System and method for creating a fluidic barrier from the leading edge of a fan blade

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 fluid passage is defined between the splitters. The turbofan engine has a plurality of vortex generators, each of the vortex generators positioned on the leading edge of a respective fan blade proximate the upstream splitter and the core stream restricting the migration of the core stream into the bypass stream through the fluid passage.

Claims

1. A turbofan engine having a fan portion in fluid communication with a core stream and a bypass stream of air; the core stream being: compressed by the fan portion and a core compressor portion, heated and expanded through a core turbine portion; the core turbine portion driving the fan portion and the compressor portion; the core turbine portion connected to a shaft; the bypass stream being compressed by the fan portion; the core stream and the bypass stream of air separated by an upstream splitter and a downstream splitter with the fan portion disposed axially between the upstream splitter and the downstream splitter, wherein a fluid passage between the core stream and the bypass stream is defined between the upstream splitter and the downstream splitter and a plurality of fan blades of the fan portion; each of the plurality of fan blades of the fan portion having a high pressure side and a low pressure side; and a plurality of vortex generators, each of the plurality of vortex generators positioned on a leading edge of a respective fan blade of the plurality of fan blades proximate the upstream splitter and the core stream; each of said plurality of vortex generators generating a plurality of vortices restricting migration of the core stream into the bypass stream through the fluid passage; wherein a radial slot is defined between an outer tip of one of the plurality of vortex generators and an inward surface of the upstream splitter, said radial slot being longer at an upstream end of said outer tip than proximate to a trailing edge of said upstream splitter.

2. The turbofan engine of claim 1, wherein one of the plurality of vortex generators comprises a low aspect vane extending from a leading edge of one of the plurality of fan blades.

3. The turbofan engine of claim 2, wherein the low aspect vane is triangular with a root and a vane leading edge, the root extending upstream of the trailing edge of the upstream splitter and the vane leading edge extending from an upstream portion of the root into the core stream and terminating on the leading edge of one of the plurality of fan blades.

4. The turbofan engine of claim 3, wherein a vertex of an intersection of the vane leading edge and the root is less than 30 degrees.

5. The turbofan engine of claim 1, wherein a pressure of the core stream is greater than a pressure of the bypass stream.

6. The turbofan engine of claim 1, further comprising a plurality of variable angle inlet guide vanes positioned proximate the upstream splitter inhibiting the bypass stream.

7. A method of preventing pressure leakage from a core stream in a high bypass turbojet engine, comprising: dividing an ambient air stream into a bypass stream and a core stream with an upstream splitter; compressing the bypass stream and the core stream with a fan, said fan between the upstream splitter and a downstream splitter dividing the bypass stream and the core stream downstream of the fan; wherein the core stream downstream of the fan has a higher pressure than the bypass stream downstream the fan; forming a plurality of vortices from a leading edge of a portion of the fan in the core stream, each of said plurality of vortices having an axis and directed into a flow of the core stream thereby preventing pressure leakage across the plurality of vortices into the bypass stream; and defining a radial slot between an outer tip of the leading edge and an inward surface of the upstream splitter, said radial slot being longer at an upstream end of said outer tip than proximate to a trailing edge of said upstream splitter.

8. The method of claim 7, further comprising restricting the bypass stream upstream of the fan.

9. The method of claim 8, wherein the step of restricting the bypass stream comprises rotating a plurality of inlet guide vanes in the bypass stream proximate the upstream splitter.

10. The method of claim 7, wherein the step of forming the plurality of vortices comprises forming a pressure differential across opposite sides of a low aspect vane positioned on the leading edge of a plurality of fan blades of the fan.

11. The method of claim 10, wherein the low aspect vane is triangular with a root and a vane leading edge, the root extending upstream of the trailing edge of the upstream splitter and the vane leading edge extending from an upstream portion of the root into the core stream and terminating on the leading edge of one of the plurality of fan blades.

12. A turbofan engine comprising: 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; an upstream splitter defining an annular first border portion between the core duct and the bypass duct; a downstream splitter defining an annular second border portion between the core duct and the bypass duct; a border region extending between a trailing edge of the upstream splitter and a leading edge of the downstream splitter; a plurality of fan blades rotating through the core duct, the bypass duct and the border region about an axis concentric with the core duct and the bypass duct, and each of the plurality of fan blades comprise a leading edge portion extending upstream of the trailing edge of the upstream splitter in the core fluid path, and a plurality of vortices originating from the leading edge portion and extending into the border region; wherein a radial slot is defined between an outer tip of the leading edge portion and an inward surface of the upstream splitter, said radial slot being longer at an upstream end of said outer tip than proximate to the trailing edge of said upstream splitter.

