EP2534341B1 - Method for the automated detection of the ingestion of at least one foreign body by a gas turbine engine - Google Patents

Description

The present invention relates to a device and method for detecting an impact on a blade of a gas turbine engine, in particular on a fan blade.

A gas turbine engine when mounted on an aircraft is susceptible to damage by objects being sucked up by the engine during use. These objects can come in various forms, for example, birds, stones or ice.

After aspiration of the objects, the latter circulate from upstream to downstream in the engine by striking different elements of the engine. This phenomenon is known to those skilled in the art under the designation "ingestion of foreign bodies".

Depending on the nature, density and relative speed of the bodies ingested by the engine, some parts of the engine can be more or less damaged.

In order to maintain a high degree of safety and reliability of the engine during its use, it is necessary to detect the damage generated by these ingestions in order to repair or replace the damaged engine components.

For commercial flights carrying passengers, gas turbine engines are inspected visually before each flight. This inspection, however, has several disadvantages. First, this visual inspection does not allow a completely reliable detection, the operators can not note small damages, the latter being, moreover, difficult to locate. Secondly, when damage is detected, it is necessary to proceed immediately to maintenance operations which requires immobilizing the aircraft and, consequently, delays his departure. This late detection of the effects of ingestion of a foreign body thus causes inconvenience for the passengers to embark in said aircraft.

It is known from the patent application FR2840358 A1 SNECMA a system for detecting rotor damage of an aircraft engine comprising means for measuring vibration and rotor speed during a given flight. However, such a system does not have the precision required to detect the ingestion of a foreign body.

It is known from the patent application EP 1312766 A2 of ROLLS-ROYCE a method of impact detection on a rotor blade in which the speed drop of the rotor is measured to emit an alarm. Such detection has the disadvantage of being poorly discriminating. Indeed, in case of pumping the motor, the rotor speed drops and an alarm is issued when no body has been ingested. To eliminate this drawback, the patent application EP 1312766 A2 teaches to add sensors to measure the torsion angle of the motor and thus improve the accuracy of the method. Such a method, with many sensors, is not satisfactory and does not allow to accurately and reliably detect ingestion of a foreign body.

• on mesure le régime instantané du rotor;
• on filtre le signal de régime du rotor de manière à dissocier sa composante statique de sa composante dynamique ;
• on compare la composante dynamique filtrée à une onde de résonance étalon du rotor afin d'obtenir un indicateur d'ingestion, l'onde de résonance étalon correspondant à la réponse impulsionelle vibratoire d'un rotor;

• on compare l'indicateur d'ingestion obtenu à un seuil de détection ;
• on émet un signal de détection d'une ingestion d'un corps étranger lorsque l'indicateur d'ingestion est supérieur au seuil de détection.

In order to overcome these drawbacks, the invention relates to a method for automatically detecting the ingestion of at least one foreign body by a gas turbine engine comprising a rotor, a method according to which:

• the instantaneous speed of the rotor is measured;
• the rotor speed signal is filtered so as to separate its static component from its dynamic component;
• the filtered dynamic component is compared with a standard resonant wave of the rotor to obtain an ingestion indicator, the standard resonance corresponding to the vibratory impulse response of a rotor;

• the ingestion indicator obtained is compared with a detection threshold;
• a detection signal of ingestion of a foreign body is emitted when the ingestion indicator is greater than the detection threshold.

The vibratory response of a rotor is its signature following an impact, that is to say, following an impulse. By standard resonant wave is meant the vibratory impulse response measured on a rotor following the ingestion of a body by said rotor.

Thanks to the invention, the transient dynamic component of the rotor speed is compared to its signature to detect ingestion. The method according to the invention is more discriminating than the method according to the prior art based solely on an amplitude thresholding of the dynamic component of the rotor speed R (t), a dynamic component of high amplitude can have several causes.

Thanks to the invention, it is possible to ignore vibrations of large amplitude (eg pumping) when the shape of the dynamic component of the rotor speed R (t) does not correspond to that of a standard resonant wave. In addition, it is possible to detect so-called "low energy" body ingestions (low mass, low speed), resulting in low amplitude vibrations, such detection being not possible with a method according to the prior art.

