GB2297384A

GB2297384A - Testing rotor blades

Info

Publication number: GB2297384A
Application number: GB9501346A
Authority: GB
Inventors: Karl Lechner
Original assignee: MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: MTU Aero Engines GmbH
Priority date: 1993-10-13
Filing date: 1995-01-24
Publication date: 1996-07-31
Also published as: GB9501346D0; DE4334799A1

Description

Testing rotor blades 2297384 This application is based on German patent

application number 4334799.1. The invention relates to a device and method for testing rotor parts, in particular blades of a turbo engine.

Rotor blades of turbo engines, in particular of gas turbines, are subject to marked and - depending on the load state of the drive - differing loads arising 10 from temperature, centrifugal forces and vibrations. The use in particular of heavy rotor blades made, for example, of Ni- or Co- based alloys leads at high rotational speeds to a reduced service life of the hub or disc, as a result of the high edge loads arising at is the outer periphery of the wheel rims.

When rotor blades are tested, varied load and output requirements have to be taken into consideration and the extent to which lightweight materials can be used in view of the actual operating states has to be 20 investigated.

Furthermore, the test devices used should make it possible to investigate extremely critical drive states, e.g. so-called surging, and the relevant effects upon the rotor blades.

Previously proposed devices are restricted to measures for exciting vibrations in the rotor blades, which are generated aerodynamically or electromagnetically in a local manner, directly at the blade itself. These measures, besides involving a high constructional effort and cost, have proved inadequate to enable testing of the flexural properties and vibration response of the blades over the entire output range and taking into account extremely variable load states.

The object of the invention is therefore to provide a device by means of which the actual operating stresses arising at rotor blades and resulting in particular from variable temperatures, rotational speeds, centrifugal forces and vibrations are comparatively easy to estimate and examine.

According to the invention there is provided a device for testing rotor blades of a turboengine, in particular a turbine, having a motor-driven, rotatably mounted shaft, disposed on which in a non-rotatable manner is a wheel disc to which the rotor blades may be detachably anchored, characterized by the provision of an electromagnetic shaking device by means of which vibrations can be impressed via the rotating shaft upon the rotor blades.

With devices using the invention it is possible to fulfil simultaneously the basic criteria tuned to an actual operating state for a blade test. Consequently, operationally at least substantially approximate state variables or parameters relevant to the blade test may be simulated, e.g. via the rotational speed with the associated centrifugal stress, via the blade temperature with the associated thermal load, and via a specific vibrational state, which may be impressed on the blades, with the associated loads and limits in terms of stress and strain (material fatigue). 25 The shaking device can simply consist of a metal tube rotating with the shaft and an electric coil surrounding the tube in order to impress a vibration on the tube, and through it the shaft and the blades, by means of electromagnetic induction. The testing apparatus preferably further includes a heating device surrounding the rotor blades, most usefully in the form of an inwardly facing chamber containing heating elements or means for the supply of hot gas, in order to apply heat locally to the blades. As a further refinement the hub of the rotor can be arranged to be cooled at the same time. This simulates the operationally prevailing temperature variation over the wheel disc so that a critical transitional temperature actually to be anticipated under operating conditions at the outer periphery of the wheel disc, particularly in the relevant blade foot region, may be adjusted or controlled.

The structural parts, e.g. the shaft bearings and its drive wheel, can be simply and securely assembled and easy to exchange by clamping them axially with a single screw clamp with spacer sleeves between or integral with the various parts. The same applies to the induction tube of the shaking device. Furthermore, by virtue of the coaxial construction of the shaking device according to some embodiments there is a practically wear-free, highly intensive load transmission without any friction between metal structural parts.

With a vibration and blade deflexion measuring device using a light beam such as a laser, amplitudes resulting from the actual operating state may be compared comparatively easily and quickly, e.g. by means of corresponding reference surfaces, with already measured and stored amplitudes (reference values), and used to control the shaking device. 25 For a more detailed understanding, examples of the invention will now be described with reference to the accompanying drawings, in which: Fig.1 shows a central longitudinal section of a complete device, 30 Fig.2 shows an alternative, shown in a section corresponding to Fig.1, for an electrically heatable rotor blade arrangement in a chamber, and Fig.3 shows a further alternative heating arrangement. Fig.1 shows a device for testing rotor blades 1 of a turbine of a gas turbine engine tuned to simulatable variable operating states of the drive.

