Guide assembly with optimised aerodynamic performance

Abstract

The invention relates to a turbine engine air flow guide assembly including: a structural arm (30); and a guide vane (21) on the lower surface of the structural arm, comprising a leading edge (22), a trailing edge (23), and a camber line (24), said vane and arm extending radially about an axis (X-X) of the turbine engine and defining therebetween an air flow channel. The structural arm (30) comprises: an upstream end (31) having a guide vane profile (21) and comprising a leading edge (32) aligned with that of the vane; and a shoulder (35) located on the lower surface of the arm, defining a neck in the channel. The assembly is characterized in that the area (A.sub.neck) of the section of the channel at the neck is between 0.7 and 0.9 times the area (A.sub.inlet) of the section of the channel at the leading edges.

Claims

1. A turbine engine air flow guide assembly comprising: a structural arm and at least one guide vane, situated at a lower surface of the structural arm and comprising a leading edge, a trailing edge and a camber line extending between the leading edge and the trailing edge, wherein the vane and the arm extend radially between an annular inner wall and an annular outer wall around an axis (X-X) of the turbine engine and define an air flow channel between them, and the structural arm comprises: an upstream end, with respect to the air flow direction in the channel, having a guide vane profile and comprising a leading edge aligned with the leading edge of the vane, and a shoulder situated at the lower surface of the arm, defining a throat in the channel upstream of which the channel is convergent and downstream of which it is divergent, wherein the area (A.sub.throat) of the section of the channel at the throat is comprised between 0.7 and 0.9 times the area (A.sub.inlet) of the section of the channel at the leading edges of the vane and of the arm.

2. The turbine engine air flow guide assembly according to claim 1, wherein the area (A.sub.throat) of the section of the channel at the throat is comprised between 0.75 and 0.85 times the area (A.sub.inlet) of the section of the channel at the leading edges of the vane and of the arm.

3. The turbine engine air flow guide assembly according to claim 2, wherein the area (A.sub.throat) of the section of the channel at the throat is comprised between 0.79 and 0.81 times the area (A.sub.inlet) of the section of the channel at the leading edges of the vane and of the arm.

4. The turbine engine air flow guide assembly according to claim 1, wherein the throat of the channel has an axial position x.sub.throat defined by:
x.sub.throat=x.sub.1/2emax0.05c where x.sub.1/2emax is the axial position of the maximum thickness section of the arm on the lower surface side and c is the length of the axial chord of the guide vane, and the axial position of the maximum thickness section of the arm on the lower surface side is comprised between the axial position of the leading edge and that of the trailing edge of the vane.

5. A bypass type turbine engine, comprising a secondary flow guide comprising a plurality of vanes arranged radially around an axis (X-X) of the turbine engine, and at least one structural arm, wherein at least one structural arm and a vane of the guide form a guide assembly according to claim 1.

Description

DESCRIPTION OF THE DRAWINGS

(1) Other features, aims and advantages of the invention will be revealed by the description that follows, which is purely illustrative and not limiting, and which must be read with reference to the appended drawings wherein:

(2) FIG. 1a, already described, shows schematically a bypass type turbine engine.

(3) FIG. 1b, already described, shows a developed schematic view of an assembly comprising a structural arm between two secondary flow guide vanes,

(4) FIG. 1c, already described, shows the aerodynamic effects of a guide vane on the lower surface 30i side of the excessively cambered structural arm,

(5) FIG. 2a shows an air flow guide assembly conforming to an embodiment of the invention.

(6) FIG. 2b illustrates schematically a turbine engine conforming to an embodiment of the invention.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

(7) With reference to FIG. 2b, a bypass type turbine engine 1 is shown comprising, as described previously a fan 10 and a guide 20 of the OGV type, to guide a secondary flow FR derived from the fan 10.

(8) The guide comprises a plurality of vanes 21 distributed regularly around a ring (not shown) centered on an axis X-X of the turbine engine, corresponding to the axis of the engine shaft.

(9) In addition, the turbine engine 1 comprises at least one structural arm 30 described in more detail below.

(10) Each assembly comprising a structural arm 30 and the vane 21 of the guide 20 adjacent to said arm on its lower surface 30i side is called an air flow guide assembly, and is represented in more detail in FIG. 2a.

(11) The vane 21 and the structural arm 30 extend radially around the axis X-X of the turbine engine, FIG. 2a being a developed view of the angular sector surrounding the axis X-X covered by the vane 21 and the arm 30. The vane 21 and the structural arm 30 define between them an air flow channel of the secondary flow.

(12) The vane 21 conventionally comprises a leading edge 22, a trailing edge 23, and a camber line 24 extending from the leading edge to the trailing edge, the camber line being the line halfway between the lower surface 30i and the upper surface of the vane.

(13) In addition the camber angle, denoted a, is defined at each point of the camber line by the angle formed between the tangent to the camber line at this point and the axis X-X of the turbine engine.

(14) The vane 21 is preferably formed so as to have a nonzero angle at its leading edge.

