AIRCRAFT TURBOMACHINE EQUIPPED WITH AN OPTIMIZED DEGASING TUBE
The degassing tube with an upstream cantilevered oil collection section addresses inefficiencies in oil recovery and pressure losses by optimizing vortex control, enhancing oil collection efficiency and reducing turbomachine oil consumption.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2020-09-14
- Publication Date
- 2026-03-20
AI Technical Summary
Existing degassing tubes in turbomachines face challenges in optimizing oil recovery and minimizing pressure losses, particularly in free vortex systems where obstacles are minimized to avoid slowing down airflow, leading to inefficiencies in oil collection and increased oil consumption.
The degassing tube is designed with an upstream cantilevered oil collection section that extends beyond the low-pressure shaft, allowing for improved control over the vortex shape and expansion, enhancing oil recovery rates while minimizing pressure losses.
This design significantly increases the oil recovery rate by ensuring oil collection in areas where the vortex maintains optimal conditions for oil separation, thus reducing turbomachine oil consumption and pressure losses.
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Abstract
Description
Title of the invention: AIRCRAFT TURBOMACHINE EQUIPPED WITH AN OPTIMIZED DEGASING TUBE Technical field of the invention
[0001] The present invention relates to an aircraft turbomachine equipped with a degassing tube. Technical background
[0002] A turbomachine, such as a turbofan engine, classically comprises an air inlet with a fan whose outlet airflow splits into an airflow which enters the engine and forms a hot flow or primary flow, and an airflow which flows around the engine and forms a cold flow or secondary flow.
[0003] The engine typically comprises, from upstream to downstream in the direction of gas flow, at least one compressor, one combustion chamber, at least one turbine, and an ejection nozzle in which the combustion gases exiting the turbine and forming the primary flow are mixed with the secondary flow.
[0004] At its downstream end, the turbomachine includes an ejection cone for the primary flow or even the primary-secondary flow mixture. This cone has an elongated shape, the upstream end of which has a larger diameter being fixed to an element of the turbomachine, such as a casing.
[0005] An oil separator is used in engines to recover oil and thus limit oil losses. This oil saving allows for the smallest possible onboard oil reservoir, resulting in weight reductions. However, the oil separator is rotationally fixed to a shaft of the turbomachine and is highly dependent on the rotational speed of this shaft and the radius at which the oil separator is installed. There are two types of oil separators: the free vortex and the forced vortex.
[0006] A free vortex is defined as one where there are relatively few obstacles in the path of the air through the oil separator, and a forced vortex as one where there are several obstacles. The free vortex takes up more space and requires only a cavity. The forced vortex takes up less space but requires obstacles such as radial pipes, a grid, etc.
[0007] Conventionally, a degassing tube runs longitudinally through the turbomachine to the ejection cone. The function of this tube is to channel the air, which has been freed of oil by the turbomachine's oil separators, to the ejection cone located downstream.
[0008] Documents FR-A1-2 957 973, FR-A1-2 957 974, FR-A1-2 993 311 and FRAI-3 075 866 describe turbomachine degassing tubes.
[0009] A degassing tube has an elongated shape and extends inside a tubular shaft low pressure of the turbomachine.
[0010] The degassing tube is designed to receive oil-free air from the turbomachine's lubrication chambers. This ventilates the lubrication chambers and connects them to the atmosphere, allowing for the extraction of the oil-free air.
[0011] There is a need to ensure optimal filtration of the oil-laden air to guarantee that a maximum amount of oil is separated from the air intended to flow into the degassing tube. The separated oil is intended to be collected and returned to the lubrication oil circuit.
[0012] In the context of free vortex oil removal and prior to the present invention, it was considered more favorable to limit as much as possible the obstacles upstream of the tube and the low pressure shaft, in order not to risk slowing down the rotating air at the outlet of the oil removal tubes and inside the blower shaft.
