EP3589843B1 - Method and device to detect an indicator for the prediction of an instability in a compressor, and corresponding use - Google Patents

Description

The invention relates to a method and a device for determining an indicator for predicting an instability in a compressor, and to the use.

background

Thermal turbo machines can be designed as axial or radial compressors.

For example, axial compressors represent a central component in aircraft engines. The operating behavior of the compressor with this or other designs is difficult to predict. For this reason, the performance data of newly developed compressors are measured on a test bench and then entered in a map. The so-called surge limit is an important part of the map. If the surge limit is exceeded, instabilities arise in the compressor, which represent an extremely high aerodynamic load on the compressor and can cause considerable structural damage. In order to be able to guarantee safe operation of the respective compressor, knowledge of the surge limit is of great importance. However, the surge limit can only be identified on the test bench if it has already been exceeded. For this reason, costly total failures of the tested compressors are accepted in the prior art when determining the surge limit.

A method and an apparatus for predicting the instability of an axial compressor are in the document EP 2 469 098 A1 disclosed.

A method for representing the surge line is in the document U.S. 5,908,462 A disclosed.

document DE 101 52 026 A1 discloses a method for determining a surge limit warning in a turbo compressor or a warning in the event of blade damage.

document US 2009/0312930 A1 discloses a device for stall prediction of an axial compressor having a rotor made of a plurality of rotor blades and a cylindrical housing which covers the outer circumference of the rotor. Furthermore, the device comprises pressure sensors, a unit for calculating key figures for evaluation the stall risk based on time series data from the pressure sensors and a signal processor for stall prediction based on the key figures The document also belongs to the relevant state of the art JP H02 286899 A .

Summary

The object of the invention is to specify a method and a device for determining an indicator for predicting instability in a compressor designed as an axial or radial compressor, which reliably allow early warning of the possible occurrence of a compressor instability.

To achieve this, a method and a device for determining an indicator for a prediction of instability in a compressor, which is designed as an axial or radial compressor, are created according to independent claims 1 and 12. Furthermore, the use of the method according to claim 11 is provided. Alternative configurations are the subject of dependent subclaims.

According to one aspect, a method for determining an indicator for a prediction of instability is created in a compressor which is designed as an axial or radial compressor. In the method, a compressor designed as an axial or radial compressor is operated in operating states which differ in terms of different values of a parameter for a flow mass flow of the compressor, whereby the operating states are passed through with decreasing flow mass flows. Values of the characteristic value for the nut mass flow for the operating states are determined. When running through the operating states, time-resolved pressure measurement values are recorded by means of a pressure sensor, the pressure sensor being arranged in a housing of the compressor upstream adjacent to an entry level of a rotor stage. The skew is determined for the operating states. An indicator for an instability of the compressor (instability indicator) is determined if a change in sign of the curve increase is determined for a curve profile of the skew over the parameter for the mass flow rate for the operating states.

According to a further aspect, the method is used when determining an operating limit of a compressor designed as an axial or radial compressor on a test bench or when monitoring an engine with an axial or radial compressor Executed compressor provided in operation, in particular when used in an aircraft engine or in a turbocharger.

According to another aspect, a device is provided for determining an indicator for a prediction of instability in a compressor which is designed as an axial or radial compressor. The device has a compressor which is designed as an axial or radial compressor. Furthermore, a measuring device is provided which is set up to determine values of a characteristic value for a flow mass flow of the compressor in operating states when the compressor is operated, the operating states differing in terms of different values of the characteristic variable for the flow mass flow of the compressor and in this case the operating states run through with decreasing flow mass flows become; and to detect time-resolved pressure measurement values when passing through the operating states by means of a pressure sensor which is arranged in a housing of the compressor upstream adjacent to an entry plane of a rotor stage. The device has an evaluation device which is set up to determine the skewness for the operating states and to determine an indicator for instability of the compressor if a change in sign of the curve increase is determined for a curve profile of the skewness over the parameter for the mass flow rate for the operating states .

With the help of the proposed technologies, an indicator can be determined in a reliable manner for thermal turbo working machines, that is to say axial or radial compressors, which indicates the possible future occurrence of an instability of the compressor. Before the surge limit is reached, measures can be taken to avoid destruction of the compressor when the surge limit is exceeded, be it on a test bench to determine an operating limit of the compressor and / or when using and operating such a compressor, for example in a turbocharger or a Aircraft engine.

When running through the various operating states, the compressor is throttled, i.e. operating states are set one after the other for which the flow mass flow decreases bit by bit.

The operation of the compressor when measuring the characteristic value for the flow rate mass flow and the measured pressure values can be carried out at one and the same speed for the rotor or rotors (rotor stages) of the compressor. Alternatively, it can be provided when Determine the indicator of the instability of the compressor using measurements at different speeds.

