Guide vane

Abstract

A gas turbine engine variable guide vane has a fixed portion on an upstream side, a movable flap on a downstream side and a transfer slot between a fixed portion trailing surface and a movable flap leading surface. The movable flap has opposite pressure and suction sides along a chord line between leading and trailing edges, and is rotatable about an axis along a movable flap span over a range of angular positions between open and closed. The trailing surface has a substantially U-shaped profile with first and second branches respectively partially around the pressure and suction sides. The transfer slot has inlet and exhaust ports respectively on the pressure and suction sides. In the closed position the suction side contacts the second branch closing the exhaust port, and in the open position the second branch directs a first air flow through the transfer slot tangentially over the suction surface.

Claims

1. A variable guide vane for a gas turbine engine comprising: a fixed portion arranged on an upstream side; a movable flap arranged on a downstream side; and a transfer slot defined between a trailing surface of the fixed portion and a leading surface of the movable flap, the movable flap having opposite pressure and suction sides extending along a chord line between leading and trailing edges, the movable flap being rotatable about an axis extending along a span of the movable flap over a range of angular positions between open and closed, the trailing surface having a substantially U-shaped profile with a first branch extending partially around the pressure side of the movable flap, and an opposite second branch extending partially around the suction side of the movable flap, the transfer slot having an inlet port arranged on the pressure side of the movable flap and an exhaust port arranged on the suction side of the movable flap, wherein in use, in the open position the suction side abuts the second branch to close the exhaust port, and in the closed position the second branch directs a first air flow passing through the transfer slot tangentially over the suction surface of the movable flap.

2. The variable guide vane as claimed in claim 1, wherein the fixed portion comprises an internal cavity, the internal cavity being in fluid communication with the transfer slot, the internal cavity being supplied with air at a pressure higher than the airflow passing through the transfer slot, and, in use, directing a second air flow into the transfer slot, directed towards the exhaust port, to thereby supplement the first air flow.

3. The variable guide vane as claimed in claim 2, wherein the internal cavity is fluidly connected to the transfer slot by a plurality of feed slots, the feed slots being arranged along the span of the movable flap.

4. The variable guide vane as claimed in claim 1, wherein the transfer slot has a convergent flow path in a direction extending from the pressure side of the movable flap to the suction side of the movable flap.

5. The variable guide vane as claimed in claim 1, wherein a camber line of the movable flap is coincident with the chord line.

6. The variable guide vane as claimed in claim 1, wherein the axis of the movable flap is offset from the chord line.

7. The variable guide vane as claimed in claim 6, wherein the offset of the axis is in a direction extending towards the pressure side of the movable flap.

8. The variable guide vane as claimed in claim 1, wherein the second branch has an elliptical sectional profile.

9. The variable guide vane as claimed in claim 2, further comprising a heater adapted to impart heat energy to the second air flow.

10. A gas turbine engine comprising a variable guide vane as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) There now follows a description of an embodiment of the invention, by way of non-limiting example, with reference being made to the accompanying drawings in which:

(2) FIG. 1 shows a schematic sectional view of a gas turbine engine incorporating a variable guide vane according to the present invention;

(3) FIG. 2 shows a sectional view of the variable guide vane of FIG. 1, with the movable flap in the open position; and

(4) FIG. 3 shows the variable guide vane of FIG. 1, with the movable flap in the closed position.

(5) It is noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention.

DETAILED DESCRIPTION

(6) Referring to FIGS. 1 to 3, a variable guide vane for a gas turbine engine according to a first embodiment of the invention is designated generally by the reference numeral 200.

(7) FIG. 1 shows a schematic arrangement of a gas turbine engine for a typical aerospace application. The gas turbine engine 100 comprises in flow series an intake 110, a fan 120, an intermediate pressure compressor 130, a high pressure compressor 140, a combustion chamber 150, a high pressure turbine 160, an intermediate pressure turbine 162, a low pressure turbine 164 and an exhaust 168. The high pressure turbine 160 is arranged to drive the high pressure compressor 140 via a first shaft 180. The intermediate pressure turbine 162 is arranged to drive the intermediate pressure compressor 130 via a second shaft 184 and the low pressure turbine 164 is arranged to drive the fan 120 via a third shaft 188. In operation air flows into the intake 110 and is compressed by the fan 120. A first portion of the air flows through, and is compressed by, the intermediate pressure compressor 130 and the high pressure compressor 140 and is supplied to the combustion chamber 150. Fuel is injected into the combustion chamber 150 and is burnt in the air to produce hot exhaust gases which flow through, and drive, the high pressure turbine 160, the intermediate pressure turbine 162 and the low pressure turbine 164. The hot exhaust gases leave the low pressure turbine 164 and flow through the exhaust 168 to provide propulsive thrust. A second portion of the air bypasses the main engine to provide propulsive thrust.

(8) Typically, the intermediate pressure compressor 130 will include airflow control in the form of variable inlet guide vanes 200 for the first stage together with variable stator vanes 200 for the succeeding stages. In this way, as the compressor speed is reduced from its design value these static vanes 200 are progressively closed in order to maintain an acceptable air angle value onto the following rotor blades.

