RU2789169C1 - Method for detecting surging and rotating stall of a compressor - Google Patents

Abstract

FIELD: engine building.

SUBSTANCE: invention relates to the field of aviation engine building. Method for detecting surging and rotating stall of a compressor is characterised by measuring the characteristic parameter Pc of compressor operation, forming the average value Pc_AV of the Pc parameter with a low-pass filter, forming a signal Pc_HF of the high-frequency component of the Pc parameter with a high-pass filter, forming the average level

of the absolute value of the signal Pc_HF of the high-frequency component of the parameter, calculating the ratio (

) of the value

to the average value Pc_AV of the parameter, and if the ratio

of the first predetermined threshold is exceeded, forming a signal on the first signalling apparatus, forming the deviation ΔPc of the parameter from the average value thereof Pc_AV, calculating the ratio (ΔPc/Pc_AV) of the deviation ΔPc to the average value of the parameter, and if the ratio ΔPc/Pc_AV falls below the second predetermined threshold, forming a signal on a second signalling apparatus, and if any of the signals of the signalling apparatus are present, forming a signal of surging/rotating stall of the compressor, so as to activate means of eliminating surging and rotating stall of the compressor in accordance thereto.

EFFECT: reduced probability of destruction of the compressor and loss of thrust in case of unstable operation of the compressor due to the reduced reaction time of the means of eliminating surging and rotating stall of the compressor and determined end time of unstable operation of the compressor.

5 cl, 3 dwg

Description

The present invention relates to the field of gas turbine engines (GTE). The invention relates to the detection of compressor surge and rotational stall and can be applied to all types of gas turbine engines, in particular to aircraft gas turbine engines such as turbojet engines, turboprop engines, etc.

A known method for detecting compressor surge, including measuring the parameters of the compressor, determining the sign and calculating the value of the time derivatives of these parameters, comparing each derivative with its threshold value and generating discrete signals that the derivatives of the parameters exceed their threshold values, with all discrete signals exceeding the derivatives of the parameters of their threshold values are delayed for a predetermined time, and a surge signal is generated in the presence of two or more delayed discrete signals simultaneously about the excess of the derivatives of the parameters of their threshold values. In a particular case, to generate a surge signal, depending on the specific features of the compressor, its operating conditions and the type of its drive, all or some of the following time derivatives of the parameters are compared with threshold values: positive derivatives of suction pressure, pressure at a characteristic point of the flow path, frequency rotor rotation and negative derivatives of discharge pressure, pressure difference between discharge and suction, pressure drop across local resistance in the inlet or outlet pipe, power consumed by the compressor (RU 2263234 C1, IPC F04D 27/02, publ. 2005).

As a result of the analysis of the known method, it should be noted that the signals of pressure (or pressure difference) of air in the compressor of a gas turbine engine have a wide spectrum, and signal differentiation leads to an increase in high-frequency noise. When using derivatives to generate a surge signal, there is a risk of generating false signals, in particular, during unstable processes in the combustion chamber (for example, when another fuel manifold is put into operation). One of the methods of noise immunity is the use of several signals according to the “AND” scheme. However, this method leads to problems associated with the combination of signals in time (phasing), and, consequently, to loss of performance. Therefore, for the noise immunity of anti-surge motor protection systems, it is advisable to use band-pass filters tuned to the actual frequencies of surge oscillations.

Closest to the claimed invention in terms of technical essence and achieved technical result is a method for detecting surge and rotating stall of a gas turbine engine compressor, including monitoring air pressure fluctuations behind the engine compressor and generating a signal to turn on surge elimination means, for example, a signal to limit fuel supply, while fluctuations the air pressure behind the compressor is controlled in parallel by broadband and low-frequency surge alarms, and the signal of the low-frequency surge alarm is maintained for a predetermined time corresponding to the maximum possible duration of surge elimination, and upon receipt of signals from both surge alarms simultaneously, a signal is generated to turn on the surge elimination means, which is fed from delay for a specified time, corresponding to the duration of one low-frequency surging air pressure fluctuation after the compressor, provided that the signal from the rockband signaling device after the specified specified delay time (RU 2374143 C1, IPC B64D 31/00, publ. 2009).