The parameter "skewness" is the third statistical moment, for the determination of which the time-resolved pressure measurement values are used. Methods for determining the skewness are known as such.

The acquisition of the time-resolved pressure measurement values can be used to measure the steady-state pressure.

The pressure sensor can be arranged in the housing of the compressor on an inner wall of the housing. The pressure sensor can be arranged flush with the surface in the housing of the compressor on the inner wall of the housing of the compressor. In this or other embodiments, a plurality of pressure sensors can also be provided, which are arranged in the housing of the compressor upstream adjacent to the entry plane of the rotor stage, for example spaced circumferentially. Provision can be made to use the time-resolved pressure measurement values acquired with the plurality of pressure sensors to determine the indicator for the instability of the compressor.

The pressure sensor can be arranged in the housing of the compressor above blade tips of blades of the rotor stage.

When recording the time-resolved pressure measurement values when running through the operating states, pressure fluctuations can be recorded in a time-resolved manner by means of the pressure sensor. In this or other embodiments, the sampling of the time-resolved pressure measurement values can take place at a frequency between approximately and 20 kHz and approximately 100 kHz, so that in the event that pressure fluctuations are measured in a time-resolved manner, they are determined with a frequency of approximately 10 kHz to approximately 50 kHz .

The change in sign of the curve rise can indicate that a local maximum has been passed. If the curve of the skewness over the characteristic variable for the flow mass flow runs through from larger to smaller values of the characteristic variable for the flow mass flow, the flow of the local maximum means that the curve rise changes from negative values to positive values.

Another indicator for the instability of the compressor can be determined if a further change in sign of the curve increase is determined for the curve shape of the skew over the parameter for the flow mass flow towards lower flow mass flows. The multiple sign changes can be determined as separate indicators of different quality for the possible or expected occurrence of an instability of the compressor, for example with regard to a different distance to the surge limit, which is based on the difference between the value of the parameter for the flow mass flow for the surge limit on the one hand and the value when the sign change on the other hand is determinable.

The change in sign of the curve rise can indicate that a local minimum has been passed.

The flow coefficient and / or the reduced mass flow for the operating states can be determined as a parameter for the flow mass flow.

Based on the determination of the indicator and / or the further indicator, a warning signal can be generated as an early warning of compressor instability and output via an output device. If the indicator and / or the further indicator are determined from the curve progression, a warning signal assigned in each case indicates to the user optically and / or acoustically that there is a risk of compressor instability in the event of a further reduction in the mass flow rate.

The compressor can be operated in operating states that are below a surge limit of the compressor. Provision is made for the throttling of the compressor and the passage through the different operating states caused by this to be interrupted before the surge limit is reached, whereupon instabilities actually occur. When testing the compressor on the test bench, damage to the compressor can be avoided, which is why multiple tests are possible. If the indicator is determined for a compressor that is in operation or in use, for example as an axial compressor in an aircraft engine, possible damage is avoided, whereby the service life can be extended. The indicator and / or the further indicator indicate a possible occurrence of an instability of the compressor before this actually occurs.

In connection with the device of an indicator for determining an instability of a compressor, the preceding explanations regarding the configuration of the method apply mutatis mutandis.

Description of exemplary embodiments

Fig. 1

eine schematische Darstellung einer Anordnung für einen Prüfstand zum Testen eines Axialverdichters;

Fig. 2

eine schematische Darstellung eines Axialverdichters im Schnitt;

Fig. 3

eine schematische Darstellung eine Radialverdichters im Schnitt;

Fig. 4

eine grafische Darstellung des Kurvenverlaufs für Betriebszustände eines Verdichters, wobei die Schiefe über dem Durchflusskoeffizienten aufgetragen ist;

Fig. 5

eine grafische Darstellung für Betriebszustände bei einer Drehzahl von 5500 Umdrehungen pro Minute, wobei die Schiefe über dem Durchflusskoeffizienten aufgetragen ist; und

Fig. 6

eine grafische Darstellung für Betriebszustände bei einer Drehzahl von 9000 Umdrehungen pro Minute, wobei die Schiefe über dem Durchflusskoeffizienten aufgetragen ist.

In the following, further exemplary embodiments are explained with reference to figures of a drawing. Here show:

Fig. 1

a schematic representation of an arrangement for a test stand for testing an axial compressor;

Fig. 2

a schematic representation of an axial compressor in section;

Fig. 3

a schematic representation of a radial compressor in section;

Fig. 4

a graphical representation of the curve profile for operating states of a compressor, wherein the skew is plotted against the flow coefficient;

Fig. 5

a graphical representation for operating states at a speed of 5500 revolutions per minute, wherein the skew is plotted against the flow coefficient; and

Fig. 6

a graphic representation for operating states at a speed of 9000 revolutions per minute, the skewness being plotted against the flow coefficient.

