EP3449100A2

EP3449100A2 - Twin spool industrial gas turbine engine with variable inlet guide vanes

Info

Publication number: EP3449100A2
Application number: EP17721939.1A
Authority: EP
Inventors: Stephen E. MURRAY; Joseph D. BROSTMEYER; Russell B. Jones; Barry J. BROWN; Justin T. CEJKA
Original assignee: Florida Turbine Technologies Inc
Current assignee: Florida Turbine Technologies Inc
Priority date: 2016-04-25
Filing date: 2017-04-25
Publication date: 2019-03-06
Also published as: WO2017189566A2; WO2017189566A3

Abstract

A large frame heavy duty industrial gas turbine engine that produces twice the power as conventional single spool industrial engines and operates at full power during a hot day. The engine includes a high spool directly driving an electric generator at a synchronous speed of the electric power grid, a low spool with a low pressure turbine (LPT) driving a low pressure compressor (LPC) from the exhaust gas from the high pressure turbine.. The low spool can operate at a higher speed than at the normal temperature conditions to produce high mass flow. A turbine with a variable IGV assembly in which vane airfoils extend between inner and outer buttons, an airfoil center of rotation being located aft of an airfoil aerodynamic center of pressure. The airfoil trailing edge (TE) extends into both buttons to eliminate gap between the airfoil TE and a static part of the turbine.

Description

TWIN SPOOL INDUSTRIAL GAS TURBINE ENGINE WITH VARIABLE

INLET GUIDE VANES

GOVERNMENT LICENSE RIGHTS

This invention was made with United States Government support under contract number DE-FE0023975 awarded by Department of Energy. The United States Government has certain rights in the invention.

TECHNICAL FIELD

The present invention relates generally to a twin spool industrial gas turbine engine, and more specifically to an industrial gas turbine engine with a second spool having a variable inlet guide vane assembly for the low pressure turbine.

BACKGROUND

A large frame, heavy duty industrial gas turbine engine is used in a power plant to drive an electric generator and produce electrical power. In the USA, the electrical power grid operates at 60 Hertz and thus the industrial engine drives a 60 Hertz electric generator that operates at 3,600 rpm. The engine directly drives the electric generator without using a gear box in order to increase efficiency of the engine, since a gear box would reduce the efficiency around 1%. A typical industrial gas turbine engine of 300MW is designed to operate at the 3,600 rpm to be in synchronous speed with the 60 Hertz electric generator. The engine is designed to produce the largest mass flow through the engine and thus produce the maximum power. The industrial engine is designed for what is referred to as an ISO day, which for example would be at a certain outside air or ambient temperature of 60 degrees F. When the outside air temperature is much higher, for example 90 degrees F, the air mass is less dense and thus the mass flow through the industrial engine will be less, resulting is less power produce by the industrial engine and therefore less electrical power produced by the electric generator. The same issues arise for an industrial engine designed for the European market which operates at 50 hertz with an engine and generator operating at 3,000 rpm. Variable angle vanes are used to vary the mass flow through compressor and turbine passages. Compared to fixed airfoils that have integral outer and inner end walls, variable vanes have leakage areas between the airfoil and the end walls. These leakage paths create undesirable aerodynamic losses. The larger the desired swing angle of the airfoil, the bigger the challenge to minimize these gaps. The cycle benefit for having an adjustable vane throat greatly outweighs the leakage debits.

Variable inlet guide vanes are used in both a compressor and a turbine.

However, the structure for a turbine variable inlet guide vane is different than for the compressor variable inlet guide vane. In a compressor, the flow path is decreasing in height as the compressed air passing through the stages of the compressor increases in pressure. Thus, the radial or spanwise height of the trailing edge of the vane decreases in the flow direction of the compressed air. This is the opposite in a turbine where the compressed gas is increasing or expanding in the flow direction. Thus, in a turbine the spanwise height of the vane at the trailing edge is increasing in height. Thus, the leakage across the ends of the vane at the trailing edge will have greater areas due to this structure.

