil (16) and a radially adjacent component of the turbine engine (12) is disclosed. In at least one embodiment, the control system (10) may be configured to distribute heating air to one or more circumferentially extending chambers (20) positioned radially outward of one or more ring segments (22) during the engine start up process to reduce the likelihood of turbine blade tip rub. The control system (10) may also be configured to distribute cooling air to the circumferentially extending chambers (20) positioned radially outward of the ring segments (22) at steady state turbine engine operation to reduce the gaps (26) between the turbine blade tips (14) and the ring segments (22) to increase the operational efficiency of the turbine engine (12) while reducing the likelihood of turbine blade tip rub during startup and hot startup conditions.

Description

ACTIVE TURBINE BLADE TIP CLEARANCE CONTROL SYSTEM

FOR TURBINE ENGINES

FIELD OF THE INVENTION

This invention is directed generally to turbine engines, and more particularly to systems for reducing gaps between turbine airfoil tips and radially adjacent components, such as, ring segments, in turbine engines so as to improve turbine engine efficiency by controlling radial clearances during operation. BACKGROUND

Turbine engines commonly operate at efficiencies less than the theoretical maximum because, among other things, losses occur in the flow path as hot compressed gas travels down the length of the turbine engine. One example of a flow path loss is the leakage of hot combustion gases across the tips of the turbine blades where work is not exerted on the turbine blade. This leakage occurs across a space between the tips of the rotating turbine blades and the surrounding stationary structure, such as ring segments that form a ring seal. This spacing is often referred to as the blade tip clearance.

Blade tip clearances are critical to turbine operation because, during transient conditions such as during engine startup or part load operation, the rotating parts (blades, rotor, and discs) and stationary parts (outer casing, blade rings, and ring segments) thermally expand at different rates. As a result, blade tip clearances can actually decrease during engine startup until steady state operation is achieved at which point the clearances can increase due to rubbing or contact of the blade tip, thereby reducing the efficiency of the engine. Thus, a need exists to reduce the likelihood of turbine blade tip rub and control this undesirably large blade tip clearance.

SUMMARY OF THE INVENTION

An active turbine blade tip clearance control system for increasing efficiency of a turbine engine by reducing the clearance between a tip of a turbine airfoil and a radially adjacent component of the turbine engine is disclosed. In at least one embodiment, the control system may be configured to distribute heating air to one or more circumferentially extending chambers positioned radially outward of one or more ring segments during the engine start up process to reduce the likelihood of turbine blade tip rub. The control system may also be configured to distribute cooling air to the circumferentially extending chambers positioned radially outward of the ring segments at steady state turbine engine operation to reduce the gaps between the turbine blade tips and the ring segments to increase the operational efficiency of the turbine engine while reducing the likelihood of turbine blade tip rub during startup and hot startup conditions.

In at least one embodiment, the active turbine blade tip clearance control system for increasing efficiency of a turbine engine by reducing the clearance between a tip of a turbine airfoil and a radially adjacent component of the turbine engine may include a rotor assembly having at least one turbine blade extending radially outward therefrom. The turbine blade may be formed from least one generally elongated airfoil having a leading edge, a trailing edge, the tip section at a first end, and a root coupled to the airfoil at an end generally opposite the first end for supporting the airfoil and for coupling the airfoil to a disc of the rotor assembly. The clearance control system may include one or more ring segments positioned radially outward from the turbine blade and may have a circumferentially extending body with a radially outer surface. The clearance control system may also include one or more circumferentially extending chambers positioned radially outward of the at least one ring segment and may be at least partially defined by the radially outer surface of the at least one ring segment. The clearance control system may include one or more circumferentially extending impingement channels positioned within the circumferentially extending chamber and positioned radially outward from the radially outer surface of the ring segment. The circumferentially extending impingement channel may include one or more impingement orifices. In at least one embodiment, the circumferentially extending impingement channel may include a plurality of impingement orifices.

In at least one embodiment, the circumferentially extending impingement channel may have a generally rectangular shaped cross-sectional area in a circumferentially extending direction with one or more impingement orifices extending through a radially inner wall of the circumferentially extending impingement channel. The impingement orifice extending through a radially inner wall of the circumferentially extending impingement channel may include a plurality of impingement orifices extending through the radially inner wall of the

circumferentially extending impingement channel. One or more impingement orifices may extend through an aft wall of the circumferentially extending impingement channel. In at least one embodiment, a plurality of impingement orifices may extend through the aft wall of the circumferentially extending impingement channel.

