GB2162582A - A variable geometry air intake for a gas turbine engine - Google Patents

Abstract

A variable geometry air-intake for a two dimensional oblique shock diffuser for a gas turbine engine in a high performance aircraft, the intake having an upper ramp 1a, a lower lip 2 pivoted at 4 to the front of the base 3 of the intake, the pivoting range being subdivided into a lower subsonic-transonic operating range A of a large angle, between a lower regulating point a and an intermediate regulating point b, and an upper supersonic operating range B of a smaller angle, between the intermediate regulating point b and an upper regulating point c, an additional double-sided flap valve 6 being controlled to operate as an air inlet in the lower operating range A in accordance with the position of lip 2 and forming an air bleed operating in the upper operating range B, also in accordance with the position of lip 2. <IMAGE>

Description

SPECIFICATION Air-intake of variable geometry This invention reiates to an air-intake of variable geometry, particularly a two-dimensional oblique thrust diffuser for a gas turbine engine of a high performance aircraft. Such air-intakes have upper ramps and an air deflection lip pivoted on the forward end of the intake and movable about a transverse shaft, the total pivot range being divided into a lower subsonic transonic operating range (A) of large angular deflection, and extending between a lower setting (a) and an intermediate setting (b), and an upper supersonic operating range (B) of a smaller angular deflection extending between the setting point (b) and an upper setting point (c).

The purpose of the air-intake is to convert as much as possible of the kinetic energy in the air stream into pressure energy with a reduction in velocity. At high Mach numbers this recuperation of energy may be considerable. In order to obtain the optimum recuperation of energy the intake air which is compressed must have low losses and be conveyed in a homogeneous state to the engine, according to the required demand at any instant.

Losses mainly arise from air friction, compressive shocks and spillages. Particular attention must be paid to the drag of the external flow which must be kept to a minimum. Non-uniform air mass is caused chiefly by pressure variations within the flow. If the aforementioned difficulties can be reduced the propulsion systemn comprising the intake and the gas turbine engine will produce, over all performance ranges, a thrust with a satisfactory degree of efficiency. The air-intake and propulsion unit will also generally interact in an aerodynamically stable manner.

At take-off and at low speeds the propulsion unit is supplied with a considerable volume of air due to the low pressure at the inlet, and this means that the narrowest cross section of the air-intake must be made as large as possible. At high speed supersonic flight the air volume at the intake is reduced owing to the high pressure, which means that a small cross section is required in order to maintain the desired position for compression shock waves in the inlet zone of the intake. A modern high performance fighter aircraft capable of flying at supersonic speed is also required to be capable of combat engagements at subsonic speeds.At take off and in subsonic flight with wide angles of incidence, therefore, the maximum intake area is required if the maximum flow of air through the propulsion unit is to be ensured; for minimum air throughput in the supersonic range, however, for example with relatively high air temperatures and part load operation as well as with high Mach numbers, the area must be small. These conflicting demands cannot be met by a fixed surface air inlet since at high angles of incidence for the aircraft in subsonic flight the air inlet, due to separation of the inflow over a fixed inlet lip, gives rise to surging in the compressor, whilst when the propulsion unit requires comparatively little air during supersonic operation, it causes humming in the intake as a result of compression oscillation, leading to instabilities in the engine system.As a fixed air intake has only a very limited range of stable operation, high performance propulsion units are provided with an adjustable intake which is controlled or regulated in accordance with a numbe of flight parameters.

The journal entitled "Oil Engine and Gas Turbine", volume 32, September 1964, pup. 3639, describes a supersonic intake in the form of a two dimensional adjustable oblique thrust diffuser with upper central movable ramps and a bleed device in the inlet end in front of a gas turbine propulsion unit. The adjustment of the upper ramps is effected in accordance with the Mach number, while the air bleed is opened if the intake enters a subcritical operating state in an undesirable manner, that is if the intake is supplying a greater quantityof air than the propulsion unit requires at any moment.

Furthermore, a further air valve functioning as an auxiliary air intake operates on take-off and landing of the aircraft in order to enable the quantity of ingoing air, normally reduced under these conditions, to be supplemented by auxiliary air taken in through the auxiliary air intake.

In DE 23 58 926 an adjustable supersonic air intake with upper movable central ramps is described, in which the particular position occupied at any moment is regulated in accordance with a measured variable which is formed by the ratio between the static pressure over the moveable ramps and the overall pressure of the external flow.

