EP0777828A1 - Compressor stall diagnostics and avoidance - Google Patents
Compressor stall diagnostics and avoidanceInfo
- Publication number
- EP0777828A1 EP0777828A1 EP96920104A EP96920104A EP0777828A1 EP 0777828 A1 EP0777828 A1 EP 0777828A1 EP 96920104 A EP96920104 A EP 96920104A EP 96920104 A EP96920104 A EP 96920104A EP 0777828 A1 EP0777828 A1 EP 0777828A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- compressor
- gas turbine
- signal
- frequency
- compression system
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- 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
- F04D27/0223—Control schemes therefor
Definitions
- This invention relates to techniques for diagnosing and avoiding stall in rotary compressors, such as aircraft jet engines.
- the flow through the compressor is essentially uniform around the annulus, i.e., it is axisymmetric, and the annulus-averaged flow rate is steady.
- the compressor is operated too close to the peak pressure rise on the compressor pressure rise versus mass flow, constant speed performance map, disturbances acting on the compressor may cause it to encounter a region on the performance map in which fluid dynamic instabilities develop, known as rotating stall and/or surge. This region is bounded on the compressor performance map by the surge/stall line. The instabilities degrade the performance of the compressor and may lead to permanent damage, and thus they should be avoided.
- Rotating stall can be viewed as a two-dimensional phenomena that produces a localized region of reduced or reversed flow through the compressor that rotates around the annulus of the flow path.
- the region is termed a "stall cell” and typically extends axially through the compressor.
- Rotating stall produces reduced output (as measured in annulus-averaged pressure rise and mass flow) from the compressor.
- the stall cell rotates around the annulus it loads and unloads the compressor blades and may induce blade fatigue failure.
- Surge is a one-dimensional phenomena defined by oscillations in the annulus-averaged flow through the compressor. Under severe surge conditions, reversal of the flow through the compressor may occur. Both types of instabilities should be avoided, particularly in aircraft applications.
- Stall margin is a measure of the ratio between peak pressure rise, i.e., pressure rise at stall, and the pressure ratio on the operating line of the compressor for the current flow rate. In theory, the greater the stall margin, the larger the disturbance that the compression system can tolerate before entering stall and/or surge. Thus, a compressor design objective is to incorporate enough stall margin to avoid operating in a condition in which an expected disturbance is likely to trigger stall and/or surge. In gas turbine engines used to power aircraft, stall margins of fifteen to thirty percent are common. Since operating the compressor at less than peak pressure rise carries with it a reduction in operating efficiency and performance, there is a trade off between stall margin and performance. Stall margin can be reduced by engine operating conditions, for instance aircraft pitch and yaw and acceleration (conditions that momentarily change increase current pressure) and over time from component wear, for instance enlarged distances between compressor blade tips and the compressor end wall.
- An object of the present invention is to avoid compressor stall, especially in aircraft jet engines.
- Another object of the present invention is diagnosing a change in base-line stall margin of a rotary compressor for repair and service. Another object is reliably comparing the stall margin of a compressor with other compressors.
- compressor flow is sensed with one or more pressure sensors to produce a signal that passed through a bandpass filter having a lower roll-off between .01 and 1 of N2 (compressor rotational frequency) and an upper roll-off between 1 and 10 of N2.
- the output from the filter is smoothed and compared with a "design value" for compressor flow unsteadiness, producing an error that is integrated.
- One or more compressor bleed valves are opened when the integral exceeds a preset threshold. According to the invention, compressor bleed valves are opened for a fixed duration when the threshold is exceeded.
- a stall controller employing the invention can be used to improve operation of a compression (pumping) system having a compressor susceptible to rotating stall under certain circumstances.
- a feature of the invention is that it can be used in gas turbine engines and cooling systems, such as some air conditioning systems or refrigeration systems.
- the general "health" of a compression system can be diagnosed by inserting a probe into the compressor flow path and viewing the output signal from a pressure probe that responds to the pressure in the probe for the signal characteristics at the rotor frequency or N2.