In addition to controlling the gaps, aerodynamic forces acting on the airfoil are considered to select the optimum rotation axis. The airfoil center of pressure is the location where the moments are zero. The rotation axis placed through the center of pressure yields no additional forces over friction to articulate the vane. This center of pressure can vary on position when the stagger angle of the airfoil is changed.

SUMMARY

A large frame heavy duty industrial gas turbine engine capable of operating within a broad range of outside air temperature while still maintaining full power output in order to drive an electric generator as full power. The industrial gas turbine engine includes a high spool with a separately operable low spool or turbocharger that produces compressed air supplied to the high pressure compressor of the high spool. The high spool includes a high pressure compressor, a combustor, and a high pressure turbine that directly drives an electric generator and operates continuously at a speed synchronous with the local electrical power grid, such as 60 Hertz or 50 hertz, to produce electrical power. The low spool or turbocharger includes a low pressure turbine that drives a low pressure compressor. The HPC, the LPT, and the LPC each includes a variable inlet guide vane assembly so that the speed of the electric generator can be operated continuously at the synchronous speed under various ambient temperatures by regulating one or more of the variable inlet guide vane assemblies.

The low spool or turbocharger is designed to operate at a higher speed than the normal operating speed of the engine at the designed for ambient temperature conditions. For a hot day (above the normal ambient temperature design condition), the low spool will need to operate at a higher speed in order to supply a higher mass flow to the high spool in order to operate at the synchronous speed of the generator during the hot day conditions.

Because of the use of the low spool as being a turbocharger for the high spool, and the use of variable inlet guide vanes for the low pressure turbine and the low pressure compressor, the industrial engine of the present invention is capable of operating at twice the power output as any known industrial gas turbine engine. At the present time, the largest known industrial engine for the 60 hertz market has a maximum power output of around 350 MW and for the 50 hertz market at around 500 MW. The twin spool turbocharged industrial gas turbine engine of the present invention can produce in excess of 500 MW for the 60 hertz engine and in excess of 720 MW for the 50 hertz engine.

A turbine variable inlet guide assembly for a gas turbine engine, such as an industrial gas turbine engine having a low pressure turbine, where the variable inlet guide vane assembly includes guide vanes having airfoils that extend between large diameter outer and inner buttons in which the airfoil trailing edge extends into the two buttons so that no gap is formed between the trailing edge and the turbine housing. The airfoil has a center of rotation that is located aft or downstream from an aerodynamic center of pressure which will decrease any gap from forming in the movement of the airfoil from an open position to a closed position and thus increase a performance of the turbine. For a given leakage gap, leakage flow amount and performance loss per unit flow is larger at aft portion of turbine airfoil due to high airfoil velocities than in front portion. In one embodiment, a large frame heavy duty industrial gas turbine engine for electrical power production includes: a high spool with a high pressure compressor, a combustor, and a high pressure turbine; an electric generator directly driven by the high spool at a speed synchronous with a local electrical power grid to produce electrical power; a low spool with a low pressure turbine and a low pressure compressor, the low spool and the high spool being connected such that turbine exhaust from the high pressure turbine drives the low pressure turbine; a compressed air line connecting the low pressure compressor to the high pressure compressor to supply compressed air to the high pressure compressor; a first variable inlet guide vane assembly for the low pressure turbine; and a second variable inlet guide vane assembly for the low pressure compressor, the variable inlet guide vane assembly for the low pressure turbine regulating a power output to drive the low pressure compressor so that the high spool can operate at full power during a normal temperature day and a hot temperature day.

In one aspect of the embodiment, the large frame heavy duty industrial gas turbine engine further includes third variable inlet guide vane assembly for the high pressure compressor.

In one aspect of the embodiment, the low spool is designed to operate at a speed higher than required for a standard iso operating temperature so that the normal mass flow will flow through the engine at hot day conditions and drive the electric generator at full power.

