EP3130762B1 - System for active adjustment of a radial gap size and corresponding aircraft engine - Google Patents

Description

The invention relates to a system for the active adjustment of a radial gap size with the features of claim 1 and an aircraft engine having the features of claim 10.

For the efficient operation of an aircraft engine, it makes sense to keep the gap between the tips of the rotating turbine or compressor blades and the surrounding housing as small as possible. So is for example from the GB 2417762 A a method for active clearance control (Tip Clearance Control, TCC) known. In this case, the housing is cooled by means of cooling air so that a defined gap is established between the rotating blade tips and the housing (or the shrouds or liners arranged thereon).

The setting, ie the regulation or control of the cooling is thereby taken over by the engine computer (EEC), which controls a corresponding valve. The aim is to set the smallest possible gap, but a squint, ie a tarnishing of the blade tip must be avoided in the housing or the shroud.

Fully modular modulated systems employ a method in which the actual gap is either measured or calculated by the engine computer. The thus determined actual gap is then compared with a desired gap and the housing cooling is adjusted accordingly by the control system.

Typically, the desired gap is set to zero when the aircraft engine provides the maximum thrust. The value for the desired gap may be greater than zero when the aircraft engine is operating in the partial load range. In this case, a sudden thrust increase leads to a gap closure, which can not be compensated quickly enough by a reduced housing cooling - and thus keeping the gap constant. Too small a target gap would lead in this case to a start.

It is therefore an object to provide efficient systems for adjusting the radial gap for the operation of aircraft engines and corresponding aircraft engines.

The object is achieved by the control system with the features of claim 1.

For this purpose, the system has a model-based adjusting device, wherein the time-dependent gap size is approximated by the model-based actuator and are taken into account only influencing variables whose time-dependent deformation behavior (eg strain behavior) is equal to or slower than the time-dependent deformation behavior of the housing (eg strain behavior) as a setpoint, the gap size in the cold state is used, this is reduced by at least one pre-stored value of a gap determined at maximum thrust of the aircraft engine, and by the model-based actuator a manipulated variable for a cooling system of the housing can be determined.

By modeling only the slower portions in the model-based actuator, an efficient overall gap size adjustment can be obtained that is commensurate with overall dynamics.

In an advantageous embodiment, the model-based actuating device for the influencing variables has a relationship for the thermal behavior of at least one rotor disk of a compressor stage and / or turbine stage and a relationship for the thermal behavior of the housing. In particular, the model-based manipulator for the influencing variables only includes relationships for the thermal behavior at least one rotor disk of a compressor stage and / or turbine stage and the thermal behavior of the housing.

An efficient embodiment for the model-based actuating device maps the dynamic deformation behavior of components by first-order step responses.

Furthermore, it is advantageous if the target value of the gap size can be determined exclusively from values which are independent of the current thrust state of the aircraft engine. This independence can be achieved in particular in that the gap components caused by the mechanical and thermal deformation behavior of a blade, the mechanical deformation behavior of a rotor disk, the thermal deformation behavior of an inlet device (eg a liner or a segment with a liner) and / or the mechanical deformation behavior of a Housing can be determined in each case at maximum thrust.

In one embodiment, the housing has at least one inlet device, in particular a liner or a segment with a liner.

In a further embodiment, calculated and / or measured values for the temperature, the pressure, the speed and / or the rotational speed are used in the determination of the manipulated variable. This provides further values for determining the manipulated variable.

If the gap size is taken into account in the input variables of the model-based adjusting device, feedback control is provided. Otherwise the system can work without feedback.

The object is also achieved by an aircraft engine having the features of claim 10.

• Fig. 1 eine schematische Darstellung eines Flugzeugtriebwerkes;
• Fig. 2 eine schematische Darstellung eines Spaltes und der Einstellung der Spaltgröße;
• Fig. 3 eine schematische Darstellung einer Ausführungsform des Systems zur Einstellung der Spaltgröße;
• Fig. 4 eine schematische Darstellung möglicher oder tatsächlicher radialer Positionen der rotor- und gehäuseseitigen Spaltänderungen:
• Fig. 5 eine schematische Darstellung unterschiedlicher Betriebszustände.

