EP0288356B1 - Method for real-time adjustment of the radial clearance between rotor and stator of a turbo machine - Google Patents

Description

The invention relates to a method of real-time adjustment of the radial clearance between a rotor and a turbomachine stator, during operation of the turbomachine.

The search for improving the performance of turbomachinery has led engine manufacturers to seek optimization of the radial clearances between the rotor and stator of a turbomachine. Maintaining, in all operating conditions, a minimum but sufficient clearance between rotor and stator has direct repercussions on the performance of the turbomachine and for obtaining maximum thrust as well as on the conditions of appearance of pumping phenomena.

To obtain the adjustment of the game, various solutions have been tried. Among others, several of them have in common the installation and use of ventilation systems which, depending on the operating phases of the turbomachine, send air currents, either cooling or heating over various fixed or rotating parts constituting the associated stator and rotor, such as, the blades, the discs, the casings, the turbine stator rings for example. Depending on the desired result, air samples are taken at various stages of the compressor or in the combustion chamber enclosure, for example. The air supply circuits are generally equipped with control valves whose control makes it possible to obtain a modulation of the flow rates and possibly temperature settings by means of mixtures produced from different sources, for example.

Numerous examples bear witness to this research. We can thus cite FR-A-2 496 753, FR-A-2 464 371, FR-A-2 431 609, FR-A-2 360 750, FR-A-2 360 749 in which the control of organs for adjusting the air flow rate such as distributors or valves is controlled by an operating parameter of the turbomachine from the measurement by sensor of a quantity such as a temperature, a speed of rotation or directly a measurement of the clearance at a given moment. In some cases, hydromechanical regulation controls the opening of the air flow control valves based on opening laws preset and programmed in advance.

GB-A-2 078 859 describes means for adjusting the radial clearance between the stator and the compressor rotor by controlling a valve regulating a ventilation air flow. Said control signal is produced from the comparison between an actual temperature of the compressor housing at the given time and a calculated reference temperature of said housing, from a signal representing the temperature of entry of the gases into the compressor and a signal representing the speed of rotation of the compressor, at this instant.

These prior solutions, however, in certain particular applications on the turbomachines covered by the invention which require finer adaptation in real time, are not generally, nor completely satisfactory. Indeed, the air samples can have a detrimental influence on the overall efficiency of the turbomachine and thus the invention aims to obtain an optimization of the radial clearances under stabilized operating conditions which takes account of this influence of the air flow. taken from performance. Likewise, under certain transient operating conditions of the turbomachine, a regulation controlled only by one or more operating parameters of the turbomachine is not sufficient to avoid either the appearance of excessively high radial clearances liable for example to cause phenomena thrust holes in acceleration phases, or accidental contacts between the fixed part of the stator and the rotating part of the rotor causing friction and damage, for example, at the level of abradable elements. The invention avoids these drawbacks by taking take into account the inertias of thermal or mechanical expansions or contractions which are different for the mechanical elements present and by involving in said control regulation of the radial clearances a real-time calculation of these inertias, in particular thermal and, in particular , the invention provides for operating the commands for opening or closing the air flow control valves by triggering them in advance, according to these calculations. In addition, the invention also provides for advance reservations corresponding to specific conditions resulting from certain operating phases of the turbomachine. This is the case in particular in a deceleration phase where, for example, various interventions by the pilot are possible, acting on the controls in particular to obtain a sudden re-acceleration.

• d'une part, un jeu j1 de consigne, correspondant à un instant T aux conditions d'utilisation et de fonctionnement de la turbomachine audit instant T et dont la valeur a été introduite en mémoire dudit calculateur à partir d'un modèle quantifié de la turbomachine comportant, en fonction des paramètres thermodynamiques de la turbomachine et des caractéristiques géométriques des pièces, les caractéristiques aérothermiques et mécaniques des éléments de stator et de rotor entre lesquels l'ajustement du jeu est recherché,
• et, d'autre part, un jeu j2 calculé en fonctionnement audit instant T par ledit calculateur à partir des données fournies et après calcul des températures et des dilatations cumulées d'origine thermique et mécanique desdits éléments de stator et de rotor considérés.

The method of real-time adjustment of the radial clearance between rotor and stator is characterized in that a flow control valve inserted in the ventilation circuit is controlled by a device actuated by the output signal of an electronic computer which is the result of a comparison between:

• on the one hand, a set j1 setpoint, corresponding to an instant T to the conditions of use and operation of the turbomachine at said instant T and the value of which has been entered into the memory of said computer from a quantified model of the turbomachine comprising, as a function of the thermodynamic parameters of the turbomachine and of the geometrical characteristics of the parts, the aerothermal and mechanical characteristics of the stator and rotor elements between which the adjustment of the clearance is sought,
• and, on the other hand, a clearance j2 calculated in operation at said instant T by said computer from the data provided and after calculation of the temperatures and cumulative expansions of thermal and mechanical origin of said stator and rotor elements considered.

