EP0543908B1 - Verfahren und mittel zur strömungskontrolle - Google Patents

Verfahren und mittel zur strömungskontrolle Download PDF

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Publication number
EP0543908B1
EP0543908B1 EP91915299A EP91915299A EP0543908B1 EP 0543908 B1 EP0543908 B1 EP 0543908B1 EP 91915299 A EP91915299 A EP 91915299A EP 91915299 A EP91915299 A EP 91915299A EP 0543908 B1 EP0543908 B1 EP 0543908B1
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Prior art keywords
flow
compressor
pressure gas
injection
station
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EP91915299A
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English (en)
French (fr)
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EP0543908A1 (de
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Christopher Freeman
Ivor John Day
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Rolls Royce PLC
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Rolls Royce PLC
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D27/00—Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids
    • F04D27/02—Surge control
    • F04D27/0207—Surge control by bleeding, bypassing or recycling fluids
    • F04D27/0215—Arrangements therefor, e.g. bleed or by-pass valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D27/00—Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids
    • F04D27/001—Testing thereof; Determination or simulation of flow characteristics; Stall or surge detection, e.g. condition monitoring
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D27/00—Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids
    • F04D27/02—Surge control
    • F04D27/0207—Surge control by bleeding, bypassing or recycling fluids
    • F04D27/0238—Details or means for fluid reinjection

Definitions

  • This invention relates to a method of and means for the control of flow disturbances in turbo-compressors, including both instabilities such as the phenomena of rotating stall and surge, in particular axial turbo-compressors, and steady state or quasi steady state disturbances.
  • Rotating stall is an aerodynamic instability which determines the maximum pressure rise capabilities of a turbo-compressor. At that maximum any further demand will lead to the formation of a small patch (usually referred to as a "cell") of disturbed flow in the blading which can then spread rapidly to engulf a large proportion of the annular cross-section of the compressor. As the stall cell forms fully, the delivery pressure at the exit from the compressor falls off just as rapidly. This type of disturbance is called rotating stall because the disturbed or "blocked" sector of the annulus will rotate with the blading, at roughly half (typically between 0.8 and 0.3) the speed of the blading.
  • the system-related instability of surge occurs when a compressor is coupled to a large downstream volume, eg. pipework in an industrial plant or the combustion chamber in a gas turbine. If the pressure rise capability of the compressor is exceeded and a stall condition is initiated there is a fall in delivery pressure which allows compressed gas in the volume downstream of the compressor to blow back through the compressor. In extreme cases this can lead to flames spewing out of the front of an engine. Venting the downstream volume in this way lowers the back pressure on the compressor; the stall condition disappears and the pressure downstream is able to rise again as the downstream volume is refilled. The stalling, venting, refilling cycle will thus start again and a continuous sequence of surge cycles can ensue if the operating conditions remain unchanged.
  • a large downstream volume eg. pipework in an industrial plant or the combustion chamber in a gas turbine.
  • a stall control system for an axial flow compressor in which signals from a number of pressure transducers within the compressor are compared with a reference signal, the value of which is related to the operating conditions in the compressor.
  • the signals from the individual transducers are compared sequentially with the reference signal so that corrective action can be initiated when an abnormal value is sensed by any one sensor.
  • the signals are also summed, and the strength of the corrective action is determined by the summed signal value.
  • the form of corrective action described in US 4196472 takes the form of a controllable bleed from the compressor gas passage, and control of the stagger angle of the stator blades is also suggested.
  • FR2248427 equivalent to GB1481031 there is described an apparatus for controlling surge in axial and radial flow compressors. This discloses using a pressure transducer to detect flow reversal in the boundary layer downstream of the rotor blade. It takes corrective action by bleeding air from a position downstream of the rotor blade and injecting the air into the compressor upstream of the rotor blade either with an upstream component or with neither upstream nor downstream components.
  • a method of controlling gas flow in a compressor comprises the steps of:
  • the series of circumferentially spaced positions is at a chosen axial station in the direction of flow through the compressor, only variations in the flow above a predetermined limit of variation are detected, and the higher-pressure gas is injected into the compressor upstream of the higher-pressure region in a circumferentially selective manner dependent upon the circumferential origins of said variations, thereby to act against flow disturbances indicated by said variations.
  • the higher-pressure gas may be injected in a series of different sectors around the compressor, the flow variations being independently sensed in each of the sectors.
  • the higher pressure gas is taken from the same sector as that into which it is injected.
  • a significant feature of the present invention the use of injected gas to counter a flow disturbance, has the advantage over the method proposed by US 4196472 that the injection of gas improves the basic surge margin of the compressor.
  • the compressor is therefore capable of operating at a higher output than would be the case with a prior art bleed system.
  • Rotating stall conditions may also be experienced in turbo-compressors at low speed, part load conditions.
  • the instability is found to occur at the front of the compressor.
  • the machine is then working at a lower compression ratio than the optimum for which it is designed the early stages are relatively highly loaded compared with the rearmost stages.
  • the flow at the front of the compressor can then reach stalling point, giving an uncontrolled loss of power.
  • the present invention can also be employed to counter this problem by the injection of higher pressure gas into the foremost stages of a turbo-compressor, preferably at the front stage, in a similar manner to that described for high speed operation.
  • any axial region of the compressor may be chosen for the flow injection, depending upon the nature of the disturbance to be countered. It is necessary to ensure that the injection pressure is sufficient to obtain an adequate energy input at a location where it will influence the flow disturbance sensed, but for greatest efficiency the pressure differential should be kept as low as is practical. If a flow is to be injected at the front of the compressor, it may not be desirable therefore to take the injected air from the compressor outlet. From the point of view of aerodynamic efficiency, it would be desirable to have a multiplicity of successive flow injection circuits along the compressor flow path, each spanning only a small part of that path, but the mechanical complexity of such an arrangement will normally be impractical.