In one aspect of the embodiment, the low spool does not rotate within the high spool.

In one aspect of the embodiment, the electric generator is a 60 hertz generator and the industrial gas turbine engine is capable of producing 500 MW.

In one aspect of the embodiment, the electric generator is a 50 hertz generator and the industrial gas turbine engine is capable of producing 720 MW.

In one embodiment, a turbine with a variable inlet guide vane assembly for a gas turbine engine includes: a variable inlet guide vane located upstream in a flow direction of a rotor blade of the turbine, the variable inlet guide vane having an airfoil, an upper button, and a lower button, the airfoil extending between the upper button and the lower button, the airfoil having a leading edge, a trailing edge, an aerodynamic center of pressure, and a center of rotation, the center of rotation being located downstream in a flow direction of the aerodynamic center of pressure of the airfoil.

In one aspect of the embodiment, the trailing edge of the airfoil is located inward in an airfoil chordwise direction from an outer radius of the upper and lower buttons.

In one aspect of the embodiment, the trailing edge of the airfoil extends into each of the upper button and the lower button such that no gap is formed between the trailing edge of the airfoil and a static structure of the turbine (such as the turbine housing) in which leakage can flow.

In one embodiment, an airfoil for a turbine variable inlet guide vane assembly, the variable inlet guide vane assembly having an outer button and an inner button, includes: a leading edge, a trailing edge, an aerodynamic center of pressure, and a center of rotation, the airfoil center of rotation being aft of the airfoil aerodynamic center of pressure, the airfoil extending between the outer button and the inner button, and an outer radius of each of the inner and outer buttons being greater than a distance of the airfoil trailing edge from the airfoil center of rotation in a chordwise direction of the airfoil.

In one aspect of the embodiment, the outer radius of each of the inner and outer buttons is less than a distance of the airfoil leading edge from the airfoil center of rotation in a chordwise direction of the airfoil.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 shows a cross section view of a twin spool industrial gas turbine engine with variable inlet guide vanes according to the present invention;

FIG. 2 shows the turbocharged industrial gas turbine engine of FIG. 1 in a combined cycle power plant with a HRSG; FIG. 3 shows an isometric view of a variable geometry vane with the rotational axis behind the airfoil center of pressure with the vane having three different positions according to the present invention;

FIG. 4 shows a top view of two adjacent variable guide vanes in the open airfoil position, the nominal airfoil position, and the closed airfoil position of the present invention;

FIG. 5 shows a side view of the turbine variable inlet guide vane with the outer diameter and the inner diameter gaps between the endwalls according to the present invention;

FIG. 6 shows a close-up view of the guide vane airfoil and the upper button arrangement of the present invention; and

FIG. 7 shows a close-up view of the guide vane airfoil and the lower button arrangement of the present invention. DETAILED DESCRIPTION

The present invention is a twin spool industrial gas turbine engine 5 (referred to herein for simplicity as the engine 5) used for electrical power production where the engine 5 can operate at full power even on a hot day when the air temperature is well above the engine design temperature. FIG. 1 shows the engine 5 with a high spool that directly drives (that is, drives without a gear box) an electric generator 55 which operates at 60 Hertz for the United States market or 50 Hertz for the European market. The high spool includes a high pressure compressor (HPC) 51 connected by the high spool shaft 50 to a high pressure turbine (HPT) 52. A high pressure combustor 53 is connected between the HPC 51 and the HPT 52. A variable inlet guide vane (IGV) assembly 57 is positioned upstream of the high pressure compressor 51. The twin spool turbocharged industrial gas turbine engine 5 of the present invention can produce in excess of 500 MW for the 60 hertz engine and in excess of 720 MW for the 50 hertz engine.

