Variable inlet guide vane for a gas turbine engine

Abstract: An inlet guide vane in a gas turbine engine comprises a strut airfoil portion 28, a flap airfoil portion 32 and a seal 72 arranged therebetween to prevent airflow through the gap 70 between the airfoil portions. The seal 72 may include a longitudinally extending tubular portion 80 that has a longitudinal axis 84 defined therethrough, a dovetail portion 82 including a rib portion 90 and a retaining feature 92. The rib portion 90 is integral with the tubular portion 80 and extends parallel to the axis 84, and the rib portion 90 extends in a direction radially outward from the axis 84. The retaining feature 92 is integral with the rib portion 90 and tapers toward the axis 84.

Description: This invention relates to gas turbine engines, and specifically to compressors thereof having selectively positionable inlet guide vanes for directing the flow of airflow entering the engine. In aircraft gas turbines engines, such as the type shown in Figure 1, compressors 10 are used to compress the air 12 entering the gas turbine engine 14. For maximum efficiency the airflow 12 entering the upstream end 16 of the compressor 10 must impinge the fan blades 18 of the compressor 10 at a precise orientation relative to the longitudinal axis 20 of the engine 14. The precise orientation is determined by the design of the engine 14 and the conditions at which the engine is operated. In order to optimize performance at a number of different operating conditions, many gas turbine engines include a mechanism for selectively controlling the angle at which the incoming air 12 impinges the first stage of compressor blades 18. As shown in Figure 1, a gas turbine engine 14 includes one or more rotor shafts 22 which are suitably supported by annular frames. Typically, a fan 18 is joined to a fan shaft 22 that is supported at its forward end in a fan inlet case. The fan inlet case includes an annular outer casing 24 and an inner shroud 26, and a plurality of circumferentially spaced apart struts 28 extending therebetween. The struts 28 are fixed relative to the inner shroud 26 and the casing 24. The struts 28 are aerodynamically shaped to direct air 12 entering the engine inlet 30 efficiently between adjacent struts 28 prior to reaching the fan 18. Such struts 28 are hereinafter referred to as "strut airfoils". Bearing 36, whose housing is attached to the inner shroud 26 of the fan inlet case supports the rotating fan shaft 22. The loads from the fan shaft 22 are transmitted through the inner shroud 26 and strut airfoils 28 to the annular casing 24. Since the air angle of impingement onto the fan blade varies as a function of the conditions at which the engine 14 is being operated, selectively positionable flaps 32 are positioned upstream of the compressor blades 18 to direct the incoming air 12 to the fan stage 18 of the compressor. Such flaps 32 are hereinafter referred to as "flap airfoils". As shown in Figure 2, each flap airfoil 32 is positioned immediately downstream of one of the strut airfoils 28 relative to the incoming airflow 12. These flap airfoils 32 are rotatable about a reference axis, and such rotation varies the angle at which the incoming airflow impinges the blades of the fan stage 18 of the compressor 10. Together, the strut airfoil 28 and the flap airfoil 32 immediately downstream thereof form an inlet guide vane. For optimum engine operating efficiency and stability, it is important that a smooth airflow transition occurs between the strut airfoil 28 and the flap airfoil 32 immediately downstream thereof at all engine operating conditions. However, in some designs of the prior art, the inlet guide vanes introduce turbulence into the airflow at certain rotational positions of the flap airfoil. This turbulence is sufficient to cause a nonintegral rotor blade vibration known as "flutter" in the blades of the fan immediately downstream of the inlet guide vanes. In severe cases, the flutter may damage a fan blade, shorten its useable life, or restrict operation of the engine. As those skilled in the art will readily appreciate, any condition which could impair normal engine operation while the aircraft is in flight, should be avoided. What is needed is a means for minimizing the amount of turbulence introduced into the airflow as air flows through the inlet guide vanes to the fan. An object of the present invention is to provide a seal for an inlet guide vane that is