METHOD OF DIFFUSING A GAS TURBINE COMPRESSION STAGE, AND DIFFUSION STAGE FOR IMPLEMENTING SAME
A diffusion stage of a radial or mixed gas turbine engine compressor includes an impeller formed by two plates, between which fluid flows in a centrifugal or inclined manner from a center towards a periphery. Blades of a cascade are distributed between the plates to channel the flow of the fluid between leading edges of the blades at the center and trailing edges at the periphery. At least one of the plates has an internal face including at least one zone with alternating hollow and bump curvatures between two adjacent blades, in at least one of two substantially perpendicular directions, in the direction of flow along the blades and in an inter-blade tangential direction.
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The invention relates to a method for diffusing the flow of air in a compression stage of a gas turbine engine, as well as to a diffusion stage capable of implementing said method.
The field of the invention relates to improving the performance levels and the pumping margin of centrifugal and mixed compressors in the diffusion assembly of the relevant stage. 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 static pressure. The operation must occur with a minimum loss of total pressure whilst maintaining a satisfactory level of stability in the compressor in order to maintain a pumping margin that is acceptable for the operation of the turbine engine.
A centrifugal compressor has at least one radial compression stage, i.e. which is capable of producing a flow of air perpendicular to the central axis of the compressor. A mixed compressor has at least one compression stage that is inclined relative to said central axis.
A diffusion assembly of a compression stage is composed of an impeller formed by two plates, between which the fluid flows in a centrifugal or inclined manner from the centre towards the periphery. Blades are distributed around the impeller between the plates. These blades form a flow cascade between the leading edges of these blades at the centre and the trailing edges on the outside.
PRIOR ARTThe plates of the radial and mixed diffusion assemblies are conventionally flat and advantageously the flow cross-sections of the fluid between the blades are tapered. The tapering of the flow cross-sections is defined by the flow cross-section at the neck of the diffuser and by the rate of deceleration between the leading and trailing edges of the cascade.
Other architectures provide axisymmetric plates connected to tapered streams in order to provide additional control of the flow cross-section and to thus optimise the diffusion in the cascade.
These solutions only allow control in one dimension, that of the variation of the flow cross-section. There is no control of the tangential heterogeneity of the flow of the fluid between two blades. However, this control allows the flow to be adjusted and optimised.
DESCRIPTION OF THE INVENTIONThe aim of the invention is to produce such a flow by implementing shape-optimised plates as these plates represent the largest surface area that is “streamed” by the flow. Non-axisymmetric shapes in the direction of the flow and in the tangential direction are thus proposed.
More specifically, the present invention relates to a method for diffusing the flow of air in a compression stage of a gas turbine engine comprising a diffusion assembly composed of an impeller formed by two plates, between which the fluid flows in a centrifugal or inclined manner from the centre towards the periphery. Blades of a cascade are distributed around the impeller between the plates so as to channel the flow of the fluid between the leading edges of these blades at the centre and the trailing edges at the periphery. In this method, at least one of the plates has at least one alternation of concave and convex curvatures in at least one of two substantially perpendicular directions, namely in the direction of flow along the blades and in an inter-blade tangential direction.
In these conditions, the three-dimensional shape of the stream of the fluid allows its flow in this stream to be redistributed and homogenised: the secondary flows, which generate load losses, are substantially reduced. The position of shocks in the transonic blade assemblies is modified and their intensity is reduced. Furthermore, the aerodynamic locking at the input of the combustion chamber that follows the compression stage is also substantially reduced.
The invention further relates to a diffusion stage of a radial or mixed gas turbine engine capable of implementing this method. Such a stage comprises an impeller formed by two plates, between which the fluid flows in a centrifugal or inclined manner from the centre towards the periphery. Blades of a cascade are distributed around the impeller between the plates and so as to channel the flow of the fluid between the leading edges of these blades at the centre and the trailing edges at the periphery. At least one of the plates has an internal face comprising at least one zone with alternating hollow and bump curvatures between two adjacent blades, in at least one of two substantially perpendicular directions, namely in the direction of flow along the blades and in an inter-blade tangential direction.
According to advantageous features, the diffusion stage has alternating hollow and bump zones between the blades, in particular up to substantially 80% (preferably up to substantially 50%) of a chord line of a blade, at the leading edge of the blades, starting upstream of the leading edge, and/or at the trailing edge, continuing to downstream of the trailing edge. These alternating hollow and bump zones can be applied to one and/or the other of the two centrifugal (radial) and mixed diffusion plates, particularly in a symmetrical manner, relative to a central plane of symmetry of the plates, or in a parallel manner when the two plates of the stage are involved.