In connection with the embodiments illustrated in the figures, the invention will be explained. It shows

• Fig. 1 a schematic representation of an aircraft engine;
• Fig. 2 a schematic representation of a gap and the adjustment of the gap size;
• Fig. 3 a schematic representation of an embodiment of the system for adjusting the gap size;
• Fig. 4 a schematic representation of possible or actual radial positions of the rotor and housing side gap changes:
• Fig. 5 a schematic representation of different operating conditions.

In Fig. 1 is schematically illustrated a per se known aircraft engine 100, in which air L flows from the front of the aircraft engine 100. The greater part of the incoming air L is passed through a bypass duct 101 and expelled accelerated at the rear end of the aircraft engine 100.

A smaller portion of the incoming air L enters the core engine 102 and is compressed there in a compressor having a plurality of compressor stages 11. The compressed air is supplied to combustion chambers 103, the compressed and heated air is then fed to a turbine with turbine stages 12, wherein the air then accelerates at the rear end of the aircraft engine 100 flows.

The rotating blades 13 of the compressor stages 11 and the turbine stages 12 are surrounded by a housing 10, wherein the details in Fig. 2 are shown in more detail. The presentation of the Fig. 1 is merely an example. The embodiments described below are also applicable in the context of other engine designs.

In Fig. 2 a section of the housing 10 is shown. Within the housing 10, a blade 15 is disposed on a rotor disk, wherein the blade tip 13 is oriented radially to the housing 10. Opposite the blade tip 13, a liner 14 is disposed in the housing 10. In one embodiment of the present invention in a turbine stage 12, the liner 14 is placed in a segment that is then connected to the housing.

Between the blade tip 13 and the housing 10, and in particular the liner 14, there is the radial gap with the gap size S.

To set the gap size S, a cooling system 200 is used in a conventional manner with the cooling air K can be applied to the outside of the housing 10. A system 1 for active adjustment of the radial gap size sets a valve 201 of the cooling system 200 so that the gap size S is adapted to the respective requirements. It is important that the blade tip 13 does not come into contact with the housing 10 or the liner 14. In the cold state, a radial relative gap height (gap / length of the blade) of 3 to 4% can be sought. When warm, a relative gap height of 1% or less is desirable.

In Fig. 3 a scheme is shown with an exemplary embodiment of the inventive system 1 for active adjustment of the radial gap size S, with which the cooling system 200 is adjustable. For the sake of simplicity, disturbances have been omitted here.

The system 1 has a model-based adjusting device M, which receives the desired value w as an input variable. The desired value w is here the gap size Sk in the cold state reduced by at least one pre-stored value of a gap portion Sm determined at maximum thrust of the aircraft engine 100. This means that the desired value w can be determined in a simple manner from once determined and then permanently stored values.

In one embodiment, the gap fraction Sm at maximum thrust is determined as a function of the thermal behavior of a blade 15, the deformation behavior of a rotor (e.g., strain behavior), the thermal behavior of the liner 14, and / or the pressure dependent behavior of the housing 10. These influencing variables react dynamically faster than other components, which will be explained in more detail below. By determining (and fixing) the values at maximum thrust, these influences can be made independently of the respective thrust. Thus, a change in the thrust does not affect the setpoint values w.

The components in the core engine 102 have different time constants T in their deformation behavior (eg, expansion in the radial direction). Stress due to the speed act on the components faster than thermal influences, since the heat transfer is slower. When accelerated, thin housings 10 absorb the thermal strains faster than massive rotor disks. In some embodiments, a fast response may have time constants significantly less than 60 seconds, more preferably less than 30 seconds.

In a deceleration process, the components are subject to different thermal inertia, which can lead to a rapid reduction of the gap size S. There is then a risk of tarnishing of the blade tips 13 against the wall of the housing 10 or the liner 14, e.g. at a re-acceleration with still hot rotor disks (hot re-slam). Thus, there is a superposition of different mechanical (e.g., speed-dependent) or thermal dynamics effects; i.e. there are faster and slower influencing factors.

For an efficient setting, the system 1 has the model-based adjusting device M whose model takes into account only influencing variables whose time-dependent deformation behavior (eg with time constant T _i ) are slower than the time-dependent deformation behavior of the housing 10 (eg with the time constant T _housing ). The deformation behavior refers in particular to the expansion behavior of the components under load.