Advantageously, before the output signal actuating the valve is sent, usage limits are imposed, in particular the maximum temperatures acceptable for the stator and the maximum temperatures as well as the maximum gradient of temperatures acceptable for the rotor.

Advantageously, said output signal can also be modified on the basis of a determination of the effect on the specific consumption of the turbomachine of the induced variations in the play between rotor and stator, air flow rates taken, vein misalignments between element rotor and stator element, aerodynamic losses caused by the samples.

• la figure 1 représente une vue schématique en demi-coupe axiale d'une turbomachine munie d'un dispositif d'ajustement en temps réel du jeu radial en rotor et stator qui est mis en oeuvre par le procédé conforme à l'invention ;
• la figure 2 représente un détail agrandi de la figure 1 montrant le réglage d'un débit d'air de refroidissement du carter de turbine ;
• la figure 3 représente dans une vue analogue aux figures 1 et 2 un circuit de ventilation du rotor de turbine associé au dispositif conforme à l'invention ;
• la figure 4 indique les étapes d'élaboration d'un signal de commande de vanne par un calculateur électronique en vue de l'ajustement du jeu.

Other characteristics and advantages of the invention will be better understood on reading the following of an embodiment of the invention with reference to the accompanying drawings or tables in which:

• FIG. 1 represents a schematic view in axial half-section of a turbomachine provided with a device for real-time adjustment of the radial clearance in rotor and stator which is implemented by the method according to the invention;
• FIG. 2 represents an enlarged detail of FIG. 1 showing the adjustment of a flow rate of cooling air of the turbine casing;
• 3 shows in a view similar to Figures 1 and 2 a ventilation circuit of the turbine rotor associated with the device according to the invention;
• FIG. 4 shows the steps for producing a valve control signal by an electronic computer with a view to adjusting the clearance.

There is shown in Figure 1 to illustrate an embodiment of the invention a turbofan engine of which only the central part has been shown and comprises a set 1 of high pressure compression, a combustion section 2 and a set 3 turbine comprising a high pressure turbine 4 and a low pressure turbine 5. These elements enter a primary propulsion assembly which is surrounded by a secondary assembly associated with a blower located upstream and not shown in the drawing and comprising a channel 6 for circulation of a secondary flow limited by an external envelope 7 and by an envelope interior 8 which also constitutes the external envelope of the primary assembly. The compression assembly 1 is surrounded on the downstream side, defined with respect to the normal direction of gas flow in the turbofan, that is to say on the high pressure side by an external casing 9, thus providing between said casing 9 and the compressor housing 10 an enclosure 11. Passages such as 12 are provided in the compressor housing 10, downstream of a determined compression stage, for example approximately two-thirds of the axial length from the compression assembly 1 from from the entrance. From the enclosure 11 and also associated with passages 13 formed in the envelope 9, are placed pipes such as 14, inside the external envelope 8 of the assembly propulsion primary. Line 14 is connected to a second line 15 provided with a flow control valve 16. The pipe 14 conveys air taken through the enclosure 11 in the compression assembly 1 and the pipe 15 routes air taken by means of an air intake mouth 17 into the circulation channel 6 of the secondary flow, through its inner envelope 8.

As shown, in more detail in FIG. 2, the air conveyed by the pipes 14 and 15 through the valve 16 enters an air manifold 18 which supplies, for example, air distribution ramps 19 placed around the casing. turbine 20 and which send on the surface of said casing 20 belonging to the turbine stator air jets through holes or multi-perforations for impact cooling of said turbine stator. The elements which have just been described thus constitute a ventilation circuit of the turbine stator and in the example shown in FIGS. 1 and 2, it is the low pressure turbine 5 of the turbofan.

Similarly, as shown in FIG. 3, a second air sampling is carried out at the level of the compression assembly 1 partially represented in FIG. 3. A pipe 21 in which is inserted a valve 22 for adjusting the flow rate conveys thus the air sampled through a passage 23 formed in the compressor casing 10 towards an enclosure 24 formed inside the turbine casing. Likewise, from the enclosure 25 of the combustion assembly 2 partially shown in FIG. 3, located between the combustion chamber 26 and its outer casing 27, a pipe 28 conveys the air inside said enclosure 24 of housing turbine. From said enclosure 24, the air is distributed to the rotor of the low pressure turbine 5. In the embodiment partially shown in FIG. 3, from the enclosure 24, the air passes through passages 29 of the stator of the low pressure turbine 5 and from there circulates from one stage to the other of the rotor, ensuring its ventilation.