  • both high and low speeds stalling can be countered with relatively simple means if there are tappings at the front, rear and intermediate regions of the compressor, so enabling an injection from the rear or outlet to the intermediate region to counter high speed stall in response to detection means at the intermediate region, and from the intermediate region to the front or entry region to counter low speed stall in response to detection means at the entry region.
  • the critical axial station or stations at which a flow disturbance will be initiated can be expected to vary with different designs of turbo-compressor and the locations of the injection and sensing means may therefore be selected empirically. There may also be a need to monitor the compressor flow near its outlet end for incipient surge conditions, independently of monitoring for rotating stall further upstream.
  • gas injection means in response to the sensing of a rotating flow variation gas may be injected sequentially through a circumferentially spaced series of ports at a station.
  • gas may be injected simultaneously through said series of ports.
  • gas injection means at a number of axially spaced stations they can be actuated in response to sensed variations at their respective stations or at other stations as appropriate.
  • the control system may be deployed at a number of axial stations, it may be operated independently at each station or the gas injection at the different stations can be coordinated, eg. to operate in unison or in a predetermined sequence.
  • the method of the present invention can also be employed to counter flow distortions where the flow distribution is non-uniform in the circumferential sense. This condition can occur in aero-engines during transient manoeuvres or when the aircraft is travelling at low speed with the engine axis at a larger angle than usual to the flight path, such as can occur at take-off. A part of the engine air intake area is then effectively "shadowed" by the cowling upstream of it and there can be break away of the flow in the first stage of the compressor.
  • an apparatus for controlling gas flow in a compressor comprising:
  • injector means comprises a circumferential array of injectors and the control means is adapted to operate the injector means in a circumferentially selective manner dependent upon the circumferential positions of the sensors detecting the flow variations, thereby to act against flow disturbances indicated by said variations.
  • control means including means whereby only sensor signals indicating flow variations above a predetermined limit of flow variation cause operation of the injector means.
  • the or each valve controlling the flow is automatically re-shut after an interval, which may be a preset period, since a continuous injection of high-pressure gas would be uneconomic. It may be preferred to do this by tapering off the initial flow whereby the flow control effect is removed gradually. This is particularly applicable when a relatively lengthy period of injection flow is needed to influence the disturbance; should the disturbance appear again before the flow has been shut off, the rate of flow can be increased again to its initial value. With repeated tapering and restoration of the flow, it is ensured that the flow is kept to the minimum to control the disturbance and is cut off as soon as the cause of the disturbance disappears.
  • a timed tapering of the injection flow is able to limit the energy input for operating the corrective system without impairing its efficiency.
  • an on-off characteristic may be equally effective and has the advantage of simplicity. If the disturbance remains when the preset interval has expired, a further period of injection can be immediately initiated. It may also be arranged that the responses of the components of the system ensure in that case that the injection flow is not interrupted between the two periods.
  • the invention can be utilised, whether the control flow is tapered off or is simply cut off, without the control means using a feedback loop. It is possible to initiate corrective action at a maximum rate when gas injection begins, subject only to the threshold disturbance level having been exceeded. If thereafter the injection flow is cut off or its rate of injection is tapered off, it can be assured that full corrective action is restored at any stage if the disturbance continues or restarts.
  • the arrangement permits considerable simplification, as compared with prior art arrangements, without impairing the ability to control disturbances. It is also possible very simply to provide manual actuating means which allows the operator to put the arrangement into operation.
  • control means comprises means for averaging the signal sensed at each said spaced position over a rolling period corresponding to the sensing of the flow at least at three circumferentially successive locations to give a series of mean values from which a flow disturbance is detected.
  • the generation of a series of operative outputs from a plurality of the sensors can then be employed to actuate the injection means in a sequential pattern.
  • control means detects at least one small sharply defined patch of stalled flow.
  • the higher pressure gas is injected toward a circumferential region that follows in the direction of rotation from said circumferential region in which said variation has been detected.
  • the flows through the injection locations are controlled by respective valves for individual ports or groups of ports.
  • groups of ports By grouping the ports the apparatus is simplified but the amount of injection air needed is increased. It may be preferred to provide multiple orifice ports spread over a sector of the circumference at each gas injection location to improve the distribution of the injected flow.
  • the outlet means comprise nozzles in which a projecting portion at each nozzle exit deflects the injection in a downstream direction.
  • the injector means comprises nozzles located between guide vanes.
  • the injector means comprise nozzles located in the inner wall compressor casing.
  • the higher pressure gas is injected toward a circumferential region that follows in the direction of rotation from said circumferential region in which said variation has been detected.
  • the flow may be directed circumferentially in an oblique direction that opposes the direction of rotation of the compressor.
  • an operative signal at one station may also be found useful for an operative signal at one station to actuate an injection flow of another station, for example, if a flow disturbance is more easily detected at a station downstream from its initiation, as for example the appearance of rotating stall nearer the compressor outlet at higher speeds.
  • the sensing means should not be disposed so close to the gas injection sites that their signals are disturbed by the inflowing gas.
  • stall cell in an axial flow compressor can grow from an undetectable disturbance to a fully developed blockage in a matter of milliseconds; this development will usually take place over about 4 to 6 revolutions of the compressor rotor.
  • the stall cell may make its first appearance at any point around the flow passage through the compressor, so that a series of spaced sensors are needed to detect the origin and development of a stall cell.
  • Experiments testing the basis of the present invention were made using a turbo-compressor with a series of hot-wire sensors spaced circumferentially around an axial position immediately ahead of the first rotor disc as shown in Fig.