- the engine on a parked aircraft can be tested by inserting the probe into a compressor bore hole and viewing on a signal analyzer the magnitude of the signal fluctuations from the probe pressure at N2 as the engine is accelerated and decelerated.
- the magnitude of the signals at N2 can be compared to known values (base-line signal values) for the compressor, indicating a change in stall margin or compared to the values for other compressors, which can provide an indication of relative stall susceptibility.
- a feature of the invention is the capability of detecting reduced stall margin as compressor components wear of time and establishing a compressor base-line characteristic that can be rechecked during routine engine and aircraft maintenance and compared with other compressors.
- Fig. 1 is a functional diagram of a gas turbine engine employing a static pressure sensor and signal processor to control the opening and closing of compressor bleed valves to avoid stall using the time varying output from the pressure sensor according to the present invention.
- Fig. 2 shows various compressor stages, compressor flow static pressure sensors, bleed valve locations and signal processing steps to control the opening and closing of the bleed valves according to the present invention.
- Fig. 3 shows transfer functions or operations used in one of the steps shown in Fig. 2.
- Fig. 4 is a schematic representation of diagnostic equipment used to test a gas turbine engine according to present invention.
- Fig. 5 is a graph of the acceleration of a gas turbine from an idling condition to a low power condition.
- Fig. 6 a plot of amplitude of the pressure fluctuations within a compressor at N2 as a function of time during the engine acceleration transient shown in Fig. 3, shows a possible change in the transients characteristics as compressor components wear, e.g., before and after compressor refurbishment.
- Fig. 7 a three dimensional plot of the magnitude of the pressure fluctuations and N2 and the duration of the fluctuation, shows the pressure fluctuations at N2 that are used for engine diagnostics according to the present invention.
- Fig. 8 a three dimensional plot of the magnitude of the pressure fluctuations and N2 and the duration of the fluctuation, shows the pressure fluctuations that typically appear at lower frequencies (below N2) to which prior art stall detection devices typically respond.
- Fig. 1 shows a bypass gas turbine turbofan engine 10 that uses a static pressure sensor 12 to provide a signal PRl with characteristics of the compressor flow 14 present at a compressor stage location, for example between the eight and ninth compressor stages.
- the signal PRl is supplied to a signal processor (SP) 16, which can be assumed to include a central processing unit and associated memory programmed to cyclically perform computation steps using the signal PRl and the control/transfer functions 20, 22, 24 and 26 in Fig. 2 to produce a signal A ⁇ Q - j .
- SP signal processor
- the invention may be used to "ground test" an aircraft engine not having the permanent sensor 12, as explained in the diagnostic section in this description.
- the engine contains a borescope inspection port 10a (known in the art for visually inspecting the compressor) at one or more compressor stages to sensor the compressor flow pressure.
- the signal processor also receives a compressor speed (N2) signal, which represents the compressor rotational speed or frequency (i.e., rotor frequency).
- N2 compressor speed
- the signal A ⁇ Qj - controls the opening of compressor bleed valves 18 using the following control law, which will be explained in more detail using the software function block diagrams in Fig. 2 and Fig. 3:
- cti an instantaneous level of unsteadiness in flow properties as manifested in the pressure signal PRl and oi is a stored or"design" value for the instantaneous level of unsteadiness.
- a so-called “FADEC” or “Full Authority Digital Electronic Control” 28 controls fuel flow to the engine combustors 30 as a function of a power lever advance PL A at a cockpit located power control 32.
- the fuel control may be assumed to include a signal processor for controlling the fuel flow based on a variety of engine operating parameters and, while a separate signal processor 16 to carry out the special sequences associated with the invention has been shown, it is conceivable that a FADEC can be programmed to perform those operations and produce the o n signal to control the bleed valves 18.
- a compressor includes a plurality of stages, that the bleed valves 18 are selectively located at certain stages and that the static pressure sensor 12 is ahead of those stages (upstream in the compressor flow), although in some applications the sensor or sensors 12 may be located behind (downstream) from the bleed valves 18.
