Discharge flow duct of a turbine engine comprising a VBV grating with variable setting

Abstract

A hub of an intermediate casing for a dual-flow turbine engine includes a discharge flow duct extending between an inner shroud and an outer shroud of the hub, the discharge flow duct leading into the secondary flow space through an outlet opening formed in the outer shroud, the outlet opening included in a discharge plane substantially tangential to the outer shroud; and discharge fins including an upstream fin and a downstream fin. An upstream acute angle between the discharge plane and the skeleton line of the upstream fin is smaller than a downstream acute angle between the discharge plane and the skeleton line of the downstream fin.

Claims

1. A hub for a dual-flow turbine engine, the hub comprising: a first shroud defining a primary flow space for a primary gas flow of the dual-flow turbine engine, a second shroud defining a secondary flow space for a secondary gas flow of the dual-flow turbine engine, a discharge stream duct extending between the first shroud and the second shroud, the discharge stream duct defining a discharge flow space for a discharge gas flow, wherein a wall of the second shroud comprises an opening, the opening being an outlet for the discharge gas flow into the secondary flow space of the second shroud, such that a discharge plane of the discharge stream duct is coincident with the wall of the second shroud comprising the opening, and an upstream fin and a downstream fin, both the upstream fin and the downstream fin disposed in the discharge stream duct at the opening, the downstream fin being downstream from the upstream fin relative to a direction of flow of the secondary gas flow in the secondary shroud, wherein: the upstream fin is located adjacent to an upstream surface of the discharge stream duct relative to the direction of flow of the secondary gas flow in the secondary shroud, the upstream fin having a skeleton line, and a leading edge arranged facing the discharge gas flow in the discharge stream duct, the downstream fin is located adjacent to a downstream surface of the discharge stream duct relative to the direction of flow of the secondary gas flow in the secondary shroud, the downstream fin having a respective skeleton line, and a leading edge arranged facing the discharge gas flow in the discharge stream duct, and an upstream acute angle (.sub.upstream) between the discharge plane and a tangent to the skeleton line at the leading edge of the upstream fin is smaller than a downstream acute angle (.sub.downstream) between the discharge plane and a tangent to the respective skeleton line at the leading edge of the downstream fin.

2. The hub according to claim 1, wherein the upstream acute angle (.sub.upstream) is substantially equal to an acute angle defined between the upstream wall surface of the discharge stream duct and the discharge plane.

3. The hub according to claim 2, wherein the upstream acute angle (.sub.upstream) is between 30 and 44 .

4. The hub according to claim 1, wherein the downstream acute angle (.sub.downstream) is substantially equal to an acute angle defined between the downstream surface of the discharge stream duct and the discharge plane.

5. The hub according to claim 4, wherein the downstream acute angle (.sub.downstream) is between 40 and 50 .

6. The hub according to claim 1, further comprising a supplementary fin comprising a leading edge, a trailing edge, and a skeleton line, the supplementary fin located between the upstream fin and the downstream fin in the discharge stream duct at the opening, and wherein an acute angle between the discharge plane and a tangent to the skeleton line at the leading edge of the supplementary fin is between the downstream acute angle (.sub.downstream) and the upstream acute angle (.sub.upstream).

7. The hub according to claim 1, further comprising a number n of supplementary fins, each supplementary fin having a leading edge and a skeleton line, wherein the supplementary fins are located and distributed at regular intervals between the upstream fin and the downstream fin, wherein a given supplementary fin is disposed at a minimum acute angle ( .sub.i_min) between the discharge plane and a tangent to the skeleton line at the leading edge of the given supplementary fin being equal to: ${}_{\mathrm{i\_min}}=i\frac{\left({}_{\mathrm{downstream}}-{}_{\mathrm{upstream}}\right)}{n+1}+{}_{\mathrm{upstream}}$ where: .sub.i_min is the minimum acute angle of the given supplementary fin, n is the number of supplementary fins, i is a rank of the given supplementary fin relative to other supplementary fins, the rank increasing between the upstream fin and the downstream fin. .sub.upstream is the upstream acute angle of the upstream fin, and .sub.downstream is the downstream acute angle of the downstream fin.

8. The hub according claim 1, wherein the skeleton line of the upstream fin and the skeleton line of the downstream fin are curved skeleton lines.

