Engine Stall Anticipation And Reaction Device

Abstract

In a compressor operating near stall and utilizing the mechanism of variable pitch stator blades to prevent stall, a floating stator blade is used to sense an imminent stall condition. The blade pivots like a weather vane in the airstream flow through the axial flow compressor. The attack angle differential between the variable pitch stator blades and the floating stator blade is sensed and utilized by electrical or fluid pressure means to change the attack angle of the variable pitch stator blades so as to prevent stall.

Description

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION

The present invention is concerned with the anticipation of stall conditions in a jet engine compressor and the prevention of a stall condition which would seriously impair the performance of the engine. The invention is more particularly concerned with the use of a freely floating stator blade as a sensor for anticipating imminent stall conditions in the compressor section of a jet engine and with controlling the variable geometry of an axial flow compressor so as to prevent a stall condition such as would seriously impair the operation of the jet engine. The problem of stall in an axial flow compressor is not a new one in the art and there have been many methods devised to sense and obviate the problem. The majority of the devices designed for obviating stall conditions in an axial flow compressor utilize sensors which are sensitive to either temperature, pressure or speed of the compressor. These variables at best are only indirect indicators of a stall condition. Another approach to the problem consists of sensing the sonic frequencies produced by an imminent stall condition and controlling the geometry of the compressor in response to the occurrence of these sounds. The problem of effectively anticipating stall by monitoring the conditions in the air flow through the compressor still remains.

SUMMARY OF THE INVENTION

This invention suggests the use of a floating stator blade to detect an imminent stall condition. The floating stator blade would be located among the variable stator blades. The installation of the floating stator blade is such that it weather cocks and positions itself with respect to the airflow past it. As a stall condition begins to form within the compressor, the floating blade, because it is essentially unrestrained, starts to move (weather cock) as the airflow changes its direction. The angle of attack of the variable stator blades do not change because these blades are held stationary by the variable geometry drive actuators, but the angle of attack of the floating blade remains more or less constant since it is free to move in response to the condition associated with the change in airflow through the compressor. If the relationship between the variable stator blades and the floating blade is derived, by mechanical means, pressure changes or electrical means, a means of sensing an imminent stall condition is available. Besides using this blade sensor to actuate the variable stator blades in a manner so as to prevent stall, it could also be used to actuate other devices such as a fuel feed control device to cut back fuel flow and assist in the overall program to eliminate complete stall in jet engines.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a stall anticipation and prevention system for jet engine compressors operating near stall conditions which is uncomplicated but still effectively sensitive.

Another object of the present invention is to provide an uncomplicated stall anticipation and prevention system for jet engine axial flow compressors operating near stall conditions which permits compressors to operate closer to the stall line without creating adverse engine operation than was before possible with such uncomplicated equipment.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram, partially in section, illustrating a mechanical-fluid control system used to sense the movement of the floating vane in the airstream and convert this movement into the physical force required to move the variable stator vanes; and