13. The turbofan engine of claim 12, further comprising a compressor, a combustor and a turbine along the core fluid path downstream of the downstream splitter.

14. The turbofan engine of claim 12, further comprising a plurality of inlet guide vanes in the bypass duct upstream of the plurality of fan blades, wherein the plurality of inlet guide vanes are selectively rotatable about a radial direction.

15. The turbofan engine of claim 12, wherein a pressure of the core duct is greater than a pressure of the bypass duct at the border region.

16. The turbofan engine of claim 12, further comprising a third border portion and said plurality of fan blades comprises a first fan and a second fan, said first fan positioned between the annular first border portion and the third border portion and the second fan positioned between the third border portion and the annular second border portion.

17. The turbofan engine of claim 12, further comprising a low aspect vane positioned on the leading edge portion of the plurality of fan blades, which generates the plurality of vortices.

18. The turbofan engine of claim 17, wherein the low aspect vane is triangular with a root and a vane leading edge, the root extending upstream of the trailing edge of the upstream splitter and the vane leading edge extending from an upstream portion of the root into the core fluid path and terminating on the leading edge portion of a respective one of the plurality of fan blades.

19. The turbofan engine of claim 12, wherein the radial slot is a passage for air from a high pressure side to a low pressure side of one of the plurality of fan blades.

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 with high pressure jets projecting from the low pressure side of Fan blades according to an embodiment of the disclosed subject matter.

(4) FIG. 4 is an illustration of a turbofan engine with high pressure jets projection from the trailing edge of an upstream splitter according to an embodiment of the disclosed subject matter.

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

(6) FIG. 6 illustrates a turbofan with vortices origination from the splitter through the fan region according to an embodiment of the disclosed subject matter.

(7) FIGS. 7a-7b shows the generation of vortices from ramps according to an embodiment of the disclosed subject matter

(8) FIGS. 8a-8d are different surface interruptions for the generation of vortices as described for embodiments of the disclosed subject matter.

(9) FIGS. 9a and 9b are illustrations of vortex generators on the leading edge of the fan according to embodiments of the present subject matter.

(10) FIG. 10 is a flow chart of a method of preventing pressure leakage.

DETAILED DESCRIPTION

(11) FIG. 3 illustrates a Bypass flow duct 31 lying radially outward from the core flow duct 29. The fan blade 42 is positioned upstream from the splitter 25 that separates air flow between the ducts. The upstream splitter 24 is positioned upstream from the fan blade 42 at the bottom of the Inlet guide vane 15. As the inlet guide vane angle is changed, the bypass flow can be inhibited and pressure within the bypass flow duct 31 can differ from the pressure present in the core flow duct 29. 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.

(12) A plurality of fluidic jets 60 that inject high pressure compressor air form the fan blade 42 into the region 50 between the upstream 24 and downstream splitter 25 form a fluid barrier 51. The high velocity jets 60 of compressed air contain enough momentum to inhibit flow leakage between the core 28 and the bypass streams 30. The jets 60 have inertia that the low pressure air flowing in the ducts cannot overcome, thereby acting as a fluid barrier 51 to limit cross flow and pressure leakage in the region 50 between the ducts.

(13) The fluid jets 60 may advantageously have a directional component in a substantial opposite direction of the local velocity or rotation of the fan proximate to the splitters and may also have a radial component towards the axis to prevent pressure leakage across the fluid jets into the bypass stream.

(14) A valve 66 in the system modulates the high pressure air such that flow can be turned on and off depending on the predicted or actual cross flow between ducts and the detrimental effects upon the engine.

(15) As noted previously, the control of air flow through the duct may be throttled to a point where it can be minimized to the point where it is almost non-existent through the use of a small and inexpensive actuator.

(16) The high pressure gas for the jets may be provided by the compressor 26 though passages 61 to the jets. An accumulator 63 may also be provided prior to the actuator/valve in order to provide an immediate source of pressure unstrained by downstream frictional losses in the passages 61. Alternatively, another source may be used to provide the high pressure air to the jets 60.

