JP6261498B2 - Method for diffusing a gas turbine compression stage and diffusion stage implementing the same - Google Patents

Description

  The present invention relates to a method for diffusing an air flow in a compression stage of a gas turbine engine, as well as a diffusion stage in which the method can be implemented.

  The field of the invention relates to improving the performance level and pumping margin of centrifugal and mixed flow compressors in the associated stage diffusion assembly. The purpose of this diffusion assembly is to convert the kinetic energy of the fluid obtained at the output of the centrifugal impeller constituting the stage into a static pressure. Operation must be performed with minimal loss of total pressure while maintaining a satisfactory level of stability within the compressor to maintain an acceptable pumping margin for turbine engine operation.

  Centrifugal compressors have at least one radial compression stage, ie a compression stage capable of producing an air flow perpendicular to the central axis of the compressor. The mixed flow compressor has at least one compression stage inclined with respect to the central axis.

  The compression stage diffusion assembly consists of an impeller formed by two plates where fluid flows between the two plates in a centrifugal or inclined manner from the center to the periphery. The blades are distributed around the impeller between the plates. These blades form a flow cascade between the leading edge of these central blades and the outer trailing edge.

  The plates of the radial and mixed flow diffuser assemblies are conventionally flat and advantageously the fluid flow cross section between the blades is tapered. The taper of the flow cross section is defined by the flow cross section at the neck of the diffuser and by the deceleration rate between the leading and trailing edges of the cascade.

  Other structures provide an axisymmetric plate connected to the tapered stream to provide further control of the flow cross section and thus optimize diffusion within the cascade.

  These solutions only allow control in one dimension, i.e., control of flow cross-section variations. There is no control of tangential non-uniformity of the fluid flow between the two blades. However, this control allows the flow to be adjusted and optimized.

  The object of the present invention is to create such a flow by using plates that are optimally shaped such that these plates exhibit a maximum surface area "streamed" by the flow. Therefore, non-axisymmetric shapes in the flow direction and tangential direction are proposed.

  More particularly, the present invention relates to a gas turbine engine comprising a diffusion assembly composed of an impeller formed by two plates where fluid flows between the two plates in a centrifugal or inclined manner from the center to the periphery. Relates to a method for diffusing an air flow in a compression stage. Cascade blades are distributed between the plates and around the impeller to direct fluid flow between the leading edge of these central blades and the surrounding trailing edge. In this method, at least one of the plates has at least one alternating concave and convex curvature in two generally perpendicular directions, ie, the direction of flow along the blade and the direction of the blade indirect direction. Have.

  In these conditions, the three-dimensional shape of the fluid stream allows the flow within the stream to be redistributed and uniformed, and the secondary flow that generates load loss is significantly reduced. The location of the impact within the transonic blade assembly is changed and its strength is reduced. Furthermore, aerodynamic rocking at the input of the combustion chamber following the compression stage is also significantly reduced.

  The invention further relates to a diffusion stage of a radial or mixed flow gas turbine engine in which the method can be implemented. Such a stage comprises an impeller formed by two plates in which fluid flows between the two plates in a centrifugal or inclined manner from the center to the periphery. Cascade blades are distributed around the impeller between the plates to direct fluid flow between the leading edge of these central blades and the surrounding trailing edge. At least one of the plates has an internal surface comprising at least one zone with alternating indentations and ridges of ridges between two adjacent blades in two generally perpendicular directions, i.e. flow along the blades. In at least one direction of direction and blade indirect direction.

  According to an advantageous feature, the diffusion stage starts with alternating indentations and ridge zones between the blades, in particular up to approximately 80% (preferably to approximately 50%) of the blade chord line, upstream from the leading edge. At the leading edge of the blade and / or at the trailing edge downstream of the trailing edge. These alternating indentations and ridge zones are located on one and / or the other of the two centrifugal (radial) and mixed flow diffuser plates, in particular symmetrically with respect to the central plane of symmetry of the plate, or on the step 2 If two plates are included, they can be applied in parallel.

  Further information, features, and advantages of the present invention will become apparent upon reading the following non-limiting description with reference to the accompanying figures.