  • Fig.1 where the outputs from six circumferentially spaced hot-wire sensors I-VI are shown, the flow into the compressor is initially in a steady state with a very low level of disturbance.
  • An emerging stall cell can first be seen as a small disturbance, namely the v-shaped peak at A in trace III, which grows progressively as it passes each successive sensor.
  • the stall cell is a fully developed disturbance rotating steadily around the annular passage.
  • FIG. 2 illustrates to the same time scale as Fig. 1 the initiation of a surge cycle, the first sign of which is the v-shaped stall cell emerging first in trace IV.
  • the subsequent development after a couple of revolutions is notably different from the development of rotating stall, and the outputs from all the sensors show a concurrent and relatively long-lived drop of flow rate.
  • Fig. 2 and Fig. 3 shows, over a longer time scale, the complete "stall-backflow-refill" sequence. Steady flow, dropping slightly as the back pressure builds up, finally breaks down and the flow reverses, steady flow being resumed again at a higher rate because of the reduced back pressure.
  • Fig. 4 illustrates in outline the axial flow compressor C equipped with flow control means in accordance with the invention.
  • the hot wire sensors 2 can be seen immediately between a ring of fixed guide vanes 4 and a ring 6 of rotor blades.
  • a circumferentially distributed series of air inlets 8 blend tangentially with the inner wall 10 of the compressor casing.
  • the inlets are directed rearwards into the adjacent rotor blade ring.
  • the inlets are set at an angle in the circumferential sense that may be determined empirically but that preferably directs them counter to the direction of rotation of the rotor.
  • the inlets 8 are connected by conduits 12 through respective fast-acting shut-off valves 14, to a series of conduits 18 leading from a number of tappings 20 similarly distributed around the circumference of the high-pressure end of the compressor to supply high-pressure air for injection through the inlets.
  • the valves 14 are normally shut but can be opened by a control circuit 22 in dependence upon the signals from the sensors 2. As will be described in more detail below, detection of a disturbance by some or all of the sensors greater than the anticipated level of noise in the steady flow at the compressor inlet triggers the opening of the valves 14 to inject onto the first ring of rotor blades 6 the high pressure flow bled from the outlet end of the compressor.
  • Fig. 5 the outputs from a series of four equispaced hot-wire sensors are shown, with a stall cell appearing first in the trace of sensor II. As the stall cell circulates past sensors III and IV, the control circuit 22 is able to confirm that the disturbance is not an instrument fault and the output from the control circuit is turned on to open the valves 14. Fig. 5 demonstrates how the injection of high pressure air immediately suppresses the stall cell.
  • Fig. 6 illustrates the same set-up in which, conversely, overriding the control unit and switching the valve 14 closed allows the stall cell to reappear and a fully developed rotating stall condition quickly establishes itself.
  • the control unit 22 should close the valves once the stall cell has been suppressed.
  • the use of a timer to switch the valves off is illustrated in an experiment that produced the traces shown in Fig. 7.
  • the steady flow is close enough to a critical condition for a stall cell to appear after a short time with the valves closed, but on each occasion when the control system is operative, the disturbance is quickly removed.
  • the trace S in Fig. 7 the control system was switched off after demonstrating its efficiency, whereupon the next re-emergence of the stall cell led to a rotating stall condition.
  • Figs. 8 and 9 show a similar experiment to that in Fig. 7, here using piezo-electric sensors, which are able to actuate the opening of the individual injection valves each operatively linked with a circumferentially adjacent sensor to inject high pressure air through the inlets 8.
  • Fig. 8 demonstrates how the disturbance is suppressed each time that an incipient stall cell is detected.
  • Fig. 9 shows the opening and closing sequence of the control valves which control the counteracting flow injection. As shown by some of the incidents in traces II and IV, it is possible to arrange for the control unit to respond to a persistent disturbance so fast that in effect the period of valve opening is extended.
  • FIG. 10 there is an illustration of the sensor traces recorded during a typical surge cycle in which the compressor of Fig. 4 delivers its output to a tank to produce a progressive pressure increase at the compressor outlet.
  • Fig. 11 the same surge cycle is shown, to a compressed time scale, in which the control system was switched on for a period in the middle of the cycle.
  • the surge cycle was suppressed by the operation of the injection valves and reappeared when the control system was switched off.
  • the trace shows an output from a single hot-wire sensor ahead of the first rotor stage.
  • Fig. 12 illustrates a typical pressure rise characteristic of an axial flow compressor. Without the use of the present invention, instability and a drastic drop in performance would be met at the point on the characteristic indicated by the arrow A. With the use of the invention, the characteristic extends to the point indicated by the arrow B before breakdown occurs. Since in actual performance it is necessary to operate with a significant safety margin because of the catastrophic consequences of breakdown, the extension of the range of operation offered by the use of the invention is able to yield a substantial improvement in performance.
  • Fig. 13 illustrates schematically the application of control apparatus according to the invention to a gas turbine which comprises an axial flow compressor A, combustion chamber C and turbine T, the compressor and turbine being coupled by a shaft S to rotate together.
  • Flow sensors are located at two axial stations, namely the sensors 102a in front of the first stage of blades disc 106a and the sensors 102b behind a stage 106b near the high pressure outlet. At each station there is a series of three or more of the sensors 102 circumferentially equally spaced around the casing.
  • a first series of injection ports 108a are distributed around the compressor casing upstream of the front stage 106a but circumferent ally offset from the sensors 102a.
  • a similar series of bleed ports 110a around the circumference of an intermediate stage of the compressor allow gas flow through conduits 116 to the lower pressure regime at the injection ports 108a when normally closed valves 114a are opened.
  • a further series of circumferentially distributed injection ports 108b adjacent the bleed ports 110a can receive higher pressure gas from similarly distributed bleed ports 110b through conduits 118 and further normally closed valves 114b.