9. The hub according to claim 8, wherein the upstream fin and the downstream fin further have a trailing edge opposite the leading edge, and wherein an angle (.sub.BF) between a tangent to the skeleton line at the trailing edge of the upstream and downstream fins and the discharge plane is equal to an average between an average acute angle () of the discharge gas flow in the discharge stream duct with respect to the discharge plane and an angle () between the direction of flow of the secondary gas flow at the outlet opening with respect to the discharge plane: ${}_{\mathrm{BF}}=\frac{+}{2}$ where: .sub.BF is the angle at the trailing edge is the average in acute angle, and is the angle between the direction of flow of the secondary gas flow at the outlet opening with respect to the discharge plane.

10. The hub according to claim 2, wherein the upstream acute angle (.sub.upstream) is betweeen 33 and 35 .

11. The hub according to claim 2, wherein the upstream acute angle (.sub.upstream) is 34 .

12. The hub according to claim 4, wherein the downstream acute angle (.sub.downstream) is between 43 and 45 .

13. The hub according to claim 4, wherein the downstream acute angle (.sub.downstream) 44 .

14. A turbine engine comprising the hub according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features, goals and advantages of the present invention will appear more clearly upon reading the detailed description that follows, and with reference to the appended drawings given by way of nonlimiting examples wherein:

(2) FIG. 1, which has been described above, is an axial section view of a hub for the intermediate casing known from the prior art,

(3) FIG. 2a illustrates an embodiment of a discharge stream duct of the intermediate casing according to the invention,

(4) FIG. 2b is a schematic view of an exemplary embodiment of a discharge stream duct of a hub of an intermediate casing according to the invention, and

(5) FIG. 3 is a schematic section view of an exemplary embodiment of a discharge fin which can be used in the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

(6) Hereafter, a hub 2 of an intermediate casing for a dual-flow turbine engine and an associated intermediate casing will now be described with reference to the appended figures.

(7) The hub 2 parts for the intermediate casing of the prior art, already described, are also present in the embodiments hereafter.

(8) In particular, a hub 2 of an intermediate casing according to the invention comprises:

(9) an inner shroud 3 configured to delimit a primary flow space 10 of the primary gas flow of the turbine engine,

(10) an outer shroud 5 configured to delimit a secondary flow space 14 of the secondary gas flow of said turbine engine, and

(11) at least one discharge stream duct 18, extending between the inner shroud 3 and the outer shroud 5.

(12) The inner shroud 3 and the outer shroud 5 are coaxial with the axis X of the hub 2.

(13) The discharge stream duct 18 leads into the primary flow space 10 through an inlet opening 4 formed in the inner shroud 3 and into the secondary flow space 14 through an outlet opening 6 formed in the outer shroud 5. Preferably, casing hub 2 comprises a plurality of discharge stream ducts 18, uniformly distributed between the inner shroud 3 and the outer shroud 5.

(14) The inlet opening 4, which is formed in the inner shroud 3 of the hub 2, can be selectively opened or closed by a door 12 depending on the phases of flight of the turbine engine. Preferably, the door 12 is movable between a closed position, wherein the door 12 closes the inlet opening 4, and an open position wherein the door 12 releases the inlet opening 4. For example, the door 12 can be mounted hinged to the inner shroud 3 or comprise a sliding trap door.

(15) The discharge stream duct 18 also comprises an upstream wall 18a and a downstream wall 18b, which extend between the intermediate space 16 and the outlet opening 6. The radially outward end of the upstream wall 18a is flush with the outer shroud 5, upstream of the outlet opening 6, while the radially outward end of the downstream wall 18b is flush with the outer shroud 5 downstream of said opening 6. The upstream wall 18a of the discharge stream duct 18 also delimits the radially outward portion of the duct 18, the downstream wall 18b delimiting its radially inward portion.

(16) The hub 2 further comprises a VBV grating comprising a set of discharge fins 20 attached in the discharge stream duct 18 at the outlet opening 6, and configured to orient a discharge gas flow F18 coming from the primary flow space 10 and inject it into the secondary flow space 14 in a direction substantially parallel to that of the secondary flow F14, so as to reduce the head losses in the secondary flow space 14.

(17) The discharge fins 20 comprise, from upstream to downstream in the gas flow direction in the secondary flow space 14, an upstream fin 22 and a downstream fin 24.

(18) The upstream fin 22 and the downstream fin 24 each comprise a leading edge BA and a trailing edge BF, opposite to the leading edge BA. The leading edge BA of a fin 22, 24 corresponds to the anterior portion of its aerodynamic profile. It faces the gas flow F18 and divides the flow of air into a lower surface air flow and an upper surface air flow. For its part, the trailing edge BF corresponds to the posterior portion of the aerodynamic profile, where the lower surface and upper surface flows rejoin.

(19) The upstream fin 22 and the downstream fin 24 further each have a lower surface wall I and an upper surface wall E, which connect the leading edge BA and the trailing edge BF and along which the lower surface and upper surface flows, respectively, pass.