One or more impingement inserts may extend aft from one or more

impingement orifices and terminate before contacting an adjacent turbine

component. The impingement insert may be releasably coupled to the

circumferentially extending impingement channel. The impingement insert may include threads on an outer surface that are configured to mate with threads on a surface forming the impingement orifice, thereby enabling the impingement insert to be threadably attached to a wall forming the circumferentially extending impingement channel.

In at least one embodiment, the circumferentially extending impingement channel may have a generally circular shaped cross-sectional area in a

circumferentially extending direction with one or more impingement orifices extending through an outer wall forming the circumferentially extending impingement channel. In at least one embodiment, the circular shaped circumferentially extending impingement channel may be formed from a plurality of impingement orifices extending through the outer wall forming the circumferentially extending

impingement channel. One or more impingement inserts may extend from one or more impingement orifices and may terminate before contacting an adjacent turbine component. The impingement insert may be releasably coupled to the

circumferentially extending impingement channel. The impingement insert may include threads on an outer surface that are configured to mate with threads on a surface forming the impingement orifice, thereby enabling the impingement insert to be threadably attached to a surface forming the circumferentially extending impingement channel. The circular shaped circumferentially extending impingement channel may include a plurality of impingement inserts, whereby each impingement insert extends from an impingement orifice and terminates before contacting an adjacent turbine component. The plurality of impingement inserts and impingement orifices without impingement inserts may be positioned in an alternating repetitive manner.

In at least one embodiment, the active turbine blade tip clearance control system may include one or more circumferentially extending impingement channel with a generally rectangular shaped cross-sectional area in a circumferentially extending direction with one or more impingement orifices extending through a radially inner wall of the circumferentially extending impingement channel. The circumferentially extending impingement channel may be positioned radially outward from a stage one turbine vane and stage one turbine blade. The clearance control system may include a plurality of circumferentially extending impingement channels having generally circular shaped cross-sectional areas in a circumferentially extending direction with one or more impingement orifices extending through an outer wall of each circumferentially extending impingement channel . A first circumferentially extending impingement channel with a generally circular shaped cross-sectional area may be positioned radially outward from a stage two turbine vane and stage two turbine blade. A second circumferentially extending

impingement channel with a generally circular shaped cross-sectional area may be positioned radially outward from a stage three turbine vane and stage three turbine blade. A third circumferentially extending impingement channel with a generally circular shaped cross-sectional area may be positioned radially outward from a stage four turbine vane and stage four turbine blade.

The clearance control system may be used to preheat the radially adjacent components to the tips of the turbine blades, such as, but not limited to the ring segments to prevent tip rub during start up or during a hot restart of the turbine engine. A heating fluid, such as, but not limited to, heated air, may be passed from the heating fluid supply source, through a flow controller to the impingement supply channel to the circumferentially extending impingement channel to preheat the ring segments. The amount of heating provided to the ring segments may be modulated by controlling the flow controller, which may be manually, via automatic control, or other appropriate manner. Once the turbine engine passes through a critical speed relative to a risk of tip rub, the clearance control system may reduce the heating of the ring segments. While the turbine engine is at steady state load or other appropriate operating conditions, the clearance control system may shutoff heating of the ring segments via the circumferentially extending impingement channels. It may be necessary to use the clearance control system to provide cooling fluid, such as, but not limited to cooling air, to the ring segments to reduce the temperature of the ring segments during steady state operation to reduce the size of the gaps between the turbine blade tips and the ring segments to increase the operational efficiency of the turbine engine at steady state.

An advantage of the active turbine blade tip clearance control system is that the clearance control system enables ring segments and related components to be heated quickly at startup to provide as large as possible clearance between turbine blade tips and the radially adjacent ring segments to avoid turbine blade tip rubbing due to cold casing and rapidly growing rotor tip pinch points.

Another advantage of the active turbine blade tip clearance control system is that the clearance control system enables ring segments and related components to be heated for hot restart to avoid turbine blade tip rubbing due to cold casing and rapidly growing rotor tip pinch points.

Yet another advantage of the active turbine blade tip clearance control system is that the clearance control system enables the heated fluid to be cutoff at steady state operating conditions and can even provide cooling fluids to the ring segments to cool the ring segments to reduce the gap between the turbine blade tips and the ring segments to increase the operational efficiency of the turbine engine.

These and other advantages and details of the clearance control system are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the presently disclosed invention and, together with the description, disclose the principles of the invention.

