Variable guide vanes for gas turbine engines

Abstract

The variable guide vane (VGV) described herein includes an airfoil that interacts with fluid within the gas path of a gas turbine engine. The airfoil is mounted to a knob and is rotatable together with the knob about an axis. The knob includes a platform surface adjacent to the airfoil that defines a portion of the gas path during use. The platform surface of the knob includes recesses for receiving a portion of an adjacent VGV therein and providing clearance between adjacent VGVs at a favorable blade angle.

Description

Technical Field

[0001] This disclosure generally relates to aircraft engines, and more specifically to variable-orientation guide vanes for gas turbine engines. Background Technology

[0002] Variable-orientation guide vanes (also known as variable-guide vanes (VGVs)) are commonly used in the compressors and fans of aircraft gas turbine engines, as well as in some turbine designs. Typically, a VGV has a main shaft passing through its axis of rotation, penetrating the housing, and allowing the VGV to be rotated using an actuation mechanism. The VGV directs air onto the rotor of the gas turbine engine at an angle of incidence desired for engine performance and efficiency. Under certain operating conditions of a gas turbine engine, it is desirable to orient the VGV at a favorable blade angle. However, in existing arrangements of VGVs, the range of motion can be limited. Improvements are desired. Summary of the Invention

[0003] In one aspect, this disclosure describes a variable-orientation guide vane for a gas turbine engine. The variable-orientation guide vane includes:

[0004] An airfoil for interacting with fluid in the gas path of the gas turbine engine, the airfoil having a leading edge and a trailing edge; and

[0005] A button portion, to which the airfoil is mounted and rotatable with the button portion about an axis during use, the button portion having a front end at an angular position corresponding to an angular position of the leading edge of the airfoil relative to the axis, the button portion including a platform surface facing the gas path during use and defining a portion of the gas path, the platform surface including a recess for receiving a portion of a nearby variable-orientation guide vane therein, the recess defining a recessed portion of the platform surface below the front end of the button portion or adjacent to the front end portion of the front end of the button portion.

[0006] In another aspect, this disclosure describes a variable guide vane assembly for a gas turbine engine. The assembly includes:

[0007] A shield, the shield including a shield surface defining a first portion of an annular gas path of the gas turbine engine, the shield including a receiving portion defined in the shield surface;

[0008] A first blade rotatably mounted inside the annular gas path, the first blade including a knob and a first airfoil mounted to the knob, the knob being received in the receiving portion of the shroud, the first knob including a platform surface adjacent to the first airfoil defining a second portion of the annular gas path, the platform surface including a recess defining a recessed portion of the platform surface; and

[0009] A second blade, rotatably mounted adjacent to the first blade inside the annular gas path, includes a second airfoil that is rotatable between: a first orientation of a portion of the second airfoil outside a recess in the platform surface of the first blade; and a second orientation of said portion of the second airfoil inside a recess in the platform surface of the first blade.

[0010] Implementation examples may include combinations of the above features.

[0011] In another aspect, this disclosure describes a method of operating adjacent variable-orientation first and second blades disposed in an annular gas path of a gas turbine engine, the first blade having a first knob portion and a first airfoil mounted to the first knob portion, the second blade having a second knob portion and a second airfoil mounted to the second knob portion, the first and second knob portions being rotatably disposed in corresponding receiving portions formed in a shroud defining a portion of the annular gas path, the first knob portion including a platform surface, the platform surface including a recess defining a recessed portion of the platform surface, the method comprising:

[0012] Rotate the first and second blades; and

[0013] When the first and second blades are rotated, a portion of the second airfoil of the second blade is received in a recess formed in the first knob portion of the first blade.

[0014] Further details of these and other aspects of the subject matter of this application will become apparent from the detailed embodiments and accompanying drawings included below. Attached Figure Description

[0015] Now refer to the attached diagram, in which:

[0016] Figure 1 An axial cross-sectional view of an exemplary turboprop gas turbine engine including variable-orientation guide vanes as described herein is shown.