  • this arrangement of ports and valves is illustrated at diametrically opposite sides, but as is described below, the circumference of the compressor is divided into a number of equal sectors, eg. 6 to 12, each of which has its own pair of valves 114a,114b and associated conduits 116,118 controlling the flow through a series of injection and bleed ports distributed over the sector.
  • Fig. 13 provides two separate recirculation systems which can be operated independently of each other.
  • the intermediate to front stage recirculation through the valves 114a intended to counter low power instabilities, is regulated by a control circuit 202a in response to the signals from the sensors 102a at the front of the compressor.
  • Recirculation from the rear to intermediate stages through the valves 114b is regulated by control circuit 202b in accordance with the signals from sensors 102b near the rear of the compressor. Further details of the control circuit 202 will be described with reference to Figs. 17 and 18.
  • Figs. 14 and 15 illustrate in more detail the air injection arrangement at a typical port 108.
  • the port is located in a ring of guide vanes 122 mounted on the casing inner wall 124 of an axial compressor.
  • Each port comprises a group of three nozzles 126 opening into the compressor gas flow passage from a plenum 128.
  • the nozzles are inclined at 30° to the axial direction to direct injected air I obliquely into the main flow F at as shallow a radial angle as possible.
  • the division of the flow through a number of nozzles helps to keep the radial angle of injection small.
  • a lip 130 shrouds the leading portion of the outlet of each nozzle.
  • the nozzles 126 may also be inclined circumferentially so that the flow through them is injected with some whirl component in a direction counter to the whirl component of the main flow through the guide vanes.
  • Fig. 15a illustrates an alternative location of the ports 126, in the axial gap between the trailing edges of the stator guide vanes 122 and the leading edges of the rotor blades 123.
  • An advantage of the arrangement shown in Fig. 15a is that the circumferential angle of injection can be more freely varied because it is not limited by the proximity of the stator guide vanes. The angle may be varied quite widely but it preferably lies between the axial direction and an angle to that direction substantially equal to the stagger angle of the rotor blades of the adjacent ring.
  • the ports 108 are disposed between each successive pair of guide vanes 122 and they are connected in groups to a series of six plenums 128 so that each plenum supplies injection air to a 60° sector of the compressor circumference.
  • Each 60° sector has its own control valve 114 and is connected to the extraction porting 110 of a corresponding 60° sector at the downstream station.
  • For each 60° sector there may be a single flow sensor 102, or a plurality of circumferentially spaced sensors, preferably at substantially the same axial station as the injection ports.
  • the sensors 102 are preferably static pressure sensors mounted flush in the casing wall, as indicated in Fig. 14.
  • FIG. 16 A preferred form of the valve 114 to obtain an appropriately fast response to the detection of a flow disturbance is shown in Fig. 16.
  • This is an oscillatory rotary valve comprising a rotor 142 mounted on a spindle 144 in a casing 146 through upper and lower bearings 148,150.
  • the rotor 142 is a hollow cylinder closely fitting but freely slidable in a cylindrical stator 152. Both rotor and stator have a series of spaced slots 154 in their cylindrical walls, and the two series of slots can be moved in and out of register by a relatively small rotary movement of the rotor. With the slots out of register flow throug the valve is blocked.
  • valve rotor When the slots are in register, gas from supply conduit 156 reaching the encircling entry chamber 158 in the valve casing 146 can flow through the slots, past the spider 159 supporting the lower bearing 150 and through the valve outlet 160.
  • the valve rotor has a lightweight construction, eg. of a carbon composite material.
  • the stator is preferably made of the same material to ensure fit is maintained over a range of temperatures.
  • Movement of the valve is controlled electromagnetically by a torque motor 162 comprising an electromagnet 164 secured in the casing and an armature 166 attached to the rotor 142.
  • the motor is displaceable between end positions which correspond to the valve open and closed states so that no mechanical stops are required to locate the rotor at either position.
  • a control circuit 202 dealing with an individual sensor output is shown in more detail in Figs. 17 and 18.
  • the electronic signal a from each sensor output is first filtered in a low-pass filter 210 to remove blade order disturbances and the filtered signal b is then processed in an integrator 212.
  • the integrator functions to give an average sensor value c over a rolling period equal to the sampling of at least three successive sensors 102 - for example if there is one sensor per sector the rolling period can be as little as one half revolution.
  • the average value gives a steady but continuously updated base level against which the magnitude of instantaneous variations can be measured.
  • the integrated output c is compared with the filtered instantaneous signal b in a subtraction unit 214, the difference d between the two signals being the perturbation, ie the divergence of the instantaneous signal from the rolling average.
  • a divider circuit 216 calculates the ratio of the perturbation d to the current average value c, so that a non-dimensional measure e of the deviation is obtained.
  • the output e from the divider circuit 216 is fed to at least a first discriminator 218 to be compared with a pre-set level X which must at least be matched if the air injection is to be operated.
  • the output f from the discriminator is on if the magnitude of the division is greater than or equal to X.
  • the pre-set perturbation operation level X is chosen to be the value that would appear in a stall condition.
  • the signals b obtained from the individual sensors and the outputs f are used to actuate an array of AND-gates 219-219n each linked to a respective valve 114.
  • Each valve is opened when its AND-gate receives both an output f and a signal from the sensor circumferentially associated with its valve, and so produces an output which operates relay 220 of the valve.
  • Each of the valves is therefore opened in turn in coordination with the circumferential position of the flow signal sensed when that signal has generated the perturbation output f. It will be seen that the valve to be opened may be for the same segment of the compressor air passage as that in which the perturbation was sensed, or it may be for a sector that follows in the direction of rotation if it is necessary to compensate for a lag in the response.