[0013] Therefore, in the current technique of a turbomachine in which the blower shaft is directly coupled to the low-pressure shaft (i.e., a turbomachine without a reduction gear), the upstream end of the degassing tube is aligned with the upstream end of the low-pressure shaft, in the same plane perpendicular to the axis of the turbomachine.
[0014] Furthermore, the addition of foam or filter cartridge at the inlet of the degassing tube, although recommended, can have negative effects on the ventilation circuit by increasing the overall pressure losses of the tube.
[0015] The present invention provides an improvement to the current technology of degassing tubes, and makes it possible to address at least one of the above problems. Summary of the invention
[0016] The invention proposes an aircraft turbomachine, comprising:
[0017] - a low-pressure body comprising a low-pressure tubular shaft extending the long and around a longitudinal axis of the turbomachine,
[0018] - a blower located at an upstream end of the turbomachine and comprising a tubular blower shaft centered on the axis and having one downstream end directly coupled to one upstream end of the low-pressure shaft, the blower shaft carrying at least one annular row of oil separator tubes extending around the axis, each of these tubes having a radial orientation with respect to this axis, and
[0019] - a degassing tube centered on the axis and extending along and inside the shaft low pressure,
[0020] characterized in that the degassing tube comprises an upstream cantilevered oil collection section, which extends axially upstream beyond the upstream end of the low-pressure shaft and which is surrounded by said blower shaft.
[0021] Unlike the prior art, the degassing tube extends upstream beyond the low-pressure shaft. As will be described below, this avoids significantly altering pressure losses while potentially allowing for a substantial improvement in oil removal. The section allows control over the shape and expansion of the vortex upstream of the pressure-stirring shaft, and increases the oil recovery rate through the free vortex effect. This solution thus reduces the turbomachine's oil consumption by decreasing the amount of oil escaping through the degassing tube.
[0022] The turbomachine according to the invention may comprise one or more of the following features, taken individually or in combination with each other:
[0023] • the upstream section is cylindrical; • the upstream section is truncated conical and flared upstream; • the degassing tube includes, in its upstream section or just downstream of this upstream section, an annular row of oil drainage holes; • the degassing tube includes, at the level of its upstream section or just downstream of this upstream section, an annular rim which extends radially outwards and whose external periphery is crenellated, this rim being configured to cooperate by dog clutching with a crenellated annular rim of the upstream end of the low pressure shaft; • the drainage holes are located in a plane perpendicular to the axis, which is located downstream of a plane passing through said rim and upstream of a plane passing through an annular sealing joint mounted between the degassing tube and the upstream end of the low pressure shaft; • the blower shaft includes an annular flange extending radially inwards and held axially tight against an annular shoulder of the low pressure shaft by a nut which is screwed onto the upstream end of the low pressure shaft; • the nut includes at its upstream end a serrated annular rim, the turbomachine further comprising an annular locking ring which is configured to cooperate by dog clutching both with the rim of the nut and the rim of the upstream end of the low pressure shaft, and to bear axially on the rim of the degassing tube; • the turbomachine further includes a split locking ring which is engaged in an annular groove in the rim of the upstream end of the low pressure shaft and which bears axially on said ring; • said section has an axial length representing between 20 and 50% of an axial distance measured between the upstream end of the low-pressure shaft and said oil drain holes; • said section has a maximum external diameter which is less than or equal to the minimum internal diameter of the low pressure shaft. Brief description of the figures
[0024] The invention will be better understood and other details, features and advantages of the invention will become apparent from the following description, given by way of non-limiting example and with reference to the accompanying drawings in which:
[0025] [Fig-1] [Fig.1] is a schematic axial cross-sectional view of a turbomachine aircraft, according to prior art,
[0026] [Fig.2] [Fig.2] is a larger-scale schematic view of part of [Fig.1],
[0027] [Fig.3] [Fig.3] is a partial schematic axial cross-sectional view of an aircraft turbomachine, according to the prior art,
[0028] [Fig.4] [Fig.4] is a very schematic view of the environment illustrated in [Fig.3], and further illustrates the prior technique,
[0029] [Fig.5] [Fig.5] is a very schematic view of the environment illustrated in [Fig.3], and illustrates a first embodiment of the invention,
[0030] [Fig.6] [Fig.6] is a very schematic view of the environment illustrated in [Fig.3], and illustrates a second embodiment of the invention,
[0031] [Fig.7] [Fig.7] is a partial schematic axial cross-sectional view of an aircraft turbomachine according to the second embodiment. Detailed description of the invention
[0032] Referring to [Fig.1], we see a turbomachine 1, which conventionally comprises a blower S, a low pressure compressor la, a high pressure compressor 1b, a combustion chamber le, a high pressure turbine Id and a low pressure turbine le.