The device comprises a motor-driven shaft 2 which at least at two points is supported rotatably in the circumferential direction; disposed nonrotatably on the shaft 2 is a wheel disc 3, to the outer periphery of which rotor blades 1 are detachably anchored, all of the rotor blades I being electrically heatable at the same time as described below. The device further comprises an electromagnetic shaking device 4, by means of which vibrations of the type to be anticipated in practice are impressed on the rotor blades 1 from the far end of the rotating shaft 2.

Here, in the conventional style of construction for turbo engines, the rotor blades 1 are anchored by their feet in, for example, axial grooves distributed at regular intervals over the periphery of the wheel rim of the wheel disc 3. In practical terms, the rotor blades 1 on the wheel disc 3 form a rotor blade row of a turbine stage in the sense of a turbine with axial throughflow. Stationary electric heating devices 5, 6 are further disposed transversely, here radially or at right angles, to the common axis A of the shaft 2 and the wheel disc 3 and axially at a distance in front of the inlet edges and behind the outlet edges of the rotor blades 1 respectively.

Electric heating means 5, 6 of any style of construction may be used; they may be, for example, spiral or zigzag or helical electric resistance heating wires which are, for example, integrated into wall- or bar-like elements; or they may be heating bars or electric induction heating elements; they may moreover also be coil-current-like electric heating means. These heating devices, e.g. in the form of bar-type heating elements, would preferably be disposed distributed uniformly over the circumference in order as far as possible to impress a uniform temperature profile upon all of the rotating rotor blades. By means of transformer control, the two heating devices 5, 6 may be heated up simultaneously to the same or to a different extent.

According to Fig.2, the rotor blades 1 may be disposed so as to be freely rotatable in the circumferential direction inside a chamber of U-shaped cross-section and open towards the common shaft and disc axis A. As is further shown in Fig.2, the heating devices 5, 6 may be disposed inside the chamber K against the straight- limbed side walls of the chamber, or perhaps integrated into the side walls.

According to a further construction of the invention as shown in Fig.3, all of the rotor blades 1 may be heated up to an operationally comparable temperature level, not by the above-mentioned electric heating devices, but by the locally targeted supply of combustion or hot gases. The possibility is then created of exploiting the energy content inherent in the hot gas flow in the sense of an additional input at the shafting 2 via the rotor blades 1. To this end, the hot gas from a header line 20 may be supplied through individual branch channels 21 frontally to the chamber and - downstream of the rotor blades 1 - may be discharged from the chamber through further channels 22 to a header line 23 and from this line into the open air. The frontal branch channels 21, particularly when arranged so as to be distributed uniformly over the periphery, may terminate, for example, in slots 24 or swirl chambers which narrow in the manner of a nozzle and from which the supplied hot gas is fed to the rotor blades 1 in a similar manner to the channel flow-off directions of upstream guide baffles.

According to Fig.1 there is associated with the wheel disc 3 a cooling device 7, which may be acted upon by compressor air and comprises channels or chambers 8, out of which the supplied compressor air may be blown as cooling air (L) from both sides towards a hub-side thickening of the wheel disc 3.

The channels 8 or chambers of the cooling device 7 may comprise impact cooling bores, out of which the cooling air L may be blown uniformly in a circumferential and axial/radial direction in a distributed manner towards the thickened hub part of the disc.

The shaft 2 has a detachably connected driving pulley, in particular belt pulley 9, via which the shaft 2 is motor-driven by means of a flat belt 10. Alternatively, the shaft 2 could be driven via gearwheels, so that a toothed disc, for example, would have to be provided instead of the belt pulley.

First and second rotary bearings 11, 12 are further provided for the shafting 2, the first rotary bearing taking the form of a ball bearing and the second the form of a roller bearing. The shafting 2 at a portion projecting axially beyond the second rotary bearing 12 verges into the wheel disc 3. The outer ring or race 13 of the first rotary bearing 11 is supported on an aero- or hydrodynamic supporting cushion P which, in a predetermined manner, forms a vibration damper operating without contact.