It is a fragmentary sectional view of a gas turbine engine provided with an air diffusion part. FIG. 6 is a perspective view of a diffusion stage, where the blade comprises one plate. FIG. 6 is a perspective view of a diffusion stage, where the blade comprises two plates. FIG. 5 is a schematic view of a plate profile in the direction of air flow along a blade, with two zones with bends alternating along the blade. FIG. 3 is a schematic view of a plate profile in the direction of air flow along a blade, with two zones with bends at the trailing edge downstream of the blade. FIG. 3 is a schematic view of a plate profile in the direction of air flow along a blade with two zones with curvatures from the upstream side of the blade to the leading edge. FIG. 4 is a schematic partial view in the blade indirect line direction where the plate has two zones with alternating curvatures. FIG. 6 is a perspective view of the general blades at the leading edge where the plate has zones with alternating bends. FIG. 6 is a schematic perspective view at the trailing edge of two blades with a flat plate and a plate having zones with alternating bends.

  The terms “downstream” and “upstream” relate to a position with respect to air flow. In all of the figures, the same reference numbers relate to the description in the text where the elements corresponding to these reference numbers are defined.

  Referring to the partial schematic cross-sectional view of the helicopter gas turbine engine 1 according to FIG. 1, the air flow F is first sucked into the outside air intake sleeve 2 and then the blades 3 of the impeller 4 of the centrifugal compressor 5. Compressed between the casings 10. The turbine has axial symmetry about the axis X′X.

  In this case, the compressor 5 is centrifugal and the compressed flow F then exits radially from the impeller 4. If the compressor is a mixed flow type, the flow exits at an angle between 0 ° and 90 ° with respect to the radial direction perpendicular to the axis X′X.

  The flow F is then rectified through a diffusion or impeller 6 disposed at the output of the compressor 4 and routed towards the intake channel 7 of the combustion chamber 8.

  In order to carry out this commutation, the impeller 6 is composed of a plurality of curved blades 60, which in this case are arranged radially between the two plates 9 around the impeller 4 and thus rotate about the axis X′X. Is done.

  FIG. 2 b shows in more detail a perspective view of the diffusing section 6 with a blade 60 firmly connected to the two plates 9. In FIG. 2a, where the plate is omitted for clarity, each blade 60 has a surface 6e, referred to as the upper side, and a surface 6i, referred to as the lower side, in a known manner. In the example shown, these faces are connected in the direction of air flow by a tapered leading edge 6a and a rounded trailing edge 6f. Each blade 60 has a flat side 6p rigidly connected to the plate 9, transverse to the upper and lower surfaces.

  Conventionally, the plate 9 of FIGS. 2a and 2b is flat. According to the invention, at least one of these plates 9 has at least one zone between two blades 60 with alternating curvatures in a space E defined between them.

  Referring to FIG. 3a, such a plate 9 is shown as a profile in the direction of the air flow F along the blade 60 from the intake of the leading edge 6a of the blade to the outlet channel 7 towards the combustion chamber. . Two zones Z1 and Z2 with alternating curvature are created along the blade 60 in the plate 9. Each of these zones has a recessed portion 91 and a raised portion 92 on the flow F side and associated with the flat surface portion 9 p of the plate 9. Zones Z1 and Z2 generally extend over approximately 80% of the length of chord 6c of blade 60 in the non-limiting example shown.

  In the figure, the plate 9 has a small thickness for ease of presentation, but in practice it has a constant thickness and the zone with alternating curvature is The air flow F is formed on the inner surface 9i of the plate. The outer surface 9e of the plate 9 can remain flat, or in this example is adapted to the shape of alternating curved ridges and dents that are reversed with respect to the dent and ridge shape of the inner surface 9i. be able to. In the first example, the plate has a variable thickness, and in the second example it has a constant thickness. In particular, the shape of the plate may depend on the method used to create the zone with alternating bends: milling, laser, electrical discharge machining, forming, stamping, etc.

  In FIGS. 3 b and 3 c, the two zones Z 1 and Z 2 with alternating bends are at the trailing edge 6 f of the blade 60 to the downstream side of the blade in the intake of the channel 7 and / or upstream of the blade 60. It is formed at the front edge 6a from the side intake portion.

  FIG. 4 shows a partial schematic view of the diffusion stage between the blades “tangential” 6t, ie between the two blades 60. FIG. Arrow F indicates the direction of air flow. The inner surface 9i of the plate 9 has two zones Z1 and Z2 with alternating curvatures extending mainly between the lower 6i and upper 6e surfaces of the two blades 60.