[0033] The rotors of the high-pressure compressor 1b and the high-pressure turbine Id are connected by a high-pressure shaft 5 and together form a high-pressure (HP) body.
[0034] The rotors of the low pressure compressor and the low pressure turbine are connected by a low pressure shaft 4 and together form a low pressure body (LP).
[0035] The blower is, for its part, carried by a blower shaft 3 whose downstream end is coupled directly to the upstream end of the BP shaft 4.
[0036] The HP and BP shafts extend along an axis A which is the axis of rotation of the turbomachine 1. In the following description, the notions of longitudinal or radial, and of inside or outside, are relative to this axis A.
[0037] The turbomachine 1 comprises structural housings. The HP body is held by two structural housings: the inter-compressor housing and the inter-turbine housing, and the body BP is held by at least two structural housings: the intermediate housing 2 and the inter-turbine housing and / or the exhaust housing 6.
[0038] The intermediate housing 2 supports bearings of the turbine shaft BP 4 which are housed in a front or upstream enclosure denoted El. The exhaust housing 6 supports bearings of the turbine shaft BP 4 which are housed in a rear or downstream enclosure denoted E2.
[0039] The enclosures are generally partly delimited by bearing supports.
[0040] The enclosure El comprises fixed and movable walls. The fixed walls of the enclosure El include an inner wall of the primary flow channel, an upstream bearing support 11, and a downstream bearing support 12. The supports 11 and 12 extend into the turbomachine and carry the bearings 14 and 10, respectively. They provide the structure between the housings and the fixed outer rings of the bearings. The movable walls of the enclosure El include the shafts 3 and 4. The bearings 10 and 14 are housed within the enclosure EL. Seals 17a and 17b are provided between the fixed and movable walls and are, for example, labyrinth seals, brush seals, segmented radial seals, etc.
[0041] The bearings 10, 14 are lubricated for their proper operation. The oil is supplied by appropriate means (arrows 16) such as nozzles, oil supply lines, etc. The bearings 10, 14 are located at the axial ends of the enclosure El and are mounted around the shafts 3, 4 respectively. The enclosure El is configured so that the air-oil mixture, which forms an oil mist inside the enclosure, is contained within it. Between the rotor and stator walls of the enclosure, for example here at the upstream and downstream ends of the enclosure, seals 17a, 17b are placed to contain the oil, and an air circuit pressurizes these seals to prevent oil leaks (arrows 17). The El enclosure is then pressurized (air enters continuously, pushing back the oil that could have escaped from the seals by capillary action) and the bearings operate in a mixed oil and air environment.The bearings are supplied with oil via a 16mm oil supply line, and oil is recovered via a dedicated recovery line. To prevent overpressure within the housing and ensure a constant flow of incoming air, the interior of the housing is vented to the air at a pressure lower than the pressure of the air entering the seals. This air, laden with oil particles, which is expelled through this pressure relief valve, must first be treated to recover almost all of the oil it carries. To achieve this, the oil-laden air is fed into an oil separator, which separates the air from the oil it carries and expels the oil-free air outside the engine. This is the principle of oil separation in a housing.