To form the supporting cushion P it is possible, for example, for a suitable lubricating fluid to be supplied in the direction of arrow S through lines in a stationary carrier T for the first bearing 11 to the radial support gap, between lateral O-ring seals; depending on the vibrational requirements, an axial supporting cushion construction may additionally be provided at the outer ring 13.

In Fig.1, the inner rings 14, 15 of the first and second rotary bearings 11, 12 are held an axial distance apart on the shafting 2 by a slip-on sleeve 16; the driving pulley 9 has a sleeve-like portion H between it and the first rotary bearing 11, resting axially against the latter's inner ring 14; the sleeve 16, the driving pulley 9 and the inner rings 14, 15 of the two pivot bearings 11, 12 are locked against rotation axially with the shafting 2 by means of a screw fastening 18.

At the end remote from the wheel disc 3 the shaking device 4 is detachably disposed on the shaft 2.

The device includes a coaxial coil tube element, in this particular case a rotationally symmetrical rolled aluminium tube 17 upon which shaking movements are impressed upon throughflow of an electromagnetic field in the axial direction of excitation R.

A spool for current coils Sp, which surrounds the aluminium tube 17 with a radial gap, is part of this shaking device 4. The current coils Sp are evenly and uniformly distributed axially and circumferentially.

The shaking device 4 operates without contact, being based on the induced eddy current principle. The shaking movement arises as a result of the reaction of an induced current in the aluminium tube 17 with the electromagnetic field from the current coils Sp. The latter may be assembled from individual coaxial copper windings.

Fig.1 further shows the transmitting and receiving part of a measuring device 19, which is provided for detecting and checking the occurrence of blade vibrations and/or blade deflexion and which, for example, uses at least one laser beam L which is interrupted at reference surfaces on the blade foot side, light pulses obtained through reflection being measured and supplied, e.g. as electrical signals, to an evaluation device.

As a reference surface it is possible to select, for example, a predetermined blade point which is characteristic for the bending movements of the blade, the laser beam pulse obtained from the reflection being processed into an electrical signal which, as a representative value of the detected deflexion, is compared with a reference value stored in the computer. For the measurement it is also possible to select, for example, two locally spaced-apart points per rotor blade, the measure for the blade deflexion being obtained from the chronologically measured sudden change of the laser beam pulses as a function of the distance between the two local points. By comparing the chronologically measured sudden changes for a number of blades with one another, it is then possible to draw conclusions about the respective dynamic component of vibrations at successive blades.

In the above-described manner or in a comparable manner it is possible by means of a high-intensity light beam, in particular a laser beam, also to draw conclusions from the rotor or disc vibrations about a specific or critical vibration response for the rotor blades. Within a closed-loop electronic control circuit, the electromagnetic shaking device 4 may be actuated with reference to a specific rotational speed by comparing electrical signals (actual values) obtained from light pulses continuously reflected on the rotor and/or blade side with reference inputs (setpoint values) and on the basis of the calculated deviations between setpoint and actual values a setpoint correction is effected, for example, by means of an electronically controlled supply of coil current.

The test jig may moreover include a chamber which can be evacuated and in which the entire rotor comprising the shaft 2 and bladed wheel disc 3 is supported in a rotatably driven manner. In this manner friction and windage losses can be extensively avoided and the drive power reduced.

is

Claims

1. A device for testing rotor blades (1) of a turboengine, in particular a turbine, having a motordriven, rotatably mounted shaft (2), disposed on which in a non-rotatable manner is a wheel disc (3) to which the rotor blades (1) may be detachably anchored, characterized by the provision of an electromagnetic shaking device (4) by means of which vibrations can be impressed via the rotating shaft (2) upon the rotor blades (1).

2. A device according to claim 1, in which, in use, the rotor blades (1) are arranged in a row, stationary electric heating devices (5, 6) being disposed transversely to the axis of the shaft (2) and the disc (3) and axially at a distance in front of the inlet edges and/or behind the outlet edges of the blades.