As a result of the analysis of this method, it should be noted that the surge signal is formed by two signaling devices, the outputs of which are combined according to the "AND" scheme. As noted above, such a solution reduces the probability of false signal generation, but leads to an increase in the system response time. Also, the use of the "AND" scheme does not allow determining the moment when the compressor exits the rotational stall: the low-frequency surge alarm only reports the moment of the beginning of the rotational stall, and its signal is immediately reset to zero, which leads to the zeroing of the output of the "AND" scheme. As a result, it becomes necessary to introduce predetermined delays when removing the surge signal. The choice of such delays is a laborious process. By choosing relatively small delays, there is a risk that the surge (or rotational stall) will not be eliminated during such a decrease in fuel consumption. The increase in delays leads to a significant reduction in engine performance and a dangerous loss of traction.

The objective of the claimed invention is to improve the reliability of the compressor.

The technical result of the present invention is to reduce the probability of destruction of the compressor and loss of thrust during unstable operation of the compressor by reducing the reaction time of the means for eliminating surge and rotating stall of the compressor and determining the moment when the unstable operation of the compressor ends.

абсолютного значения сигнала Пк_ВЧ высокочастотной составляющей параметра, вычисляют отношение (

) величины

к среднему значению Пк_СР параметра, и при превышении отношения

первого заранее определенного порога формируют сигнал на первом сигнализаторе, формируют отклонение ΔПк параметра от его среднего значения Пк_СР, вычисляют отношение (ΔПк/Пк_СР) отклонения ΔПк к среднему значению параметра, и при снижении отношения ΔПк/Пк_СР ниже второго заранее определенного порога формируют сигнал на втором сигнализаторе, а при наличии любого из сигналов сигнализаторов формируют сигнал помпажа/вращающегося срыва компрессора, в соответствии с которым включают средства ликвидации помпажа и вращающегося срыва компрессора.The specified technical result is achieved by the fact that in the method for detecting surge and rotating stall of the compressor, the characteristic parameter Pk of compressor operation is measured, the average value of Pk _SR of the parameter Pk is formed by a low-frequency filter, the signal _{Pk of} the high-frequency component of the parameter Pk is formed by a high-frequency filter, the average level is formed

the absolute value of the signal PK _RF high-frequency component of the parameter, calculate the ratio (

) values

to the average value of PC _SR parameter, and when the ratio is exceeded

of the first predetermined threshold, a signal is generated on the first signaling device, the deviation ΔPk of the parameter from its average value Pk _SR is formed, the ratio (ΔPk / Pk _SR ) of the deviation ΔPk to the average value of the parameter is calculated, and when the ratio ΔPk / Pk _SR decreases below the second predetermined threshold, a a signal on the second signaling device, and in the presence of any of the signals of the signaling devices, a compressor surge/rotating stall signal is generated, in accordance with which the compressor surge and rotating stall elimination means are turned on.

Significant features may have development and addition.

The air pressure signal behind the last stage of the compressor is used as a characteristic parameter of the compressor operation.

As a characteristic parameter of the compressor operation, the pressure drop signal at the local resistance in the compressor inlet or outlet pipe is used.

As a low-frequency filter, a Butterworth filter of at least the second order, made in the form of series-connected and feedback-covered integrators, is used, and the input signal of the first integrator is used as a signal of the high-frequency component of the parameter.

To form the average level of the absolute value of the parameter, a non-recursive filter with a predetermined time window is used.

The essence of the claimed invention is illustrated by graphic materials, which show:

in fig. 1 is a diagram of a system that implements the claimed method;

in fig. 2 is a graph of the transient process during a rotating compressor stall;

fig. 3 is a diagram of a Butterworth filter of the third order, made on integrators covered by feedback.

The system (Fig. 1) contains a sensor 1 for measuring the characteristic parameter Pk of the compressor operation, for example, the air pressure behind its last stage.

The output of the sensor 1 is connected to the first low-frequency filter 2 (LPF), to the series-connected high-frequency filter 3 (HPF), the rectifier 4 and the second low-frequency filter 5, and the second (inverting) input of the adder 6. The output is connected to the first input of the adder 6. first LPF 2.

The system contains two dividers 7 and 8. The output of the second low-pass filter 5 is connected to the input of the divider 7, the output of the first low-pass filter 2 is connected to the input of the divider 8. The output of the adder 6 is connected to the input of the divisible divider 8, the output of the first low-pass filter 2 is connected to the input of the dividend divider 7.