(20) The upstream fin 22 and the downstream fin 24 are adjacent to the upstream wall 18a and the downstream wall 18b, respectively. The upstream wall 18a and the downstream wall 18b generally do not extend in parallel into the zone adjacent to the outer shroud 5, as shown schematically in FIG. 2b. Moreover, the inclination of the upstream fin 22 in the discharge stream duct is different from that of the downstream fin 24, which allows a reduction in the risks of separation or of recirculation of the secondary flow F14 in the secondary stream.

(21) More precisely, the upstream fin 22 and the downstream fin 24 are oriented in the discharge stream duct 18 so that the angle .sub.upstream, called the upstream angle, between a discharge plane P and a tangent T to the skeleton line C at the leading edge BA of the upstream fin 22 is different from the angle, .sub.downstream, called the downstream angle, between the discharge plane P and a tangent T to the skeleton line C at the leading edge BA of the downstream fin 24.

(22) The skeleton line C is understood to be a fictitious line which comprises the set of points equidistant from the upper surface wall E and from the lower surface wall I of a given fin.

(23) By discharge plane P is meant here a fictitious plane tangent to the outer shroud 5 at the outlet opening 6. The discharge plane P therefore intersects the upstream wall 18a and the downstream wall 18b and comprises the outlet cross-section of the discharge stream.

(24) The upstream .sub.upstream and downstream .sub.downstream angles have been illustrated in FIG. 2b by way of indication. These angles are acute so as to orient the flow F18 coming from the discharge stream duct 18 and align it with the secondary flow F14.

(25) It will be noted that the upstream .sub.upstream and downstream .sub.downstream angles correspond to the angle of incidence of the fluid, that is the angle at which the gas flow F18 in the discharge stream duct 18 sees the corresponding fin 22, 24. Yet, the flow direction of the gas flow F18 in the duct 18 is not constant between the upstream wall 18a and the downstream wall 18b, due in particular to the inclination of the discharge stream duct 18 with respect to the flow direction of the primary flow and the relative inclination of the upstream 18a and downstream 18b walls: that is why the adaptation of the angle of incidence of the fins 22, 24 depending on their position in the discharge stream duct 18 allows a reduction in the risks of separation by locally modifying the angle of the flow F18 in the zone of the fins 22, 24 so that it is as close as possible to the flow angle F14, which allows the aerodynamic losses to be limited.

(26) The Applicants have noted, in particular, that the local orientation of the gas flow F18 at the outlet opening 6 was more inclined at the downstream wall 18b than at the upstream wall 18a. The upstream acute angle .sub.upstream is therefore preferably smaller than the downstream acute angle .sub.downstream. Such an orientation of the upstream fin 22 and of the downstream fin 24 thus allows an improvement in the circulation of the gas flow F18 at the VBV grating, and in particular at the upstream fin 22, but also allows the best deflection of the gas flow F18 prior to its entry into the secondary flow space 14 so as to limit aerodynamic losses.

(27) In one embodiment, the upstream angle .sub.upstream and the downstream angle .sub.downstream, are selected near the inclination angles of the upstream wall 18a and the downstream wall 18b, respectively, with respect to the discharge plane P.

(28) The upstream acute angle .sub.upstream can for example be comprised between 30 and 44, preferably between 33 and 35, 35 for example.

(29) The downstream acute angle .sub.downstream can, for its part, be comprised between 40 and 50, preferably between 43 and 45, 44 for example.

(30) The discharge fins 20 can further comprise supplementary fins 26, extending between the upstream fin 22 and the downstream fin 24. The appended FIGS. 2a and 2b illustrate for example a VBV grating comprising three discharge fins 22, 24, 26.

(31) These supplementary fins 26 then also each comprise a leading edge BA, a trailing edge BF and lower I and upper E surface walls.

(32) For each of the supplementary fins 26, the angle .sub.i between the discharge plane P and the tangent T to the skeleton line C at the leading edge BA of the supplementary fin 26 is preferably comprised between the upstream angle .sub.upstream upstream and the downstream angle .sub.downstream.

(33) According to a first embodiment, the angle .sub.i can be substantially equal to the downstream angle .sub.downstream. The Applicant has in fact noted that the reduction of the upstream angle .sub.upstream with respect to the downstream angle .sub.downstream already allowed a strong reduction in the separations of the flow F18 during its introduction into the flow 14.