Advantageously, this method is implemented without the addition of a sensor and without any structural modification.

Preferably, the standard resonant wave of the rotor corresponds to the impulse response of the first mode of torsion of the rotor.

Advantageously, the search in the filtered dynamic component of the impulse response of the first mode of torsion of the rotor, whose characteristics are known elsewhere, makes it possible to obtain an ingestion rate which makes it possible to qualify a vibration.

Indeed, the impulse response of the first mode of torsion is present only after a transient excitation in torsion of the rotor, which is typical of an ingestion of foreign body. In this way, ingestion is detected reliably and accurately.

More preferably, a convolution product is made between the filtered dynamic component and the standard resonant wave to obtain the ingestion indicator.

According to a first variant, the standard resonant wave is measured directly on the rotor of the engine on which the detection method is implemented.

Thus, the characteristics of the impulse response of the first mode of torsion of the rotor (frequency, damping) are determined experimentally.

According to a second variant, the standard resonance wave is theoretically defined as a function of the characteristics of the impulse response of the first mode of torsion of the rotor (frequency, damping, etc.).

Preferably, the rotor is a low pressure rotor of a gas turbine engine, the filtered dynamic component is compared to a standard resonant wave of the low pressure rotor to obtain an ingestion indicator, the resonance wave standard corresponding to the vibratory impulse response of a low pressure rotor.

• la figure 1 représente une mesure du régime du rotor basse pression au cours du temps ;
• la figure 2 représente la composante dynamique du régime du rotor basse pression de la figure 1 ;
• la figure 3 représente une onde de résonance étalon du rotor basse pression et
• la figure 4 représente l'indicateur d'ingestion correspondant à une mesure de ressemblance entre la composante dynamique du régime du rotor et une onde de résonance étalon dudit rotor.

The invention will be better understood with the aid of the appended drawing in which:

• the figure 1 represents a measurement of the low pressure rotor speed over time;
• the figure 2 represents the dynamic component of the low-pressure rotor regime of the figure 1 ;
• the figure 3 represents a standard resonant wave of the low-pressure rotor and
• the figure 4 represents the ingestion indicator corresponding to a measurement of resemblance between the dynamic component of the rotor speed and a standard resonant wave of said rotor.

The invention relates to a method for accurately detecting ingestion of a foreign body by a dual-body gas turbine engine comprising a low-pressure rotor shaft and a high-pressure rotor shaft, a fan being secured to the low rotor. pressure.

With reference to the figure 1 the rotational speed R (t) of the low pressure rotor is measured over time by means of a voice wheel, known as such to those skilled in the art, arranged to measure the angular velocity of the rotor shaft. low pressure rotor. It goes without saying that the low-pressure rotor speed could also be measured by other means, in particular by accelerometers arranged in the engine.

Following this measurement, a substantially constant curve 1 is obtained over time around the static speed of the low-pressure rotor Rs. figure 1 the rotational speed R (t) is normalized with respect to the maximum value of the low pressure rotor speed. On the figure 1 , the static Rs of the low-pressure rotor is of the order of 85% of the maximum speed.

During the measurement period, a body of low mass (about 50g) is ingested by the engine. Curve 1, representing the speed of the fan R (t), has an oscillation 2 at the time of ingestion of the body by the engine, this oscillation being very small, of the order of 0.5% of the value of the static regime Rs. This oscillation can not be detected directly following the measurement of the low-pressure rotor R (t). Indeed, such oscillations may be related to measurement noise or to phenomena other than ingestion, in particular, the pumping phenomena of the engine.

In known manner, the low-pressure rotor R (t) regime measured by the phonic wheel has a static component Rs and a dynamic component Rd (t) and decomposes in the following form: $$\mathrm{R}\left(\mathrm{t}\right)=\mathrm{Rs}+\mathrm{Rd}\left(\mathrm{t}\right)$$

To highlight the oscillation 2, the low pressure rotor R (t) regime is filtered to retain only the dynamic component Rd (t) of the signal, for example, by means of bandpass filtering centered on the frequency of the standard resonance wave.