FIG. 2 illustrates another embodiment of the invention in schematic form in which the free-floating blade is spring loaded to follow the normal stator blade positions but allowed freedom, within the limits of the applied loads, to move in response to airflow direction changes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With more particular reference to FIG. 1 of the drawing which illustrates a preferred embodiment of the invention functioning in relation with the fuel feed and control system 22 of a standard jet engine, the variable stator vane actuating mechanism of standard and well-known jet engines is actuated in response to the floating blade means. Free floating blade 1 is located among the variable stator blades of a compressor and is effectively damped against oscillation by damping means 21. Upon a change in the direction of airflow through the axial flow compressor, the floating blade 1, pivots on its axis to follow the direction of change in the airflow. The helical screw follower 2 attached to the shaft of the floating blade rotates in the same direction as the blade. Assuming for illustration's sake that the rotation of blade 1 is in a counterclockwise direction, as illustrated by the arrow, the follower 3 of lever 4 rides in the grooves of helical screw 2 as it rotates. The direction of rotation tends to cause follower 3 to ride up causing end 5 to move downwards as indicated by the arrow. This downward motion of end 5 causes spring 6 to expand placing a force on lever 7 which pivots at the point indicated. Lever 7 in turn places a force on piston rod 8, in a direction indicated by the arrow, to move piston 9 to the right, as indicated by the arrow, so as to lie under cylinder vent F.sub.1 while still lying over low-pressure outlet F.sub.3. Because of the spindle type construction of piston 9, cylinder vent F.sub.1 discharges its high-pressure fuel around the smaller circumference of piston 9 into outlet F.sub.3 and back into the fuel feed and control system of the jet engine. This causes a decrease in pressure on one side of piston 15 of the stator vane actuator cylinder 16. Piston 15 will move in the low-pressure direction, as indicated by the arrow, causing linkage shaft 10 attached to piston 15 to move in that direction also. The movement of linkage shaft 10 will cause feedback cable 11 to move in the direction indicated by the arrow. The variable stator blade mechanism, including linkage 12 and linkage 13 will move as indicated and variable stator vane 14 will move to follow the direction of movement of floating blade 1. Because of the movement of feedback cable 11, an expanding force is exerted on spring 17 in the direction indicated by the arrow, which places a force on piston rod 18 connecting spring 17 and piston 9, tending to bring piston 9 back to its null position as shown. When the piston 9 is in this null position, high-pressure fluid conductors 19 and 20 having outlets F.sub.2 and F.sub.1 are at equal pressure and piston 15 will remain in the position it took on the last movement of variable stator blade 14. Piston inlets F.sub.4 and F.sub.5 are the high-pressure boost inlets coming from the fuel feed and control system of the jet engine. Piston outlet F.sub.3 is the low-pressure outlet going to the fuel feed and control system of the engine. There is a substantial pressure differential between the two high-pressure fuel inlets F.sub.4 and F.sub.5 and the low-pressure fuel outlet F.sub.3.

As can be readily seen, if the free-floating blade 1 tended to move in a clockwise direction the helical screw follower 2 would follow that movement and so would the other mechanical elements of the system. The direction of system movement would be opposite to the directions indicated by the arrows in FIG. 1.

From the foregoing explanation of the embodiment shown in FIG. 1 it is clear that free floating blade 1 moves in response to a stall condition and the variable stator blade 14 follows the direction of movement of floating blade 1 so as to prevent stall in the axial flow compressor.

Stall conditions generally being of the intermittent type, free-floating blade 1 will follow the changing airflow which should soon return to normal again causing the control equipment to actuate in a manner so as to reposition variable stator blade 14 in the newly desired position taken by free-floating blade 1. It should be pointed out that this system is not designed to allow a compressor to operate in a continuous stall condition but rather allows the compressor to accommodate an intermittent stall condition without feeling any deleterious effects therefrom and thereafter go back to operating on its designed performance curve.

Referring now to FIG. 2 which shows another embodiment of the invention, the floating stator blade 28 is mounted in the variable stator blade section of a compressor housing by means of bearings and shafts connecting the floating blade to rotating shaft 23 which by means of bevel gear drive shafts 24 and 26 of the variable stator blades and the free-floating blade, respectively. The floating blade 28 will line up with the variable stator blade 25 and follow, due to the tension exerted by spring 27 caused by the rotating force exerted by shaft 23, the position of variable stator blade 25. As a stall condition begins to occur in the axial flow compressor, the free-floating blade 28 will tend to change its direction in accordance with the direction of flow in the compressor. The variable stator blade 25, however, is held stationary by the rotating shaft 23 its beveled gears and shaft 24. Because of the rotation of free-floating blade 28 and the stationary condition of stator blade 25, the spring 27 is placed in a compressive or expansive state. This state is sensed by means of strain gauges placed on spring 27 which indicate by a small electrical signal of either a negative or positive polarity whether the spring has been placed in compression or expansion. These signals are carried to an amplifier 31 by cables 29 and 30. The amplifier 31 amplifies these signals and feeds them to the variable stator actuator mechanism 32 which can be any well-known mechanism such as a motor drive which will rotate shaft 23 in the appropriate direction as indicated by the magnitude and direction of signals produced by the strain gauges. The variable stator blade 25 is thus caused to line up with the position assumed by free-floating blade 28 thereby removing the tension or compression of spring 27. The strain gauges therefore will produce no output and no further changes in the geometry of the stator blades will occur until another change in the airflow direction occurs in the axial flow compressor which will again rotate free-floating blade 27 and again cause the control equipment to go through its functional relationships. As can be seen, floating blade 28 can rotate in either a clockwise or counterclockwise direction in response to any direction change in the airflow giving an effective response to an imminent stall condition. It is contemplated that variable stator actuating mechanism 32, besides actuating shaft 23, to rotate variable stator blades 25, could also be used to actuate other devices such as the fuel feed control of a jet engine to cut back fuel flow and thereby assist in the overall program to eliminate complete stall conditions in the jet engine. The strain gauges used are standard gauges well known in the art and adapted to produce a positive or negative output depending on the force applied to them. The strain gauge amplifier 31 is well known in the art and the variable stator actuating mechanism can be any of a number of motor means responsive to the amplifier output to drive the rotating shaft 23 in either direction, as required. The output 33 of variable stator actuator mechanism 32 is a force which can act mechanically to increase or decrease jet fuel flow and further aid in stall prevention. Such a method is well known in the art and is not seen as needing further discussion.