Thus, the time-dependent deformation behavior of the housing 10 serves as a reference for the dynamic processes that are taken into account in the model M or even not taken into account.

In a particular embodiment of the system 1 with the model-based actuator M, e.g. taking into account the thermal behavior of the turbine rotor disks (i.e., the material from the shaft to the root of the blades 15) and the thermal behavior of the housing 10. These dynamic factors are comparatively slow. Faster influences, such as the thermal behavior of the blades 15, the influence of the centrifugal force on the blades 15 or the influence of the pressure on the housing 10 are not taken into account by the model-based adjusting device M.

The turbine engine rotor disk and housing 10 thermal variables essential to the model-based actuator M are stored in appropriate form of mathematical relationships (e.g., differential equation, difference equation, transfer function) in the model-based actuator M. It is the goal, with the manipulated variable y for the cooling system 200 to set the best value for the gap size S.

One possibility for modeling is to approximate the temporal deformation behavior, such as the dynamic strain behavior x _i (t) for a component i by means of first-order jump functions: $$x_i\left(t\right)=x_{i.\infty }+\left(x_i\left(0\right)-x_{i.\infty }\right)\left(e^{\frac{-t}{T_i}}\right)$$

Here, classes of step responses x _i (t) can be formed for components with fast and slow expansion behavior, wherein the class division can be done on the basis of the time constant T _i . In addition, in the model for the step response, a constant x _{i , ∞ is used} for the steady state value of the expansion behavior.

The jump functions for all components i (eg blade 15, segment with liner, housing 10, rotor disk) whose time constants T _{i are} above a certain limit are used for the model-based adjusting device M.

In addition to these slow influencing variables, values (calculated and / or measured) for the temperature, the pressure, the speed and / or the rotational speed can also be used in the determination of the manipulated variable y. In Fig. 3 this is represented by a second model component M '.

A model-based adjusting device M, which relies on the slower influencing variables, is more efficient than a model that takes into account both fast and slow influencing variables. The rapid changes in the influencing variables can generally not be compensated quickly enough by the cooling system 200, so that the exclusive consideration of the slower influencing variables leads to a calmer setting of the gap sizes. The manipulated variable y is not subject to such strong fluctuations.

In Fig. 3 a controller is shown without feedback, ie the values for the gap size S (ie the controlled variable) are not included in the determination of the manipulated variable y. However, it is also possible to include the gap size S directly or via variables dependent thereon in the determination of the manipulated variable y, so that a control loop with feedback is present. The gap size S would then be linked to the desired value w.

In Fig. 4 is the time-dependent behavior of the different components with varying load shown in a schematic manner. In the upper part of the band 20 is shown, in which the inner wall of the housing 10 can move. In the lower part of the belt is 21, in which the rotor disk can move.

The thick solid line 22 represents the radial changes to blade tip 13 which are relatively high frequency. The actual position of the inner housing wall 23 is in Fig. 4 represented by a solid line.

With minimal cooling (Min TCC), the wall 23 of the housing 10 occupies a radially outward position radially. At maximum cooling (Max TCC), the housing 10 contracts relatively far, so that the radius has become smaller. In this case, the rotor would penetrate the housing at high speed and damage it.

So that it does not come to start the blade tip 13 in the housing 10, the wall of the housing 10 must be positioned so that the maximum possible position of the blade 14 is radially smaller than the position of the housing 10, in Fig. 4 the solid line 23.

By in connection with Fig. 3 described model-based adjusting device M, the thermal expansions of the rotor disk and the housing 10 are considered together; in one embodiment, just these too.

In Fig. 5 the expansions of the different components for two different load cases are shown in a schematic manner. It is about the filling of the gap size in the cold state Sk.

In the left part of the Fig. 5 In two bars, the expansion parts of the components are shown, which occur at maximum power, but each with different cooling.

The left-hand bar graph shows the thermal expansion ratio of the rotor disk D and the fraction of the centrifugal force CF with the cooling off (0%). This means that the housing 10 has no significant share of the gap closure.

If the cooling is increased from 0% to 40%, which is shown in the middle bar graph, then the deformation C of the housing 10 affects the gap closure. Thus, the closure is composed of three portions, namely the two relatively slow thermal portions of the rotor disk D, the housing C and the fast portion CF. The slow components find their way into the model-based controller M.