Further information, features and advantages of the present invention will become apparent upon reading the following non-limiting description, with reference to the appended drawings, in which:
The terms “downstream” and “upstream” relate to positions in relation to the flow of air. In all of the figures, identical reference numerals relate to the passages in the description in which the elements that correspond to these reference numerals are defined.
With reference to the partial cross-sectional schematic view of a helicopter gas turbine engine 1 according to
In this case the compressor 5 is centrifugal and the compressed flow F then exits radially from the impeller 4. When the compressor is mixed, the flow exits inclined at an angle of between 0° and 90° relative to a radial direction, perpendicular to the axis X′X.
The flow F then passes through a diffuser or impeller 6, disposed at the output of the compressor 4, in order to be rectified and routed towards intake channels 7 of a combustion chamber 8.
In order to carry out this rectification, the impeller 6 is composed of a plurality of curved blades 60 that are arranged between two plates 9 at the periphery of the impeller 4, in a radial manner in this case, and thus rotate about the axis X′X.
Conventionally, the plates 9 of
With reference to
In the figures, the plate 9 has a low thickness in order to simplify the presentation, but in reality it has a certain thickness and the zones with alternating curvatures are formed on the internal face 9i of the plate where the air flow F flows. The external face 9e of the plate 9 can remain flat or can also conform to the bump and hollow shapes of the alternating curvatures, which are reversed in this example relative to the hollow and bump shapes of the internal face 9i. In the first instance, the plate has a variable thickness and, in the second instance, it has a constant thickness. In particular, the shape of the plates can depend on the method used to produce the zones with alternating curvatures: by milling, laser, spark erosion, forming, stamping, etc.
In
The perspective inter-blade view of
At the trailing edges 6f, the homogenisation of the air flow F is shown in perspective view in
The invention is not limited to the embodiments described and shown. Therefore, in the examples shown, the curvatures are alternated in the direction of flow of the fluid F but also in the tangential direction 6t. In other variants, the zones with alternating curvatures can be juxtaposed so that portions of the surface area with the same type of curvature, either hollow or bump, can be close together.
Claims
1.-9. (canceled)
10. A method of diffusing a flow of air in a compression stage of a gas turbine engine including a diffusion assembly including an impeller formed by two plates, the method comprising:
- fluid flowing between the two plates in a centrifugal or inclined manner from a center towards a periphery, blades of a cascade being distributed around the impeller between the plates to channel the flow of the fluid between leading edges of the blades at the center and trailing edges at the periphery,
- wherein at least one of the plates includes at least one alternation of concave and convex curvatures in a direction of flow along the blades.
11. A method for diffusing flow of air according to claim 10, wherein at least one of the plates also includes at least one alternation of concave and convex curvatures in an inter-blade tangential direction that is substantially perpendicular to the direction of flow along the blades.
12. A diffusion stage of a radial or mixed gas turbine engine compressor capable of implementing the method according to claim 10, comprising:
- an impeller formed by two plates, between which the fluid flows in a centrifugal or inclined manner from a center towards a periphery,
- blades of a cascade being distributed around the impeller between the plates to channel the flow of the fluid between leading edges of the blades at the center and trailing edges at the periphery,
- wherein at least one of the plates includes an internal face including at least one zone with alternating hollow and bump curvatures between two adjacent blades.
13. A diffusion stage according to claim 12, wherein at least one of the plates includes an internal face further including at least one zone with alternating hollow and bump curvatures between two adjacent blades in an inter-blade tangential direction.
14. A diffusion stage according to claim 12, further comprising alternating hollow and bump zones between the blades, up to substantially 80%, or up to substantially 50%, of a chord line of a blade.
15. A diffusion stage according to claim 13, further comprising hollow and bump zones at the leading edge of the blades, starting upstream of the leading edge.
16. A diffusion stage according to claim 13, comprising hollow and bump zones at the trailing edge of the blades, continuing to downstream of the trailing edge.
17. A diffusion stage according to claim 13, wherein the alternating hollow and bump zones are applied to one and/or the other of the two plates for centrifugal and mixed diffusion.
18. A diffusion stage according to claim 17, wherein the alternating zones, are applied to the plates in a symmetrical manner, relative to a central plane of symmetry of the plates, or in a parallel manner.
Type: Application
Filed: Jun 19, 2012
Publication Date: May 15, 2014
Applicant: TURBOMECA (Bordes)
Inventors: Laurent Pierre Tarnowski (Pau), Nicolas Bulot (Assat), Jerome Yves Felix Gilbert Porodo (Pau)
Application Number: 14/126,989
International Classification: F04D 19/00 (20060101);