(9) The variable guide vane 200 comprises a fixed portion 210 arranged on an upstream side 202 of the guide vane 200, a movable flap 220 arranged on a downstream side 204 of the guide vane 200, and a transfer slot 240 defined between a trailing surface 212 of the fixed portion 210 and a leading surface 222 of the movable flap 220.

(10) The fixed portion 210 has a streamlined upstream side with the downstream side being shaped to accommodate the leading edge surfaces 222 of the movable flap 220.

(11) The movable flap 220 has an aerofoil cross-sectional profile with opposing pressure and suction sides 224,226 extending along a chord line 228 between a leading edge and a trailing edge. In the present arrangement, a camber line 230 of the movable flap 220 is coincident with the chord line 228, thus providing the movable flap 220 with a symmetric, or uncambered, aerofoil cross-section. In other arrangements, the movable flap 220 may have an asymmetrical or cambered cross-sectional profile.

(12) The movable flap 220 is rotatable about an axis 232 extending along a span of the movable flap 220 over a range of angular positions between open and closed. In the present arrangement, the axis 232 is offset 233 from the chord line 228 of the movable flap 220 in the direction of the pressure side 224 of the movable flap 220. In other arrangements, the axis 232 may be positioned on the chord line 228 or, alternatively, may be offset 233 towards the suction side of the movable flap 220.

(13) The trailing surface 212 of the fixed portion 210 has a substantially U-shaped cross-sectional profile having a first branch 214 and an opposite second branch 216.

(14) The first branch 214 extends partially around the pressure side 224 of the movable flap 220, with the space between the first branch 214 and the pressure side 224 defining an inlet port 242 to the transfer slot 240. The second branch 216 extends partially around the suction side 226 of the movable flap 220, with the space between the second branch 216 and the suction side 226 defining an exhaust port 244 to the transfer slot 240. The second branch 216 has an elliptically shaped sectional profile.

(15) The transfer slot 240, comprising the space between the trailing surface 212 of the fixed portion 210 and the leading surface 222 of the movable flap 220, is an elongate slot 240 extending along the entire span of the movable flap 220. In other arrangements, the transfer slot 240 may extend only partially along the span of the movable flap 220.

(16) The transfer slot 240 has an inlet port 242 arranged on the pressure side 224 of the movable flap 220 and an exhaust port 244 arranged on a suction side of the movable flap 220. In the present arrangement, the transfer slot 240 has a convergent cross-sectional profile in a direction from the inlet port 242 to the exhaust port 244.

(17) The fixed portion 210 comprises an internal cavity 260 extending along a spanwise length of the fixed portion 210. This internal cavity 260 is fluidly connected to the transfer slot 240 via a plurality of feed slots 264. These feed slots 264 are arranged along the length of the internal cavity 260 in an equi-spaced linear array. In other arrangements, the feed slots 264 may be asymmetrically arranged along the spanwise length of the internal cavity 260.

(18) As mentioned above, the movable flap 220 is rotatable between an open position (shown in FIG. 2) and a closed position (shown in FIG. 3). In this context, the terms open and closed are used to refer to the degree of restriction imposed on the airflow into the compressor by the variable guide vanes 200. In other words, in the open position the movable flap 220 is positioned so as to be substantially aligned with the fixed portion 210, which provides minimum restriction to the intake air flow. Similarly, in the closed position the movable flap 220 is rotated such that its suction side 226 moves towards the intake air flow, so restricting and redirecting the intake air flow into the compressor.

(19) With the movable flap 220 in the open position, an air flow entering the compressor of the engine passes over the fixed portion of the variable guide vane 200. In this position, the suction side 226 of the movable flap 220 abuts the second branch 216 of the trailing surface 212 of the fixed portion 210 to close off the exhaust port 244. In normal operation, the suction side 226 of the movable flap 220 will be close to but not in contact with the second branch 216 of the trailing surface 212. However, contact between these surfaces 226,216 may occur under some operational conditions. In any event, with the movable flap 220 in the open position there can be no flow through the transfer slot 240.

(20) As the movable flap 220 is rotated towards the open position, the suction side 226 of the movable flap 220 moves away from the second branch 216 and the exhaust port 244 opens. This allows a first air flow 250 to pass through the transfer slot 240.

(21) Since the pressure on the pressure side 224 of the movable flap 220 is higher than that on the suction side 226, the first air flow 250 will enter the inlet port 242 of the transfer slot 240. The convergent cross-sectional profile of the transfer slot 240 will further accelerate the velocity of the first air flow 250 along the transfer slot 240.

(22) The internal cavity 260 of the fixed portion 210 is provided with a pressurised air feed, in this arrangement taken from a later stage of the compressor. This pressurised air is fed, as a second air flow 262, through the feed slots 264 between the internal cavity 260 and the transfer slot 240, and into the transfer slot 240 where it supplements the first air flow 250.

(23) The combined first and second air flows 250,262 then exit the transfer slot 240 through the exhaust port 244. The elliptically shaped profile of the exhaust port 244 directs the exhaust flow tangentially over the suction surface 226 of the movable flap 220. This tangential flow serves to re-energise the boundary layer on the suction side 226 of the movable flap 220. This in turn acts to minimise pressure loss resulting from flow separation across the suction side 226.

(24) The foregoing description of various aspects of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person of skill in the art are included within the scope of the invention as defined by the accompanying claims.