The present invention is also a variable inlet guide vane for a turbine in which a rotational axis of the airfoil is located aft of the aerodynamic center of pressure on the airfoil in order to eliminate leakage gaps at the two endwalls. This is done to articulate the turbine vane at the entrance of a low pressure turbine on an axis well aft of the aerodynamic center of pressure. The use of this aft places rotation axis in combination with large diameter end wall buttons, minimized the clearance gaps of the OD and ID interface of the airfoil to end walls. By placing rotation center aft of the aerodynamic center of pressure leakage gap over aft portion of airfoil is minimized. For a given leakage gap, leakage flow amount and performance loss per unit flow is larger at aft portion of turbine airfoil due to high airfoil velocities than in front portion.

The rotational axis centered aft of airfoil's aerodynamic center of pressure creates forces on the vane that makes the system inherently want to close, which is seen as a negative system function. However, the benefit of minimizing the airfoil to end wall gaps creates a performance improvement over today's state of the art (i.e. configurations in which the axis is forward of the airfoil's aerodynamic center of pressure). Additional safeties on the sync ring system that is driven to articulate the vane stems would ensure that the actuator force will have full command to position the vanes at the desired angle.

Referring again to FIG. 1, a low spool with a low pressure turbine (LPT) 61 is connected by the low spool shaft 60 to a low pressure compressor (LPC) 62. The low spool functions as a turbocharger for the high spool. A first variable inlet guide vane assembly 58 is positioned upstream of the LPT 61. A second variable inlet guide vane assembly 64 is positioned upstream of the LPC 62. The high spool can operate separately from the low spool since the high spool does not rotate outside (that is, concentric with) of the low spool, as in a typical twin spool gas turbine engine, such as those that power an aircraft. Further, the high spool directly drives the electric generator 55 at a speed that his synchronous with a speed of a local electrical power grid to produce electrical power. The LPC 62 includes an outlet volute 63 into which the compressed air flows from the LPC 62. The compressor outlet volute 63 is connected to an inlet volute 56 of the HPC 51 through a compressed air line 67, such as a tube, conduit, or pipe.

FIG. 2 shows the twin spool turbocharged industrial gas turbine engine of FIG. 1 in a combined cycle power plant where a heat recovery steam generator (HRSG) 40 is used to produce steam from the exhaust from the low pressure turbine (LPT) 61 that is then used to drive a second electric generator 38. Hot turbine exhaust flow from the LPT 61 flows through line 68 and into the HRSG 40 to produce steam that flows through a high pressure steam turbine 36 and then a low pressure steam turbine 37 that both drive the second electric generator 38. The cooler exhaust from the HRSG 40 flows out of a stack 41 that is connected to the HRSG 40. A first intercooler 65 can be used to cool the compressed air from the low pressure compressor (LPC) 62 in the compressed air line 67 with a flow control valve 66. A turbine airfoil cooling circuit can also be used in which some of the compressed air from the LPC 62 is passed through a second intercooler 71 and then a cooling circuit compressor 72 driven by a motor 73 to increase the pressure so that the turbine airfoil 76 can be cooled by the flow of compressed air therethrough and have enough pressure left over to flow into the high pressure combustor 53. The compressed air line 75 between the cooling circuit compressor 72 and the turbine airfoil 76 and the compressed air line 77 between the turbine airfoil 76 and the high pressure combustor 53 channel the cooling air to and from the air cooled turbine airfoils, such as the stator vanes, respectively. A boost compressor 78 with flow control valve 80 can be used to pressurize air for the high pressure compressor (HPC) 51.

In operation, compressed air from the HPC 51 flows into the high pressure combustor 53, where fuel is burned to produce a hot gas stream that flows into the high pressure turbine (HPT) 52. Hot exhaust from the HPT 52 then flows into the LPT 61 that is used to drive the LPC 62. Compressed air from the LPC 62 flows through the compressed air line 67 and into the inlet of the HPC 51 (for example, into the inlet volute 56). The high spool drives the electric generator 55 and thereby produces electricity. The three sets of variable inlet guide vanes 57, 58, 64 are used to regulatethe flow of compressed air into the HPC 51, LPT 61, and LPC 62, respectively.

