FR2478196A1 - DAMPING OF TURBOMACHINE BLADES - Google Patents

Abstract

THE VIBRATIONS OF A TURBOMACHINE VANE 10 WITHOUT A SHELL OR FRICTION DAMPER ARE DAMPENED BY A DAMPER THAT EXTENDS ALONG A BORE THROUGHOUT THE VANE. THE SHOCK ABSORBER INCLUDES ONE OR MORE FIRST COMPONENTS 16 IN FRICTIONAL CONTACT WITH ONE OR MORE SECOND COMPONENTS 15 WHICH ARE IN CONTACT WITH THE WALL OF THE DAWN 10. THE FIRST COMPONENTS 16 ARE TRANSVERSALLY MOBILE IN BORE 3 AND COMPONENTS 15 , 16 ARE IN CONTACT WITH ONE WITH THE OTHERS AT THE LEVEL OF TWO PAIRS OF SURFACES CONFRONTING MUTUALLY. THE PAIRS OF CONFRONTING SURFACES ARE ARRANGED IN PLANS FORMING A CERTAIN ANGLE ALONG THE LENGTH OF BALEAGE 13, ALTERNATIVELY IN DIFFERENT DIRECTIONS.

Description

24 78196

  The present invention relates to turbomachinery blades

  nes, and in particular the damping of induced vibrations

in these blades.

  When it comes to large compressor blades, for example fan blades of a bypass type gas turbine engine, it is known how to use platforms, usually called dampers by

  friction at locations along the aerodynamic

  to dampen vibrations due to torsion,

  and the beating of dawn. These shock absorbers by

  interact with each other to form

  makes a continuous platform that dampens vibrations.

  These shock absorbers add an undesirable weight and the

  blades and discs or drums on which the

  blades are mounted must therefore be considerably

  forced to withstand the high centrifugal forces

  friction damping. In addition, the provision of friction dampers complicates the

  machining, compromises aerodynamic efficiency

  dawn and introduces heavily stressed areas in vulnerable areas of the dawn. There is therefore a very valid reason for eliminating shock absorbers

by friction.

  It is also known how to provide turbine blades with advanced shells for reducing gas leaks.

  at the tips of the blades and to determine the damping

  the vibration of the blades in a manner quite similar to that of which the friction dampers act on the compressor blades. In this case also, the turbine rotors comprising peak-envelope vanes have many of the disadvantages listed above, and

  There are therefore good reasons for eliminating the use of

  and to deal with the problem of depreciation

  vibrations and the control of games at

spikes separately.

  It is also known how to dampen blades not provided with an envelope by means of elastic blocks fixed below the platform of the root, but it is then necessary that the dawn

  have a larger profile to achieve sufficient flexion

  and efficient depreciation. The result is

  fest by an increase in the charges applied to the

turn of the disc.

  The present invention proposes a way of damping the vibrations induced in turbine engine blades that do not comprise friction dampers of airfoil envelopes.

  tip or any other known vibration dampers.

  The advantages offered by the invention consist mainly in the fact that the vibration damper is contained inside the blade and therefore does not compromise the aerodynamic efficiency of the blade. In addition, the manner in which the vibration damper is designed allows adequate damping without imposing excessive centrifugal forces on the blades and rotors on which the blades are mounted. In addition, the blades of the invention are easier to manufacture and to machine and are therefore less expensive to manufacture than the blades provided with friction dampers or envelopes.

peak.

  According to the present invention, it is proposed a dawn

  for a turbomachine comprising an aerodynamically shaped portion

  a root, a bore extending in the direction of the

  point of dawn which is distant from the root, and an amorphous

  vibration weaver extending along the bore, the damper comprising one or more first movable components transversely in the bore and one or more second components in frictional contact with the wall of the bore

  the bore, the first component, or each first component

  being in contact with one or more second compounds

  two pairs of mutually contacting surfaces disposed at spaced regions along the bore, a first pair of contacting surfaces being inclined along the length of the bore, and a second pair of surfaces in contact converging towards the first pair of contacting surfaces, the shape and position of the pairs of contacting surfaces being such that, in use, a transverse movement of the first component, or each first component, compensates for the axial movement of the second component, or various second components, caused by flexing of the blade relative to the length of the bore, and ensures that the first component, or each first component, makes frictional contact with one or several second components, so as to damp the

vibrations of dawn.