[0017] Figure 2A and Figure 2B It is a schematic representation of guide vanes with variable orientation at different angular positions;

[0018] Figure 3 It is a perspective view of two exemplary adjacent variable-orientation guide vanes rotatably mounted in the annular gas path of a gas turbine engine;

[0019] Figure 4 yes Figure 3 Enlarged perspective view of the components of the variable orientation guide vane;

[0020] Figure 5 yes Figure 3 A schematic side view of one of the variable-orientation guide vanes together with the shroud surface;

[0021] Figure 6A This is a perspective view of an exemplary button portion of a variable-orientation guide vane in which no recess is formed, showing the baseline geometry of the platform surface of the button portion;

[0022] Figure 6B yes Figure 6A A three-dimensional view of the button, wherein the recess is formed in the surface of the platform;

[0023] Figure 7 yes Figure 6B A schematic top view of the variable-orientation guide vanes; and

[0024] Figure 8 This is a flowchart of a method for operating guide vanes with variable orientation. Detailed Implementation

[0025] The following disclosure describes variable guide vanes (VGVs), associated components, gas turbine engines, and methods. In some embodiments, the VGVs described herein can allow for an extended range of motion and thus allow for more advantageous blade angles. Under certain operating conditions of the gas turbine engine (such as at lower power outputs and / or at idle), a relatively advantageous blade angle may be desired for the VGV. In some embodiments, the VGV as described herein may include a knob configured to provide additional clearance between adjacent VGVs to widen spatial constraints and allow adjacent (i.e., adjacent) VGVs to adopt relatively advantageous blade angles without colliding with each other.

[0026] The term “connection” or “coupled” can include direct connection / coupled (where two elements are in contact with each other) and indirect connection / coupled (where at least one additional element is located between the two elements).

[0027] As used herein, the terms “substantially” and “generally” may be used to modify any quantitative representation that may be permitted to change without causing a change in the essential function associated with it.

[0028] Various aspects of the embodiments are described with reference to the accompanying drawings.

[0029] Figure 1 This is a schematic axial cross-sectional view of an exemplary counter-flow turboprop gas turbine engine 10, including one or more VGV 12s as described herein. Despite the following description and... Figure 1 Specifically, a turboprop gas turbine engine is used as an example; however, it should be understood that aspects of this disclosure are equally applicable to other types of gas turbine engines, including turbine shaft and turbofan gas turbine engines. The gas turbine engine 10 can be of the type that is preferably configured to drive a load such as a propeller 14 in subsonic flight via a low-pressure shaft 16 (sometimes referred to as a "power shaft") coupled to a low-pressure turbine 18. In some embodiments, the propeller 14 may be coupled to the low-pressure shaft 16 via a reduction gearbox (not shown). The low-pressure turbine 18 and the low-pressure shaft 16 may be part of a first shaft portion of the gas turbine engine 10, referred to as the low-pressure shaft section. The gas turbine engine 10 may include a second or high-pressure shaft section, which includes a high-pressure turbine 20, an (e.g., multi-stage) compressor 22, and a high-pressure shaft 24.

[0030] Compressor 22 draws ambient air into engine 10 via an annular radial air inlet duct 26, increases the pressure of the drawn air, and delivers the pressurized air to combustor 28. At combustor 28, the pressurized air mixes with fuel and is ignited to produce an annular hot combustion gas flow. High-pressure turbine 20 extracts energy from the thermally expanded combustion gases, thereby driving compressor 22. The hot combustion gases leaving high-pressure turbine 20 can be further expanded, flow through, and drive low-pressure turbine 18, where they are accelerated. The combustion gases can then exit gas turbine engine 10 via exhaust duct 30.