located in the gap between the strut airfoil and the flap airfoil to prevent the flow of air through the gap. Another object of the present invention is to provide a method of preventing turbulence in airflow entering the fan of a gas turbine engine. US-A-3990810 and US-A-4097187 both disclose gas turbine vane assemblies as set forth in the preamble to claim 1. US-A-1998791 discloses a sealing strip for use in sealing refrigerator doors. From a first aspect the present invention provides a gas turbine inlet guide vane as claimed in claim 1. The invention also provides a seal as claimed in claim 12 and a method of preventing turbulence in air entering the fan of a gas turbine engine as claimed in claim 21. A preferred embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which: FIG. 1 is a schematic view of a gas turbine engine. FIG. 2 is a cross sectional view of a guide vane of the prior art. FIG. 3 is a partial cross sectional view of an engine inlet showing an inlet guide vane. FIG. 4 is a cross sectional view of an inlet guide vane incorporating a seal of the present invention. FIG. 5 is a side view of a seal of the present invention. FIG. 6 is a cross sectional view of a seal of the present invention taken along line 6-6 of FIG. 5. FIG. 7 is a cross sectional view of a seal of the present invention taken along line 7-7 of FIG. 5. FIG. 8 is a cross sectional view similar to the view of FIG. 6 showing a seal of the present invention retained in the retaining slot of the strut airfoil in the free state prior to the flap airfoil installation. Air flowing past an inlet guide vane has a tendency to flow from the pressure side of the inlet guide vane to the suction side of the inlet guide vane. The inventors have discovered that this tendency is great enough to cause air flowing past an inlet guide vane to flow through the gap between the strut airfoil and the flap airfoil thereof. The inventors have further determined that this flow of air through the gap can cause separation of the airflow from the suction side of the inlet guide vane, which introduces turbulence into the airflow entering the fan blades. It is this turbulence that can cause the blades of the fan to flutter and ultimately fail at certain engine operating conditions. An inlet guide vane 100 embodying the present invention is shown in Figure 3 in the inlet of a gas turbine engine. As those skilled in the art will readily appreciate, the inlet comprises an inner shroud 26 and an annular casing 24 spaced radially outward from the inner shroud 26. A plurality of inlet guide vanes 100 extend radially from the inner shroud 26 to the casing 24. Each inlet guide vane includes both a strut airfoil 28 and a flap airfoil 32. The strut airfoils 28, which are preferably spaced uniformly about the circumference of the inner shroud 26, structurally support the annular casing 24 in spaced relation to the inner shroud 26. Accordingly, each of the strut airfoils 28 is fixedly secured to the inner shroud 26 and the casing 24. As in the prior art, the strut airfoils 28 are aerodynamically shaped to deflect air entering the inlet 30 around the strut airfoil 28. Immediately downstream of each strut airfoil 28 is a flap airfoil 32, as shown in Figure 3. Each of the strut airfoils 28 has a strut first end 42 adjacent the inner shroud 26, and a strut second end 44 in spaced relation to the first end 42 and adjacent to the annular casing 24. Additionally, each of the strut airfoils 28 has a strut leading edge surface 46 and a strut trailing edge surface 48. As shown in Figures 3 and 4, first 50 and second 52 strut airfoil surfaces extend from the strut leading edge surface 46 to the strut trailing edge surface 48 and from the strut first end 42 to the strut second end 44 thereof, and as shown in Figure 4, the first and second strut airfoil surfaces 50, 52 are in spaced relation to each other. Referring again to Figure 3, each of the flap airfoils 32 has a flap first end 54 adjacent the inner shroud 26, and a flap second end 56 in spaced relation to the first end 54 and adjacent to the annular casing 24. Additionally, each of the flap airfoils 32 has a flap leading edge surface 58 and a flap trailing edge surface 60. Referring to Figures 3 and 4, first 62 and second 64 flap airfoil surfaces extend from the flap leading edge surface 58 to the flap trailing edge surface 60 and from the flap first end 54 to the flap second end 56 thereof, and as shown in Figure 4, the first