Adaptive vertical lift engine (AVLE) fan

Abstract

A turbofan engine has a fan portion in fluid communication with a core stream and a bypass stream of air separated by splitters disposed both upstream and downstream of the fan portion. A blade splitter (shroud) on the fan partially spans the fan blade thus separating the core and bypass streams downstream while leaving a gap upstream for communication between the flows. The communication gap expands the operational range of the fan over fans without the communication gap.

Claims

1. A turbofan engine comprising: a first fan; a core duct defining a portion of a core fluid path; a bypass duct defining a portion of a bypass fluid path, the bypass duct concentric with the core duct and radially displaced from the core duct; a downstream splitter defining an annular border portion between the core duct and the bypass duct; and downstream of the first fan; an annular border region extending between a leading edge of the first fan and a leading edge of the downstream splitter; the annular border region separating the core fluid path and the bypass fluid path, wherein the first fan rotates through the annual border region; a shroud within the annular border region, extending between blades in the first fan, the shroud having a leading edge downstream from a leading edge of the blades and upstream of a midchord of the blades, wherein the shroud rotates with respect to the downstream splitter; a seal between a trailing edge of the shroud and the leading edge of the downstream splitter; the seal restricting migration from the core fluid path to the bypass fluid path; a variable inlet guide vane upstream of the first fan, the variable inlet guide restricting a bypass flow through the bypass fluid path at a first position and not restricting the bypass flow at a second position; and an additional splitter, a second fan, and a second seal, the second fan positioned upstream of the first fan, said second fan comprising a second shroud extending axially from a trailing edge of the second fan to at least to a local midchord of a blade of the second fan but short of a leading edge of the second fan, the second seal connecting a trailing edge of the second shroud with a leading edge of the additional splitter.

2. A turbofan engine comprising: a fan; a core duct defining a portion of a core fluid path; a bypass duct defining a portion of a bypass fluid path, the bypass duct concentric with the core duct and radially displaced from the core duct; a splitter defining an annular border portion between the core duct and the bypass duct; and downstream of the fan; an annular border region extending between a leading edge of the fan and a leading edge of the splitter; the annular border region separating the core fluid path and the bypass fluid path, wherein the fan rotates through the annual border region; a shroud within the annular border region, extending between blades in the fan, the shroud having a leading edge downstream from a leading edge of the blades and upstream of a midchord of the blades, wherein the shroud rotates with respect to the splitter; a seal between a trailing edge of the shroud and the leading edge of the splitter; the seal restricting migration from the core fluid path to the bypass fluid path, wherein the seal and the leading edge of the splitter do not overlap; and a variable inlet guide vane upstream of the fan, the variable inlet guide restricting a bypass flow at a first position and not restricting the bypass flow at a second position.

3. The turbofan engine of claim 2, wherein a pressure in the core fluid path is higher than a second pressure in the bypass fluid path when the variable inlet guide vane is at the first position.

4. The turbofan engine of claim 2, further comprising an upstream splitter defining an annular first border portion between the core duct and the bypass duct.

5. The turbofan engine of claim 2, wherein the seal is selected from the group consisting of labyrinth seal, lip seal and carbon seal.

6. The turbofan engine of claim 2, wherein the shroud extends axially forward from a trailing edge of the fan no more than ⅔ of a local chord on the fan.

7. The turbofan engine of claim 2, wherein the shroud extends axially forward from a trailing edge of the fan no more than ¾ to ½ of a local chord on the fan.

8. The turbofan engine of claim 2, wherein the fan has a blade span and the shroud is radially located on the middle third of the blade span.

9. The turbofan engine of claim 2, wherein the shroud is concentric with the fan.

10. The turbofan engine of claim 4, further comprising a communication gap between a trailing edge of the upstream splitter and the leading edge of the shroud, the communication gap having an axial component between the trailing edge of the upstream splitter and the leading edge of the blade that is greater than or equal to another axial component between the leading edge of the blade and the leading edge of the shroud.