[0031] In some embodiments, the VGV 12 may be adapted to be installed in the core gas path 32 of the engine 10. For example, the VGV 12 may be a variable inlet guide vane disposed upstream of the compressor 22. Alternatively, the VGV 12 may be disposed between the two rotor stages of the compressor 22. The gas path 32 may have a generally annular shape and may have a central axis A, which may correspond to the central axis of the engine 12 and may also correspond to the axis of rotation including the shaft portion of the compressor 22. A plurality of VGV 12 may be distributed within the annular gas path 32 and at an angle about the central axis A. In other words, a plurality of VGV 12 may be arranged to define a circular array of VGV 12 within the annular gas path 32. The VGV 12 may have a controllable variable orientation that can be controlled by a controller of the engine 10 based on the operating parameters of the engine 10. In some embodiments, the orientation of the VGV 12 may be changed synchronously via a coordinating ring or via another suitable drive mechanism.

[0032] Figure 2A and Figure 2B It is a schematic representation of a VGV 12 that is oriented differently relative to the central axis A and also relative to the fluid flow F in the annular gas path 32. Figure 2A This illustrates the case where VGV 12 is aligned with its central axis A. In other words, the chord C of VGV 12 can be approximately parallel to the central axis A. This orientation of VGV 12 can correspond to a reference (e.g., zero) orientation where the blade angle α is equal to 0. In this case, the annular gas path 32 can be substantially wide open, and VGV 12 can exert a relatively small influence on the flow F at its current incident angle with the flow F.

[0033] Figure 2B The diagram shows the VGV 12 oriented with a non-zero blade angle α, where the VGV 12 is tilted towards the central axis A and towards the overall direction of the flow F. In this case, compared to... Figure 2A Compared to the previous configuration, the effective area of ​​the annular gas path 32 can be reduced by the orientation of the multiple cooperating VGVs 12. The VGVs 12 can also provide a greater influence on the convection F in this orientation. The VGVs 12 can rotate within an orientation range (e.g., blade angle α). In some embodiments, the VGVs 12 can be... Figure 2A The zero-angle position is rotated in one or both directions, such that the blade angle α can be positive or negative, for example, relative to the central axis A. In some embodiments, the orientation range of VGV 12 can be symmetrical or asymmetrical about the zero position. For example, VGV 12 can be rotated in one direction to a more favorable blade angle α than in the opposite direction.

[0034] Figure 3This is a perspective view of two exemplary adjacent VGVs 12A, 12B rotatably mounted to a shroud 34. The shroud 34 may be a radially inner shroud ring relative to an annular gas path 32. The shroud 34 may include a shroud surface 36 defining a portion of the radially inner boundary of the annular gas path 32. The VGV 12A may include an airfoil 38A mounted to a knob 40A. The airfoil 38A may interact with the fluid flow F within the gas path 32 and may include a leading edge 42A and a trailing edge 44A. The airfoil 38A and the knob 40A may rotate as a unit about a blade axis VA. The blade axis VA may be partially radially or substantially entirely radially oriented relative to a central axis A. The airfoil 38A may be integrally formed with the knob 40A (e.g., cast, machined), or may be formed separately and attached to the knob 40A, for example, by welding. The button portion 40A may define a platform for the VGV12A and may include a platform surface 46A facing the gas path 32 and adjacent to the airfoil 38, defining a portion of the gas path 32 at the radial end of the airfoil 38A. The platform surface 46A may include a recess 48A for receiving a portion (e.g., trailing edge) of the adjacent VGV12 therein. The recess 48A may define a recessed (e.g., sunken, recessed) portion of the platform surface 46A below the peripheral portion outside the recess 48A. The button portion 40A may be received in a receiving portion 50A formed in the shroud 34. The receiving portion 50A may be formed in the shroud surface 36 and open to the gas path 32.