  Both types of components may consist of a flexible filament wound helically and extending

  along the bore. For example, the first and second

  each can be in the form of an elongated flexible filament helically wound and extending along the bore, the helices of the two filaments have the same pitch and

  are wound in the same direction around the longitudinal axis

  In the bore, the windings of a filament are

  placed between the windings of the other filament, and the first

  first component is in contact with the second component along

  two axially spaced zones extending helically

  is lying. Alternatively, the damper may comprise a series of first components spaced along the bore and a series of second components interposed between first axially adjacent components. For example, the first and second components may both comprise annular rings, or washers, which may have a circular, triangular or trapezoidal cross-sectional shape. Preferably, the rings defining the

  second components are split circumferentially (that is,

  to say that they understand. slots extending in direction

  radial). The cross sections of each ring

can be different.

  Each second component may be constituted by an annular ring, and each first component may be a member provided with a convex surface (such as a ball

  may be spheroidal, obloidal, proloidal or ellipsoid

  dale) which is in contact with two second components along circumferentially extending contact zones and the tangent to the convex surface of the contact zone forms an angle with the longitudinal axis of the bore. The second components may be constituted by a series of balls disposed loosely around the wall of the bore at spaced intervals along the bore, and the first components are arranged between two sets of balls and are in contact with the balls in planes containing the tangent to the contact areas between the balls

and the first component.

  When the first component, or each first component

  and the second component, or each second component, has a substantially triangular cross-sectional shape, the first and second components can be arranged

  so that one edge of the triangular cross-sections

  gules tip alternately radially inwardly and radially outwardly relative to the bore, the first and second components being in contact with one another

  with the others on two sides of their transverse sections.

dirty triangular.

  The first component, or each first component, and the second component, or each second component, may have a substantially trapezoidal cross-sectional shape with two converging sides, and the first and second components are arranged so that the converging sides of each cross section converge alternately in the direction of a radially outer position and a radially internal position, and the first and second components are in contact with each other by their

converging surfaces.

  Various embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which

  FIG. 1 represents a turbine blade, incorporates

  a form of vibration damper constructed according to

2478,196

  FIG. 2 shows in greater detail a portion of the vibration damper of the blade of FIG. 1, FIGS. 3 to 8 show different shapes of the damper shown in the dawn of FIG. FIGS. 1 and 2 show a turbine blade intended for a gas turbine engine comprising an aerodynamic portion 11 and a root 12. The root has the traditional shape of a fir tree which allows the blade to be mounted in slots of complementary shape spaced around the

  perimeter of the rotor disk or drum.

  The blade is provided with a blind bore 13 cast or machined in the dawn from the end of the blade.

  root, and the diameter of the bore is typically gold.

  it is 6.0 mm (0.25 inch), but it can naturally be larger or smaller. The dawn is provided with a vibration damper which serves to dampen the vibrations of the dawn manifested in any mode relative to the axis

of the bore.

  The damper comprises two coiled wires 15, 16

  helicoidally in the same direction around the longitudinal axis

  nal of the bore, and having a common pitch. The wires 15, 16 have

  a substantially triangular cross-sectional shape.

  The overall diameter of the two components 15, 16 is just

  slightly smaller than the diameter of the bore 13.

  One of the components 15 is wound so that one vertex of its cross-section points radially inward and one side of the triangle is in contact with the wall of the bore. The other component 16 is wound so as to have an apex of its cross-section pointing radially outwards and disposed in the interstices of the windings of the other component 15. As a result, the vertices point alternately inwards and outwards. outward along the bore. It will be seen that the components 15, 16 have surfaces facing each other and in contact with each other, arranged alternately according to

  opposite angles with respect to the longitudinal axis.

2-478196

  In other words, each component 15 or 16 makes contact with its opponent on two sides of its section

triangular cross section.

  The component 16 has a diameter slightly smaller than that of the other component 15 so as to be able to move

transversely in the bore.