[0042] The venting of the enclosure is carried out by a degassing tube 20 which passes axially through the turbine shaft BP 4, from the upstream enclosure El to the ejection cone 6b of the turbomachine.
[0043] The oil separator generally comprises an annular row of oil separator tubes 21 which pass radially through the blower shaft 3 and allow the passage of oiled air radially from the outside to the inside, from the enclosure El to a cavity R arranged upstream of the degassing tube 20 (arrow 18).
[0044] Under free vortex effect, the rotational speed of the oiled air increases rapidly as it approaches the drive shaft A, and the oil is centrifuged onto the internal walls of the blower shaft 3. This oiled air is expelled through the degassing tube (arrow 70), where the remaining oil is further centrifuged and deposited on the internal surface before returning to the chamber El (arrows 71 and 19). Meanwhile, air flows axially from downstream to upstream, passing around the tube 20 and inside the shaft 4 (arrow 33). This air combines with the air from arrows 17 to pressurize the seals and prevent oil leaks.
[0045] Fig. 3 is a more concrete example of the coupling area between the shafts 3, 4 and the implantation of the oil removal tubes 21.
[0046] The downstream end 3a of the blower shaft 3 includes internal splines 3b complementary to external splines 4b of the upstream end 4a of the BP shaft 4. The end 3a is engaged on the end 4a by axial translation from upstream to downstream.
[0047] The end 3a of the blower shaft 3 includes an annular rim 3c which extends radially inwards and which is held axially tight against an annular shoulder 4c of the BP shaft 4 by a nut 30 which is screwed onto the upstream end of the BP shaft 4.
[0048] As can be seen in the drawing, the rim 3c and the shoulder 4c are axially interposed between the nut 30, located upstream, and the grooves 3b, 4b, located downstream.
[0049] The degassing tube 20 extends along and inside the shaft BP 4 and its upstream end 20a is located in a plane P perpendicular to the axis, which passes through the upstream end 4a of the shaft BP 4 as well as through the upstream end of the nut 30 in the example shown.
[0050] The operating principle of the free vortex degassing tube 20 is as follows. The chamber El is vented to the atmosphere via the tube 20; in doing so, a flow of oil-laden air from the chamber El passes through the BP shaft 4, through the oil-cleaning tubes 21, and is finally ejected downstream of the engine by means of the tube 20. The tubes 21 ensure that the air is correctly driven into rotation by the shaft 4.
[0051] To quantify this rotation, it is known to use the coefficient Ke, which is the ratio between the tangential velocity of the air and the tangential velocity of the reference frame of the shaft BP 4 at that same point. Thus, at the outlet of the tubes 21, the air is carried along at the same velocity as the shaft 4, and therefore Ke equals 1.
[0052] As air is drawn in through tube 20, its radius decreases. As a corollary, since the flow is assumed to be a free vortex, the air, which retains its angular momentum, rotates faster and faster and thus sees its coefficient Ke increase.
[0053] The rotational speed of the air near the motor axis A is therefore much higher than that of the motor. In doing so, the oil droplets carried by the air are centrifuged (as illustrated in [Fig. 3]) and are redirected into the enclosure El by means of secondary conduits 32 arranged in or around the tubes 21. In this way, the air entering the degassing tube 20 is de-oiled.
[0054] The main problem with the solution illustrated in Figures 2 and 3 is the presence of a plane P' where the oil can no longer be recovered. Indeed, as can be seen in [Fig. 3], once the oiled air has passed beyond plane P', it is no longer recoverable. Even if the oil droplets are centrifuged, they are projected onto the tube 20 and then pushed downstream by the airflow.
[0055] Furthermore, Navier-Stokes simulations have shown that the drag coefficient Ke is maximal a little downstream of tube 20 (Ke = 17), while recovery is at best achieved with a Ke equal to 11.
[0056] In the context of free vortex oil removal and prior to the present invention, it was considered more favorable to limit as much as possible the obstacles upstream of the tube 20 and the shaft BP 4, in order not to risk slowing down the rotating air at the outlet of the oil removal tubes 21 and inside the blower shaft 3.