Fig. 1 shows a schematic representation of an arrangement for a test stand for measuring or determining an axial compressor. A rotor 2 with blades 3 and a drive device 4 for rotating the rotor 2 are arranged in a flow pipe 1. Stator blades are installed downstream of the rotor 2. Fig. 1 also shows a front view.

To measure parameters, a Prandtl tube 5 and a pressure sensor 6 are provided, which are arranged on a tube wall 7 in such a way that, in relation to an inlet plane of the rotor 2 upstream adjacent to the inlet plane on the inside of the tube wall 7, pressure measurement values can be recorded in a time-resolved manner . The Prandtl tube 5 is used to measure the dynamic pressure in the flow tube 1.

The pressure sensor 6 is used to measure the static, unsteady pressure. The pressure measurement is carried out in a time-resolved manner, with pressure fluctuations, for example, being measurable with a high time resolution in a frequency range from approximately 10 kHz to approximately 50 kHz.

When running in Fig. 1 a further pressure sensor 6a is provided with which time-resolved pressure measurement values comparable to the measurement with the pressure sensor 6 can be recorded and which can alternatively be omitted.

Furthermore, a pressure measuring device 9 is provided in order to measure the static pressure at a compressor outlet. In combination with the pressure measurement data from the Prandtl tube 5, a pressure ratio generated by the compressor can be determined.

Fig. 2 shows a schematic representation of an axial compressor 20 in which, for example, several stage packages 20.1,..., 20.5 are arranged one behind the other and each have a vane rotor and a vane stator, which are arranged in a compressor housing 21. The pressure sensor 6 is comparable to the illustration in FIG Fig. 1 , arranged adjacent to the entry level of the first stage package 20.1. Alternatively, the pressure sensor 6 can also be arranged adjacent to the entry level of one of the later stage packages 20.2,..., 20.5 in order to acquire the measured values for the time-resolved pressure measurement.

Fig. 3 shows a schematic representation of a radial compressor 30 with rotor 31 and stator 32, the pressure sensor being arranged in a comparable position.

With the help of the in Fig. 1 Different operating states can be set for the compressor, for example with a constant speed of the rotor 2. In the case of throttling of the compressor when running through the operating states, these are characterized by an increasingly lower flow mass flow. When running through the operating states, the mass flow rate for the respective operating state and associated pressure measurement values recorded in a time-resolved manner are measured with the aid of the pressure sensor 6. The skewness (third static moment) can be determined as an integral parameter from the measured values for the static unsteady pressure, as is known as such.

The recorded measured values can be evaluated with the help of an evaluation device (not shown), for example by means of a computer, which has a processor and a memory having. The evaluation device can be connected to the various elements of the measuring device in order to exchange electronic data and signals. An output for outputting optical and / or acoustic signals can be connected to the evaluation device, in particular for outputting one or more warning signals.

Fig. 4 shows a schematic representation for a curve 40 that results when running through the various operating states with decreasing flow mass flow when the skew is plotted over a parameter for the flow mass flow, with FIG Fig. 4 the flow coefficient ϕ is specified.

If the course of the curve 40 is considered from larger flow coefficients to smaller ones, it results that a local minimum 41 is passed through first, before a local maximum 43 is passed through before reaching the surge line 42. When passing through the local extrema 41, 43 is found a change in sign for the rise of curve 40 takes place, which can be determined in each case as an indicator for the approach to surge limit 42. In this case, the local maximum 43 and the local minimum 41 each form indicators of different quality because they are “differently far” away from the surge line 42 in relation to the flow coefficient ϕ.

The Fig. 5 and 6th show graphical representations for experimental values at speeds of 5500 and 9000 revolutions per minute, the skewness being plotted against the flow coefficient ϕ. The characteristic curve is shown as it is for Fig. 4 was explained.

Further aspects for determining the instability indicator (s) are explained below.

If the axial compressor is on a test bench (cf. Fig. 1 ), all possible operating points can be approached in a targeted manner. The mass flow that flows through the compressor and the pressure that the compressor builds up are controlled separately via a throttle mechanism. The following explains how to determine the operating limit of the compressor.

With the aid of the drive device 4, the compressor is operated at a certain speed. While the speed remains constant, the outlet opening of the compressor is successively reduced, as a result of which the mass flow is reduced and the pressure built up increases. The so-called throttling of the compressor can only be carried out until the operating limit is reached. This means that at every speed there is a maximum possible pressure build-up from which the stable aerodynamics inside the compressor collapse - the compressor starts to "pump".