Figure 1 is a cross-sectional view of a turbine engine with an active turbine blade tip clearance control system. Figure 2 is a cross-sectional view of the turbine assembly of the turbine engine of Figure 1 with the active turbine blade tip clearance control system.

Figure 3 is a detail view of the active turbine blade tip clearance control system positioned in the turbine engine of Figure 1 .

Figure 4 is detail view of an impingement insert of the active turbine blade tip clearance control system insert taken at detail line 4-4 in Figure 3.

Figure 5 is a detail perspective view of the impingement insert taken at detail line 5-5 in Figure 4. DETAILED DESCRIPTION OF THE INVENTION

As shown in Figures 1 -5, an active turbine blade tip clearance control system 10 for increasing efficiency of a turbine engine 12 by reducing the clearance between a tip 14 of a turbine airfoil 16 and a radially adjacent component 18 of the turbine engine 12 is disclosed. In at least one embodiment, the control system 10 may be configured to distribute heating air to one or more circumferentially extending chambers 20 positioned radially outward of one or more ring segments 22 during the engine start up process to reduce the likelihood of turbine blade tip rub. The control system 10 may also be configured to distribute cooling air to the circumferentially extending chambers 20 positioned radially outward of the ring segments 22 at steady state turbine engine operation to reduce the gaps 26 between the turbine blade tips 14 and the ring segments 22 to increase the operational efficiency of the turbine engine 12 while reducing the likelihood of turbine blade tip rub during startup and hot startup conditions.

In at least one embodiment, the active turbine blade tip clearance control system 10 may be configured to reduce the clearance between the tips 14 of turbine airfoils 16 and one more radially adjacent components 18 of the turbine engine 12. The turbine engine 12 may include a rotor assembly 24 having one or more turbine blades 16 extending radially outward therefrom. The turbine blade 16 may be formed from one or more generally elongated airfoils 30 having a leading edge 32, a trailing edge 34, the tip section 14 at a first end 36, and a root 38 coupled to the airfoil 30 at a second end 40 generally opposite the first end 36 for supporting the airfoil 30 and for coupling the airfoil 30 to a disc of the rotor assembly 24. The turbine blade 16 may have any appropriate shape, size and configuration either already developed or heretofore yet to be developed. The turbine blade 16 may extend radially outward such that the tip 14 is positioned in close proximity to a turbine component 18 positioned radially outward from the turbine blade 16. One or more turbine components 18 may be positioned radially outward from the turbine blade 16. In at least one embodiment, the turbine components 18 positioned radially outward from the turbine blade 16 include, but are not limited to, one or more ring segments 22. The ring segments 22 may be positioned radially outward from the turbine blade 16 and may have a circumferentially extending body 44 with a radially outer surface 46. One or more ring segments 22 may be positioned end to end to extend circumferentially around the rotor assembly 24 to form a ring radially outward of the tips 14 of the turbine blades 16.

The clearance control system 10 may include one or more circumferentially extending chambers 20 positioned radially outward of one or more ring segments 22 and the radially outer surfaces 46 of the ring segments 22. In at least one

embodiment, the circumferentially extending chamber 20 may be formed at least in part by the radially outer surface 46 of the ring segment 22 and by a shield 28 protecting the circumferentially extending chamber 20 from the effects from the combustion volume. The clearance control system 10 may include one or more circumferentially extending impingement channels 50 positioned within the circumferentially extending chamber 20 and positioned radially outward from the radially outer surface 46 of the ring segment 22. The circumferentially extending impingement channel 50 may include one or more impingement orifices 52. In at least one embodiment, the clearance control system 10 may include a plurality of impingement orifices 52.

The circumferentially extending impingement channels 50 may be supplied with heating fluid or cooling fluid, or both, via one or more impingement supply channels 54. One or more impingement supply channels 54 may be coupled to each of the circumferentially extending impingement channels 50. The impingement supply channels 54 may have any appropriate configuration. The impingement supply channels 54 may be coupled to a heating fluid supply source 56 or may be coupled to a cooling fluid supply source 58, or both. In at least one embodiment, flow of heating fluid from the heating fluid supply source 56 may be controlled with one or more flow controllers 60, which may be, but it not limited to being, a valve. Similarly, the flow of cooling fluid from the cooling fluid supply source 58 may be controlled with one or more flow controllers 60, which may be, but it not limited to being, a valve.