  In operation, a bending of the dawn in door-to-door

  false along the bore 13 tends to increase the gap between the windings of the component 15 on one side of the longitudinal axis and simultaneously compresses the windings in

  a point diametrically opposed to the gap which is increased

  you. This causes a lateral displacement in the bore of the radially inner component 16 and simultaneously provides space for any axial movement of the component 15. The centrifugal forces applied to the components 15 and 16 due to the rotation of the rotor on which the blade is mounted cause the components 15 and 16 to come into contact with the end of the bore and the component 16 is brought into contact with the component 15 and to urge it into contact with the

  boring wall, and at the same time a trans-

  component 16 transmits a friction force to the

  component 15 which damps the vibrations of the dawn.

  The wound members 15, 16 may be made by the outer casing of a control cable sold in the United Kingdom of Great Britain under the trademark "Bowdenex". "Bowdenex" cables are designed to be used as control cables in situations where it is not possible to tolerate variations in the average length of the inner core with respect to the outer core due to flexing of the cable . The outer casing of the "Bowdenex" cable comprises two coiled members, one of which is triangular with one apex pointing radially inwardly and the other of circular cross-section, and has been found useful for forming the vibration damper of the

present invention.

2478,196

  7. Other cross-sectional shapes of the components and 16 are possible, and these cross sections may be for example, as shown in Figure 3, substantially trapezoidal with two converging sides. In this case, the components 15, 16 are arranged so that their converging sides converge alternately to radially internal and radially external positions as one progresses along the bore. Here again, the surfaces in mutual confrontation are arranged in planes alternately inclined in opposite directions by

relative to the axis of the bore.

  The cross-sectional shape of the components 15, 16 may be circular, as shown in FIG. 4, and in this case the tangents to the contact area between the components are located in inclined planes relative to each other.

  to the longitudinal axis of the bore.

  It is possible to build a component 15 or 16

  so that its cross-sectional shape is different

  rent from that of the other. For example, one component may have a triangular cross section while the other may be circular or trapezoidal in section, provided that the components 15 and 16 are in mutual contact in alternately inclined planes in opposite directions. If desired, the two components 15 or 16 of the

  Figures t to 4 may be replaced by a series of

  spaced along the bore. Examples of such

  shock absorbers are shown in Figures 5 to 8.

  Referring to Figure 6, the two components 15 and 16 comprise a number of triangular ring rings of triangular cross section, as shown in Figure 2, spaced along the bore. Each ring 15 is provided with a radial slot which allows it to be distended and to be fixed in the bore. The rings 16 are provided with radially extending, closed slots and have an outer diameter slightly smaller than the bore for

  able to move transversely in this bore.

  The rings 15 or 16 may have a circular, triangular or trapezoidal cross-sectional shape, such as

shown in Figures 5 to 7.

  With reference to FIGS. 5 to 7, each component is constituted by an annular ring which may be of a shape

  in triangular, circular or trapezoid cross-section

  zoldale, or whatever else. Both sets of components

  no need to have the same shape, provided that the

  16 are free to move transversely in the bore and to make contact with the components in inclined planes alternately in directions

  different from the longitudinal axis of the bore.

  Referring to FIG. 8, component 15 of FIGS. 1 to 4 is replaced by a series of discrete annular rings circumferentially split and spaced along the bore, and components 16 of FIGS. 1 to 4 are replaced by a series of beads that may be spherical, ovoldal, proloidal or ellipsoidal. The balls 16 are free to move transversely and each makes contact with two axially adjacent rings 15 along a circumferentially extending contact zone, the tangent to this surface being disposed in an inclined plane alternately along the length 'bore, in directions

  different from the longitudinal axis of the bore.

  In all the embodiments described above, the components 15, 16 establish mutual contact in

  planes arranged alternately in different directions

  are progressing along the bore. This effectively means

  components 16 are arranged in recesses

  the shape of which is decreasing and which, when the blade is bending, grip the component 16 and urge it to the side. In addition, the relative rotation of one section of the bore relative to another produces a relative sliding of the components 15, 16 and between the bore and the components 15 and 16. The centrifugal forces applied to the components 15 and 16 solicit them in contact with each other and

  The vibrations of dawn are dampened by the dissipation of energy.

  friction by surfaces in confrontation of components

and 16.