The rest of the gap closure at maximum power and 40% cooling almost then the fast Sm shares together. This amount can be determined once and can then be used again and again, as in the setpoint specification in the above-described (see Fig. 3 ) Embodiment is the case.

The right-hand bar graph shows the case of medium power consumption but higher cooling (60%). The slower rates of gap closure, i. the proportion D of the rotor disk and the proportion C of the housing expansion correspond in the sum of the two proportions at maximum power, but less cooling in the middle bar graph.

The fraction CF of the centrifugal strain is smaller because the rotational speeds are lower at medium power. If the target value calculation is done by means of the fast expansion components at maximum thrust (middle bar chart), the right-hand bar chart leaves a small gap, which is necessary as a safety margin when switching from medium power to maximum power. This shows that the setpoint determination in terms of Fig. 3 makes sense.

LIST OF REFERENCE NUMBERS

1

System for the active adjustment of a radial gap size

10

casing

11

compressor stage

12

turbine stage

13

blade tips

14

Inlet device, liner

15

blade

20

Band of housing positions

21

Band of blade tip position

22

Actual blade tip position

23

Actual housing position

100

Jet Engine

101

Bypass duct

102

Core engine

103

combustion chamber

200

cooling system

201

Valve

C

Thermal expansion rate Housing due to cooling

CF

Elongation due to centrifugal forces

D

thermal expansion ratio of the rotor disk

L

incoming air

K

incoming cooling air

M

Model-based adjusting device

S

Gap size, radial (set size, controlled variable)

sk

Gap size in the cold state

sm

Gap content at maximum thrust

T

time constant

w

setpoint

y

manipulated variable

Claims (10)

1. System for the active setting of a radial clearance size (S) between a blade tip (13) of at least one compressor stage (11) and / or at least one turbine stage (12) of an aircraft engine (100) and a housing (10) that surrounds the at least one compressor stage (11) and / or the at least one turbine stage (12),
   characterized by having

   a) a model-based setting device (M), wherein the time-dependent clearance size (S) can be approximated by the model-based setting device (M), with only those influencing variables being taken into account that have a time-dependent deformation behavior which is equal to or slower than the time-dependent deformation behavior of the housing (10), wherein

   b) the clearance size in the cold state (Sk) serves as the set point (w), with that clearance size being reduced by at least one previously saved value of a clearance proportion (Sm) that is determined at maximal thrust of the aircraft engine (100), and wherein

   c) a control variable (y) for a cooling system (200) of the housing (10) can be determined by the model-based setting device (M).
2. System according to claim 1, characterized in that the model-based setting device (M) for the influencing variables comprises a relationship for the thermal behavior of at least one rotor disc of a compressor stage (11) and / or turbine stage (12) and a relationship for the thermal behavior of the housing (10).
3. System according to claim 1 or 2, characterized in that the model-based setting device (M) for the influencing variables comprises only relationships for the thermal behavior of at least one rotor disc of a compressor stage (11) and / or turbine stage (12) and the thermal behavior of the housing (10).
4. System according to at least one of the preceding claims, characterized in that the model-based setting device (M) models the dynamic deformation behavior of structural components by step responses of the first order.
5. System according to at least one of the preceding claims, characterized in that the set point (w) of the clearance size (S) can be determined exclusively from values that are independent of the current thrust state of the aircraft engine (100).
6. System according to at least one of the preceding claims, characterized in that that clearance proportion (Sm), which is established at maximal thrust, is determined depending on the thermal behavior of a blade, the deformation behavior of a rotor, the thermal behavior of an inlet device and / or the pressure-dependent behavior of the housing (10).
7. System according to at least one of the preceding claims, characterized in that the housing (10) has at least one inlet device, in particular a liner (14), or a segment comprising a liner.
8. System according to at least one of the preceding claims, characterized in that calculated and / or measured values for the temperature, the pressure, the speed and / or the rotational speed are used in determining the control variable (y).
9. System according to at least one of the preceding claims, characterized in that the clearance size (S) is taken into account in the input values of the model-based setting device (M).
10. Aircraft engine with at least one system according to the claims 1 to 9.

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