This regulating system ensures that the intake supplies the air throughput required to obtain, over the whole operating range during the supersonic flight, optimum thrust.

Both the aforementioned intake constructions, as far as adjustment of the inlet geometry is concerned, are designed in particular for supersonic operation and not specially for flight conditions with extreme angles of incidence in the subsonic range.

DE 1 066 429 descries a two dimensional supersonic inlet in the form of a two sided oblique thrust diffuser in which the front edges are constructed, above and below the central cone, as pivotable air interception edges. This patent does not describe a system by which the lower and upper air interception edges can be controlled or regulated by any particular parameters.

In DE 28 33 771 relating to an adjustable air inlet for gas turbine jet propulsion units for driving high performance aircraft, with a lower air interception edge articulated to the base of the air intake and movable about a transverse pivot, requires that the entire pivoting range of this air interception edge be sub-divided from a functional point of view into a lower subsonic-transonic operating range A, of a greater angle, between a lower regulating point and an intermediate regulating point, and an upper supersonic operating range B, of a smaller angle, between the intermediate regulating point and an upper regulating point. This enables advantageous operating conditions to be obtained over the entire subsonic and supersonic flight range, even under extreme conditions, including take-off.

This invention seeks to provide an even more advantageous operational system for the supply of air to the propulsion unit, both in a subsonic and supersonic range.

According to this invention there is provided a variable geometry air-intake for a gas turbine engine for a high performance aircraft, the intake having an upper inlet ramp and a lower inlet lip pivotaily mounted to the base ofthe intake on a transverse shaft, the range of pivoting movement of the lip being divided into a lowersubsonic-transonic operating range (A) of a large angle and lying between a lower adjustment point (a) and an intermediate adjustment point (b), and an upper supersonic operating range (B) of a smaller angle and lying between the intermediate regulating point (b) and an upper regulating point (c), wherein the intake further includes an additional air inlet means effective in the lower operating range (A) and in accordance with the position of the lip, and an air bleed means effective in the upper operating range (B) and in accordance with the position of the lip in said range.

This arrangement provides that in subsonic flight the approach air is provided, in accordance with the Mach number and angle of incidence of the aircraft, with a variable complex air intake adapted to the geometrical shape and to the size of the intake cross section, so that even with extreme angles of incidence the separation of the flow and the resulting compressor surge will be avoided not only by the front lip and the auxiliary air inlet but in particular by their interaction and adaptation to each other.

Furthermore, due to the automatically controlled interaction of the lip edge and bleed device, the invention enables the air intake in supersonic operation, even with extremely low airthroughputs, to operate in an optimum manner and be comparatively free of losses and with, as far as possible, minimum resistance and maximum pressure recuperation by proportioned bleed and variable inlet geometry, to keep the operating point of the inlet between the two aerodynamic limits of hum on the one hand and surging on the other even under unusual operating states such as with minimum air throughput Preferably the additional air inlet means and the air bleed means are constructionally combined in the form of a two sided flap valve positioned immediately behind the lip, each side of the valve effecting control of an air inlet aperture and an air bleed aperture respectively.

The air inlet valve and air bleed valve and the lip will preferably be actuated togetherthrough a mechanical linkage such as a parallelogram system.

In a preferred embodiment the air inlet means and the air bleed means or the air inlet valve part and air bleed valve part are controlled in such a way as to be in a closed position (b') when the lip is within an intermediate adjustment range (C) on either side of the intermediate regulating point (b). This has the advantage of limiting both the additional air supply and the air bleed action to the particular performance ranges in which these measures are specifically necessary for the improvement of the air inflow, so that the overall efficiency of the air inlet, as considered over the entire operating range, is increased by reducing the resistance.

Preferably operatively connecting the lip and the air inlet and air bleed valve is a cam means driven in accordance with the movement of the lip, the cam means having two control profiles and an intermediate profile joining same with a constant radius of curvature, the first profile determining the movement of the air inlet valve and air bleed valve between the lower regulating point (a') and intermediate regulating point (b') during a movement of the lip from the lower regulating point (a) to a regulating point (u) still within the lower operating range (A), the intermediate profile maintaining the air inlet and air bleed valve closed until the lip has moved from said point (u) to a point (v) in the upper operating range (B), following which the second profile defines the movement of the air inlet valve and air bleed valve from the intermediate regulating point (b') to the upper regulating point (c') during movement of the lip from the point (v) to the upper point (c).