The Applicant has noticed that when a body strikes the blower after ingestion, the low pressure rotor, connected to the blower, responds by vibrating in its first mode of torsion, in the manner of a bell, by emitting a resonance wave whose frequency and shape is specific to the rotor. This vibratory response following a brief shock is the impulse response of the first mode of torsion of the low pressure rotor. Thanks to this characteristic response, it is possible to discriminate the vibratory disturbances resulting from the body ingestions of disturbances resulting from noise or external phenomena, and this, well, that their influences on the low pressure rotor R (t) regime are almost identical from a total point of view.

Indeed, ingestion or pumping lead to the appearance of oscillations whose overall appearance is similar when analyzing the engine speed. Nevertheless, only the oscillations whose shape and amplitude are similar to those of the impulse response of the low-pressure rotor correspond to ingestion of a foreign body.

Following ingestion of a foreign body, the dynamic component Rd (t) of the low pressure rotor speed signal R (t) is thus generally in the following form: $$\mathrm{Rd}\left(\mathrm{t}\right)=\mathrm{VS}\left(\mathrm{t}\right)\mathrm{.}\cos \left({\mathrm{w}}_{\mathrm{T}}\left(\mathrm{t}\right)*\mathrm{t}+\mathrm{\Phi }\right)$$

In this formula, C (t) .cos (w _T (t) * t + Φ) is the perturbation due to the vibratory response of the low-pressure rotor following ingestion. This perturbation depends on an amplitude parameter C (t), a phase parameter Φ and a pulse parameter w _T corresponding to the first torsion mode of the low pressure rotor.

The low pressure rotor has several low frequency twist modes. When ingesting foreign bodies, only the first mode of torsion will respond significantly. The impulse response of the latter will therefore be a signature characteristic of ingestion. Following ingestion, C (t) will vary strongly in one form: $$\mathrm{VS}\left(\mathrm{t}\right)=\mathrm{VS}\mathrm{.}\exp \left(-\mathrm{t}/{\mathrm{\tau }}_{\mathrm{T}}\right)$$

This is the amplitude of the disturbance and is a function of the "severity" of the ingestion, the amplitude of the disturbance being very small compared to the value of the static regime Rs. The damping parameter τ _T is a function of the damping of the first mode of torsion of the low pressure rotor and the natural frequency of this mode.

Thus, during an ingestion of a foreign body by the engine, the dynamic component Rd (t) of the low-pressure rotor strongly resembles the impulse response of the first torsion mode e (t) of the low-pressure rotor, shown in FIG. figure 3 . The impulse response of the first rotor twist mode e (t) is compared with the dynamic response Rd (t) of the low pressure rotor R (t) to determine if a body has been ingested by the engine. In other words, the filtered dynamic component is compared with a standard resonance wave e (t) of the low-pressure rotor in order to obtain an ingestion indicator T _ING corresponding to a measurement of resemblance between the standard resonant wave e (t) and the dynamic component Rd (t) of the measured speed signal.

In order to make the comparison, it is necessary to previously determine the standard resonance wave e (t).

According to a first implementation of the invention, this wave corresponds to the impulse response of the first mode of torsion of the rotor.

According to a first variant, the first mode of torsion of the rotor is a "specific" mode, the characteristics (frequency, damping) of the first mode of torsion being measured directly on the low pressure rotor on which will be implemented the detection of ingestion, the detection being then carried out "Custom-made" with the standard resonance wave the vibratory impulse response first mode of torsion of the rotor. The setting of the detection method with a specific mode makes it possible to implement an accurate detection adapted to said low pressure rotor. Indeed, each rotor has an impulse response of its first mode of torsion of its own. In other words, different rotor models have different impulse responses.

According to a second variant, the impulse response of the first mode of torsion of the rotor is determined analytically by calculation.

According to a second variant, the standard resonance wave e (t) corresponds to the sum of a plurality of torsion modes of the same low-pressure rotor, preferably the first 2 or 3 modes of torsion of a low rotor. pressure. A standard resonant wave e (t) comprising several torsion modes makes it possible to increase the reliability of the detection and its accuracy.