The various flow control valves, such as 16 and 22, inserted in the pipes which convey the air from the ventilation circuit both to the stator and to the rotor of the low pressure turbine 5 can be of any known type, such as the valves already used in similar applications in particular for turbomachine ventilation circuits and each valve is associated with a control device, also of a known type, regulating a passage opening by means of a displacement. According to the invention and remarkably, each device for controlling a flow control valve in the ventilation circuit is connected to an electronic computer symbolized at 30. More particularly, said valve control device is actuated by a signal output respectively S₁ for valve 16, S₂ for valve 22 which are emitted by said computer 30. The remarkable results of the invention consist in obtaining, in all operating conditions of the turbomachine, both stabilized and transient, an optimized setting of the air flow through the valves, such as 16, 22 of the ventilation circuit. This adjustment makes it possible in particular to adjust in real time, at all times and under all these operating conditions, the radial clearance between the rotor and the stator of the low pressure turbine 5, in the embodiment which has just been described, at a value optimized. To obtain this result, the output signal, S₁ or S₂, of the electronic computer 30 actuating the control device of the air flow control valves 16 or 22 is produced in the manner described below.

• les paramètres thermodynamiques et en particulier, les régimes de rotation, les températures des gaz, les formules analytiques des températures des prélèvements d'air ;
• les caractéristiques géométriques des éléments mécaniques telles que les rayons des pièces, les jeux obtenus à froid par construction, les caractéristiques des matières utilisées telles que les coefficients de dilatation thermique d'une part et mécanique, d'autre part ainsi que les temps de réponse correspondants.

Quantified data constituting a model of the turbomachine are introduced into the computer 30. These data correspond to the thermal and dynamic characteristics of the machine and include:

• thermodynamic parameters and in particular, rotation regimes, gas temperatures, analytical formulas for the temperatures of air samples;
• the geometrical characteristics of the mechanical elements such as the radii of the parts, the clearances obtained cold by construction, the characteristics of the materials used such as the coefficients of thermal expansion on the one hand and mechanical, on the other hand as well as the response times correspondents.

• les températures maximales admissibles au niveau du stator,
• les températures maximales ainsi que le gradient thermique maximal admissibles au niveau du rotor.

The data also include the imposed usage limits such as:

• the maximum admissible temperatures at the stator level,
• the maximum temperatures as well as the maximum admissible thermal gradient at the level of the rotor.

Different optimizations are also introduced, taking particular account of the effect on specific consumption of various factors and their

• jeux radiaux entre rotor et stator,
• consommations d'air prélevés par les circuits de ventilation,
• pertes aérodynamiques occasionnées par les prélèvements,
• facteurs de désalignements de veine.

correlations:

• radial clearances between rotor and stator,
• air consumption taken from the ventilation circuits,
• aerodynamic losses caused by the samples,
• vein misalignment factors.

At an instant T of the operation of the turbomachine, the computer 30 thus obtains a value j1 of the radial clearance, of the setpoint to be obtained between the rotor and the stator at a determined point, from the data entered representing the model of the turbomachine. Note that this point can be located at the end of the movable rotor blade, the clearance being taken between the end of the blade and the cooperating surface of an abradable lining placed inside the corresponding stator ring. . This point can also be located at the level of the interval of a labyrinth seal, between ends of wipers and abradable surface or else at the lower end of fixed stator vanes. An embodiment has been described for the application to a low pressure turbine but, of course, the invention applies in the same way to the adjustment of any radial clearance between the rotor and the stator of a turbomachine, at the level of a compressor or a turbine.

At time T, the computer 30 also calculates, from the measured values of the thermodynamic parameters of the turbomachine (temperatures and rotation speeds), the temperatures of the elements of rotor and stator as well as the state of expansion of these elements, including both thermal and mechanical expansion. These calculations also take into account the thermal state of the turbomachine and the evolution of the parameters corresponding to particular operating conditions such as stabilized or transient phases, accelerations or decelerations, cold or hot starts. From these calculations, the computer 30 finally determines the radial clearance j2 obtained in operation.

The computer 30 then establishes the comparison between the clearance j2 in operation at time T and the reference clearance j1.

Depending on the difference between j2 and j1 obtained, the output signal produced is emitted, actuating the control device for the flow control valves so as to cancel this difference and a new operation in real time is triggered at time T + ΔT .

After the comparison between the calculated clearance j2 and the reference clearance j1, a correction element can also intervene in the preparation of the output signal. In particular, a simulation check is made by the computer 30 that the radial clearances to be imposed allow the rapid succession of a re-acceleration phase, in particular when the turbomachine is in a progressive deceleration phase and which can be triggered, by example, by the intervention of the pilot. This simulation allows anticipation taking response times of the different mechanical elements of stator and rotor in presence.