and second flap airfoil surfaces 62, 64 are in spaced relation to each other. Each flap airfoil 32 is rotatable about a reference axis 66 relative to the strut airfoil 28 immediately upstream thereof. This reference axis 66, or "trunnion axis", is fixed relative to the strut airfoil 28. The leading edge surface 58 of each flap airfoil 32 is in spaced relation to the trailing edge surface 48 of the strut airfoil 28 immediately upstream thereof, defining a gap 70 therebetween. Located in the gap 70 of each inlet guide vane, and preferably secured to the trailing edge surface 48 of the strut airfoil 28 thereof, is an inlet guide vane seal 72, as shown in Figure 4. The seal 72 of each inlet guide vane 100 extends from the trailing edge surface 48 of the strut airfoil 28 to the leading edge surface 58 of the flap airfoil 32 immediately adjacent thereto, thereby preventing the flow of air through the gap 70. As shown in Figure 5, the seal 72 has a longitudinally extending tubular portion 80 and a dovetail portion 82, and a longitudinal axis 84 extends the length of the tubular portion 80. The tubular portion 80 includes first and second surfaces 86, 88, and both surfaces 86, 88 are in spaced relation to the longitudinal axis 84, as shown in Figure 6. The second surface 88 is located radially outward from the first surface 86 relative to the longitudinal axis 84, and the second surface 88 is covered with a lubricious material, such as PTFE (Teflon TM). As used herein, the term "lubricious material" means a material that having a coefficient of friction not greater than 0.04 when in contact with the flap airfoil leading edge surface 58. The dovetail portion 82 includes a rib portion 90 that is integral with the tubular portion 82, and a retaining feature 92 for securing the seal 72 to the trailing edge 48 of a strut airfoil 28, as shown in Figure 7. Preferably, the retaining feature 92 is a tapered washer, as shown in Figure 5. The rib portion 82 extends along the tubular portion 80 parallel to the longitudinal axis 84, and the rib portion 82 also extends in a direction 94 radially outward from the longitudinal axis 84. The tubular portion 80 and the rib portion 82 are made of an elastomeric material, such as silicone rubber. For durability, the tubular portion 80 includes a reinforcing fiber mesh 96 embedded therein between the first and second surfaces 86, 88. As shown in Figures 5-7, the retaining feature 92 is integral with the rib portion 82 and tapers toward the longitudinal axis 84. The retaining feature 92, which is made of a rigid material such as titanium or aluminum, is preferably embedded into the rib portion 82 of the seal 72. As shown in Figure 8, the trailing edge 48 of the strut airfoil includes a retaining slot 102 that tapers in a direction away from the leading edge 46 of the strut airfoil 28. The slot 102 extends the length of the trailing edge 48, and dovetail portion 82 must be slid into the slot from one of the ends 42, 44 of the strut airfoil 28. The width of the slot 102 is only slightly greater than width of the retaining feature 92 so that once the dovetail portion 82 is received therein, the seal can only be detached from the strut airfoil 28 by sliding the retaining feature 92 out one of the ends 42, 44 of the strut airfoil 28. In operation, air flowing past the inlet guide vanes 100 is prevented from passing through the gap 70 between each flap airfoil 32 and the strut airfoil 28 immediately upstream thereof. Thus, the mechanism described above that causes separation on the suction side of the inlet guide vanes is eliminated, thereby preventing the turbulence that can result from such separation. Accordingly, the fan blades immediately downstream of the inlet guide vanes are not subjected to the type of airflow distortions that cause the flutter and associated engine damage described above. The present invention minimizes turbulence in the airflow entering the fan by eliminating the cause of airflow separation at the inlet guide vane. The present invention thus prevents the detrimental effect that flutter can have on the fan of gas turbine engines at certain engine operating conditions. Although the invention has been shown and described with respect to a preferred embodiment thereof it should be understood by those skilled in the art that other various changes and omissions in the form and detail of the invention may be made without departing from the scope thereof, as defined by the claims.