(15) The structural arm 30 is of the integrated guide vane type, i.e. it comprises an upstream end portion 31 having the profile of a guide vane.

(16) In particular, the upstream end portion 31 has a leading edge 32 aligned with that of the vanes 21 of the guide 20, i.e. at the same level with respect to the axis X-X, and has, at least at its leading edge, the same thickness and the same camber angle as a vane 21 of the guide 20.

(17) The structural arm 30 further includes a downstream portion 33, firmly attached to the upstream end portion 31 and directly adjacent thereto.

(18) The structural arm 30 is advantageously of the auxiliary type, meaning that its main function is that of transmitting power from the turbine engine to the rest of the airplane.

(19) In this regard, to support the loads required for this power transmission, the walls of the downstream portion 33 adjacent to the portion 31 are advantageously manufactured by casting. Moreover, the downstream portion 33 includes a hollow zone 34 called a keep-out zone dedicated to the implantation of utilities, and in particular one or more transmission shafts, and lines, connections, etc. if required.

(20) Thus, the upstream portion 31 of the structural arm forms one of the vanes 21 of the guide 20 of the turbine engine. If the turbine engine comprises several identical structural arms 30 distributed around the axis X-X, it advantageously comprises as many guide assemblies like that of FIG. 2a, each comprising a structural arm and the vane of the guide adjacent thereto, on its lower surface 30i side.

(21) Returning to FIG. 2a, the junction between the profiled upstream end portion 31 and the hollow zone 34 forms, on the lower surface 30i side of the structural arm 30, a shoulder 35, which reduces the section of the channel extending between the arm 30 and the vane 21. The section considered is a developed section of the angular sector around the axis X-X covered by the vane 21 and the arm 30, i.e. a two-dimensional zone defined by the intersection between the channel extending between the vane 21 and the arm 30 and a cylinder with an axis X-X of equal radius comprised between the radius of the vane root and the radius of the vane tip, preferably comprised between 5 and 95% of the radial height of the vane and of the arm, the intersection then being developed.

(22) The axial position of the section of the arm 30, transverse to the axis X-X, having a maximum thickness on the lower surface 30i side of the arm, is denoted x.sub.1/2emax, this thickness being measured between the camber line and the surface on the lower surface 30i side. This section of the arm with a maximum thickness resulting from the shoulder 35 and from the hollow zone 34, it is located at an axial position comprised between the axial positions of the leading edge 22 and of the trailing edge 23 of the vane 21.

(23) Noted mathematically, if the origin of the axis with respect to which the axial position x.sub.1/2emax is measured is brought back to the leading edge of the vane:
0.0<x.sub.1/2emax1.0c
Where c is the axial chord of the vane, i.e. the distance, measured in the direction of the axis X-X between the leading edge and the trailing edge of the vane.

(24) This geometry of the arm 30 defines, in the channel extending between the arm 30 and the vane 21, a throat, i.e. a minimum-section zone of the channel, upstream of which the channel is convergentwith a decreasing section from upstream to downstream with respect to the air flow directionand downstream of which the channel is divergentwith an increasing section from upstream to downstream.

(25) The axial position of the throat of the channel is denoted x.sub.throat, the area of the section of the channel at the throat A.sub.throat and the area of the inlet section, located at the leading edges 22 and 32, A.sub.inlet.

(26) The area of a section of the channel is calculated as the integral, over the height of the channel measured in the radial direction around the axis X-X, of the distance extending between the lower surface 30i of the arm and the upper surface of the vane at the section considered.

(27) The inventors have determined that the aerodynamic performance of the air flow guide assembly depend on the degree of shrinkage of the channel between the inlet section and the throat section.

(28) More precisely, to avoid a shock wave and boundary layer separation phenomenon, the ration between the area A.sub.throat of the section of the channel at the throat and the area A.sub.inlet of the section of the channel at the inlet must be less than 0.9.

(29) Moreover, to avoid static pressure distortions in the guide 20 connected with too low a flow rate in the channel situated between the arm 30 and the vane 21, the same ratio must be greater than 0.7.

(30) Thus it is noted:

(31) $0.7\frac{A_{\mathrm{throat}}}{A_{\mathrm{inlet}}}0.9$

(32) Preferably, we have

(33) $0.75\frac{A_{\mathrm{throat}}}{A_{\mathrm{inlet}}}0.085$

(34) More advantageously, we have:

(35) $0.79\frac{A_{\mathrm{throat}}}{A_{\mathrm{inlet}}}0.81$

(36) In fact, the inventors have observed that an optimum value of this ratio can be 0.8 for some engines.

(37) Moreover, the position of the throat must be close to the axial position of the maximum thickness section on the lower surface 30i side of the arm 30, and more specifically:
x.sub.throat=x.sub.1/2emax0.05c

(38) The position of the throat and the area of the section of the channel at the throat allow, with a fixed geometry of the guide arm 30, to determine the camber line of the vane 21 and therefore to also determine the geometry of the vane.

(39) Thus a configuration of a guide assembly is proposed, allowing optimization of the aerodynamic performance of this assembly.