11. The turbofan engine of claim 2, further comprising an upstream splitter on the variable inlet guide vane, the upstream splitter having a trailing edge axially displaced from the leading edge of the fan.

12. The turbofan engine of claim 2, wherein the shroud extends axially forward from a trailing edge of the fan no more than ⅞th of a local chord on the fan.

13. The turbofan engine of claim 2, wherein the shroud is concentric with the fan.

14. The turbofan engine of claim 11, further comprising a communication gap between a trailing edge of the upstream splitter and the leading edge of the partial midspan shroud, the communication gap having an axial component between the trailing edge of the upstream splitter and the leading edge of the fan that is at least equal to another axial component between the leading edge of the fan and the leading edge of the partial midspan shroud.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1a and 1b are illustrations representing conventional turbofan engines.

(2) FIG. 2 is an illustration of the Bypass and primary stream flow paths.

(3) FIG. 3 is an illustration of a turbofan engine according to an embodiment of the disclosed subject matter.

(4) FIG. 4 is an illustration of a turbofan engine without an upstream splitter according to an embodiment of the disclosed subject matter.

(5) FIG. 5 is an illustration of with multiple fan stages according to embodiments of the disclosed subject matter.

(6) FIG. 6 is an illustration of the blade splitter according to embodiments of the disclosure subject matter.

DETAILED DESCRIPTION

(7) FIG. 3 illustrates a Bypass flow duct 31 lying radially outward from the core flow duct 29. The fan 42 is positioned upstream from the splitter 25 that separates air flow between the ducts. The inlet guide vane splitter 24 is positioned upstream from the fan 42 at radially inward of the adjustable inlet guide vane 15. As the inlet guide vane 15 angle is changed, the bypass flow may be inhibited and pressure within the bypass flow duct 31 may differ from the pressure present in the core flow duct 29. In prior systems, air can cross between the two ducts in the vicinity of the fan blade in region 50 as shown in FIG. 1b thus causing detrimental engine performance in the core as described previously.

(8) FIG. 3 illustrates a blade splitter 26 within the fan 42 and a splitter 25 behind the fan 42. The splitter assembly 27 (blade splitter 26 and splitter 25) interface with each other with a rotating seal or discourager located just behind the fan 42. The blade splitter 26 extends axially at least past the midchord 43 of the fan 42. It is advantageous to have a long enough splitter to discourage flow migration but not long enough that the flow and pressure communication between core and bypass is affected which may adversely affect the operating range of the fan 42. In FIG. 3, the inlet guide vane 15 also employs an inlet guide vane splitter 24. Unlike the blade splitter 26 and splitter 25, the inlet guide vane splitter 24 positioned upstream from the fan blade 42 at the bottom of the inlet guide vane 15 remains axially displaced from the blade splitter 26 to preserve flow communication. FIG. 4 illustrates an embodiment without an upstream splitter.

(9) The leading edge of the blade splitter 26 as shown in FIG. 3 is located axially just forward of the midchord line 43, however, it is envisioned that an axial location between ¾ and ½ of the local cord from the trailing edge will obtain the desired balance between stream separation and flow communication. FIG. 3 illustrates the embodiment in which the leading edge of the blade splitter 26 is located at the ⅔ of the local chord from the fan's trailing edge. The trailing edge of the blade splitter 26 terminates proximate to the trailing edge of the fan 42 at the interface with the downstream splitter 25. As noted above the interface may be a seal or discourager 37. The seal or discourager 37 may be carbon seal, a labyrinth seal, lip seal or another conventional type seal. Favorable characteristics of the seal 37 include minimal interference with the bypass and core flows, minimum friction and minimum manufacturing and assembly cost. Moreover, the seal or discourager 37, need only restrict flow from the core to the bypass duct, a hundred percent seal is not required.