  • a further discriminator 218' in the circuit of Fig. 18 may also receive the signal e and be tuned to respond with an output f' at a level X' that is greater than the value that would appear in normal engine operating conditions such as acceleration and deceleration, but is less than the level that would appear in a stall condition. This can for example be used to counter flow distortion at extreme flight altitudes, for example.
  • a store 222 has addresses 223 for the outputs from the discriminators 218 for all of the sensors, of each stage.
  • an output f ⁇ (e>X) occurs, that signal is held for at least the rolling period of the integrator 212, as determined by the input signal of compressor speed N.
  • the values held in the store are extracted in step with the scanning of the addresses 223 and are summed in an addition circuit 224 for all of the sensors in the stage.
  • Comparator 228 determines if the summed signals exceed predetermined values, whereupon a valve control circuit 232 is actuated to open the injection valve or valves 114 to the appropriate compressor locations. Simultaneously, a timer 234 is actuated to close the valves 114 again after a set period, which may correspond to as little as one or two revolutions of the compressor.
  • the circuit of Fig. 18 can be further expanded by including a respective further addition circuit 226 for the sensors of different stages but similar circumferential position. It can be expected that these signals will reinforce each other if rotating stall is present.
  • a comparator 230 determines if the summed signals exceed predetermined values to open the valve control circuit 232 in the manner already described.
  • Fig. 19 shows a gas turbine having an installation according to the invention with isolation valves 250 which are similar to the valves 114 but are designed for 3-way operation.
  • Each valve 250 has three alternative positions, (i) closed, in which the conduits 252,254,256 communicating with the valve are isolated from each other, (ii) a first operative position, in which conduits 252,254 are connected together and the conduit 256 remains isolated, and (iii) a second operative position in which the conduits 254,256 are connected together and the conduit 252 is isolated.
  • the valve 250 illustrated and its associated conduits of course represent only one of a series of such air circulation devices distributed at spaced intervals around the circumference of the compressor to take air from and deliver it to rings of nozzles at the chosen take-off and injection stages.
  • the control system shown in Fig. 19 includes an inlet temperature sensor 262 and a shaft speed sensor 264 which provide inputs through A-D convertors 266,268 of temperature T and rotational speed N to an operating unit 270.
  • the unit 270 operates on the inputs to produce an output N ⁇ T which represents the corrected speed, a parameter of flow conditions in the compressor.
  • a processing unit 280 operates in the manner already described with reference to the units 202, in accordance with signals from static pressure sensors 282,284 indicating a flow disturbance actuating the opening of the valves 250 to produce a fixed period of air injection.
  • the value of the N ⁇ T value is input to the processor 280 to determine whether the output from the unit 280 actuates the valve 250 to open the path 254,252 or the path 256,254.
  • Lower values of N ⁇ T indicate lower power operation of the compressor and the valve 250 is actuated so that air tapped from the intermediate station is injected into the front of the compressor via the conduits 252.
  • Higher values of N ⁇ T indicate that any disturbance to be acted upon requires correction in the downstream stages and the valve 250 so opens that air from the compressor exit is injected into the intermediate stage via the conduits 254.
  • the method of control according to the invention can also operate to counter a steady flow distortion, ie. some element of circumferential asymmetry in the flow which, although not necessarily leading to a catastrophic disruption of the flow, reduces the efficiency of the turbo-compressor.
  • the control systems would be arranged to act on the appropriate single injection valves or selected groups of the valves at a particular station and sector when a steady flow distortion is indicated by the signals sensed.
  • the circumferentially corresponding injection conduits at two or more stations may share the same control valve. If injection is required only to counter incipient surge conditions, a circumferential series of injection conduits may be connected to a common control valve.
  • the amount of opening may be graduated, or the injected flow volume may be reduced if the valve is opened and closed several times in quick succession.
  • an initial command opens the valve eg. up to 25%, and then if there is a further command from the logic circuitry to open the valve it is opened wider. In this way detection of a minor unstable condition correctable by partial opening of the valve will not excite an excessive response with the resulting loss of engine efficiency.
  • the form of response may also be matched to the type of instability being detected.
  • the distortion will circulate around the circumference of any particular stage and if the distortion is sensed in sequence by the associated sensors, it may not be necessary to inject pressure air through all the inlets associated with that stage. A sequential injection in phase with the distortion may then be sufficient. That does not apply if the distortion is sensed simultaneously by all the sensors, indicating a surge condition.
  • the speed of response of the system is dependent upon the level of discrimination, which must be sufficiently low to enable corrective action to be initiated before any significant loss of engine power occurs, yet must not be so sensitive as to respond to the normal and inevitable variations that occur in the operation of an axial flow compressor, such as the blade to blade differences and the wake disturbances of each blade giving a blade passing frequency variation. This latter is usually the most significant noise component in the axial flow compressor of an aero engine and would give a variation there of about 2%.
  • the limiting value for initiating corrective action ie. the value of X for the discriminators 218 (Fig. 17), would thus be set above the 2% level in such an installation.

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  • Control Of Positive-Displacement Air Blowers (AREA)

Claims (35)

  1. Verfahren zur Steuerung einer Gasströmung in einem Kompressor (C), welches die folgenden Schritte umfaßt:
    - es wird die Strömung an einer Reihe von in Umfangsrichtung um den Kompressor herum im Abstand zueinander angeordneten Stellen (2) abgefühlt;
    - es werden Veränderungen in der Strömung in einem Umfangsbereich relativ zu einem anderen Umfangsbereich festgestellt; und
    - bei Feststellung einer solchen Änderung wird unter höherem Druck stehendes Gas in den Kompressor eingeblasen (8),
    dadurch gekennzeichnet,
    - daß das unter höherem Druck stehende Gas allgemein in Richtung der Strömung durch den Kompressor eingeblasen wird;
    - daß das unter höherem Druck stehende Gas von einem unter höherem Druck stehenden Bereich des Kompressors stromab der in Umfangsrichtung im Abstand zueinander liegenden Stellen (2) abgenommen und in einen in Umfangsrichtung liegenden Bereich eingeblasen wird, in dem die Änderung festgestellt wurde, und daß das unter höherem Druck stehende Gas in den Kompressor unter einem radial gerichteten Winkel von nicht wesentlich mehr als 30 ° eingeblasen wird.