Under International Organization for Standardization (ISO) standards, on a standard day where the ambient outside temperature is 60 degrees F, the engine 5 will operate at full power as designed. However, on a hot day (for example, 90 degrees F), the density of the air is less and therefore with a conventional engine, flow of air through the engine will be low and the engine will operate at a lower power level. In a single spool industrial engine, only one shaft is used and that shaft drives the electric generator. Thus, a currently known single spool industrial engine is designed to operate at one speed during cold or hot days but not both, and that speed is the speed of the electric generator which is 60 hertz in the USA market and 50 hertz in

European market. On a hot day (for example, 90 degrees F), the currently known single spool industrial engine will operate at the design speed, but with less power because of the lower density air and thus lower volume flow through the engine. With a conventional currently known two spool industrial engine, limitations to the compressor 53, LPC 62, HPT 52 and/or LPT 61 structural design and absence of a turbine variable inlet guide vane will not allow the physical speed of the gas generator compressor/turbine to be increased to the level required to maintain ISO day (the design speed) engine flow/power.

In the twin spool engine of the present invention, in contrast, the high spool is used to drive the electric generator 55 and thus operates continuously (3,600 rpm for a 60 Hertz engine or 3,000 rpm for a 50 Hertz engine) during different ambient temperatures at the designed speed of the electric generator 55. On a hot day, to make up for the less dense air, the low spool with the LPC 62 is operated at a higher speed so that more compressed air is passed into the HPC 51 to keep the power output consistent. The IGV assembly 58 to the LPT 61 can be closed to increase the pressure ratio across the LPT 61 and therefore increase the output power of the LPT 61 to drive the LPC 62 at the higher speed and produce more compressed air for the HPC 51. A key component of this invention is to design the LPT 61 so that its physical speed

(rpm) can be increased to higher levels when the ambient temperature (that is, outside air temperature) is greater than ISO day conditions without exceeding structural limits. Thus, the low spool is designed to operate at a higher speed than the normal speed at the designed for ambient temperature conditions. For example, the low spool is designed to operate at the 90 degrees F condition as well as the 60 degrees F condition so that the low spool can operate at the higher speed during the hot days (90 degrees F) so that the high spool can operate at full power. Thus, the arrangements of the IGV assemblies 57, 58, 64 and their operation can be used to produce a constant mass flow through the high spool so that the full power of the engine 5 is used to drive the electric generator 55.

The LPC 62 and LPT 61 of the engine 5 are designed for a physical speed higher than required for the standard ISO operating temperature (60 degrees F) so that the normal mass flow will flow through the engine at hot day conditions and drive the electric generator 55 at full power. On a hot day (say, 90 degrees F), the flow through the engine 5 is maintained at ISO day levels by varying the IGV assemblies 57, 58, 64 to increase the speed of the low spool relative to ISO day while maintaining the speed of the high spool at the electric generator design speed. Thus, the engine 5 will operate at full power regardless of the ambient outside air temperature.

FIG. 3 shows an isometric view of a variable inlet guide vane 10 with the rotation axis behind the airfoil center of pressure. FIG. 4 shows a mid-span section of the airfoils in FIG. 3 with circle radius indicating the throat area change as the vane angle is articulated about the selected vane rotation axis. FIG. 5 shows the outer diameter and inner diameter gaps between the outer diameter and inner diameter end walls that are minimized for diverging turbine flow paths with variable guide vanes articulated with axis of rotation aft of the airfoil center of pressure.