Claims: A gas turbine variable inlet guide vane comprising: a fixed airfoil portion (28); a rotatable airfoil portion (32) spaced from the fixed airfoil portion (28) so as to define a gap (70) therebetween; and a seal (72) located in the said gap (70) to prevent flow of air through the gap (70); said seal (72) comprising: a longitudinally extending tubular portion (80), said tubular portion (80) having a longitudinal axis (84) defined therethrough; characterised in that : said seal further comprises a dovetail portion (82) including a rib portion (90) and a retaining feature (92), said rib portion (90) being integral with said tubular portion (80) and extending parallel to said axis (84), and said rib portion (90) extending in a direction radially outward from said axis (84), said retaining feature (92) being integral with said rib portion (90) and tapering toward said axis (84); and in that said dovetail portion (82) of said seal is received within a mating slot (102) provided in one of said airfoil portions. The guide vane of claim 1 wherein the tubular portion of said seal (72) comprises first and second surfaces (86,88), which are in spaced relation to said axis, said second surface (88) being radially outward from said first surface (86) relative to said axis (84). The guide vane of claim 1 or 2 wherein the tubular portion (80) and the rib portion (90) of said seal (72) are made of an elastomeric material. The guide vane of claim 3 wherein the elastomeric material is silicone rubber. The guide vane of claim 3 or 4 wherein the tubular portion (80) of said seal (72) includes a reinforcing fiber mesh embedded therein. The guide vane of any preceding claim wherein the external surface (88) of the tubular portion (80) of said seal (72) is covered with a lubricious material. The guide vane of claim 6 wherein said lubricious material is PTFE. The guide vane of any preceding claim wherein the retaining feature (92) of said seal (72) is embedded into the rib portion (90). The guide vane of any preceding claim wherein the retaining feature (92) of said seal (72) is made of a rigid material. The guide vane of claim 9 wherein the retaining feature (92) is made of a metal. A guide vane as claimed in any preceding claim wherein said slot (102) is formed in the fixed airfoil portion (28). A seal (72) for use in a guide vane as claimed in any preceding claim comprising: a longitudinally extending tubular portion (80), said tubular portion (80) having a longitudinal axis (84) defined therethrough; and characterised in that it comprises: a dovetail portion (82) including a rib portion (90) and a retaining feature (92), said rib portion (90) being integral with said tubular portion (80) and extending parallel to said axis (84), and said rib portion (90) extending in a direction radially outward from said axis (84), said retaining feature (92) being integral with said rib portion (90) and tapering toward said axis (84); and in that the retaining feature (92) of said seal (72) is made of a rigid material. The seal of claim 12 wherein the tubular portion of said seal (72) comprises first and second surfaces (86,88), which are in spaced relation to said axis, said second surface (88) being radially outward from said first surface (86) relative to said axis (84). The seal of claim 12 or 13 wherein the tubular portion (80) and the rib portion (90) of said seal (72) are made of an elastomeric material. The seal of claim 14 wherein the elastomeric material is silicone rubber. The seal of claim 14 or 15 wherein the tubular portion (80) of said seal (72) includes a reinforcing fiber mesh embedded therein. The seal of any of claims 12 to 16 wherein the external surface (88) of the tubular portion (80) of said seal (72) is covered with a lubricious material. The seal of claim 17 wherein said lubricious material is PTFE. The seal of any of claims 12 to 18 wherein the retaining feature (92) of said seal (72) is embedded into the rib portion (90). The seal of any of claims 12 to 19 wherein the retaining feature (92) is made of a metal. A method for preventing turbulence in air entering a fan (18) of a gas turbine engine, said method comprising: providing an engine inlet (30), said inlet having an inner shroud (26), an annular casing (24) spaced radially outward from the inner shroud (26), and a plurality of inlet guide vanes extending radially from the inner shroud (26) to the casing (24), each of said guide vane including a strut airfoil (28) and a flap airfoil (32), said strut airfoil (28) of each inlet guide vane in spaced relation to said flap airfoil thereof so defining a gap (70) therebetween, said flap airfoil (32) of each inlet guide vane being rotatable about a reference axis (66) relative to said strut airfoil thereof; and, providing a seal (72) in each inlet guide vane, each seal (72) being located in said gap (70) of said inlet guide vane and extending from said strut airfoil (28) to said flap airfoil (32) thereof, thereby preventing the flow of said air through said gap (70), whereby said seal comprises: a longitudinally extending tubular portion (80), said tubular portion (80) having a longitudinal axis (84) defined therethrough; characterized in that said seal further comprises : a dovetail portion (82) including a rib portion (90) and a retaining feature (92), said rib portion (90) being integral with said tubular portion (80) and extending parallel to said axis (84), and said rib portion (90) extending in a direction radially outward from said axis (84), said retaining feature (92) being integral with said rib portion (90) and tapering toward said axis (84) and being made of a rigid material. A method as claimed in claim 21, characterised in that said seal is a seal as claimed in any of claims 13 to 20.

Inventors: HORVATH LAJOS H, SUROWKA WACLAW I, HORVATH, LAJOS H., SUROWKA, WACLAW I.
Applicants: UNITED TECHNOLOGIES CORP, UNITED TECHNOLOGIES CORPORATION
Application year: 1998
Main classification: F01D17
IPC codes: F01D5, F02C7, F02C9, F01D17, F02K3