  2. Verfahren nach Anspruch 1, bei welchem die Reihe der in Umfangsrichtung im Abstand zueinander liegenden Stellen (2) an einer gewählten axialen Station in Strömungsrichtung des Kompressors (C) befindlich ist und nur Änderungen in der Strömung festgestellt werden, die über einem vorbestimmten Grenzwert der Änderung liegen, und das unter höherem Druck stehende Gas in den Kompressor (C) stromauf des unter höherem Druck stehenden Bereichs in einer in Umfangsrichtung selektiv gewählten Weise eingeblasen wird, in Abhängigkeit von dem in Umfangsrichtung befindlichen Ursprung dieser Änderungen, wodurch der durch die Veränderungen angegebenen Störströmung entgegengewirkt wird.
  3. Verfahren nach den Ansprüchen 1 oder 2, bei welchem das unter höherem Druck stehende Gas in eine Reihe von unterschiedlichen Sektoren um den Kompressor herum eingeblasen wird, wobei die Strömungsänderungen unabhängig voneinander in jedem der Sektoren abgefühlt werden.
  4. Verfahren nach Anspruch 3, bei welchem das unter höherem Druck stehende Gas aus dem gleichen Sektor abgenommen wird, in den es eingeblasen wird.
  5. Verfahren nach einem der vorhergehenden Ansprüche, bei welchem das Einblasen des unter höherem Druck stehenden Gases nach Beginn allmählich vermindert wird.
  6. Verfahren nach einem der vorhergehenden Ansprüche, bei welchem das Einblasen von unter höherem Druck stehenden Gas nach einer vorbestimmten Zeitdauer beendet wird.
  7. Verfahren nach einem der Ansprüche 2 bis 6, bei welchem die Strömungsänderungen, die über einem vorbestimmten Änderungsgrenzwert liegen, an einer von mehreren Stationen festgestellt werden, die im Abstand zueinander in Strömungsrichtung angeordnet sind, und wobei das Einblasen von unter höherem Druck stehenden Gas benachbart zu jener einen Station gemäß dieser Feststellung eingeleitet wird.
  8. Verfahren nach einem der Ansprüche 2 bis 6, bei welchem Strömungsänderungen, die über dem vorbestimmten Änderungsgrenzwert liegen, an einer von mehreren Stationen festgestellt werden, die in Strömungsrichtung im Abstand zueinander liegen, wobei das Einblasen von unter höherem Druck stehenden Gas in einem beträchtlichen Abstand stromauf dieser einen Station gemäß der Feststellung eingeblasen wird.
  9. Verfahren nach Anspruch 8, bei welchem die Strömungsänderungen wenigstens an einer ersten Station benachbart zum Einlaß des Kompressors und an einer zweiten Station im mittleren Teil des Strömungspfades durch den Kompressor abgefühlt werden und das unter höherem Druck stehende Gas eingeblasen wird, um den Strömungsänderungen entgegenzuwirken, die an jeder Station festgestellt werden, wobei das unter höherem Druck stehende Gas für die erste Station benachbart zur zweiten Station abgezapft wird und das unter höherem Druck stehende Gas für die zweite Station stromab der zweiten Station abgezapft wird.
  10. Verfahren nach einem der vorhergehenden Ansprüche, bei welchem eine Strömungsstörung festgestellt wird und ein abgefühltes Signal der Strömungsveränderung an jeder der in Umfangsrichtung im Abstand zueinander liegenden Stellen während einer Umlaufperiode in einen Durchschnittswert umgeformt wird, entsprechend dem Abfühlen der Strömung an wenigstens drei in Umfangsrichtung aufeinanderfolgenden Stellen, um eine Reihe von Mittelwerten des abgefühlten Signals zu liefern.
  11. Verfahren nach Anspruch 10, bei welchem ein Differenzsignal von dem abgefühlten Signal und dem Mittelwertsignal abgeleitet und ein Maß für die relative Größe des Differenzsignals erlangt wird, wobei das unter höherem Druck stehende Gas eingeblasen wird, wenn die relative Größe des Differenzsignals für jede der Abfühlstellen über einem vorbestimmten Änderungsgrenzwert liegt.
  12. Verfahren nach einem der Ansprüche 1 bis 11, bei welchem das Einblasen des unter höherem Druck stehenden Gases eingeleitet wird, wenn die Strömungsveränderungen über dem vorbestimmten Änderungsgrenzwert aufeinanderfolgend für wenigstens einige der in Umfangsrichtung im Abstand zueinander liegenden Stellen abgefühlt werden.
  13. Verfahren nach einem der vorhergehenden Ansprüche, bei welchem bei der Feststellung von Veränderungen wenigstens ein kleiner scharf definierter Flecken abgerissener Strömung festgestellt wird.
  14. Verfahren nach einem der vorhergehenden Ansprüche, zur Steuerung der Strömung in einem Axialkompressor, bei welchem das unter höherem Druck stehende Gas in einer Richtung eingeblasen wird, die eine Umfangskomponente in Gegenrichtung zur Drehrichtung des Kompressorrotors hat.