[0057] The present invention proposes a solution to this problem by means of a degassing tube 20 which includes an upstream section 34 in cantilever for oil collection.
[0058] This section 34 extends axially upstream beyond the upstream end 4a of the BP 4 shaft and is surrounded by the blower shaft 3 (figures 5 and 6).
[0059] In the embodiment of [Fig.5], the section 34 has a general cylindrical shape. It is centered on the axis A and therefore extends upstream to the vicinity of a plane P” passing through the oil removal tubes 21 in the example shown.
[0060] At its downstream end, the section 34 may include an annular row of oil drainage or evacuation holes 36. These holes 36 are preferably regularly distributed around the drive axis A and are preferably oriented radially with respect to this axis A. They allow the oil projected by centrifugal force onto the inner surface of the tube to be evacuated radially outwards from the tube 20 and the section 34 and towards the aforementioned conduits 32.
[0061] In the embodiment of [Fig.6], the section 34 has a general frustoconical shape flared upstream. It is centered on the axis A and also extends upstream to the vicinity of a plane P” passing through the oil removal tubes 21 in the example shown.
[0062] This section 34' does not include holes 36 and the oil is drained here up to the free end of section 34', due to centrifugal forces and the truncated conical shape of this section.
[0063] Fig. 7 illustrates another more concrete embodiment in which the section 34” has a general truncated conical shape flared upstream and further includes an annular row of drainage holes 36 at its downstream end.
[0064] The degassing tube 20 includes, at the level of its upstream section 34' ' or just downstream of this upstream section, an annular rim 38 which extends radially outwards and whose external periphery is crenellated.
[0065] This rim 38 is configured to cooperate by dog clutching with a serrated annular rim 40 of the upstream end 4a of the BP 4 shaft.
[0066] The nut 30 includes at its upstream end a serrated annular rim 42. An annular locking ring 44 is configured to cooperate by dog engagement with both the rim 42 of the nut 30 and the rim 40 of the upstream end 4a of the shaft BP 4, and to bear axially on the rim 38 of the degassing tube 20.
[0067] A split locking ring 46 is engaged in an annular groove 48 of the rim 40 of the upstream end 4a of the shaft BP 4 and bears axially on the ring 44 to retain it axially upstream.
[0068] The section 34'' further includes a radially external annular rim 50 which cooperates by axial support with an internal cylindrical surface of the end 4a of the shaft BP4 to ensure the centering of the tube 20 and the section in the shaft BP4.
[0069] This rim 50 includes a peripheral groove open radially outwards and in which is housed an annular sealing gasket 52.
[0070] As can be seen in the drawing, the drainage holes 36 are located in a plane PI perpendicular to the axis A, which is located downstream of a plane P2 passing through the rim 38 and upstream of a plane P3 passing through the joint.
[0071] In the example shown, the 34” section has an axial length L1 representing between 20 and 50% of an axial distance RI measured between the upstream end 4a of the shaft BP 4 and the oil drain holes 21.
[0072] By way of example, the 34” section has a maximum external diameter Dmax which is less than or equal to the minimum internal diameter Dmin of the BP 4 shaft.
[0073] As mentioned above, during operation, oiled air passes radially from the outside to the inside through the oil removal holes 21, and therefore from the enclosure El to the cavity R arranged upstream of the degassing tube 20 (arrow 18).
[0074] Under free vortex effect, the rotation speed of the oiled air increases rapidly as it approaches the motor axis A and the oil is centrifuged on the internal walls of the blower shaft 3 to return to the enclosure El (arrows 19).
[0075] This oily air is then expelled through the degassing tube (arrow 70) where the remaining oil is further centrifuged and deposited on the internal surface of section 34”. The oil 71a that settles upstream of the drainage holes 36 is discharged to the upstream free end of the section 34”, and the oil 71b that settles downstream of the holes 36 is discharged through these holes. This oil 71b then flows through the teeth of the rims 42, 40 and, together with the oil 71a, flows over the inner surface of the shaft 3 to the conduits 21.