FIG. 3 shows one of the airfoils in the variable inlet guide vane 10 for a turbine where the airfoil 11 extends between an outer or upper button 12 and an inner or lower button 13 with an adjustment shaft 14 extending out from the outer button 12. The two buttons 12 and 13 are relatively large diameter buttons when compared to prior art buttons. FIG. 3 shows the airfoil in one of three positions with the open airfoil position 11 A at one extreme, the closed airfoil position 11C at the other extreme, and the airfoil nominal position 1 IB in-between. Although all three positions are shown in FIG. 3, it will be understood that the airfoil 11 will be in one of the three positions shown at any one time. The airfoil center of rotation (CR) is shown as the dashed line. As a non- limiting example, the variable inlet guide vane 10 may be used in a turbine, such as the LPT 61, and may be upstream in a flow direction of a rotor blade of the turbine.

FIG. 4 shows a top view of two adjacent airfoils in the turbine variable inlet guide vane assemblies with the airfoil shown in the three positions 11 A, 11B, and 11C. The aerodynamic center of pressure (CP) and the center of rotation (CR) are shown for each of the two airfoils 11. As seen in FIG. 4, the center of rotation (CR) of each airfoil 11 is located aft of the aerodynamic center of pressure CP (that is, the CR is located downstream in a flow direction of the CP). As the adjacent airfoils 11 rotate about the center of rotation (CR), the spacing between adjacent airfoils 11 changes from DA to DC, where DA is the spacing between adjacent airfoils at the 11A position and DC is the spacing between adjacent airfoil at the 11C position. DA is greater than DC. The spacing DB is the spacing between adjacent airfoils at the nominal position 1 IB. The three circles in FIG. 4 represent a circle from the trailing edge with a radius equal to the spacing between adjacent airfoils at the various three positions 11A to 11C.

FIG. 5 shows one of the airfoils 11 of the turbine variable inlet guide vane assemblies of the present invention with the upper button 12 and the lower button 13 at the two ends of the airfoil 11 and mounted to a turbine housing or other turbine static structure 23. The center of rotation (CR) is located aft of the aerodynamic center of pressure (CP) (that is, closer to the trailing edge TE of the airfoil 11 than to the leading edge LE of the airfoil 11). Because the airfoil 11 ends at the two buttons 12 and 13, as the airfoil 11 pivots from the open airfoil position 11A to the closed airfoil position 11C, no gap is formed between the airfoil trailing edge (TE) region and the button. As seen in FIG. 5, the airfoil trailing edge (TE) is located inward in a chordwise direction of the airfoil from the outer radius of each of the two buttons 12 and 13. Put another way, an outer radius of each of the inner 12 and outer 13 buttons is greater than a distance of the airfoil trailing edge (TE) from the airfoil center of rotation (CR) in a chordwise direction of the airfoil. This is the structure that provides for elimination of any gaps between the trailing edge (TE) of the airfoil (11) and a static structure 23 of the turbine in which leakage can flow. The radius of each of the buttons 12, 13 is less than a distance of the airfoil leading edge (LE) from the airfoil center of rotation (CR) in a chordwise direction of the airfoil. Gaps 21 and 22 do exist in the leading edge regions of the airfoil 11 (and the gaps change from the airfoil positions 11 A to 11C) because the leading edge (LE) of the airfoil 11 is located outward in the chordwise direction of the airfoil from the outer radius of the two buttons 12 and 13. Thus, because no gap is formed between the trailing edge (TE) and the turbine housing or other turbine static structure 23, no leakage can flow across any gap (for example, across a gap 21, 22 between the leading edge (LE) and the turbine housing 23. Since the airfoil trailing edge height is greater than the leading edge height, the gap would be increased when the airfoil was pivoted between positions. Gap leakage flow would be more critical in a turbine than in a compressor because of the hot gas temperature in the turbine. Hot gas leakage causes performance loss as well as short life for the parts due to erosion and thermal stress issues.

FIG. 6 shows the airfoil 11 at the upper button 12 with the airfoil extending from the button in which no gap is formed. FIG. 7 shows a similar structural arrangement between the airfoil and the lower button 13. No gap is formed in the lower span on the TE either. Thus, as the airfoil pivots from the open to the closed position, no gaps are formed at the trailing edge regions in which leakage could flow.