  The components 15, when they are in the form of rings, are split circumferentially to allow them to be inserted into the bore and to be distended to come into frictional contact with the wall of the core.

  when they are subjected to centrifugal forces.

Claims (14)

R E V E N D I C A T I 0 N S   A turbomachine blade, comprising an aerodynamically shaped portion, a root, a bore extending towards the tip of the blade which is remote from the root, and a vibration damper extending along the bore, characterized in that the damper comprises   one or more first movable transverse components (15)   in the bore (13) and one or more second components   sants (15) in frictional contact with the wall of the bore (13), the first component (16), or each first component   (16), being in contact with one or more second   sant (15) at two pairs of mutually contacting surfaces disposed at spaced regions along the bore (13), a first pair of the contacting surfaces being disposed in an inclined plane with respect to the length   of the bore (13), and a second pair of   wherein the shape and position of the pairs of surfaces in contact are such that, in use, a transverse movement of the first component (16), or each first component, is arranged in a plane converging towards the first pair plane; (16) compensates for the axial movement of the second component (15), or various second components (15), caused by the bending of the blade (10) relative to the length of the bore (13), and ensures that the first component (16), or each first component (16), makes frictional contact with one or more of the second   components (15) for damping the bending of the blade (10).   2. blade according to claim 1, characterized in that the damper comprises a second component (15) which is common to a series of first components (16) spaced along the bore (13) and each first component (16). ) makes contact with the second component (15) in two   regions axially spaced along the bore (13).   3. blade according to claim 1, characterized in that the damper comprises a series of first components (16) spaced along the bore (13) and a series of second components (15) interposed between first components axially adjacent.   4. blade according to claim 1, characterized in   what the first and second components (15,16) pre-   each feel in the form of an elongated flexible filament wound helically and extending along the bore (13), the helices of the two filaments are likewise not and wound in the same direction about the longitudinal axis of the bore (13), the windings of a filament are interposed between   the windings of the other filament, and the first component   sant (16) makes contact with the second component (15) Io along two axially spaced and helically extending regions. - 5. blade according to claim 3, characterized in that each second component is constituted by an annular ring, and each first component (16) is a member provided with a convex surface which is in contact with two   second components (15) along contact areas   circumferentially and the tangent to the convex surface of the contact area forms an angle with the axis longitudinal bore (13).   6. blade according to claim 5., characterized in that each first component (16) is constituted by a ball.   7. blade according to any one of the claims   1 to 5, characterized in that the first component (16), or   each first component (16) has a cross-sectional shape circular versale.   8. blade according to any one of the claims   1 to 4, characterized in that the first component (16), or   each first component (16) has a shape in trans section triangular versale.   9. blade according to any one of claims 1   to 4, characterized in that the first component (16), or each first component (16), has a sectional shape Trapezoidal transverse.   A blade according to any of the claims   1 to 9, characterized in that the second component (15), or each second component (151, has a sectional shape circular cross.   Dawn according to any one of the claims   1 to 9, characterized in that the second component (15), or   each second component (15) has a cross-sectional shape triangular versale.   - 12. blade according to any one of the claims   1 to 9, characterized in that the second component (15) has a   shape in trapezoidal cross-section.   13. blade according to any one of the claims   1 to 5, characterized in that the first component (16), or each first component (16), and the second component (15), or each second component (15), has a substantially triangular cross-sectional shape, and the first and second components (16, 15) are arranged in such a way that an edge of the triangular transverse sections points alternately radially inwards and radially outwards with respect to the bore (13),   the first and second components (16, 15) being in con-   with each other on both sides of their triangular cross-sections.   14. blade according to any one of the claims   1 to 5, characterized in that the first component (16), or each first component (16), and the second component (15), or each second component (15), has a substantially trapezoidal cross-sectional shape, with two converging sides, and in that the first and second components 30 (16, 15) are arranged such that the converging sides of each transverse section converge alternately towards a radially external position and a radially internal position, and in that the first and second components (16, 15) establish mutual contact   on their converging contact surfaces.