  The perspective view between the blades of FIG. 5 at the leading edge 6a shows in more detail the plate 9 with zones Z1 with alternating bends between the two blades 60. FIG. The zone shows a concave curved portion 91 on the lower side 6 i of the blade 60 and a raised curved portion 92 on the upper side 6 e of the other blade 60. This alternating bends allows the pressure between the lower and upper sides of each blade 60 to be equal. The section at the neck 6s between the leading edges 6a is retained.

  The homogenization of the air flow F at the trailing edge 6f is shown in the perspective view of FIG. Due to the flat plate 90 (represented by the diagonal lines in the figure) between the two blades 60, aerodynamic locking is created in the zone Z0 having a very small amount of movement. In this form of the prior art, the main air flow (arrow F) has a high Mach number. In contrast, in the plate 9 with alternating bends according to the invention, the aerodynamic rocking zone is omitted and the air flow F has a lower Mach number and is provided with a flow cross section. It is made uniform while occupying all of the above.

  The invention is not limited to the embodiments described and shown. Accordingly, in the illustrated example, the curved portions are alternated in the direction of the flow of the fluid F, but are also alternated in the tangential direction 6t. In other variations, zones with alternating bends may be juxtaposed so that portions of the surface area with the same type of bends, whether indented or raised, can approach each other.

Claims (8)

A gas comprising a diffusion assembly composed of a diffusion part (6) formed by two plates (9) in which fluid flows between the two plates (9) in a centrifugal or inclined manner from the center to the periphery In the method of diffusing the air flow (F) in the compression stage (5) of the turbine engine (1), the blades (60) of the cascade are arranged between the plates (9) of the diffusion part (6). A method of guiding a fluid flow between a leading edge (6a) and a surrounding trailing edge (6f) of a central blade (60) by being distributed around, wherein at least one of the plates (9) one, but at least one alternating concave curved portion (91) and the curved portion of the convex surface (92) has in the direction of flow along said blade (60) (F),
At least one of the plates (9) also has at least one alternating concave curve (91) and convex curve (92) with respect to the direction of flow (F) along the blade (60). A method comprising having a blade indirect line direction (6t) that is substantially vertical.   2. The method according to claim 1, comprising a diffusion part (6) formed by two plates (9) in which the fluid flows between the two plates (9) in a centrifugal or inclined manner from the center towards the periphery. In a radial or mixed flow gas turbine engine compressor diffusion stage that can be implemented, blades (60) of cascades are distributed around the diffusion (6) between the plates (9). A diffusion stage that guides fluid flow between the leading edge (6a) of the central blade (60) and the surrounding trailing edge (6f), wherein at least one of the plates (9) Characterized in that it has an internal surface (9i) with at least one zone (Z1, Z2) with alternating dents (91) and ridges (92) bends between two adjacent blades (60). Diffusion stage.   At least one of said plates (9) has two adjacent inner faces (9i) further comprising at least one zone (Z1, Z2) with alternating indentations (91) and ridges (92) bends The diffusion stage of a radial or mixed flow gas turbine engine compressor according to claim 2, having a blade indirect line direction (6t) between the blades (60).   Starting from the upstream side of the leading edge, alternating dents (91) and ridges (92) zones (Z1, Z2) between the blades, up to approximately 80% of the chord line (6c) of the blade (60) The diffusion stage according to claim 2, characterized in that it has a leading edge and / or a trailing edge downstream of the trailing edge.   4. A dent and ridge zone (Z1, Z2) starting at the upstream side of the leading edge (6a) at the leading edge (6a) of the blade (60). A diffusion stage at the leading edge of the blade according to claim 1.   4. A dent and ridge zone (Z1, Z2) at the trailing edge (6f) of the blade (60) that extends downstream of the trailing edge (6f). A diffusion stage at the leading edge of the blade.   4. The alternating dent and ridge zone (Z1, Z2) applied to one and / or the other of the two plates (9) for centrifugal and mixed flow diffusions, A diffusion stage at the leading edge of the blade.   The alternating dent and ridge zones (Z1, Z2) are applied to one and the other of the two plates (9) for centrifugal and mixed flow diffusion and the alternating zones (Z1, Z2) Are applied symmetrically with respect to the central plane of symmetry of the plate (9) or the alternating indentation and ridge zones (Z1, Z2) are applied to the two for centrifugal and mixed flow diffusion. Diffusion stage according to claim 3, wherein the diffusion stage is applied to one of the plates (9) and the alternating zones (Z1, Z2) are applied to the plate (9) in parallel.

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