  15. Verfahren nach einem der vorhergehenden Ansprüche, bei welchem der vorbestimmte Grenzwert der Strömungsänderung nicht wesentlich kleiner ist als 2 % des Mittelwertes der Hauptströmung durch den Kompressor.
  16. Vorrichtung zur Steuerung einer Gasströmung in einem Kompressor (C) mit den folgenden Merkmalen:
    - es ist ein Feld von Sensoren (2) vorgesehen, um die Strömung an einer Reihe von in Umfangsrichtung des Kompressors im Abstand zueinander liegenden Stellen abzufühlen und auf die Strömung bezogene Signale zu liefern;
    - es sind Steuermittel (22) vorgesehen, die mit den Sensoren in Verbindung stehen, um Veränderungen in der Strömung in einem umfänglichen Bereich relativ zu der Strömung in einem anderen Bereich festzustellen und Steuersignale zu liefern, wenn derartige Änderungen festgestellt werden; und
    - es ist eine Einblasvorrichtung (8, 14) vorgesehen, die bei Empfang der Steuersignale wirksam gemacht wird, um unter höherem Druck stehendes Gas in den Kompressor einzublasen,
    dadurch gekennzeichnet, daß die Einblasvorrichtung (8, 14) so ausgebildet ist, daß das unter höherem Druck stehende Gas allgemein in Richtung der Hauptströmung durch den Kompressor (C) eingeblasen wird, daß Mittel vorgesehen sind, um das unter höherem Druck stehende Gas von einem Bereich des Kompressors (C) mit höherem Druck stromab der in Umfangsrichtung im Abstand zueinander liegenden Stellen abzuziehen, und daß die Einblasvorrichtung (8, 14) so angeordnet und ausgebildet ist, daß das unter höherem Druck stehende Gas in einem Umfangsbereich eingeblasen wird, in dem die Änderung festgestellt wurde, wobei die Einblasvorrichtung (8, 14) so angeordnet ist, daß das unter höherem Druck stehende Gas in den Kompressor (C) unter einem radial gerichteten Winkel von nicht wesentlich mehr als 30 ° eingeblasen wird.
  17. Vorrichtung nach Anspruch 16, bei welcher die Einblasvorrichtung (8, 14) aus einer in Umfangsrichtung angeordneten Reihe von Injektoren (8) besteht und die Steuervorrichtung (22) die Einspritzvorrichtung (8, 14) in Umfangsrichtung selektiv in Abhängigkeit von den in Umfangsrichtung befindlichen Stellen der Sensoren (2) betätigt, durch welche die Strömungsänderungen festgestellt wurden, wodurch den Strömungsstörungen entgegengewirkt wird, die durch die Veränderungen angezeigt wurden.
  18. Vorrichtung nach einem der Ansprüche 16 oder 17, bei welcher die Steuervorrichtung (22) Mittel aufweist, durch die nur Sensorsignale, die Strömungsänderungen über einem vorbestimmten Strömungsgrenzwert anzeigen, die Einblasvorrichtung in Tätigkeit setzen.
  19. Vorrichtung nach einem der Ansprüche 16 bis 18, bei welcher die Sensoren (102a, 102b) an mehreren Stellen angeordnet sind, die in Strömungsrichtung im Abstand zueinander befindlich sind, und bei der die Einblasvorrichtung (108a, 108b, 114a, 114b) Injektoren (108a, 108b) aufweist, die an den Stellen oder in der Nähe davon vorgesehen sind, wobei die Steuervorrichtung (202a, 202b) das Einblasen einleitet, wenn an diesen Stellen Strömungsveränderungen festgestellt wurden.
  20. Vorrichtung nach einem der Ansprüche 16 bis 18, bei welchem die Sensoren (102a, 102b) an mehreren Stellen angeordnet sind, die in Strömungsrichtung hintereinander im Abstand zueinander angeordnet sind, und bei welcher die Einblasvorrichtung (108a, 108b, 114a, 114b) Injektoren (108b) aufweist, die in einem beträchtlichen Abstand stromauf von einer der Stellen (102b) angeordnet sind, wobei die Steuervorrichtung (114b) das Einblasen einleitet, wenn an dieser einen Station die Strömungsänderung festgestellt wurde.
  21. Vorrichtung nach Anspruch 16, welche Sensoren (102a) aufweist, die an einer ersten axialen Station benachbart zum Einlauf des Kompressors (C) angeordnet sind, und bei welcher Sensoren (102b) an einer zweiten axialen Station im mittleren Abschnitt des Strömungspfades durch den Kompressor angeordnet sind, wobei die Einblasvorrichtung einen ersten Injektor (108a) aufweist, der an der ersten Station (102a) oder in der Nähe hiervon vorgesehen ist, während ein zweiter Injektor (108b) in einem beträchtlichen Abstand stromauf der zweiten Station (102b) vorgesehen ist und wobei eine Leitung (116) den ersten Injektor (108a) mit der Hauptströmung des Kompressors (C) stromab der ersten Station (102a) verbindet, während eine zweite Leitung (118) den zweiten Injektor (108b) mit der Hauptströmung des Kompressors (C) stromab der zweiten Station (102b) verbindet.
  22. Vorrichtung nach Anspruch 21, bei welcher die Einspritzvorrichtung Ventile (250) aufweist, die beiden Leitungen (252, 254, 256) gemeinsam sind, um selektiv das Einblasen über eine der Leitungen (252, 256) gemäß Signalen der Steuervorrichtung (280) zu blockieren.