In at least one embodiment, as shown in Figures 2 and 3, one or more circumferentially extending impingement channels 50 may have a generally rectangular shaped cross-sectional area in a circumferentially extending direction with at least one impingement orifice 52 extending through a radially inner wall 62 of the circumferentially extending impingement channel 50. The impingement orifice 52 may have any appropriate size and configuration. In at least one embodiment, the clearance control system 10 may include plurality of impingement orifice 52 extending through a radially inner wall 62 of the circumferentially extending impingement channel 50. One or more impingement orifices 52 may extend through an aft wall 64 of the circumferentially extending impingement channel 50. In at least one embodiment, a plurality of impingement orifices 52 may extend through the aft wall 64 of the circumferentially extending impingement channel 50.

One or more impingement inserts 66 may extend aft from the impingement orifice 52 and terminate before contacting an adjacent turbine component 18. The impingement insert 66 may be configured to extend an effective exhaust outlet 78 of an impingement orifice 52 into a closer position relative to an adjacent turbine component 18, thereby increasing the effectiveness of the impingement jet 68 being exhausted from the impingement orifice 52. The impingement insert 66 may be releasably coupled to the circumferentially extending impingement channel 50. The impingement insert 66 may include threads 70 on an outer surface 72 that are configured to mate with threads 70 on a surface 74 forming the impingement orifice 52, thereby enabling the impingement insert 66 to be threadably attached to a wall 76 forming the circumferentially extending impingement channel 50. The

impingement insert 66, as shown in Figure 5, may include one or more slots 108 at a distal end enabling the impingement insert 66 to be rotated via a Philips head screw driver or the like. In at least one embodiment, as shown in Figures 2 and 3, one or more circumferentially extending impingement channels 50 may have a generally circular shaped cross-sectional area in a circumferentially extending direction with at least one impingement orifice 52 extending through an outer wall 76 forming the

circumferentially extending impingement channel 50. In at least one embodiment, the circular shaped circumferentially extending impingement channels 50 may have a plurality of impingement orifices 52 extending through the outer wall 76 forming the circumferentially extending impingement channel 50. One or more impingement inserts 66 may extend from one or more impingement orifices 52 and may terminate before contacting an adjacent turbine component 18. The impingement insert 66 may be releasably coupled to the circular shaped circumferentially extending impingement channel 50. The impingement insert 66 may include threads 70 on the outer surface 72 that are configured to mate with threads 70 on the surface 74 forming the impingement orifice 52, thereby enabling the impingement insert 66 to be threadably attached to the wall 76 forming the circumferentially extending

impingement channel 50.

In at least one embodiment, a plurality of impingement inserts 66 may extend from an impingement orifice 52 and terminate before contacting an adjacent turbine component 18. The plurality of impingement inserts 66 and impingement orifices 52 without impingement inserts 66 may be positioned in an alternating repetitive manner between the impingement inserts 66. The exhaust outlets 78 of the impingement inserts 66 may be aligned with aspects of the adjacent turbine component 18 that have an outer surface 46 further from the circumferentially extending impingement channel 50 than aspects of the adjacent turbine component 18 aligned with the impingement orifices 52. In at least one embodiment, as shown in Figure 3, the impingement orifices 52 may be aligned with the surfaces 46 of the adjacent turbine component 18 that are generally perpendicular to a longitudinal axis 80 of the impingement orifice 52. The exhaust outlets 78 of the impingement inserts 52 may be generally aligned with surfaces 46 of the adjacent turbine component 18 that are nonorthogonal to the longitudinal axis 80 of the impingement orifice 52, such as, but not limited to, corners 82 and the like. The exhaust outlets 78 of the impingement inserts 52 may also be directed to surfaces that are farther from the outer wall 76 than is necessary for efficient impingement cooling.