In one embodiment, a large frame heavy duty industrial gas turbine engine for electrical power production includes: a high spool with a high pressure compressor (51), a combustor (53), and a high pressure turbine (52); an electric generator (55) directly driven by the high spool at a speed synchronous with a local electrical power grid to produce electrical power; a low spool with a low pressure turbine (61) and a low pressure compressor (62), the low spool and the high spool being connected such that turbine exhaust from the high pressure turbine (52) drives the low pressure turbine (61); a compressed air line (67) connecting the low pressure compressor (62) to the high pressure compressor (51) to supply compressed air to the high pressure compressor (51); a first variable inlet guide vane assembly (58) for the low pressure turbine (61); and a second variable inlet guide vane assembly (64) for the low pressure compressor (62), the variable inlet guide vane assembly (58) for the low pressure turbine (61) regulating a power output to drive the low pressure compressor (62) so that the high spool can operate at full power during a normal temperature day and a hot temperature day.

In one aspect of the embodiment, the large frame heavy duty industrial gas turbine engine further includes third variable inlet guide vane assembly (57) for the high pressure compressor (51).

In one aspect of the embodiment, the low spool is designed to operate at a speed higher than required for a standard iso operating temperature so that the normal mass flow will flow through the engine (5) at hot day conditions and drive the electric generator (55) at full power.

In one aspect of the embodiment, the low spool does not rotate within the high spool. In one aspect of the embodiment, the electric generator (55) is a 60 hertz generator and the industrial gas turbine engine (5) is capable of producing 500 MW.

In one aspect of the embodiment, the electric generator (55) is a 50 hertz generator and the industrial gas turbine engine (5) is capable of producing 720 MW.

In one embodiment, a turbine with a variable inlet guide vane assembly for a gas turbine engine includes: a variable inlet guide vane (10) located upstream in a flow direction of a rotor blade of the turbine, the variable inlet guide vane (10) having an airfoil (11), an upper button (12), and a lower button (13), the airfoil (11) extending between the upper button (12) and the lower button (13), the airfoil (11) having a leading edge (LE), a trailing edge (TE), an aerodynamic center of pressure (CP), and a center of rotation (CR), the center of rotation (CR) being located downstream in a flow direction of the aerodynamic center of pressure (CP) of the airfoil (11).

In one aspect of the embodiment, the trailing edge (TE) of the airfoil (11) is located inward in an airfoil chordwise direction from an outer radius of the upper and lower buttons (12, 13).

In one aspect of the embodiment, the trailing edge (TE) of the airfoil (11) extends into each of the upper button (12) and the lower button (13) such that no gap is formed between the trailing edge (TE) of the airfoil (11) and a static structure of the turbine in which leakage can flow.

In one embodiment, an airfoil (11) for a turbine variable inlet guide vane assembly, the variable inlet guide vane assembly having an outer button (12) and an inner button (13), includes: a leading edge (LE), a trailing edge (TE), an aerodynamic center of pressure (CP), and a center of rotation (CR), the airfoil center of rotation (CR) being aft of the airfoil aerodynamic center of pressure (CP), the airfoil (11) extending between the outer button (12) and the inner button (13), and an outer radius of each of the inner and outer buttons (12, 13) being greater than a distance of the airfoil trailing edge (TE) from the airfoil center of rotation (CR) in a chordwise direction of the airfoil (11).

In one aspect of the embodiment, the outer radius of each of the inner and outer buttons (12, 13) is less than a distance of the airfoil leading edge (LE) from the airfoil center of rotation (CR) in a chordwise direction of the airfoil (11). It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.