The system contains two comparators 9 and 10 and a logical element 11 "OR". The output of the divider 7 is connected to the input of the first comparator 9, and the output of the divider 8 is connected to the input of the second comparator 10. The outputs of the comparators 9 and 10 are connected to the inputs of the logic element 11 "OR".

LPF 2 generates at its output the average value of Pc _SR characteristic parameter of the compressor.

HPF 3 generates at its output signal PC _RF high-frequency component of the characteristic parameter of the compressor.

абсолютного значения высокочастотной составляющей характерного параметра работы компрессора.LPF 5 generates an average level at its output

the absolute value of the high-frequency component of the characteristic parameter of the compressor.

The adder 6 generates the deviation ΔPk of the characteristic parameter of the compressor from its average level:

ΔPk=Pk _SR -Pk.

Divisor 7 forms a ratio

Divider 8 forms the ratio ΔPk/Pk _SR .

The chain of elements 3, 4, 5, 7, 9 is the first signaling device, the chain of elements 2, 6, 8, 10 is the second.

The logical element OR 11 generates at its output the signal "Surge/Rotating Stall".

The system can be assembled from known blocks and elements.

As sensor 1 for measuring a characteristic parameter of the compressor operation, tensoresistive air or gas pressure sensors can be used that measure pressure at characteristic points of the compressor, for example, behind its last stage, or tensoresistive pressure drop sensors at local resistance in the inlet or outlet pipe or T-shaped nozzle.

The low and high frequency filters used in the system are standard, for example, the well-known third-order Butterworth filter can be used as the first LPF 2 and HPF 3. The second LPF 5 can be a first order analog filter or a digital non-recursive moving average filter with a predetermined time window.

The time constants of the analog filters and the time window of the non-recursive filter depend on the frequency of air pressure fluctuations during surge and rotational stall, as well as on the dynamic characteristics of the compressor.

Rectifier 4, dividers 7, 8, adder 6, comparators 9, 10, logic element 11 "OR" are standard.

The second input of the adder 6 is inverting.

The first comparator 9 generates at its output a logic one signal when the input value of the comparator 9 exceeds a predetermined threshold.

The second comparator 10 generates at its output a logic one signal when the input value of the comparator 10 falls below a predetermined threshold.

The response thresholds of the comparators 9, 10 are selected depending on the characteristics of the compressor: the level of reduction of the characteristic parameter of the compressor and the amplitude of its oscillations in the event of surge or rotational stall.

As a characteristic parameter, any parameter characterizing the stability of the compressor operation can be used, for example, the air pressure behind the last stage of the compressor or the pressure drop across the local resistance. The choice of a characteristic parameter does not affect the logic of the anti-surge protection. An example is considered below, when the pressure after the last stage of the compressor is used as a characteristic parameter.

With stable operation of the compressor at steady and transient engine operation, there are practically no pressure pulsations behind the last stage of the compressor, and due to the choice of the cutoff frequency of the high-frequency filter, HPF 3 generates a signal at its output that is close to zero, which, having passed through rectifier 4 and being filtered by LPF 5, will lead to the formation of a zero signal at the input of the divider 7, and consequently, a zero signal at the output of the divider 7, and the operation of the comparator 9 will not occur. In turn, the average pressure level generated by the first LPF 2 practically coincides with its instantaneous value measured by sensor 1. A zero signal is formed at the adder 6, a zero signal is also formed at the output of the divider 8, and comparator 10 does not operate. The output of the element "OR" 11 is also a zero signal.

By choosing the cutoff frequency of the LPF 2, the signal of the average pressure level generated by the first LPF 2 practically coincides with its instantaneous value, or the relative deviation (formed by the divider 8) is so small that the comparator 10 does not operate. There are no high-frequency pulsations characteristic of the rotating stall regime. The output of the element "OR" 11 is also a zero signal.

When an unstable operation of the compressor occurs, a sharp decrease in pressure occurs behind its last stage (see the graph in Fig. 2).

The graph illustrates:

P _K - change in air pressure behind the last stage of the compressor in the event of a rotating stall;

U ₉ - signal on the first signaling device (comparator signal 9);

U ₁₀ - signal on the second signaling device (signal of the comparator 10).