In at least one embodiment, the clearance control system 10 may include at least one circumferentially extending impingement channel 50 having a generally rectangular shaped cross-sectional area in a circumferentially extending direction with at least one impingement orifice 52 extending through a radially inner wall 62 of the circumferentially extending impingement channel 50. The circumferentially extending impingement channel 50 may be positioned radially outward from a stage one turbine vane 84 and a stage one turbine blade 86. In at least one embodiment, the stage one turbine vane 84 may be formed from a plurality of turbine vanes 88 assembled into a circumferentially extending row, and the stage one turbine blade 86 is formed from a plurality of turbine blades 16 assembled into a circumferentially extending row aft of the stage one turbine vanes 84. The clearance control system 10 may include a plurality of circumferentially extending impingement channels 50 having generally circular shaped cross-sectional areas in a circumferentially extending direction with one or more impingement orifices 52 extending through an outer wall 76 of each circumferentially extending impingement channel 50. More specifically, the clearance control system 10 may include a first circumferentially extending impingement channel 94 with a generally circular shaped cross-sectional area positioned radially outward from a stage two turbine vane 90 and a stage two turbine blade 92. The stage two turbine vane 90 and the stage two turbine blade 92 may be configured similarly to the stage one turbine vane 84 and stage one turbine blade 86, respectively. The clearance control system 10 may include a second circumferentially extending impingement channel 96 with a generally circular shaped cross-sectional area that is positioned radially outward from a stage three turbine vane 98 and a stage three turbine blade 100. The stage three turbine vane 98 and the stage three turbine blade 100 may be configured similarly to the stage one turbine vane 84 and stage one turbine blade 86, respectively. The clearance control system 10 may include a third circumferentially extending impingement channel 102 with a generally circular shaped cross-sectional area is positioned radially outward from a stage four turbine vane 104 and stage four turbine blade 106. The stage four turbine vane 104 and the stage four turbine blade 106 may be configured similarly to the stage one turbine vane 84 and stage one turbine blade 86, respectively.

The clearance control system 10 may be used to preheat the radially adjacent components 18 to the tips 14 of the turbine blades 16, such as, but not limited to the ring segments 22 to prevent tip rub during start up or during a hot restart of the turbine engine 12. A heating fluid, such as, but not limited to, heated air, may be passed from the heating fluid supply source 56, through a flow controller 60 to the impingement supply channel 54 to the circumferentially extending impingement channel 50 to preheat the ring segments 22. The amount of heating provided to the ring segments 22 may be modulated by controlling the flow controller 60, which may be manually, via automatic control, or other appropriate manner. Once the turbine engine passes through a critical speed relative to a risk of tip rub, the clearance control system 10 may reduce the heating of the ring segments 22. While the turbine engine 12 is at steady state load or other appropriate operating conditions, the clearance control system 10 may shutoff heating of the ring segments 22 via the circumferentially extending impingement channels 50. It may be necessary to use the clearance control system 10 to provide cooling fluid, such as, but not limited to cooling air, to the ring segments 22 to reduce the temperature of the ring segments 22 during steady state operation to reduce the size of the gaps 26 between the turbine blade tips 14 and the ring segments 22 to increase the operational efficiency of the turbine engine 12 at steady state.

The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of this invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of this invention.

Claims

CLAIMS What is claimed is:

1 . An active turbine blade tip clearance control system (10) for increasing efficiency of a turbine engine (12) by reducing the clearance between a tip (14) of a turbine airfoil (16) and a radially adjacent component of the turbine engine (12), characterized in that:

a rotor assembly (24) having at least one turbine blade (16) extending radially outward therefrom;

wherein the at least one turbine blade (16) is formed from at least one generally elongated airfoil (30) having a leading edge (32), a trailing edge (34), the tip section (14) at a first end (36), and a root (38) coupled to the airfoil (30) at an end (40) generally opposite the first end (36) for supporting the airfoil (30) and for coupling the airfoil (30) to a disc of the rotor assembly (24);

at least one ring segment (22) positioned radially outward from the at least one turbine blade (16) and having a circumferentially extending body (44) with a radially outer surface (46);

at least one circumferentially extending chamber (20) positioned radially outward of the at least one ring segment (22) and including the radially outer surface (46) of the at least one ring segment (22);

at least one circumferentially extending impingement channel (50) positioned within the at least one circumferentially extending chamber (20) and positioned radially outward from the radially outer surface (46) of the at least one ring segment (22); and

wherein the at least one circumferentially extending impingement channel (50) includes at least one impingement orifice (52).

2. The active turbine blade tip clearance control system (10) of claim 1 , characterized in that the at least one circumferentially extending impingement channel (50) includes a plurality of impingement orifices (52).

3. The active turbine blade tip clearance control system (10) of claim 1 , characterized in that the at least one circumferentially extending impingement channel (50) has a generally rectangular shaped cross-sectional area in a circumferentially extending direction with at least one impingement orifice (52) extending through a radially inner wall (62) of the at least one circumferentially extending impingement channel (50).