Claims

While several preferred embodiments of the present invention have been illustrated and described it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

1. An apparatus for anticipating and preventing stall in axial flow jet engine compressors which have one or more stages and utilize variable stator blades to control operating characteristics of the compressor having a compressor housing adapted for rotatably mounting said variable stator blades thereon comprising

at least one floating stator blade per variable stator blade stage rotatably mounted among said variable stator blades so as to allow said floating stator blade to align itself with airstream flow in said compressor;

a follower means responsive to rotational movement of said floating stator blade;

a damping means restraining said floating stator blade from freely rotating in response to minute direction changes in said airstream flow;

a control means responsive to actuation by said follower means; and

adjustment means responsive to said control means to actuate said variable stator blades to follow the movement of said floating stator blade whereby a complete stall condition is averted.

2. The stall anticipating and preventing apparatus as recited in claim 1 wherein said follower means comprises

a shaft rigidly attached to said floating stator blade so as to rotate with said floating blade; and

rotary motion to linear motion conversion means responsive to rotation of said shaft to actuate said control means.

3. The stall anticipating and preventing apparatus as recited in claim 2 wherein said control means comprises

a fluid flow directing means responsive to a force exerted by said motion conversion means to direct high-pressure fluid flow;

high-pressure fluid conductors for transmitting said directed fluid flow;

a fluid pressure activated piston responsive to fluid flow transmitted by said conductors to actuate said adjustment means; and

feedback means responsive to movement of said piston to apply a force opposite in direction to the force applied by said motion conversion means being of sufficient strength to reposition said fluid flow directing means to a null position.

4. The stall anticipating and preventing apparatus as recited in claim 1 further comprising a fuel feed means responsive to said control means for decreasing volume of fuel flow to the jet engine.

5. An apparatus for anticipating and preventing stall in axial flow jet engine compressors which have one or more stages and utilize variable stator blades to control operating characteristics of the compressor having a compressor housing adapted for rotatably mounting said variable stator blades thereon comprising

at least one floating stator blade per variable stator blade stage rotatably mounted among said variable stator blades so as to allow said floating stator blade to align itself with airstream flow in said compressor;

a follower means responsive to rotational movement of said floating stator blade; said follower means comprising a shaft rigidly attached to said floating stator blade so as to rotate with said floating blade, and a resilient means rigidly attached and deformably responsive to rotation of said shaft;

a control means responsive to actuation by said follower means; and

adjustment means responsive to said control means to actuate said variable stator blades to follow the movement of said floating stator blade whereby a complete stall condition is averted.

6. The stall anticipating and preventing apparatus as recited in claim 5 wherein said control means comprises

a transducer responsive to deformation of said resilient means;

a transducer amplifier; and

variable stator actuating means responsive to said transducer amplifier to rotatably actuate said adjustment means.

7. The stall anticipating and preventing apparatus as recited in claim 6 wherein said adjustment means comprises

a rotating shaft responsive to said variable stator actuating means;

rotatable shafts rigidly attached to said variable stator blades so as to rotate with said variable stator blades; and

bevel gear combinations transmitting rotary motion from said rotating shaft to the rotatable shafts of said variable stator blades and said floating stator blade.

8. The stall anticipating and preventing apparatus as recited in claim 5 further comprising a fuel feed means responsive to said control means for decreasing volume of fuel flow to the jet engine.