Fan platform fin

The invention relates to a fan platform of a bypass turbomachine having a primary stream and a secondary stream. The platform defines a portion of the surface of the nose around which the primary stream flows and that carries blades extending radially outwards from said platform. Between two adjacent blades, the platform has at least one rib projecting into the space between the two blades, said rib being designed to participate in compressing the primary air stream.

The present invention relates to a fan platform for a bypass turbomachine having a primary stream and a secondary stream, the platform defining a portion of the surface of the nose about which the primary stream flows and carrying blades that extend radially outwards from the platform.

BACKGROUND OF THE INVENTION

In a turbomachine, the incoming air splits into two streams, a primary stream that flows in the more central region, and a secondary stream that surrounds the primary stream circumferentially. The radially-outer boundary of the primary stream, i.e. the region where the primary and secondary streams meet, forms substantially a cylinder of axis parallel to the main axis of the turbomachine. On coming into contact with the nose of the turbomachine, the central region of the primary stream flows while turning and following the wall of the nose of the turbomachine, which nose is conical in shape, flaring in the flow direction of the air as far as the inlet to a circumferential passage, where the wall of the nose becomes progressively parallel to the main axis of the turbomachine. A portion of the conical wall of the nose, upstream from the passage in the flow direction of the primary stream, is constituted by a platform referred to as the fan platform and that serves to carry blades. These blades serve to compress the air of the primary streams and to impart axial rotary motion thereto. By progressing along the cone between the blades of the fan up to the inlet to the passage, while also turning, the primary stream is also compressed radially between the wall of the cone and the secondary air stream, and its inner boundary moves away from the main axis of the turbomachine. This mechanism serves to obtain air at the inlet to the passage that is compressed and that presents energy that has been increased since it is turning relative to the main axis of the turbomachine at a mean radius (average distance from the main axis) that is greater than its initial mean radius.

The primary and secondary streams separate at the inlet to the circumferential passage surrounding the nose of the turbomachine, the primary stream penetrating into the passage while the secondary stream flows along the radially-outer surface of the annular wall defining the outside of the passage. Within the passage there are situated blades that extend radially and that enable the primary stream to be compressed further. It is desirable for the air of the primary stream penetrating into the passage to be as highly compressed as possible, so as to facilitate the compression work performed on said air by the low pressure compressor of the passage. The efficiency with which the air of the primary stream is compressed by the fan blades increases with increasing number of blades. Nevertheless, such blades are expensive. It can be advantageous to reduce the number thereof. In addition, reducing the number of blades reduces the weight of the platform, and thus its inertia. Nevertheless, in a fan platform having fewer blades, it is more difficult to compress the air that passes between the blades. This makes the work to be performed by the compressor downstream therefrom more difficult to achieve.

The present invention seeks to remedy those drawbacks, or at least to attenuate them.

OBJECT AND SUMMARY OF THE INVENTION

The invention seeks to provide a fan platform for a turbomachine that enables the air of the primary stream to be compressed as efficiently as possible for a given number of blades carried by the platform.

This object is achieved by the fact that the platform, between two adjacent blades, includes at least one rib projecting into the space between the two blades, said rib being designed to participate in compressing the air of the primary stream, and extending in the space defined between the blades within the 40% thereof that is furthest downstream in the flow direction of the primary stream.

By means of these ribs that project into the space where the primary stream flows, the air of the primary stream passing between the blades is compressed more than it would be in a configuration without ribs. Furthermore, each rib serves to attenuate the amplitude of the vortex that develops from the leading edge of each blade (i.e. the end of the blade that is furthest upstream in the flow direction of the primary stream) where the rib meets the platform. These vortices are regions of turbulence that are undesirable since they reduce the performance of the blades. A platform of the invention is thus substantially as efficient as a platform carrying a larger number of blades, but overall it is less expensive and lighter in weight since the ribs are less expensive to make than a blade and they comprise less material, taking the place of some of the blades.

Advantageously, said at least one rib extends in the space defined between the blades within the 30% furthest downstream in the flow direction of the primary stream.

This position for the rib serves to diminish the amplitude of the vortex that develops from the leading edge of a blade and that creates a region of turbulence that disturbs the flow of air between the blades.

MORE DETAILED DESCRIPTION

FIG. 1shows the front portion of a bypass turbomachine of main axis A. For reasons of symmetry about the axis X, only the top half of the turbomachine is shown. In the description below, the term “front” is used to designate the portion of a part that is situated upstream relative to the stream of air passing through the turbomachine, and the term “rear” is used to designate the portion of a part that is situated further downstream in said stream of air.

The front of the turbomachine has a nose10with its tip pointing forwards, i.e. to the left inFIG. 1. The nose begins by flaring towards the right following substantially the shape of a cone, and then the walls of the nose become progressively parallel to the axis A so as to form substantially a cylinder of axis A. The nose10is surrounded by a substantially cylindrical outer casing17having as its axis the axis of symmetry A. The radially inner surface18of the outer casing17and the surface12of the nose10define between them an annular region in which the stream of air flows. The turbomachine advances from right to left, thus the stream of air flows between the outer casing17and the nose10from left to right in the direction of arrow F.