(34) According to a second embodiment, the angle .sub.i can be comprised between the upstream angle .sub.upstream and the downstream angle .sub.downstream. For example, the angle .sub.i of the fins can be progressively inclined between the downstream angle .sub.downstream and the upstream angle .sub.upstream, depending on the position of each supplementary fin 26 between the downstream wall 18b and the upstream wall 18a, which allows taking into account the progressive inclination of the gas flow F18 in the discharge stream duct between the downstream wall 18b and the upstream wall 18a.

(35) In the exemplary embodiment illustrated in FIGS. 2a and 2b, the duct 18 comprises three discharge fins 20: one upstream fin 22, one downstream fin 24 and a supplementary fin 26, located halfway between the upstream fin 22 and the downstream fin 24. The angle .sub.i is then preferably comprised between the downstream angle .sub.downstream and the upstream angle .sub.upstream. For example, for a downstream angle .sub.downstream of 44, and an upstream angle .sub.upstream of 34, the angle .sub.i can for example be comprised between 34 and 44, typically 41.

(36) Generally, for a duct 18 comprising n supplementary fins 26 and therefore n+2 discharge fins 20, the angle .sub.i of the in supplementary fin 26 (the numbering of the supplementary fins 26 being accomplished from upstream to downstream in the gas flow direction in the secondary flow space, and i being comprised between 1 and n) can be comprised between downstream the angle .sub.downstream and a minimum angle .sub.i.sub._.sub.min such that:

(37) ${}_{\mathrm{i\_min}}=i\frac{\left({}_{\mathrm{downstream}}-{}_{\mathrm{upstream}}\right)}{n+1}+{}_{\mathrm{upstream}}$
where: .sub.i.sub._.sub.min is the minimum acute angle of the supplementary fin 26 .sub.upstream is the upstream acute angle .sub.downstream is the downstream acute angle.

(38) Thus, for a duct 18 comprising four discharge fins 20 with an upstream angle of 20 a downstream angle of 50, an angle .sub.1min of 30 is obtained for the 1.sup.st supplementary fin 26 and an angle .sub.2min of 40 for the 2.sup.nd supplementary fin 26.

(39) Such an orientation also allows each supplementary fin 26 to be individually oriented depending on the local angle of incidence of the gas flow F18 in the discharge stream duct 18.

(40) The discharge fins 20 can be straight, that is have a lower surface wall I and an upper surface wall E that are substantially flat and parallel.

(41) As a variant, the discharge fins 20 can have a curved skeleton line C, so as to improve the deflection of the gas flow F18 coming from the primary flow space, to align it with the secondary flow F14.

(42) For example, for a given fin 22, 24, 26 of the VBV grating, the angle .sub.BFi between the tangent T to the skeleton line C at the trailing edge BF of the fin 22, 24, 26 and the discharge plane P can be equal to the average of the local flow angle .sub.i (at the fin under consideration) of the gas flow F18 in the discharge stream duct 18 with respect to the discharge plane P and the angle between the flow direction of the secondary stream and the discharge plane P, at the outlet opening 6.

(43) Thus, the angle .sub.BFi of a given fin 20 can be defined as follows:

(44) ${}_{\mathrm{BFi}}=\frac{{}_i+}{2}$

(45) One then obtains, for each fin 22, 24, 26, a specific curved skeleton line C.

(46) Alternatively, the discharge fins 20 of a given VBV grating can be identical, so as to simplify in particular the manufacture of the hub 2 and to reduce its manufacturing cost. To this end, no matter what the fin 22, 24, 26 of the VBV grating, an average angle , corresponding to the average of the local flow angles of the gas flow F18 in the discharge stream duct 18, is determined, this angle then being used to determine the angle .sub.BF for all the fins 20:

(47) ${}_{\mathrm{BF}}=\frac{+}{2}$

(48) It will be noted that the average angle , the local angle .sub.i and the angle of the direction of the secondary flow 14 are acute angles.

(49) The average angle can for example be determined by averaging the local angles .sub.i. It will be understood, of course, that the measurement of the angles .sub.i is carried out only when the discharge stream is delivering, that is when the turbine engine is in transient operation (mainly during takeoff and during landing) and that the door 12 is in the open position to collect a portion of the gas in the primary flow space 10. Yet, when the discharge stream is delivering, the flux of the gas flow F18 in the discharge stream duct 18 is substantially constant and reproducible: the determination of the local angles .sub.i is therefore reproducible to some degree, to within 2.

(50) As a first approximation, the average angle S can be approximated by the average of the local angles at the upstream fin 22 and at the downstream fin 24.

(51) One could in particular start with an aerodynamic profile of the NACA (acronym of National Advisory Committee on Aeronautics) type so as to dimension the discharge fins based on their angle .sub.BF1 or .sub.BF, a profile of the NACA54115 type for example.