To create the curve according to Fig. 3 the following parameters are recorded or calculated in the course of the gradual throttling. The flow parameter plotted on the x-axis represents a similarity parameter for comparing different compressor mass flows and is determined during the test. As an alternative to the flow parameter, the "reduced mass flow" can also be determined at each operating point. The choice between the two similarity parameters has no influence on the evaluation. For the parameter to be plotted on the y-axis, a high-resolution pressure fluctuation over time is measured at each operating point at the blade tips. The pressure signal of any length can be reduced to an integral parameter, the third statistical moment - skewness. In the following, the pair of values, consisting of the flow coefficient (reduced mass flow) and the skew, is shown in the diagram in Fig. 3 transfer. The process is repeated for all subsequent operating points.

The proposed method can use pairs of values for two consecutive operating points in the various configurations for the early detection of compressor pumps in order to determine a local curve slope . As soon as the sign of the difference quotient changes for the first time during the throttling process (see local minimum 41 in Fig. 3 ), this event is interpreted as a preliminary stage for compressor pumping. If there is another sign change in the following (cf., local maximum 43 in Fig. 3 ), the last operating point set characterizes the last stable operating point before reaching the surge limit 42. At this point, the method provides for the issuing of a corresponding recommendation to abort the throttling process in order to prevent the surge limit from being exceeded.

The invention is defined solely in the following claims.

Claims (12)

1. Method for determining an indicator for predicting an instability in a compressor which is designed as an axial or centrifugal compressor, comprising the following steps:

   - operating a compressor designed as an axial or centrifugal compressor in operating states which differ by different values of a parameter for a flow mass flow of the compressor, wherein in this situation the operating states are passed through with decreasing flow mass flows;

   - determining the values of the flow mass flow parameter for the operating states;

   - detecting time-resolved pressure readings when passing through the operating states by means of a pressure sensor (6) which is disposed in a housing of the compressor adjacently upstream of an entrance plane of a rotor stage (2);

   - determining the skewness for the operating states,

   characterized in that the following step is performed additionally

   - determining an indicator for instability of the compressor when a sign change of the curve rise is determined for a curve progression of the skewness over the parameter for the flow mass flow for the operating states.
2. Method according to claim 1, characterized in that the pressure sensor (6) is disposed inside the compressor housing on an inner wall of the housing.
3. Method according to claim 1 or 2, characterized in that the pressure sensor (6) is disposed inside the compressor housing above blade tips of vanes (3) of the rotor stage (2).
4. Method according to at least one of the preceding claims, characterized in that when detecting the time-resolved pressure readings while passing through the operating states by means of a pressure sensor (6), pressure fluctuations are detected in time-resolved manner.
5. Method according to at least one of the preceding claims, characterized in that the sign change of the curve rise indicates passage through a local maximum (43).
6. Method according to at least one of the preceding claims, characterized in that a further indicator for the instability of the compressor is determined if a further change of sign of the curve rise is determined for the curve progression of the skewness over the parameter for the flow mass flow towards lower flow mass flows.
7. Method according to claim 6, characterized in that the change in sign of the curve rise indicates passage through a local minimum (41).
8. Method according to at least one of the preceding claims, characterized in that the flow coefficient and/or the reduced mass flow are determined as a parameter for the flow mass flow for the operating states.
9. Method according to at least one of the preceding claims, characterized in that, starting from the determination of the indicator and/or the further indicator, a warning signal is generated as an early warning of compressor instability and output via an output device.
10. Method according to at least one of the preceding claims, characterized in that the compressor is operated in operating states which are below a surge limit of the compressor.
11. Method according to at least one of the preceding claims, in which:

    - the compressor stands on a test bench and an operating limit is determined, or

    - the compressor is in operation in an engine and the engine is monitored.
12. Apparatus for determining an indicator for predicting an instability in a compressor which is designed as an axial or centrifugal compressor, with:

    - a compressor designed as an axial or centrifugal compressor;

    - a measuring apparatus which configured

    - to determine, during operation of the compressor, values of a flow mass flow parameter of the compressor in operating states, wherein the operating states differ by different values for the flow mass flow parameter of the compressor, and wherein the operating states are passed through with decreasing flow mass flows; and

    - to detect time-resolved pressure readings when passing through the operating states by means of a pressure sensor (6) which is disposed in a housing of the compressor adjacently upstream of an entrance plane of a rotor stage; and

    - an evaluation device which is configured

    - to determine the skewness for the operating states, and

    - to determine an indicator for an instability of the compressor if a change in sign of the curve rise is determined for a curve progression of the skewness over the parameter for the flow mass flow for the operating states.

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