Set back, i.e. towards the rear, relative to the front end of the outer casing17, there is an annular wall20substantially in the form of a circular cylinder about the axis of symmetry A. This annular wall20co-operates with the nose10to define an annular passage5. The annular wall20splits the stream of air into a primary stream1that enters the passage5, and a secondary stream2that surrounds the primary stream1circumferentially. Thus, the primary stream is defined by the nose10and the secondary stream, and then by the nose10and the annular wall20, while the secondary stream is defined by the primary stream and by the radially-inner surface18of the outer casing17, and then by the annular wall20and by the radially-inner surface18of the outer casing17. The region of separation between the primary stream1and the secondary stream2in front of the annular wall20is thus substantially in the shape of a cylinder3having the axis A as its axis of symmetry.

As it progresses through the turbomachine, the secondary stream2is thus of constant section and occupies an annular volume defined by the cylinder3and the radially-inner surface18of the outer casing17. In contrast, given that the nose10is conical in shape, the cross-section of the annular region through which the primary air stream1flows decreases as the air progresses through the turbomachine (from left to right inFIG. 1), since this region is defined outwardly by the cylinder3and inwardly by the surface12of the nose10which moves progressively away from the axis A in the flow direction of the air stream. The air that penetrates into the passage5is thus compressed.

In addition, a circumferential portion of the surface12of the nose10, in front of the passage5, is constituted by a fan platform40carrying blades30. These blades30are distributed around the circumference of the platform40at regular intervals, and serves to compress and impart axial rotary motion to the air of the primary stream1.

As shown inFIGS. 2 and 3, the blades30are curved along their width (the width of a blade being its dimension substantially in the direction of the main axis A of the turbomachine) such that each blade30presents a concave face32and a convex face33that meets at the front at the leading edge34and at the rear at the trailing edge35. The concave faces32of the blades30face in the direction of rotation of the platform40, this direction of rotation being represented inFIGS. 2 and 3by an arrow R, going from left to right. The arrow R is thus substantially perpendicular to the axis A. The convex face33of a blade30is situated facing the concave face32of the adjacent blade30. Two adjacent blades30define a space38. The primary stream flows in the space38from the leading edges34of the blades30towards the trailing edge35, in the direction of arrow F, and it is compressed as it passes therethrough.

The platform40includes a rib50that extends along a line that is at substantially equal distances from two adjacent blades30. The rib50possesses a leading edge54situated towards the front, and a trailing edge55situated towards the rear. The rib50is in the form of a fin that extends radially outwards from the platform40, i.e. it is substantially perpendicular to the platform40. The rib50may be rectilinear or it may be curved in a manner similar to the blades30and in the same direction. The rib50is smaller in height than the blades30, or indeed much smaller. The rib50may be forged together with the platform40. The rib50may alternatively be machined in the platform40.

As shown inFIG. 3, the leading edge54forms an angle with the platform40that is smaller than the angle formed by the trailing edge55with the platform40, such that the tip56of the rib50, i.e. the point of the rib that is furthest from the platform40, is closer to the location where the trailing edge55meets the platform40than the location where the leading edge54meets the platform40. For example, the tip56may be in line with the trailing edge55which is itself rectilinear. By way of example, the trailing edge55may extend radially perpendicularly to the platform40so that the tip56is situated radially over the location where the trailing edge55meets the platform40. Alternatively, as shown inFIG. 4, the rib50may have a trailing edge55that is rounded.

InFIGS. 2 and 3, the rib50is situated in the rearmost region of the space38, i.e. closer to the trailing edges35of the blades30than to there leading edges34. Thus, the rib50is more effective at attenuating the amplitude of the vortex60that develops in the space38from the leading edge34of the blade30. For example, the rib50is positioned in such a manner that 60% of the space38is situated in front of the location where the leading edge54meets the platform40, and 40% of the space38is situated behind the location where the leading edge54meets the platform40. By way of example, the rib50is positioned in such a manner that 70% of the space38is situated in front of the location where the leading edge54meets the platform40, and 30% of the space38is situated behind the location where the leading edge54meets the platform40.

The rib50may be situated entirely in a plane that is radial relative to the axis A and perpendicular to the platform40. The rib50may also have its radially-outer end510inclined in the direction of rotation of the platform40, as represented by arrow R inFIG. 5A, i.e. from left to right. Thus, the radially-outer end510forms an angle with the radially-inner portion of the rib that is perpendicular to the platform40, in the manner shown inFIG. 5A. The rib50may also include along its radial direction a plurality of successive portions that are inclined relative to one another in the direction of rotation of the platform40.

As shown inFIG. 5B, the rib50may also be curved over its entire radial extent in the direction of rotation of the platform40, as represented by arrow R. Under such circumstances, the portion of the rib50where it meets the platform40may be perpendicular to the platform or it may be inclined relative to the platform40in the direction opposite to its direction of rotation.

The present application is not limited to the embodiments described above. Thus, between each pair of adjacent blades30there may be a plurality of ribs50. For example, the platform40may have two ribs50between adjacent pairs of blades30, as shown inFIG. 6.