- the signal processor 16 is programmed to carry out steps that achieve the functions of blocks 20, 22, 24 and 26.
- the pressure signal PRl, produced by the sensor 12 will have a time varying characteristic, creating a compressor flow 14 signature, including an indication of the flow unsteadiness along with flow and sensor noise.
- the pressure signal PRl is narrowly filtered at block 20, the bandpass frequency ranging from .1N2 to N2 with 2-pole roll-offs at the upper and lower frequencies. An effect is smoothing the signal PRl.
- the output from the filter function 20, signal PR2 is used in an absolute value 22 function to produce absolute value signal PR2 for the spectrum of information passed through the filter function 20.
- the output from the block 22 is applied to a low pass filter with a roll off at 1Hz, producing the signal PR3, which in effect is measure of the unsteady flow condition associated with an imminent compressor stall, in other words remaining stall margin.
- the next block 26 starts the operations shown in Fig. 3.
- the precursor PR3 is subtracted from a stored value A ma ⁇ (block 32), which is a maximum or design value for the precursor and if exceeded manifests an unstable compressor flow in the value of signal Error 1.
- a ma ⁇ block 32
- the output, Error 2 from a second summer 36 would be Error 1.
- the value for Error 2 is integrated at operation 38.
- the output from the integration step is limited at operation 40 and the output A jnt (from the limiter 40) is scaled with operation 42, producing the bleed control output signal A- ⁇ - j .
- the bleed valves 18 are commanded to open completely if A con has exceeded a stored threshold; otherwise, the bleed valves 18 remain completely closed.
- the block 44 should be capable of performing either of the following operations once the bleed valves are opened. It can provide a signal to reduce the value of A max slightly, e.g., by 10 percent while the bleed valves are open and return A max to its full value when the bleed valves close again (the open signal is discontinued). Alternatively, as shown by the dotted block, a timer function 44a can be employed to open the bleed valves for a fixed interval when the A ⁇ ,- signal is produced.
- the output from the operation 40 is subtracted from the output from the integrator operation 38 at summer 46, and the error from the summer 46 is scaled with operation 34 and applied to the summer 36, which reduces Error2, preventing the integrator operation from "winding up" beyond the value of A jnt over time.
- the bleed valves 18 will rapidly open when the precursor (signal PRl) indicates a flow condition near the stall boundary; that is, the time varying flow characteristics, normally found at the early stages of a rotating stall, are within the bandwidth of filter 20 and last long enough for o to exceed the threshold.
- equipment for performing a diagnostic test on the gas turbine engine 10 on an aircraft includes a probe 50 with a dynamic pressure sensor 52 at one end to produce a time varying pressure signal TP on the line 53, which is one input to a data acquisition system 54.
- One end of the pressure probe 50 is inserted into the borescope inspection port 10a to tap the compressor gas flow.
- the dynamic pressure sensor 52 is located on the other end of the pressure probe 50 and the signal TP manifests the pressure (fluctuations) within the probe, hence the pressure of the compressor flow.
- Compressor rotor disk speed or rotational frequency N2 is transmitted over the line 57, providing a second input to the to the data acquisition system 36, which provides an indication of compressor pressure vs. N2 on a monitor 58.
- the data acquisition system can be assumed to be programmed with a software package capable of measuring the amplitude of the fluctuations in signal TP at N2 as a function of time during the engine operation as a function of time and providing electrical signals that represent those amplitudes at different values for N2.
- the graph of Fig. 5 plots the acceleration transient of a gas turbine engine.
- the Y-axis represents N2 in rotations per minute (rpm) during the acceleration transient.
- the X-axis represents time in seconds (sec) that it takes the gas turbine engine to achieve the particular frequency, where zero (0) seconds is defined as the start of the engine acceleration transient.
- the value of N2 changes continuously during the acceleration transient.