In this case, there is a discrepancy between the instantaneous value of the Pk parameter and its average value formed by LPF 2. The discrepancy has a negative sign (the instantaneous pressure is greater than the average). When the error value decreases below the threshold of operation of the comparator 10, the comparator 10 generates a single signal at its output, which leads to the formation of the “Surge / Rotating Stall” signal on the logic element 11. This signaling device does not have delays in its structure, therefore the system response is determined by the rate of decline pressure in case of unstable operation of the compressor.

Following the decrease in pressure, pulsating pressure oscillations occur in the compressor path of characteristic high frequency (see Fig. 2). HPF 3 selects these oscillations, then rectifier 4 and LPF 5 form a signal equivalent to the average level of high-frequency oscillations. Divider 7 forms the relative level of high-frequency oscillations. When this level is exceeded, the threshold of operation of the comparator 9, the comparator is triggered.

As the average pressure level (filter discharging) generated by the LPF 2 approaches its Instantaneous value, the relative deviation signal generated by the divider 8 drops, and the comparator 10 generates a zero signal. As long as there are pulsating oscillations in the air path of the compressor, a single signal is stored at the output of the comparator 9. As a consequence, the output of the element "OR" 11 is supported by a single signal.

Compressor surge and rotational stall elimination means perform the necessary actions to restore stable operation of the compressor and can be implemented in various ways, in particular in the form of a compressor instability elimination system.

The task of the system to eliminate the unstable operation of the compressor is to increase the stability margins of the compressor, which is achieved by reducing the operating mode of the compressor and the air flow through it. Depending on the design features of the compressor, the system can issue commands to cover the compressor inlet guide vanes, open anti-surge valves and air bypass valves. When using a compressor as part of gas turbine engines, the system also sends a command to reduce fuel consumption in the combustion chamber of the gas turbine engine.

When the stable operation of the compressor is restored, the level of pulsation oscillations drops, the comparator 9 reverses and the “Surge/Rotary Stall” signal is removed at the “OR” element 11 (see Fig. 2).

Noise immunity and, as a result, the reliability of the system operation is determined by the frequency characteristics of the high and low frequency filters, which should ensure the isolation of the pressure dip and the pulsation component in transient operating modes.

The average value and the variable component of the characteristic parameter of the compressor operation can be distinguished using a Butterworth filter, for example, implemented using integrators covered by feedback (see Fig. 3). The output of the last integrator is the average value of the pressure after the compressor, the signal coming to the input of the first integrator is the variable pressure component. The order of the filter is determined by the requirements for attenuation in the transition region, which is necessary for frequency selection of the transition modes of the control system and pressure fluctuations in the event of loss of gas-dynamic stability.

The proposed method provides reliable formation of a signal of unstable operation of the compressor, signals the end of unstable operation and provides an almost instantaneous response of the surge elimination system. The application of the method increases the reliability of the compressor and reduces the time of loss of thrust by the engine.

Claims (15)

1. A method for detecting compressor surge and rotational stall, characterized in that: measure the characteristic parameter PC of the compressor operation, form the average value of PK _SR parameter PK by a low-pass filter, form a signal Pk _of the high-frequency component of the parameter Pk by a high-frequency filter, form the middle level

the absolute value of the signal PC _RF high-frequency component of the parameter, calculate the ratio (

) values

to the average value of PC _SR parameter, and when exceeding the ratio

the first predetermined threshold form a signal on the first signaling device, form the deviation ΔPk of the parameter from its average value Pk _SR , calculate the ratio (ΔPk/Pk _SR ) of the deviation ΔPk to the average value of the parameter, and when the ratio ΔPk/Pk _SR decreases below the second predetermined threshold, a signal is generated on the second signaling device, and in the presence of any of the signaling devices, a compressor surge/rotating stall signal is generated, in accordance with which the compressor surge and rotating stall elimination means are turned on. 2. The method according to p. 1, characterized in that the air pressure signal downstream of the last stage of the compressor is used as a characteristic parameter of the compressor operation. 3. The method according to claim 1, characterized in that the pressure drop signal at the local resistance in the inlet or outlet pipe of the compressor is used as a characteristic parameter of the compressor operation. 4. The method according to claim 1, characterized in that as a low-frequency filter, a Butterworth filter of at least the second order is used as a low-frequency filter, and the input signal of the first integrator is used as a signal of the high-frequency component of the parameter. 5. The method according to claim 1, characterized in that a non-recursive filter with a predetermined time window is used to form the average level of the absolute value of the parameter.

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