The movement of the air inlet valve and air bleed valve between the lower point (a') and the intermediate point (b') and the corresponding movement of the lip from the lower point (a) to the intermediate point (b) or point (u) and thence to the upper point (c) is not proportional but is digressive and progressive in relation to the course taken by the movement of the lip, such that the air inlet and air bleed valve from the lower regulating point (a') to the intermediate regulating point (b'), closes the additional air inlet at an increasing rate, while between the intermediate regulating point (b') and upper regulating point (c') it initially opens the air bleed aperture at a reduced rate.

By such means account can be taken of the laws governing the air inlet over the entire operating range, by enabling the quantities of air flowing through per unit of time to be maximalized along a reference control line or reference regulating line. In this connection attention is drawn to the DE 28 33 771 mentioned earlier, describing control and regulating programs. This makes it possible to accommodate very high aircraft angles of incidence even in the subsonic range and also very low air throughputs and to obtain satisfactory degrees of efficiency even in the supersonic range.

Two embodiments according to the invention are shown by way of example in the accompanying drawings, wherein: Figure 1 shows an adjustable supersonic airintake with a movable air interception edge and a bleed valve which is coupled to the interception edge via a linkage, and Figures 2a to 2d show a generally similar airintake but with a cam device operatively situated between the interception edge and the air intake and air bleed.

As may be seen from Figure 1, the air-intake is constructed as a one-sided oblique-thrust diffuser and has an upperfixed lip 1 extending forwards with an upper ramp 1a and a lower movable air interception edge 2. The latter is pivoted to the front of the base 3 of the inlet by a transversal shaft 4 and has raised side parts 2a. The air intake lip 2 is thus of a spade shape. In the subsonic transonic speed range (from O to about 1.3 Mach) the air intake lip 2 is adjusted, over a lower operating range A, between a lower point a and an intermediate points defined as-0 and being the normal position of a rigid lip. The adjustment angle bA is a maximum at the point a.In the supersonic speed range (from about 1.3 Mach onwards) the lip 2 is adjusted, in an upper operating range B, between the intermediate point b and an upper point c. The adjustment angle OB reaches a maximum at point c.

Behind the lip 2 the base 3 of the inlet includes an additional air inlet and air bleed aperture 5 which is controlled by a double sided flap valve 6 with a central pivot 7. This valve 6 with a front flap and a rear flap is hereinafter termed the inlet and bleed valve 6, or simply valve, by reason of its dual function.

The lip 2 is actuated by a hydraulic actuator 8 of which the rod 9 is pivoted to a crank 10 rigidly connected to the inlet and bleed valve 6. A thrust rod 11 connects the crank 10 to a front crank 12 rigidly connected to the lip 2.

The relationships between the positions of the lip 2 and the valve 6 are such that if the lip 2 is positioned at the lower regulating point a, the valve 6 will likewise be situated at the lower regulating point a'. The same applies to the regulating points b and c and b' and c'. The air inlet channel is thus supplied with additional air in the operating range A' through the valve 6, so that the loss of ingoing air into the main air inlet occurring under extreme flight conditions, with high angles of incidence for the aircraft, is balanced out by the aforementioned additional quantity of air.

As may be seen from Figures 2a to 2d, a cam disc is provided between the lip 2 and the valve 6 and this consists of a quadrant gear 13 in a fixed position on the shaft 4 and a gear 14 which is driven by the quadrant and to which the cam 15 is rigidly connected. The cam has a first control part 15a, an intermediate track 15b with a constant radius of curvature and a second control part 1sic.

This cam also drives a follower 16 which slides in a guide 17 integral with the body of the aircraft and Which by means of a pin engages a slotted arm 19 of the crank 1 0a. By means of a spring 20 the roller shaft 16 is held against the track of the cam 15. The quadrant 13 is driven by the shaft4through the crank 12a, which in turn is actuated by the thrust bar 11a.

The cam system between the lip 2 and valve 6 functions as follows: The transmission between the driving quadrant 13 and the gear 14 and the lift of the first cam part 15a are selected to ensure that when the lip 2 is displaced from the regulating point a as far as point u still within its lower operating range A, the valve 6 or the front flap thereof will at the same time move from the regulating point a' to the regulating point b', where valve part 5 is then closed. When the lip 2 moves from the regulating point u to a regulating point vin the upper operating range B (central regulating range C) the valve 6 and the part 5 remain closed. This result is produced by the constant radius of curvature of the track 1 5b of the cam 15.