- the data acquisition system 54 tracks N2 and compiles the amplitude of pressure fluctuation at those rotor frequencies as the engine accelerates.
- FIG. 6 illustrates the plot of the pressure fluctuations (amplitude of signal TP) at the rotational frequency of the rotor disk (Y-axis) as a function of time (X-axis) during the initial three (3) seconds of the acceleration transient described above, starting at time zero (0) seconds.
- the dashed line represents the response of a healthy engine with a known high stall margin.
- the solid line defines the response of a deteriorated engine, one prone to stalls and/or surges with a known low stall margin.
- the magnitude of amplitude of the pressure fluctuation can be correlated to engine health.
- an upper threshold can be established to determine if a particular compression system is healthy.
- the upper threshold can be established by measuring the amplitude of the pressure fluctuations at the rotor frequency of an engine with a known low stability margin. Once the upper threshold is established, the amplitude of pressure fluctuations at the rotor frequency of other engines can be compared to the pre- established upper threshold. Such comparison allows differentiation between a healthy engine and an engine prone to stalls and/or surges.
- diagnoses can be made by monitoring the pressure disturbances at the rotor frequency during a particular transient maneuver while the engine remains on the wing of a grounded or parked aircraft.
- an engine having a maximum amplitude of pressure fluctuation at the rotor frequency that approaches the upper threshold would need of refurbishment. Refurbishment is known to lower the maximum amplitude of pressure fluctuation at the rotor frequency and therefore, lower the likelihood of a stall and/or surge.
- the pressure fluctuations appear hundreds of rotor revolutions prior to an actual stall and/or surge.
- the X-axis shows the time in seconds before the stall, the stall and/or surge occurring approximately at zero (0) seconds.
- the Z-axis shows the strength of the pressure disturbance in pounds per square inch squared (ps ) or amplitude squared.
- the Y- axis indicates the engine order, the frequency of the pressure fluctuation (the value of TP) divided by N2 (the rotational frequency of the rotor disk), the value one (1) being the rotational frequency of the rotor disk and one half (0.5) being one half of the rotational frequency of the rotor disk.
- N2 pre-stall pressure disturbance at N2 can be detected a few seconds in advance of the stall and/or surge.
- the value of N2 in this example is approximately one hundred (100) revolutions per second.
- monitoring the pressure fluctuations at N2 detects the pre-stall condition several hundred rotor revolutions prior to an actual stall.
- the preferred embodiment described herein used an unsteady pressure quantity as a form of measurement.
- Other unsteady flow parameters can be monitored to predict the onset of a stall and/or surge and to diagnose the health of the engine.
- gas density, velocity, temperature, or any other unsteady flow quantity can be monitored to determine the onset of the stall and/or surge.
- the velocity can be measured by using hot wire anemometers or a pitot-static tube.
- the temperature can be measured by using a fine wire thermocouple.
- the engine can be subjected to a particular transient mode and an upper threshold can be established, but as long as the unsteady flow fluctuations are monitored at N2, an accurate sign of reduced stall margin and engine health will be produced.
- the test or diagnostic equipment described and depicted in Fig. 2 is an example of test equipment that can be used to monitor the amplitude of pressure fluctuations according to the invention. Other equipment can be substituted for monitoring the pressure fluctuations within the compressor.
- the data acquisition system can be either a digital data acquisition system, digital tape, FM analog tape or any other type of a system having capability of recording the pressure disturbances (sensor output) with sufficient frequency bandwidth to resolve the disturbances to rotational frequency of the rotor disk.
