Turbine rotor blade with protrusions on the suction side to avoid flow separation

0001The invention relates to a turbine rotor blade, in particular a blade of a low-pressure turbine wheel of an airplane turbojet engine, whose aerodynamic behavior is improved to avoid "delamination" of the boundary layer of the jet engine. air relative to the surface of the dawn, mainly at the rear of the extrados area.

0002In the design of new forms of turbine blades, in particular the blades fitted to the wheel of the same stage of the turbine, it is desired to increase the performance by modifying certain structural parameters. In particular, to reduce the weight of the turbine, one of the solutions is to reduce the number of blades, which involves redrawing the blade profiles to respect the angles of exit and to compensate as much as possible, the loss of yield.

0003In this approach, it is possible to highlight risks of "delamination" harmful to the entrained air, extrados. These turbulent disturbances that originate in the vicinity of certain areas of the dawn, extrados, are very expensive in performance. The invention makes it possible to attenuate these phenomena of separation.<patcit id="pcit0001" dnum="US3578264A"><text>US 3578264</text></patcit> discloses a turbine blade with protrusions on the extrados side.

0004More particularly, the invention relates to a turbine blade as defined by claim 1.

0005For the determination of the location of such protuberances along the trailing edge, we proceed from a representation of the extrados side separation zone (this representation can be obtained by calculation) and we choose to place such protuberances in the vicinity of the maximum disturbance zone as determined without these protuberances.

0006In doing so, it is generally standard to place at least one aforementioned protuberance substantially halfway up the trailing edge.

0007Other protuberances may advantageously be placed in the vicinity of the radially inner end of said trailing edge and / or in the vicinity of the outer radial end of said trailing edge.

0008Generally, the calculations result in placing several aforementioned protuberances distributed along the outer radial third of said trailing edge.

0009The shape of such a protuberance is preferably generally that of a rounded stud projecting from the surface of the extrados with smooth connection thereto.

0010A median section of the protuberance, perpendicular to the trailing edge, has the shape of a half-wave with smooth connection to the extrados surface.

0011In addition, another section of said protuberance perpendicular to said middle section is in the form of a wave having a central end and side waves damped. In other words, seen according to this section, said protrusion is similar to the waveform caused to the flat surface of a liquid by the drop of a drop of liquid, this waveform is not, however, isomorphic circumferentially around from the central point.

0012The invention will be better understood and other advantages thereof will appear more clearly in the light of the description which follows, given solely by way of example and with reference to the appended drawings in which:<ul id="ul0001" list-style="dash" compact="compact"><li>the <figref idref="f0001">figure 1</figref> is a partial perspective view of a turbine rotor wheel provided with blades according to the invention;</li><li>the <figref idref="f0001">figure 2</figref> is a partial section of the blade, illustrating the profile of a protuberance according to the invention;</li><li>the <figref idref="f0002">figure 3</figref> is a partial section in another plane illustrating the profile of said protuberance;</li><li>the <figref idref="f0002">figure 3A</figref> is a view similar to the <figref idref="f0002">figure 3</figref> illustrating a variant; and</li><li>the <figref idref="f0002">figure 4</figref> is a schematic view illustrating a step of the method of determining the number and locations of the protuberances along the trailing edge.</li></ul>

0013The <figref idref="f0001">figure 1</figref> represents a plurality of rotor blades 11, in this case blades generally oriented radially at the periphery of a rotary disc 13. Conventionally, each blade, of a certain progressive thickness from front to back, is curved between an edge of 15 and a trailing edge 17. The concave portion or intrados 19 is smooth. The convex or extrados portion 21 is smooth over most of its surface except, according to the invention, some protuberances 25 distributed at the trailing edge and along the trailing edge 17. In general, such protrusion 25 preferably has the overall shape of a rounded stud projecting from the surface of the extrados 21 with smooth connection thereto.

0014Preferably, the profile of the section of the protuberance, perpendicular to the surface of the extrados at the point where it is located, evolves between the shapes illustrated in FIGS. <figref idref="f0001">figures 2</figref> and <figref idref="f0002">3</figref>.

0015So, as shown in <figref idref="f0001">figure 2</figref>a median section of said protuberance 25 made perpendicular to the trailing edge 17 is in the form of a single half-wave with a smooth connection to the upper surface 21. It should be noted that the slope of this half-wave is smaller towards the upper surface. forward than backward. According to this section, the protuberance is connected with continuity to the trailing edge.

0016However, if we consider another section of the same protrusion perpendicular to the previous, that is to say parallel to the trailing edge as shown <figref idref="f0002">figure 3</figref>it is noted that the latter has a more complex shape, namely one or more corrugations having a central extremum 27 and damped lateral waves 28. On the variant of FIG. <figref idref="f0002">figure 3A</figref>it can be seen that the section of the protuberance 25 comprises several corrugations that are damped on either side of the extremum. As mentioned earlier, this section is comparable to the wave produced at the calm surface of a liquid by the drop of a drop of liquid. If we "turn" around the protuberance, we go from one section to another, with continuity, in a quarter turn.

0017The preferred form of the protuberance being thus defined, the locations of such protuberances and the manner of determining these locations will now be described.

0018The <figref idref="f0002">figure 4</figref> represents schematically and from left to right the different phases of the positioning of the protuberances on a blade 11 seen according to the extrados surface 21. The grayed portion represents the so-called "delamination" zone 30 on the extrados side and in the vicinity of the edge leak.

0019We see that without protuberance, this separation zone 30 extends over virtually the entire height of the blade from the trailing edge, with a maximum width substantially halfway up. Analysis of this form leads to placing a first protuberance 25a in the vicinity of the maximum disturbance zone, that is to say halfway up the blade, at the trailing edge. The result of this first simulation, not shown, shows a decrease in the disturbance surface at mid-height but persistent disturbances at the radial ends, internal and external. This leads to placing another protuberance 25b in the vicinity of the radially inner end of the trailing edge and / or in the vicinity of the outer radial end 25c of the trailing edge. Thus, for example, the arrangement of three protuberances, as indicated, which also corresponds to the embodiment visible on the <figref idref="f0001">figure 1</figref>, results in reducing the width of the disturbance zone or detachment zone over substantially the entire radial height of the blade with, however, a zone of pronounced disturbance persistence between the central protuberance and the outer protuberance.

0020It is found that, according to the method developed in the context of the invention, placing a fourth protuberance 25d along the outer radial third of the trailing edge between the central protuberance 25a and the outer protuberance 25c results in reducing this last zone of separation.