(17) The high pressure fluid jets 60 originate from orifices on the low pressure side of the blades 42 wherein the plurality of orifices are radially proximate the upstream and downstream splitters in the region 50. The plurality of orifices extend between the trailing edge of the upstream splitter 24 and the leading edge of the downstream splitter 25. The fluid jets may advantageously having radial component directed into the core flow 28 as well as an axial component pointing downstream in the core flow 28. It is envisioned that the compressed air drawn from the compressor 26 would represent 2-3% of the total compressor output and thus would not be a significant source of loss.

(18) FIG. 4 illustrates another embodiment of a turbofan engine 10. As shown the fan blade 42 is positioned upstream from a splitter 24 that separates air flow between the ducts. An upstream splitter 24 is positioned upstream from the fan blade 42 at the bottom of the inlet guide vane 15. As the inlet guide vane angle is changed, pressure within the bypass flow duct 31 can differ from the pressure present in the core flow duct 29. Air can cross between the two ducts in the vicinity of the fan blade 42 in region 50 thus causing detrimental engine performance.

(19) As shown in FIG. 4, fluid jets 60 that inject high pressure compressor air from the trailing edge of the upstream splitter 24 into the region 50 between the upstream 24 and downstream splitters 25. As described previously these jets 50 have enough momentum or inertia such that the low pressure air flowing in the ducts cannot overcome it and thus the jets 50 acts as a fluid barrier 51 to limit cross flow between the ducts. As also discussed previously, a valve/actuator 66 in the system may regulate the high pressure air such that flow can be turned on and off depending on the predicted or actual cross flow between ducts, and the corresponding detrimental effects on engine performance, an accumulator 63 may also be added. The high pressure jets 60 are preferably distributed proximate to the trailing edge of the upstream splitter 24. The high pressure jets may be also be position on either the core 28 or bypass side 30 of the upstream splitter 24 since the jets 60 have an energy independent of the flow within the ducts. The reliance on free stream flow is discussed below with respect to creation of vortices. The high pressure gas for the jets 60 is supplied by the compressor 26 via passages 61. The jets 60 and passages 61 are distributed circumferentially along the trailing edge.

(20) FIG. 6 illustrates a turbofan engine with concentric core and bypass flow paths and variable inlet guide vanes in the bypass duct. As shown, pressure differences between the core duct and the bypass duct can cause cross flow between the ducts in the area of the fan blade. In FIG. 6, the Bypass flow duct lies radially outward from the Core flow duct. A fan blade is positioned upstream from a downstream splitter that separates air flow between the ducts. An upstream splitter is positioned upstream from the fan blade at the bottom of the inlet guide vane.

(21) As the inlet guide vane angle is changed, pressure within the bypass flow duct can differ from the pressure present in the core flow duct. The working fluid in this example air can cross between the two ducts in the vicinity of the fan blade and cause detrimental engine performance as explained previously.

(22) FIGS. 7a-7b illustrate the upstream splitter 24 with a plurality of vortex generators 70. The vortex generator 70 results in counter rotating vortices 72 that are paired and circumferentially positioned around the exit plane (trailing edge) of the upstream splitter 24. The vortices 72 are generated or tripped by several mechanisms as described further below, these mechanisms involve interruptions in the surface which disrupt and trip the bypass flow 30 or core flow 28. In FIGS. 7a-7b, the vortex pairs are tripped using intermittent subtle ramps or wedges that initiate a vortex 72. It is a localized pressure differential in the flow which initiates the vortices 72. The vortices 72 have momentum that tends to maintain its flow position in the region 50 between the ducts that inhibits flow and pressure loss between the ducts. The vortex 72 has momentum that the relative low pressure air from flowing in the ducts cannot overcome thereby causing the series of adjacent vortices to act as a fluidic barrier 51 to limit cross flow between the ducts.

(23) While for ease of illustration, the surface interruptions are shown on the top side or outside surface of the upstream splitter 24. In FIGS. 7a-7b, the surface interruptions are preferably on the inner surface of the upstream splitter interrupting the core flow. This arrangement becomes more advantageous as the bypass flow/pressure is substantially decreased by the by the closing inlet vane guides 15 in the bypass flow path 30.