[0035] In some embodiments, VGV 12B may, but does not necessarily, be substantially the same as VGV 12A, and may be offset at an angle from VGV 12A in gas path 32 relative to the central axis A. Figure 3 Only two VGVs 12A and 12B are shown, but it should be understood that more than two VGVs 12A and 12B may be distributed circumferentially around the shroud 34 and mounted in the respective receiving sections. The receiving section 50C is shown without the VGVs installed to illustrate an exemplary internal configuration of the receiving section 50C. The VGV 12B may include an airfoil 38B mounted to the knob 40B. The airfoil 38B may interact with the fluid flow F within the gas path 32 and may include a leading edge 42B and a trailing edge 44B. The airfoil 38B and the knob 40B may rotate as a unit about the blade axis VB. The blade axis VB may be oriented radially or substantially entirely radially relative to the central axis A. The knob 40B may include a platform surface 46B, which includes a recess 48A for receiving a portion of the VGV 12A (e.g., the trailing edge 44A).

[0036] Figure 3The shield 34 is shown as a radially inner shield of the annular gas path 32, and the knobs 40A, 40B are located at the radially inner ends of their respective VGVs 12A, 12B. However, it should be understood that aspects of this disclosure can also be applied to the radially outer shield and to the knobs located at the radially outer ends of their respective VGVs 12A, 12B. For example, recesses 48A, 48B or other types of cutouts or notches can be replaced or additionally incorporated into the radially outer knobs to provide additional clearance (i.e., to prevent interference) between adjacent VGVs 12A, 12B.

[0037] Figure 4 yes Figure 3 Enlarged perspective view of the button portions 40A and 40B of VGV 12A and 12B shown. VGS 12A and 12B can include a first orientation (e.g., α = 0, as...). Figure 2A The blades rotate within a range of angle α (as shown in the diagram), wherein a portion of the airfoil 38A of the VGV 12A (e.g., trailing edge 44A) is outside the recess 48B of the platform surface 46B of the VGV 12B. The range of blade angle α may include more advantageous orientations, such as... Figure 4 As shown, a portion of the airfoil 38A of VGV 12A (e.g., trailing edge 44A) is received inside a recess 48B on the platform surface 46B of VGV 12B.

[0038] The presence of the recess 48B allows a portion of the airfoil 38A to radially overlap the button portion 46B, and thus provides additional clearance to expand the orientation range of VGV 12A without interference between VGV 12A and VGV 12B. In other words, in Figure 4 With the orientation shown in VGV 12A, when viewed along the blade axis VB, a portion of the airfoil 38A may overlap the periphery of the knob 40B (e.g., partially circular). Chamfers 52A and 52B may be respectively positioned at the joints between the airfoils 38A and 38B and the corresponding knobs 40A and 40B.

[0039] Figure 5 This is a schematic side view of the VGV 12B. In some embodiments, the VGV 12A may have substantially the same construction as the VGV 12B. The knob 40B may have a front end 54B and a rear end 56B. When the blade angle α of the VGV 12B is at... Figure 2AIn the zero orientation shown, the front end 54B can be the foremost region of the button portion 40B facing the oncoming fluid flow F. In other words, the front end 54B of the button portion 40B can be positioned at an angular position corresponding to the angular position of the leading edge 42B of the airfoil 38B relative to the blade axis VB. The rear end 56B can be diametrically opposite to the front end 54B and can be the rearmost region of the button portion 40B with respect to the oncoming fluid flow F.

[0040] The recess 48B may define a recessed portion of the platform surface 46B below the platform surface 46B at or adjacent to the front end portion 58B of the button portion 40B. In some embodiments, when the blade angle α of VGV 12B is at Figure 2A In the zero orientation shown, some platform surfaces 46 outside the recess 48B can be substantially flush with the shroud surface 36. Therefore, when the blade angle α of VGV 12B is at zero orientation, the platform surfaces 46 and the shroud surface 46 can cooperate to define a relatively smooth boundary of the gas path 32, which has small discontinuities to interact with the fluid flow F.