By way of example, to implement the comparison, a convolution product is produced between the dynamic response of the low pressure rotor Rd (t) and the standard wave e (t) to obtain a ingestion indicator T _ING . $$T_{\mathit{ING}}\left(t\right)=\int e\left(u\right)\cdot R\left(t-u\right)\cdot du$$

It goes without saying that other comparison algorithms could also be suitable. Preferably, the comparison algorithms are set to take into account distortions of the standard resonance wave (delay, noise, etc.).

The ingestion indicator T _ING , represented on the figure 4 , allows to qualify the suspicious oscillation 2 detected in the measurement of the low pressure rotor R (t). The more the dynamic response of the low pressure rotor Rd (t) resembles the theoretical impulse response characteristic of a shock response (here, ingestion of a foreign body), plus the value of the ingestion indicator T _ING will be high.

After calculating the ingestion indicator T _{ING, it} is compared with a detection threshold S of determined value, an ingestion alarm being emitted when the ingestion indicator T _ING exceeds said detection threshold S.

The value of the detection S is determined so as not to generate an alarm for T _ING indicator values corresponding to the normal operation of the engine and which can be described as noise. This detection threshold is thus obtained by applying a margin to the average level of the "noise" Sb. This margin is a function of the characteristics of the signal "noise" as well as the desired level of detection reliability. With reference to the figure 4 a margin of 70% separates the detection threshold from the average noise level.

This method is very selective because the ingestion indicator T _ING for a noise signal (excluding ingestion) is low since, in the absence of ingestion, the impulse response of the first mode of torsion is not present. in the signal. The noise signal does not resemble the impulse response of the first mode of torsion.

When ingestion is detected, the alarm generated can be directed directly to the pilot of the aircraft, on which the engine is mounted, to be consulted in real time, or stored in a memory to be consulted. subsequently, for example, for an inspection of the engine, be transmitted in real time to the maintenance services of the airline to allow it to anticipate and organize, at the next stopover, a detailed inspection impacted engine and all necessary maintenance actions.

It goes without saying that different alarm thresholds can be defined so as to distinguish different kinds of ingestion (more or less energetic ingestions, more or less severe ingestions).

The invention has been described here for a double-shaft turbine engine but it goes without saying that the invention applies similarly to an engine with a single or more than two rotors.

Claims (6)

1. A method for the automated detection of the ingestion of at least one foreign body by a gas turbine engine comprising a rotor, a method wherein:

   - the instantaneous speed (R(t)) of the rotor is measured;

   - the speed signal (R(t)) of the rotor is filtered in order to separate the static component (Rs(t)) from the dynamic component (Rd(t)) thereof;

   - the filtered dynamic component (Rd(t)) is compared to a standard resonance wave (e(t)) of the rotor so as to obtain an ingestion indicator (T_ING), the standard resonance wave (e(t)) corresponding to the vibrational impulse response of a rotor;

   - the ingestion indicator (T_ING) being obtained is compared to a detection threshold (S); and

   - a foreign body ingestion detection signal is emitted when the ingestion indicator (T_ING) is higher than the detection threshold (S).
2. The method according to claim 1, wherein the standard resonance wave (e(t)) of the rotor corresponds to the impulsion response of the first torsion mode of the rotor.
3. The method according to claim 2, wherein the standard resonance wave (e(t)) is theoretically defined as a function of the characteristics of the impulsion response of the first torsion mode of the rotor.
4. The method according to claim 2, wherein the standard resonance wave (e(t)) is directly measured on the rotor of the engine on which the detection method is implemented.
5. The method according to any of claims 1 to 4, wherein a convolution product between the filtered dynamic component (Rd(t)) and the standard resonance wave (e(t)) is implemented.
6. The method according to any of claims 1 to 5, wherein the rotor is a low pressure rotor of a gas turbine engine, the filtered dynamic component (Rd(t)) is compared to a standard resonance wave (e(t)) of the low pressure rotor so as to obtain an ingestion indicator (T_ING), the standard resonance wave (e(t)) corresponding to the vibrational impulsion response of a low pressure rotor.

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