Claims

What is claimed is:

1. A large frame heavy duty industrial gas turbine engine (5) for electric power production, the large frame heavy duty industrial gas turbine engine comprising: a high spool with a high pressure compressor (51), a combustor (53), and a high pressure turbine (52);

an electric generator (55) directly driven by the high spool at a speed synchronous with a local electrical power grid to produce electrical power;

a low spool with a low pressure turbine (61) and a low pressure compressor (62), the low spool and the high spool being connected such that turbine exhaust from the high pressure turbine (52) drives the low pressure turbine (61);

a compressed air line (67) connecting the low pressure compressor (62) to the high pressure compressor (51) to supply compressed air to the high pressure compressor (51);

a first variable inlet guide vane assembly (58) for the low pressure turbine (61); and

a second variable inlet guide vane assembly (64) for the low pressure compressor (62),

the variable inlet guide vane assembly (58) for the low pressure turbine (61) regulating a power output to drive the low pressure compressor (62) so that the high spool can operate at full power during a normal temperature day and a hot temperature day.

2. The large frame heavy duty industrial gas turbine engine (5) of claim 1, further comprising:

a third variable inlet guide vane assembly (57) for the high pressure compressor (51).

3. The large frame heavy duty industrial gas turbine engine (5) of claim 1, wherein the low spool is designed to operate at a speed higher than required for a standard iso operating temperature so that the normal mass flow will flow through the engine (5) at hot day conditions and drive the electric generator (55) at full power.

4. The large frame heavy duty industrial gas turbine engine (5) of claim 1, wherein the low spool does not rotate within the high spool.

5. The large frame heavy duty industrial gas turbine engine (5) of claim 1, wherein:

the electric generator (55) is a 60 hertz generator; and

the industrial gas turbine engine (5) is capable of producing 500 MW.

6. The large frame heavy duty industrial gas turbine engine (5) of claim 1, wherein:

the electric generator (55) is a 50 hertz generator; and

the industrial gas turbine engine (5) is capable of producing 720 MW.

7. A turbine with a variable inlet guide vane assembly for a gas turbine engine comprising:

a variable inlet guide vane (10) located upstream in a flow direction of a rotor blade of the turbine, the variable inlet guide vane (10) having an airfoil (11), an upper button (12), and a lower button (13), the airfoil (11) extending between the upper button (12) and the lower button (13),

the airfoil (11) having a leading edge (LE), a trailing edge (TE), an aerodynamic center of pressure (CP), and a center of rotation (CR), the center of rotation (CR) being located downstream in a flow direction of the aerodynamic center of pressure (CP) of the airfoil (11).

8. The turbine with a variable inlet guide vane assembly of claim 7, wherein the trailing edge (TE) of the airfoil (11) is located inward in an airfoil chordwise direction from an outer radius of the upper and lower buttons (12, 13).

9. The turbine with a variable inlet guide vane assembly of claim 7, wherein the trailing edge (TE) of the airfoil (11) extends into each of the upper button (12) and the lower button (13) such that no gap is formed between the trailing edge (TE) of the airfoil (11) and a static structure of the turbine in which leakage can flow.

10. An airfoil (11) for a turbine variable inlet guide vane assembly, the variable inlet guide vane assembly having an outer button (12) and an inner button (13), the airfoil (11) comprising:

a leading edge (LE), a trailing edge (TE), an aerodynamic center of pressure (CP), and a center of rotation (CR),

the airfoil center of rotation (CR) being aft of the airfoil aerodynamic center of pressure (CP),

the airfoil (11) extending between the outer button (12) and the inner button (13), and

an outer radius of each of the inner and outer buttons (12, 13) being greater than a distance of the airfoil trailing edge (TE) from the airfoil center of rotation (CR) in a chord wise direction of the airfoil (11).

11. The airfoil of claim 10, wherein the outer radius of each of the inner and outer buttons (12, 13) is less than a distance of the airfoil leading edge (LE) from the airfoil center of rotation (CR) in a chordwise direction of the airfoil (11).