- software packages that can be used in the analysis of the pressure and rotor speed data are
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Sustainable Development (AREA)
- Control Of Positive-Displacement Air Blowers (AREA)
Abstract
Description
Claims
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US42733495A | 1995-04-24 | 1995-04-24 | |
US427334 | 1995-04-24 | ||
US1318796P | 1996-03-12 | 1996-03-12 | |
US13187 | 1996-03-12 | ||
PCT/US1996/005309 WO1996034207A1 (en) | 1995-04-24 | 1996-04-17 | Compressor stall diagnostics and avoidance |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0777828A1 true EP0777828A1 (en) | 1997-06-11 |
EP0777828B1 EP0777828B1 (en) | 2002-08-21 |
Family
ID=26684545
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP96920104A Expired - Lifetime EP0777828B1 (en) | 1995-04-24 | 1996-04-17 | Compressor stall avoidance |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0777828B1 (en) |
AU (1) | AU5850796A (en) |
DE (1) | DE69623098T2 (en) |
WO (1) | WO1996034207A1 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2015021522A1 (en) | 2013-08-16 | 2015-02-19 | Milani Paulo Giacomo | Axial turbomachines with rotary housing and fixed central element |
CN110608187A (en) * | 2019-10-30 | 2019-12-24 | 江西理工大学 | Axial flow compressor stall surge prediction device based on frequency characteristic change |
Families Citing this family (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2804732B1 (en) | 2000-02-03 | 2002-04-12 | Snecma | PROCESS FOR EARLY DETECTION OF AERODYNAMIC INSTABILITY IN A TURBOMACHINE COMPRESSOR |
EP2193400B1 (en) | 2007-09-17 | 2014-12-10 | Danmarks Tekniske Universitet | An electromagnetic beam converter |
EP2971700B1 (en) | 2013-03-14 | 2019-12-25 | United Technologies Corporation | Pressure sensor noise filter prior to surge detection for a gas turbine engine |
US10037026B2 (en) | 2014-09-25 | 2018-07-31 | General Electric Company | Systems and methods for fault analysis |
WO2016087393A1 (en) | 2014-12-01 | 2016-06-09 | Danmarks Tekniske Universitet | Multi-wavelength generalized phase contrast system and method |
CN114962305B (en) * | 2021-02-25 | 2023-09-26 | 中国航发商用航空发动机有限责任公司 | Online detection method, device, system, equipment and medium for instability of gas compressor |
US20240255070A1 (en) * | 2023-01-30 | 2024-08-01 | The Boeing Company | System, method, and valve assembly for surge protection |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4137710A (en) * | 1977-01-26 | 1979-02-06 | United Technologies Corporation | Surge detector for gas turbine engines |
IL94506A (en) * | 1989-05-30 | 1993-07-08 | United Technologies Corp | Acceleration control for a gas turbine engine with duct pressure loss compensation |
US5275528A (en) * | 1990-08-28 | 1994-01-04 | Rolls-Royce Plc | Flow control method and means |
JPH06147189A (en) * | 1992-11-11 | 1994-05-27 | Hitachi Ltd | Propagating stall preventing device of compressor |
US5448881A (en) * | 1993-06-09 | 1995-09-12 | United Technologies Corporation | Gas turbine engine control based on inlet pressure distortion |
-
1996
- 1996-04-17 WO PCT/US1996/005309 patent/WO1996034207A1/en active IP Right Grant
- 1996-04-17 EP EP96920104A patent/EP0777828B1/en not_active Expired - Lifetime
- 1996-04-17 DE DE69623098T patent/DE69623098T2/en not_active Expired - Lifetime
- 1996-04-17 AU AU58507/96A patent/AU5850796A/en not_active Abandoned
Non-Patent Citations (1)
Title |
---|
See references of WO9634207A1 * |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2015021522A1 (en) | 2013-08-16 | 2015-02-19 | Milani Paulo Giacomo | Axial turbomachines with rotary housing and fixed central element |
CN110608187A (en) * | 2019-10-30 | 2019-12-24 | 江西理工大学 | Axial flow compressor stall surge prediction device based on frequency characteristic change |
Also Published As
Publication number | Publication date |
---|---|
DE69623098T2 (en) | 2002-12-19 |
EP0777828B1 (en) | 2002-08-21 |
DE69623098D1 (en) | 2002-09-26 |
WO1996034207A1 (en) | 1996-10-31 |
AU5850796A (en) | 1996-11-18 |
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