• en 100a, les données fournies au calculateur 30,
• en 100b, la détermination de l'état thermique de la turbomachine,
• en 101, le calcul des températures du rotor et du stator,
• en 102, le calcul des dilatations thermiques et mécaniques,
• en 103, le calcul du jeu radial en fonctionnement,
• en 104, la comparaison entre le jeu radial calculé en 103 et le jeu objectif correspondant disponible en mémoire du calculateur 30,
• en 105 un résultat d'égalité obtenu,
• en 106, un résultat d'inégalité obtenu,
• en 106a, une optimisation en termes de rendement, performances, consommation spécifique,
• en 106b, l'action sur les vannes de réglage de débit,
• en 107, une vérification par anticipation d'évolution comportant en particulier une hypothèse de réaccélération rapide,
• en 107a, une action éventuelle sur les vannes de réglage de débit selon le résultat obtenu en 107,
• en 108, le bouclage des opérations pour un nouvel ajustement en temps réel du jeu radial entre rotor et stator à l'instant T + ΔT,
• en 109, une action éventuelle sur l'ensemble de régulation 31 de la turbomachine.

In addition, a connection can also be provided between the computer 30 and the actual regulation assembly of the turbomachine, symbolized at 31 in the figures. Indeed, in certain operating phases of the turbomachine, in particular in transient conditions, for example under acceleration, in order to respect the objective clearance and particularly the optimization with respect to different limitations, a signal also imposing a limitation, a time acceleration for example, can be sent by the computer 30 to the regulation assembly 31. The diagram in FIG. 4 summarizes the intervention of the computer 30 for the adjustment of the radial clearance between rotor and stator and symbolizes the instant T;

• in 100a, the data supplied to the computer 30,
• in 100b, the determination of the thermal state of the turbomachine,
• in 101, the calculation of the temperatures of the rotor and the stator,
• in 102, the calculation of thermal and mechanical expansions,
• in 103, the calculation of the radial clearance in operation,
• in 104, the comparison between the radial clearance calculated in 103 and the corresponding objective clearance available in the memory of the computer 30,
• in 105 a result of equality obtained,
• in 106, an inequality result obtained,
• in 106a, an optimization in terms of yield, performance, specific consumption,
• in 106b, the action on the flow control valves,
• in 107, a verification by anticipation of evolution comprising in particular a hypothesis of rapid re-acceleration,
• in 107a, a possible action on the flow control valves according to the result obtained in 107,
• in 108, the completion of operations for a new real-time adjustment of the radial clearance between rotor and stator at time T + ΔT,
• in 109, a possible action on the regulating assembly 31 of the turbomachine.

Claims (4)

1. Process for the adjustment in real time of the radial clearance between a rotor and a stator of a gas turbine by means of a device which includes a cooling circuit comprising at least one air take-off, at least one airflow regulating valve placed in the said circuit and at least one distribution device to ensure the cooling and/or heating of at least one defined zone of the rotor and/or the stator characterised in that the said valve(s) (16, 22) is (are) controlled by a device activated by the output signal (S₁, S₂) of an electronic computer (30) which is the result of a comparison between:

- on the one hand, a design clearance j1 corresponding to an instant T under conditions of use and operation of the gas turbine at the instant T and whose value has been entered in the memory of the said computer from a quantified model of the gas turbine comprising, as a function of the thermodynamic parameters of the gas turbine and the geometric characteristics of the components of the stator and rotor in relation to which an adjustment of the clearance is desired,

- and, on the other hand, a clearance j2 calculated during running at the said instant T by the said computer on the basis of the data supplied and after calculation of the temperatures and the cumulative expansions of thermal and mechanical origin in the said stator and rotor components under consideration

2. Process for the adjustment in real time of the radial clearance between a rotor and a stator of a gas turbine in accordance with Claim 1 in which the electronic computer (30), connected to the main engine control system (31), emits a signal imposing limitations on use during certain phases of the operation of the gas turbine.

3. Process for the adjustment in real time of the radial clearance between a rotor and a stator of a gas turbine in accordance with either of Claims 1 or 2, in which the production of the output signal ( S₁, S₂) by the computer (30) takes account of the maximum temperatures permissible for the stator and the maximum temperatures and thermal gradient permissible for the rotor.

4. Process for the adjustment in real time of the radial clearance between a rotor and a stator of a gas turbine in accordance with any of Claims 1 to 3 in which the computer (30) introduces a correction to the clearance on the basis of an optimisation prepared as a function of the effect on the specific fuel consumption of the gas turbine of predetermined factors comprising mainly the radial clearances between the rotor and stator, the consumption of air drawn off by the cooling circuits and the factor of the misalignment of the airflow.

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