4. The active turbine blade tip clearance control system (10) of claim 3, characterized in that the at least one impingement orifice (52) extending through a radially inner wall (62) of the at least one circumferentially extending impingement channel (50) comprises a plurality of impingement orifices (52) extending through the radially inner wall (62) of the at least one circumferentially extending impingement channel (50).

5. The active turbine blade tip clearance control system (10) of claim 3, further characterized in that at least one impingement orifice (52) extending through an aft wall (64) of the at least one circumferentially extending impingement channel (50).

6. The active turbine blade tip clearance control system (10) of claim 5, characterized in that the at least one impingement orifice (52) extending through an aft wall (64) of the at least one circumferentially extending impingement channel (50) comprises a plurality of impingement orifices (52) extending through the aft wall (64) of the at least one circumferentially extending impingement channel (50).

7. The active turbine blade tip clearance control system (10) of claim 5, further characterized in that an impingement insert (66) extending aft from the at least one impingement orifice (52) and terminating before contacting an adjacent turbine component (18).

8. The active turbine blade tip clearance control system (10) of claim 7, characterized in that the impingement insert (66) is releasably coupled to the at least one circumferentially extending impingement channel (50).

9. The active turbine blade tip clearance control system (10) of claim 7, characterized in that the impingement insert (66) includes threads (70) on an outer surface (72) that are configured to mate with threads (70) on a surface (74) forming the at least one impingement orifice (52), thereby enabling the impingement insert (66) to be threadably attached to a wall forming the at least one circumferentially extending impingement channel (50).

10. The active turbine blade tip clearance control system (10) of claim 1 , characterized in that the at least one circumferentially extending impingement channel (50) has a generally circular shaped cross-sectional area in a

circumferentially extending direction with at least one impingement orifice (52) extending through an outer wall (76) forming the at least one circumferentially extending impingement channel (50).

1 1 . The active turbine blade tip clearance control system (10) of claim 10, characterized in that the at least one impingement orifice (52) extending through an outer wall (76) forming the at least one circumferentially extending impingement channel (50) comprises a plurality of impingement orifices (52) extending through the outer wall (76) forming the at least one circumferentially extending impingement channel (50).

12. The active turbine blade tip clearance control system (10) of claim 1 1 , further characterized in that an impingement insert (66) extending at least one impingement orifice (52) and terminating before contacting an adjacent turbine component (18).

13. The active turbine blade tip clearance control system (10) of claim 12, characterized in that the impingement insert (66) is releasably coupled to the at least one circumferentially extending impingement channel (50).

14. The active turbine blade tip clearance control system (10) of claim 13, characterized in that the impingement insert (66) includes threads (70) on an outer surface (72) that are configured to mate with threads (70) on a surface (74) forming the at least one impingement orifice (52), thereby enabling the impingement insert (66) to be threadably attached to a wall (76) forming the at least one circumferentially extending impingement channel (50).

15. The active turbine blade tip clearance control system (10) of claim 1 1 , further characterized in that a plurality of impingement inserts (66) whereby each impingement insert (66) extends from an impingement orifice (52) and terminates before contacting an adjacent turbine component (18), wherein the plurality of impingement inserts (66) and impingement orifices (52) without impingement inserts (66) are positioned in an alternating repetitive manner.

16. The active turbine blade tip clearance control system (10) of claim 1 , characterized in that the at least one circumferentially extending impingement channel (50) comprises at least one circumferentially extending impingement channel (50) having a generally rectangular shaped cross-sectional area in a circumferentially extending direction with at least one impingement orifice (52) extending through a radially inner wall (62) of the at least one circumferentially extending impingement channel (50), wherein the at least one circumferentially extending impingement channel (50) is positioned radially outward from a stage one turbine vane (84) and stage one turbine blade (86); and

wherein the at least one circumferentially extending impingement channel (50) comprises a plurality of circumferentially extending impingement channels (50) having generally circular shaped cross-sectional areas in a circumferentially extending direction with at least one impingement orifice (52) extending through an outer wall (76) of each circumferentially extending impingement channel (50);

wherein a first circumferentially extending impingement channel (94) with a generally circular shaped cross-sectional area is positioned radially outward from a stage two turbine vane (90) and stage two turbine blade (92);

wherein a second circumferentially extending impingement channel (96) with a generally circular shaped cross-sectional area is positioned radially outward from a stage three turbine vane (98) and stage three turbine blade (100); and

wherein a third circumferentially extending impingement channel (102) with a generally circular shaped cross-sectional area is positioned radially outward from a stage four turbine vane (104) and stage four turbine blade (106).