[0041] In some embodiments, the shield surface 36 may not be parallel to the central axis A. For example, the shield surface 36 may be tilted toward the central axis A depending on the position of VGV 12B along the gas path 32. In some embodiments, the button portion 40B may have a non-uniform (e.g., tapered) configuration, wherein the thickness T1 at the front end 54B of the button portion 40B may be greater than the thickness T2 at the rear end 56B. The specific configuration of the button portion 40B may depend on the orientation of the shield surface 36 and also the orientation of the blade axis VB, such that some or most of the platform surface 46B may be substantially flush with the shield surface 36.

[0042] The recess 48B may have a maximum depth at a location D relative to one or more portions outside the platform surface 46B. The location D of the recess 48B may also be below the cover surface 36. Along the central axis A, the recess 48B may be positioned closer to the front end 54B of the button 40B than to the rear end 56B of the button 40B. Furthermore, along the central axis A, the location D with the maximum depth may be positioned closer to the front end 54B of the button 40B than to the rear end 56B of the button 40B. At location D of the recess 48B, the button 40B may have a thickness T3. In some embodiments, the thickness T1 of the button 40B at the front end 54B may be greater than the thickness T3. In some embodiments, the thickness T3 may be greater than the thickness T2 of the button 40B at the rear end 56B. Figure 5 As shown, the thicknesses T1, T2, and T3 can be measured along a direction approximately parallel to the blade axis VB.

[0043] Figure 6AThis is an enlarged perspective view of an exemplary button portion 140 of a VGV 112 in which the recess 48B is not formed, showing the reference / baseline geometry of the platform surface 146 of the button portion 140 on which the airfoil 138 can be mounted. The VGV 112 may have substantially the same construction as the VGV 12A, except for the absence of the recess 48B. Similar elements are identified using reference numerals that have been increased by 100. Depending on the process chosen for manufacturing the VGV 12B, in some embodiments, the VGV 112 may be a precursor to the VGV 12B before the recess 48B is formed (e.g., machined) into the button portion 140.

[0044] Figure 6B This is an enlarged perspective view of the individual button portion 40B, showing the recess 48B formed in the platform surface 46B. The recess 48B may have a concave shape facing the gas path 32 (shown in...). Figure 5 (Middle). The recess 48B may be located outside the chamfer 52B defined at the junction of the button portion 40B and the airfoil 38B. The recess 48B may include the periphery of the button portion 40B (i.e., radially outwardly opening) to allow a portion of the VGV 12A to laterally enter the recess 48B and overlap the button portion 40B with a larger (i.e., more advantageous) blade angle α. For example, the location D of the maximum depth may be located at or near the periphery of the button portion 40B. Thus, the depth of the recess 48B may gradually increase toward the periphery of the button portion 40B.

[0045] In some embodiments, the recess 48B may have a generally streamlined / profiled overall shape to provide favorable aerodynamic conditions. The shape, size, and location of the recess 48B may be selected based on the specific application and the spatial constraints and clearances desired by the blade geometry. For example, the recess 48B may include one or more transition surfaces 60B that provide a smooth / blended transition with the surrounding portion of the platform surface 46B disposed outside the recess 48B. In some embodiments, the transition surface 60B may provide a chamfered surface blend with the portion of the platform surface 46B disposed outside the recess 48B. In some embodiments, the transition surface 60B may provide a tangentially continuous surface continuity with the portion of the platform surface 46B disposed outside the recess 48B. In some embodiments, the transition surface 60B may provide a curvature-continuous surface continuity with the portion of the platform surface 46B disposed outside the recess 48B. In some embodiments, the transition surface 60B may provide such surface continuity with the platform surface 46B at or near the front end 54B of the button portion 40B or the front end portion 58B of the front end 54B of the button portion 40B.

[0046] Figure 7This is a schematic top view of VGV 12B. The recess 48B can be positioned in the left front quadrant of the button portion 40B. In some embodiments, depending on the orientation range of VGV 12, a second recess 48B can be positioned in the opposite right front quadrant of the button portion 40B. The two recesses 48B can be mirror images of each other, or they can have different shapes and sizes, depending on the clearance requirements on each side of the airfoil 38B.