  23. Vorrichtung nach einem der Ansprüche 16 bis 21, bei welcher ein Ventil (114) vorgesehen ist, um selektiv das Einblasen von unter höherem Druck stehender Luft zu verhindern, wobei das Ventil (114) ein begrenzt drehbares Ventil ist, das einen zylindrischen Stator (152) und einen zylindrischen Rotor (142) aufweist, der im Gleitsitz im Stator (152) angeordnet ist, wobei Stator (152) und Rotor (142) jeweils mit einer Reihe von in Umfangsrichtung im Abstand zueinander liegenden Öffnungen (154) versehen sind, die in und außer Deckung gebracht werden können, indem der Rotor (142) gedreht wird, um das Ventil zu öffnen und zu schließen.
  24. Vorrichtung nach Anspruch 23, bei welcher ein elektromagnetischer Antrieb die Endstellungen des Drehantriebs des Rotors bestimmt.
  25. Vorrichtung nach einem der Ansprüche 16 bis 24, bei welcher die Einblasvorrichtung Strömungssteuermittel aufweist, um die Strömung durch die Einblasvorrichtung zu steuern, wobei die Strömungssteuervorrichtung nach einer Schließstellung vorgespannt ist.
  26. Vorrichtung nach einem der Ansprüche 16 bis 25, welche mit Sensoren und einer Einblasvorrichtung für jeden der unterschiedlichen Sektoren des Kompressors versehen ist, wobei Leitungen die Einblaseinrichtung mit einem Bereich höheren Druckes des Kompressors in jedem Sektor verbinden und die Steuervorrichtung die Arbeitsweise der Einblasvorrichtung in jedem Sektor steuert.
  27. Vorrichtung nach Anspruch 26, bei welcher wenigstens sechs Sektoren vorgesehen sind.
  28. Vorrichtung nach einem der Ansprüche 16 bis 27, bei welcher die Steuervorrichtung (22) wenigstens einen kleinen scharf definierten Fleck der abgerissenen Strömung feststellt.
  29. Vorrichtung nach einem der Ansprüche 16 bis 28, bei welcher der Auslaß Düsen (126) aufweist, bei denen ein vorspringender Abschnitt (30) am Austritt jeder Düse (126) das Ausblasen in stromabwärtiger Richtung ablenkt.
  30. Vorrichtung nach einem der Ansprüche 17 bis 29, welche Mittel (22) aufweist, um das Einblasen von unter höherem Druck stehendem Gas in einer vorbestimmten Zeitperiode zu vermindern oder abzusperren.
  31. Vorrichtung nach einem der Ansprüche 17 bis 30, bei welcher die Steuervorrichtung Mittel aufweist, um die Signale, die an jeder der im Abstand zueinander liegenden Stellen während einer Umlaufperiode abgefühlt wurden, einer Durchschnittsbildung zu unterwerfen, entsprechend dem Abfühlen der Strömung an wenigstens drei in Umfangsrichtung aufeinanderfolgenden Stellen, um eine Reihe von Mittelwerten zu liefern, von denen her eine Strömungsstörung festgestellt wird.
  32. Vorrichtung nach Anspruch 31, welche Mittel aufweist, um ein Differenzsignal zwischen dem augenblicklich abgefühlten Signal und dem Mittelwertsignal zu erzeugen, wobei Mittel vorgesehen sind, um die relative Größe des Differenzsignals festzustellen und ein Betätigungssignal für das Einblasen zu erzeugen, nachdem eine relative Größe festgestellt wurde, die über einem vorbestimmten Pegel gegenüber jeder der Abfühlstellen liegt.
  33. Vorrichtung nach einem der Ansprüche 16 bis 32, bei welcher die Einspritzeinrichtung (8, 14) Düsen (126) aufweist, die zwischen Leitschaufeln (122) angeordnet sind.
  34. Vorrichtung nach einem der Ansprüche 16 bis 33, bei welcher die Einblasvorrichtung (8, 14) Düsen (126) aufweist, die in der Innenwand (124) des Kompressorgehäuses angeordnet sind.
  35. Vorrichtung nach einem der Ansprüche 16 bis 34, bei welcher das unter höherem Druck stehende Gas in einen in Umfangsrichtung befindlichen Bereich eingeblasen wird, der in der Drehrichtung dem Umfangsbereich folgt, in welchem die Strömungsänderung festgestellt wurde.
EP91915299A 1990-08-18 1991-08-19 Verfahren und mittel zur strömungskontrolle Expired - Lifetime EP0543908B1 (de)

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GB909018188A GB9018188D0 (en) 1990-08-18 1990-08-18 Flow control method and means
GB9018188 1990-08-18
PCT/GB1991/001407 WO1992003661A1 (en) 1990-08-18 1991-08-19 Flow control method and means

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FR2804732B1 (fr) * 2000-02-03 2002-04-12 Snecma Procede de detection precoce des instabilites aerodynamiques dans un compresseur de turbomachine
GB2413158B (en) * 2004-04-13 2006-08-16 Rolls Royce Plc Flow control arrangement
US7811050B2 (en) * 2006-12-28 2010-10-12 General Electric Company Operating line control of a compression system with flow recirculation
DE102007035927A1 (de) * 2007-07-31 2009-02-05 Mtu Aero Engines Gmbh Regelung für eine Gasturbine mit aktiv stabilisiertem Verdichter
DE102012100339A1 (de) * 2012-01-16 2013-07-18 Universität der Bundeswehr München Verfahren und Vorrichtung zur Stabilisierung eines Verdichterstroms
EP3296573A1 (de) * 2016-09-20 2018-03-21 Siemens Aktiengesellschaft Methodik zur behandlung von umlaufendem strömungsabriss in einem gasturbinen-verdichter

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WO2012091216A1 (ko) * 2010-12-30 2012-07-05 한국항공우주연구원 축류 압축기 및 그의 유체 안정화 제어 방법

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EP0543908A1 (de) 1993-06-02
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JPH05509143A (ja) 1993-12-16
DE69122258T2 (de) 1997-01-30
DE69122258D1 (de) 1996-10-24

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