When the lip 2 is displaced from the regulating point vto the regulating point c the valve 6 moves from the point b' to the point c'. In this range B' it acts as an air bleed for the purpose of ensuring that when the air inlet is in the sub-critical operating state surplus air will be removed from the air inlet channel to the outside air in order to prevent hum in the engine.

The closing movement of the valve 6 from its lower point a' to its intermediate point b' need not be proportional to the sequence of movements of the lip 2 from its lower point a to intermediate point b or the point u, but must be progressive and digressive in relation thereto, that is when the lip 2 is situated, for example, halfway between points a and b, the valve 6 may already have covered three quarters of its movement between its regulating points a' and b'. The valve 6 thus moves in advance of the lip 2 at an increasing rate towards the closing position b'. The sequence of movements in the upper operating ranges B and B' between the lip and the valve 6 likewise need not be proportional. In this case the movement of the valve 6 may lag behind that of the lip, that is when the lip 2 for instance has already covered three quarters of its path over the range B the valve 6 has only moved halfway along the path between the points b' and C.

The relationships between the regulating movements of the lip 2 and the valve 6 can be determined by appropriate construction of the cam parts 1 5a and 1 sic and the intermediate track 1 sub.

Claims (7)

1. A variable geometry air-intake for a gas turbine engine for a high performance aircraft, the intake having an upper inlet ramp and a lower inlet lip pivotally mounted to the base of the intake on a transverse shaft, the range of pivoting movement of the lip being divided into a lower subsonic transonic operating range (A) of a large angle and lying between a lower adjustment point (a) and an intermediate adjustment point (b), and an upper supersonic operating range (B) of a smaller angle and lying between the intermediate regulating point (b) and an upper regulating point (c), wherein the intake further includes an additional air inlet means effective in the lower operating range (A) and in accordance with the position of the lip, and an air bleed means effective in the upper operating range (B) and in accordance with the position of the lip in said range.

2. An air-intake in accordance with Claim 1, wherein the additional air inlet means and the air bleed means are constructionally combined in the form of a two sided flap valve positioned immediately behind the lip, each side of the valve effecting control of an inlet air aperture and an air bleed aperture respectively.

3. An air-intake in accordance with Claim 2, wherein the inlet valve part and air bleed valve part are both actuated together through a linkage.

4. An air-intake in accordance with Claim 1 or 2, wherein the air inlet means and the air bleed means or the air inlet valve part and air bleed valve part are controlled in such a way as to be in a closed position (b') when the lip is within an intermediate adjustment range (C) on either side of the intermediate regulating point (b).

5. An air-intake in accordance with Claim 4, wherein operatively connecting the lip and the air inlet and air bleed valve is a cam means driven in accordance with the movement of the lip, the cam means having two control profiles and an intermediate profile joining same with a constant radius of curvature, the first profile determining the movement of the air inlet valve and air bleed valve between the lower regulating point (a') and intermediate regulating point (b') during movement of the lip from the lower regulating point (a) to a regulating point (u) still within the lower operating range (A), the intermediate profile maintaining the air inlet and air bleed valve closed until the lip has moved from said point (u) to a point (v) in the upper operating range (B), following which the second profile defines the movement of the air inlet valve and air bleed valve from the intermediate regulating point (b') to the upper regulating point (c') during movement of the lip from the point (v) to the point (c).

6. An air-intake in accordance with Claim 5, wherein the movement of the air inlet valve and air bleed valve between the lower point (a') and the intermediate point (b'), and the corresponding movement of the lip from the lower point (a) to the intermediate point (b) or point (u) and thence to the upper point (c), is not proportional but is digressive and progressive in relation to the course taken by the movement of the lip, such that the air inlet and air bleed valve from the lower regulating point (a') to the intermediate regulating point (b'), closes the additional air inlet at an increasing rate, while between the intermediate regulating point (b') and upper regulating point (c') it initially opens the air bleed aperture at a reduced rate.

7. An air-intake for an aircraft gas turbine engine constructed and arranged to function substantially as herein described with reference to Figure 1 or Figures 2a to 2d of the accompanying drawings.