(10) FIG. 5 is an illustration of an additional splitter with multiple fan stages according to embodiments of the disclosed subject matter. The forward fan 42 and rear fan 41 may be nested with a midstream splitter 25a between them. In such case, the midstream splitter 25a downstream from the inlet guide vane splitter 24 by communication gap 55, would interface with the blade splitter 26a with a seal or discourager 37a and terminate prior to the second fan 41 as to preserve a second communication gap 54, a second blade splitter 26b, would likewise interface with the second splitter 25b. An additional guide vane 15b may also be between the forward fan 42 and rear fan 41, intersecting the midstream splitter 25a. The guide vane 15b while shown operating on both the bypass flow 30 and core flow 28, may also be limited to only one of the flows, likewise the guide vane 15b may fixed as shown or adjustable. Thus communication between the streams is maintained while separating the flows the allowing a wide operating range with reduced leakage.

(11) FIG. 6 is a detailed illustration of the blade splitter 26 on fan blade 42. The fan 42 has a leading edge 141, trailing edge midchord line 43 and a midspan chord 146. The blade splitter 26 includes a leading edge 126 and trailing edge 127. The trailing edge 127 interfaces with the leading edge 128 of the downstream splitter 25 via a seal or discourager 37. The downstream splitter 25 is fixed with respect to the engine casing (not shown). An upstream splitter 24 is axially forward of the fan 42. As shown in FIG. 6, the blade is generally divided radially into thirds, the first third 101 near the root, the middle third 103 and outer third 105. The blade splitter is preferably located in the middle third 103. The leading edge 126 of the blade splitter 26 preferably is forward of the midchord 43 and is proximate the midspan cord 146, the overlap of the blade splitter 26 on the blade being shown as S.sub.b and the length of the midspan chord shown as C.sub.local. The ratio of S.sub.b/C.sub.local being from ⅞ to ½, preferably from ¾ to ½, and specifically around ⅔rds.

(12) The communication gap 55 by which communications between the bypass flow and core flow is maintained is function of the axial distance from the upstream splitter 24 and the leading edge 126 of the blade splitter 26. The communication gap 55 includes an axial component (A.sub.S) between the trailing edge of the upstream splitter 24 and the leading edge 141 of the fan 42 (A.sub.S is typically minimized, but for the now recognized advantageous communication between flows) and an axial component (A.sub.B) between the leading edge 141 of the fan 42 and the leading edge 126 of the blade splitter 26. The communication gap (G) equaling A.sub.B+A.sub.S, (i.e. G is a function of A.sub.S and C.sub.local) where A.sub.S is preferably less than or equal to A.sub.B and non-zero when the overlap is ⅔ or lower. The communication gap 55 may also be less than or equal to the chord length C.sub.local and preferably less than or equal to the overlap S.sub.b. For example, where S.sub.B is ½ C.sub.local, the gap G may approach ½ C.sub.local with A.sub.S approaching zero, whereas when S.sub.B is ⅞ C.sub.local, the gap may be ½ C.sub.local, where A.sub.S is greater than A.sub.B. The communication gap ranging between ⅛ C.sub.local and C.sub.local, preferably between ⅛ C.sub.local and ½ C.sub.local. A balance exists between advantageously increasing S.sub.B to minimize leakage while maintaining an adequate communication gap G as to not detrimentally restrict the operating range.

(13) The blade splitter may, advantageously, also minimize vibration and dynamics. Typically, shrouds used for this purpose are at higher spans, but while the disclosed shroud is not primarily a vibration reduction feature, but given its structure it may be beneficial to address these issues as well as the aerodynamic and performance discussed herein.

(14) While preferred embodiments of the present invention have been described, it is to be understood that the embodiments described are illustrative only and that the scope of the invention is to be defined solely by the appended claims when accorded a full range of equivalence. Many variations and modifications naturally occurring to those of skill in the art from a perusal hereof.