(24) FIGS. 8a-8d illustrate several examples of surface interruptions envisioned for creating the vortices. FIG. 8a shows a plurality of ridges 77 extending into the core stream 28. The ridges 77 are oblique to the flow in order to initiate the vortices 72. FIG. 8b shows a plurality of blades 73 also oriented oblique to the air flow. The blades 73 may also be rotated as to change their orientation. For example, where the pressure differential between the bypass 30 and core paths 28 proximate the fan in region 50 is small, the need for a fluid barrier 51 is diminished and thus the blades 73 may be oriented with the flow in a first position 74 and only orient oblique to the flow when the pressure differential becomes significant in a second position 75. FIG. 8c shows the plurality of flaps 76 extending into the core stream 28. Similarly as described with respect to the blades, the flaps 76 may be in a flush first position 74 when a fluid barrier 51 is not required and may be extended to a second position 75 to initiate the vortices 72 when desired. FIG. 8d shows a plurality of grooves 78 recessed into the upstream splitter 24 in order to trip the flow and generate the vortices 72 as the fluid barrier 51. The grooves 78 may extend to the end of the upstream splitter 24 or terminate proximate but before the trailing edge.

(25) As noted previously, the interruptions may be arranged to create complimentary pairs of vortices as shown in FIGS. 7a-7b, one rotating clockwise and the other rotating counter clockwise. Alternatively, the interruption may be arranged to create vortices that each rotate the same direction, or alternating between different directions as shown in FIGS. 7a-7b and FIG. 8a.

(26) FIG. 9a illustrates the generation of vortices 72 from the leading edge of the fan. As shown, a vane 82 extends from the leading edge 81 of the fan proximate the upstream splitter 24. In FIG. 9a or 9b, the vane 82 is shown in the core stream 28, however while less preferable, the vane 82 may be in the bypass flow 30 as well. The vane 82, in FIG. 9a acts as a low aspect ratio wing, and thus spills air from the high pressure side of the blade 42 to the low pressure side, thus generating vortices 72 that extend along the border region 50 between the bypass 30 and core stream 28. As shown in FIG. 9b, the vane 82 may be an extension of the fan blade 42 upstream, in which a significant gap 83 between the vane 82 and the upstream splitter 24 allows high pressure air to escape to the low pressure side which also results in the creation of vortices 72 as a fluid barrier 51. In addition the vane 82 may be stepped in order to produce a series of vortices on each blade and creating a radial gradient of vortices.

(27) An embodiment of the vane may be triangular with a root and vane leading edge. The root extending upstream of a trailing edge of the upstream splitter and the vane leading edge extending from an upstream portion of the root into the core stream and terminating on the leading edge of one of the plurality of fan blades. The vane 82 may also be of many other known wing shapes that facilitate spillage to create vortices.

(28) Alternatively other surface disruptions may be utilized on the leading edge 81 of the fan 42 to create the vortices which act as fluid barriers between the core and bypass streams. For example, groves or protrusions similar to those described in FIGS. 8a-8d can be added to the fan blades to generate the vortices.

(29) FIG. 5 is an illustration of a third splitter with multiple fan stages according to embodiments of the disclosed subject matter. The fans 42 may be nested with a midstream or third splitter 19 between them. In such case, the third splitter 19 would advantageously also be provided with similar surface interruptions or jets to provide a fluid barrier 51 between the third splitter 19 and downstream splitter 25.

(30) FIG. 10 shows a flow chart of a method of reducing the work performed on the bypass stream 30, while preventing a pressure drop in the core stream 28. The ambient air stream is divided into a bypass stream and a core stream as shown in block 101. It is not uncommon for the ambient air stream to be divided into multiple bypass or core streams, and the method is equally applicable in those instances, and thus is not so limited to the examples shown. In block 103, the flow in the bypass stream in restricted. Typically this will be through the use of inlet guide vanes 15 as shown in FIG. 1B and described above. The flow may also be restricted by completely or partially closing off the bypass duct or ducts. The step of restricting the bypass flow may be accomplished prior to, contemporaneously or subsequent to the step of dividing the streams.

(31) A fluid barrier 51 is then created between the upstream and downstream splitters proximate the fan to prevent leakage and pressure loss from the core duct to the lower pressure bypass duct as shown in block 105. As discussed above, the fluid barrier 51 may be established through jets 60 on the low pressure side of the blade as shown in FIG. 3, jets 60 originating from the upstream splitter 25 as shown in FIG. 4. The fluid barrier 51 may also be established through the use of vortices, from the splitter 24 as shown in FIGS. 7a-8d, or vortices created from vane 82 or gap 83 by the fan 42 as shown in FIGS. 9a-9b. The core stream is compressed by the fan, without the leakage into the bypass duct as shown in block 107, and work on the bypass field by the fan is thus reduced by minimizing pressure leakage and restricting the amount of mass flow in the bypass stream.

(32) While preferred embodiments of the present disclosure have been described, it is to be understood that the embodiments described are illustrative only and that the scope of the disclosure 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.