[0076] The proposed solution increases the oil recovery rate in a degassing tube 20 by better controlling the vortex shape. The upstream section of the degassing tube 20 allows for both better control of the vortex expansion and ensures that the maximum Ke is reached in an area where oil can still be recovered, thus optimizing the amount of oil recovered.
Claims
Demands
1. Aircraft turbomachine (1), comprising: - a low-pressure body having a low-pressure tubular shaft (4) extending along and around a longitudinal axis (A) of the turbomachine, - a fan (S) located at an upstream end of the turbomachine and having a fan tubular shaft (3) centered on the axis (A) and a downstream end (3a) of which is directly coupled to an upstream end (4a) of the low-pressure shaft (4), the fan shaft carrying at least one annular row of oil separator tubes (21) extending around the axis, each of these tubes having a radial orientation with respect to this axis, and - a vent tube (20) centered on the axis and extending along and inside the low-pressure shaft (4), characterized in that the vent tube (20) comprises an upstream section (34, 34', 34”) cantilevered oil collection system,which extends axially upstream beyond the upstream end (4a) of the low-pressure shaft (4) and which is surrounded by said blower shaft (3).
2. Turbomachine (1) according to claim 1, wherein the upstream section (34) is cylindrical.
3. Turbomachine (1) according to claim 1, wherein the upstream section (34', 34") is frustoconical and flared upstream.
4. Turbomachine (1) according to any one of the preceding claims, wherein the degassing tube (20) comprises, in its upstream section (34, 34”) or just downstream of this upstream section, an annular row of oil drainage holes (36).
5. Turbomachine (1) according to any one of the preceding claims, wherein the degassing tube (20) comprises, at its upstream section or just downstream of this upstream section, an annular rim (38) which extends radially outwards and whose outer periphery is crenellated, this rim being configured to cooperate by dog clutching with a crenellated annular rim (40) of the upstream end (4a) of the low-pressure shaft (4).
6. Turbomachine (1) according to all claims 4 and 5, wherein the drain holes (36) are located in a plane (PI) perpendicular to the axis (A), which is located downstream of a plane (P2) passing through said rim (38) and upstream of a plane (P3) passing through an annular sealing joint (52) mounted between the degassing tube (20) and the upstream end (4a) of the low pressure shaft (4).
7. Turbomachine (1) according to any one of the preceding claims, wherein the blower shaft (3) comprises an annular rim (3c) extending radially inwards and held axially tight against an annular shoulder (4c) of the low-pressure shaft (4) by a nut (30) which is screwed onto the upstream end (4a) of the low-pressure shaft (4).
8. Turbomachine (1) according to claim 7, depending on claim 5 or 6, wherein the nut (30) comprises at its upstream end a serrated annular rim (42), the turbomachine further comprising an annular locking ring (44) which is configured to cooperate by dog-engagement both with the rim (42) of the nut (30) and the rim (40) of the upstream end (4a) of the low-pressure shaft (4), and to bear axially on the rim (38) of the vent tube (20).
9. Turbomachine (1) according to claim 8, wherein it further comprises a slotted locking ring (46) which is engaged in an annular groove (48) of the rim (40) of the upstream end (4a) of the low pressure shaft (4) and which bears axially on said ring (44).
10. Turbomachine (1) according to any one of the preceding claims, wherein said section (34, 34', 34") has an axial length (Ll) representing between 20 and 50% of an axial distance (RI) measured between the upstream end (4a) of the low pressure shaft (4) and said oil-cleaning holes (21).
11. Turbomachine (1) according to any one of the preceding claims, wherein said section (34, 34', 34") has a maximum external diameter (Dmax) which is less than or equal to the minimum internal diameter (Dmin) of the low pressure shaft (4).