[0047] The recessed portion 48B can be relative to the normal direction. Figure 7 The blade axis VB of the page extension is offset at an angle from the front end 54B of the button portion 40B. Therefore, in some embodiments, the front end 54B of the button portion 40B may not have any portion of the recess 48B. In other words, the front end 54B of the button portion 40B may be outside the recess 48B. The position D of the maximum depth of the recess 48B may be offset at an angle from the front end 54B of the button portion 40B. In some embodiments, the position D of the maximum depth of the recess 48B may, for example, be offset at an angle β between 30 and 60 degrees from the front end 54B relative to the blade axis VB.

[0048] Viewed along the blade axis VB, the knob portion 40B may have a periphery P. In various embodiments, the periphery P may be partially or fully circular, or have another shape. For example, most of the periphery P of the knob portion 40B may be generally circular. The portion of the periphery P at and near the rear end 56B may be non-circular (e.g., linear). In some embodiments, the leading edge 42B of the airfoil 38B may be disposed within the periphery P. In some embodiments, the trailing edge 44B of the airfoil 38B may be disposed outside the periphery P.

[0049] Figure 8 This is a flowchart of method 100 for operating VGV 12A, 12B or using other VGVs as described herein. Aspects of method 100 may be combined with aspects of VGV 12A, 12B and other methods or actions disclosed herein. In various embodiments, method 100 may include:

[0050] Rotate the first and second VGVs 12A, 12B (box 102) in the (e.g., annular) gas path 32; and

[0051] When the first and second blades are rotated, a portion of VGV 12A is received in a recess 48B formed in the knob portion 40B of VGV 12B.

[0052] In various embodiments, the button portion 40B may be located radially inside or radially outside of the airfoil 38B of the VGV 12B.

[0053] refer to Figure 7As shown in the peripheral P, when the portion of VGV 12A is received in the recess 48B, the portion of VGV 12A (e.g., the trailing edge 44A) can be disposed inside the peripheral P of the button portion 40B. In other words, when the portion of VGV 12A is received in the recess 48B, the portion of VGV 12A (e.g., the trailing edge 44A) can radially overlap the platform surface 46B of the button portion 40B.

[0054] The embodiments described in this document provide non-limiting examples of possible implementations of the present technology. Upon reading this disclosure, those skilled in the art will recognize that changes can be made to the embodiments described herein without departing from the scope of the present technology. Further modifications can be made by those skilled in the art regarding this disclosure, which will be within the scope of the present technology.

Claims

1. A variable-orientation guide vane for a gas turbine engine, the variable-orientation guide vane comprising: An airfoil that interacts with fluid in the gas path of the gas turbine engine, the airfoil having a leading edge and a trailing edge; as well as A button, to which the airfoil is mounted and rotatable with the button about an axis during use, the button having a front end at an angular position corresponding to an angular position of the leading edge of the airfoil relative to the axis, the button including a platform surface facing the gas path during use and defining a portion of the gas path, the platform surface including a recess in which a portion of a nearby variable-orientation guide vane is received, the recess defining a recessed portion of the platform surface lower than the front end portion of the platform surface at or adjacent to the front end of the button.

2. The variable-orientation guide vane according to claim 1, wherein, The location of the maximum depth of the recess is offset from the axis at an angle between 30 and 60 degrees from the front end of the button.

3. The variable-orientation guide vane according to claim 1, wherein, The maximum depth of the recess is located closer to the front end of the button than to the rear end of the button.

4. The variable-orientation guide vane according to claim 1, wherein: The button portion has a first thickness along the axis at its front end; and The first thickness of the button portion is greater than the second thickness of the button portion along the axis at the location of the maximum depth of the recess.

5. The variable-orientation guide vane according to claim 1, wherein, The recessed portion is located outside the chamfered transition portion between the button portion and the airfoil.