3. A device according to claim 2, in which the heating devices are disposed uniformly distributed over the circumference of the rotor blade row.

4. A device according to any of claims 1 to 3, and including a chamber (K) which is U-shaped in crosssection, the open side being towards the axis (A), in which chamber the rotor blades (1) are disposed so as to'be freely rotatable in the circumferential direction.

5. A device according to claim 4 when appendant to claim 2, in which the heating devices (5, 6) are disposed inside the chamber (K).

6. A device according to claim 4 or 5, in which the heating devices (5, 6) are disposed against the straight-limbed side walls of the chamber (K).

7. A device according to any preceding claim and further including a cooling device (7), which may be acted upon by compressor air and comprises channels or chambers (8), in order to blow cooling air (L) towards both sides of a thickened portion towards the hub of the wheel disc (3).

8. A device according to claim 7, in which the channels (8) or chambers comprise impact-cooling bores, out of which the cooling air may be blown uniformly in the circumferential and radial directions in a distributed manner towards the disc thickened portion.

9. A device according to any preceding claim, in which the shaft (2) has at least one driving pulley, in particular a belt pulley (9), which is detachably connected to the shaft and is motor-driven by means of a flat belt (10).

10. A device according to any preceding claim, in which the shaft (2) is mounted on first and second is axially spaced rotary bearings (11, 12) and, at a portion which projects axially beyond the second pivot bearing (12), merges into the wheel disc (3); and in which the outer ring (13) of the first pivot bearing is supported on an aero- or hydrodynamic supporting cushion (P).

11. A device according to claim 10, in which the inner rings (14, 15) of the first and second rotary bearings (11, 12) are held an axial distance apart on the shaft (2) by a slip-on sleeve (16), the driving pulley (9) having a sleeve-like portion (H) which bears axially against the inner ring (14) of the first rotary bearing (11), and the sleeve (16), the driving pulley (9) and the inner rings (14, 15) of the two rotary bearings being locked axially with the shaft (2) in a manner secure against rotation.

12. A device according to any preceding claim, in which the shaking device (4) includes an electrically conducting member (17) disposed on the shaft (2) at the end remote from the wheel disc (3), upon which member axial shaking movements can be impressed by applying an electromagnetic field.

11-

13. A device according to claim 12 when appendant to claim 11, in which the conducting member is a rotationally symmetric rolled aluminium tube (17), which together with the driving pulley (9), the sleeve (16) and the two inner rings (14, 15) of the pivot bearings is lockable against rotation on the shaft (2) by means of an axial screw clamp (18).

14. A device according to any preceding claim and further comprising a measuring device (19) for detecting and checking the occurrence of blade or rotor vibrations and/or blade flexion, which device uses at least one high-intensity light beam (L), which is interrupted and reflected at reference surfaces on the blade or rotor, these reflected light pulses being measured and evaluated.

15. A device according to claim 14, in which the shaking device (4) is actuated by means of an electronic control device which is connected to the measuring device (19).

16. A device according to claim 1 and including a chamber (K') surrounding the rotor blades (1), and a means for the application of combustion or hot gas, which is supplied to and discharged from the chamber (K') at points disposed at regular intervals in the circumferential direction.

17. A device according to claim 16, in which the hot gas is supplied via the chamber W) in a nozzle like manner to the rotor blades (1).

18. A device according to any preceding claim, further including an evacuable chamber for the entire rotor assembly comprising the shaft (2) and bladed wheel disc (3).

19. A device for testing rotor blades (1) of a turboengine, in particular a turbine, having a motor- driven, rotatably mounted shaft (2), disposed on which in a non-rotatable manner is a wheel disc (3) to which the rotor blades (1) may be detachably anchored, characterised by the provision of a device (5, local heating of the blades (1).

6) f or

20. A device substantially as described herein 5 with reference to the accompanying drawings.

21. A method for testing rotor blades, in which the blades (1) are mounted on a wheel disc (3), itself located on a motor-driven shaft; characterised in that vibrations are superimposed on the shaft as it rotates.