6. The variable-orientation guide vane according to claim 1, wherein: The button portion includes a periphery when viewed along the axis; The leading edge of the airfoil is positioned inside the periphery; and The trailing edge of the airfoil is positioned outside the perimeter.

7. The variable-orientation guide vane according to claim 1, wherein, The recess includes a transition surface that provides tangential-continuous surface continuity with the outer portion of the platform surface outside the recess.

8. The variable orientation guide vane of claim 1, wherein the recess includes a transition surface that provides tangential-continuous surface continuity with the front end portion of the platform surface.

9. A variable guide vane assembly for a gas turbine engine, the assembly comprising: A shield, the shield including a shield surface defining a first portion of an annular gas path of the gas turbine engine, the shield including a receiving portion defined in the shield surface; A first blade rotatably mounted inside the annular gas path, the first blade including a knob and a first airfoil mounted to the knob, the knob being received in a receiving portion of the shroud, the knob including a platform surface adjacent to the first airfoil defining a second portion of the annular gas path, the platform surface including a recess defining a recessed portion of the platform surface; as well as A second blade is rotatably mounted adjacent to the first blade inside the annular gas path. The second blade includes a second airfoil and is rotatable between the following two: a portion of the second airfoil of the second blade is oriented outside a first orientation in a recess on the platform surface of the first blade; And the second orientation of the portion of the second airfoil of the second blade inside the recess in the platform surface of the first blade.

10. The variable guide vane assembly according to claim 9, wherein: The first blade can rotate relative to the central axis of the annular gas path within an orientation range; and When the chord of the first blade is approximately parallel to the central axis of the annular gas path, the peripheral portion of the platform surface outside the recess is approximately flush with the surface of the shield.

11. The variable guide vane assembly according to claim 9, wherein: The first blade can rotate around its axis; The button portion has a first thickness along the axis at its front end; The first thickness of the button portion is greater than the second thickness of the button portion along the axis at the location of the maximum depth of the recess.

12. The variable guide vane assembly according to claim 9, wherein, The knob is positioned radially inside the first airfoil relative to the annular gas path.

13. The variable guide vane assembly according to claim 9, wherein, The portion of the second airfoil of the second blade is the trailing edge of the second airfoil.

14. The variable guide vane assembly according to claim 9, wherein, The recess is positioned closer to the front end of the button than to the rear end of the button.

15. The variable guide vane assembly according to claim 9, wherein, The recessed portion of the recess is lower than the front end of the platform surface at or near the front end of the button.

16. The variable guide vane assembly of claim 15, wherein, The recess includes a transition surface that provides tangential-continuous surface continuity with the front end portion of the platform surface of the button.

17. A method of operating adjacent variable-orientation first and second blades disposed in an annular gas path of a gas turbine engine, the first blade having a first knob portion and a first airfoil mounted to the first knob portion, the second blade having a second knob portion and a second airfoil mounted to the second knob portion, the first and second knob portions being rotatably disposed in corresponding receiving portions formed in a shroud defining a portion of the annular gas path, the first knob portion including a platform surface, the platform surface including a recess defining a recessed portion of the platform surface, the method comprising: Rotate the first blade and the second blade; as well as When the first blade and the second blade are rotated, a portion of the second airfoil of the second blade is received in a recess formed in the first knob portion of the first blade.

18. The method according to claim 17, wherein, The first button is located on the radially inner side of the airfoil of the first blade.

19. The method of claim 17, wherein, When the portion of the second airfoil of the second blade is received in the recess formed in the first knob portion of the first blade, the portion of the second airfoil of the second blade radially overlaps the platform surface of the first blade relative to the annular gas path.

20. The method of claim 17, wherein: The first blade can rotate around its axis; The first button portion has a periphery when viewed along the axis; and When the portion of the second airfoil is received in the recess, the trailing edge of the second airfoil of the second airfoil is positioned inside the periphery of the first button portion.

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