EP2959107A1

EP2959107A1 - Wheel of a turbine, compressor or pump

Info

Publication number: EP2959107A1
Application number: EP14713161.9A
Authority: EP
Inventors: Thierry Lefevre
Original assignee: Thy Engineering
Current assignee: Thy Engineering
Priority date: 2013-02-21
Filing date: 2014-02-20
Publication date: 2015-12-30
Also published as: WO2014128407A1; CN105121786A; FR3002271A1; US20150377026A1; JP2016511358A

Abstract

The invention relates to a wheel (2, 2') of a rotating machine for a fluid, comprising blades (22) that project on the front surface thereof (210). On one portion of the front surface (210) which is at least 70% of the diametrical range that defines the blade installation area (22), the front surface (210) is tangential to a cone, the tip of which is pointed forward and the vertex angle of which is between 154° and 170°. The invention also relates to a rotating machine and a turbocompressor comprising such a wheel.

Description

TURBINE, COMPRESSOR OR PUMP WHEEL

DESCRIPTION

Technical area

The present invention relates to a rotating machine wheel for a gaseous or liquid fluid, such as a centrifugal compressor, centrifugal pump or centripetal turbine wheel. It also relates to a compressor, a centrifugal pump or a centripetal turbine provided with such a wheel, and a turbocharger at least one of the wheels is of this type.

State of the art

Rotating machines such as centripetal type turbines or centrifugal type compressors are widely used in industry, particularly in the field of thermal engines. In one application, a turbine coupled on the same shaft to a compressor is used to form a turbocharger. The turbine is powered by the exhaust gas from an engine and drives the compressor that compresses fresh air for engine boosting. Some compressors are driven by an electric motor and some turbines are used as generators of electrical energy.

Figures 5 and 6 show a centrifugal compressor 1 1 according to the prior art. The compressor 1 1 comprises a compressor body January 1 and a rotating part rotatably mounted on the compressor body January 1. The rotating part comprises a compressor wheel January 12 mounted on a shaft 1 14 rotating on a bearing January 13 of the compressor body 1 January. The compressor wheel 1 12 comprises a hub 1 120 and a set of blades 1 121 fixed to the hub. The compressor body 1 1 1 has an axial opening placed opposite the hub 1 120 and which constitutes a inlet duct 1 1 10. The compressor body 1 1 1 further comprises a volute 1 1 12 around the compressor wheel 1 12. The volute 1 1 12 has a peripheral opening 1 1 1 1 placed on the periphery of the compressor wheel 1 12 and opens through an outlet conduit 1 1 13 which extends substantially in a direction tangential to the compressor wheel 1 12. A gaseous fluid flows from the axial opening 1 1 10 to the peripheral opening 1 1 1 1 being driven by the compressor wheel 1 12. The geometry of the blades 1 121 is designed so that the compressor wheel January 12 provides mechanical energy to the gases, this mainly by accelerating, the kinetic energy and obtained then being converted into pressure form, mainly in volute 1 1 12.

A centripetal turbine has a structure quite similar to that of a centrifugal compressor described above, but the flow direction of the gas is reversed and the work is supplied to the machine by the fluid. In the case of a gaseous turbine, the geometry of the blades is studied so that the gases relax by crossing the wheel of the turbine and return energy to it.

The configurations conventionally known for working with a gaseous fluid operate at very high speeds of rotation, of the order of 200,000 revolutions per minute. The technology used to make it possible to achieve such speeds is very specific, particularly at the bearings which can only be hydrostatic and therefore require to be supplied with pressurized lubricant by a pump. Moreover, such speeds can not be reached commonly when the wheel of a compressor is driven by an electric motor.

However, the automobile industry has seen a strong trend towards a decrease in engine capacity, with the overall aim of reducing fuel consumption levels, which has led to the need to develop, particularly for over-fueling, rotating machines that are effective at low engine speed and therefore for low gas flow rates.

A significant increase in pressure is obtained by rotating centrifugal machines when the fluid is liquid. These machines are called pumps which are generally distinguished by large diameter wheels with flat flanges on which the blades are implanted. Such machines are limited in rotation speed because of the diameter of the wheels, involving high centrifugal forces.

The invention therefore aims to provide a rotating machine wheel that achieves high efficiency for a low fluid flow.

Description of the invention

With these objectives in view, the subject of the invention is a rotating machine wheel for a fluid, the wheel having a wheel axle and having a hub arranged to mount the rotary wheel around the wheel axle, a flange fixed on the hub and extending substantially in a radial plane relative to the wheel axis, the flange having a front face, blades projecting from the front face, each of the blades extending at most between a central circle and a peripheral circle located on the front face, at least one blade extending to the central circle and at least one blade extending to the peripheral circle, characterized in that an inner circle and an outer circle on the face front between the central circle and the peripheral circle have a difference in diameters of at least 70% of the difference in diameters between the central circle and the peripheral circle, the inner and outer circles belonging to a first cone of revolution the tip of which is oriented towards the front and whose angle at the apex is between 154 ° and 170 °, and in that a second cone having for its axis of revolution the wheel axle and the tip of which is oriented forward, tangent to the front face in any circle between the inner and outer circles, has an apex angle less than or equal to 170 °. When a rotating machine is called to operate at low fluid flow, a set of constraints encourages to constitute a fluid flow extending substantially in a radial plane and having a relatively low axial component. For a compressor or centrifugal pump, the work done on the fluid is proportional to the product of the speed of rotation and the difference of the input and output radius of the blade. It is therefore necessary to use wheels allowing the radial circulation of the fluid over a great length. This is the case, more generally, for all rotating machines that must have good performance at low speed.

Thus, for a compressor, it will be that the trailing edges of the blades are placed at a large diameter while the leading edges should be located as close as possible to the axis of rotation of the wheel. But the enlargement of the outlet diameter of the blading tends to enlarge the exit area because the height of the blades can be reduced to a limited extent, except to induce significant losses, because the clearance between the blades and the compressor body would stop being much less than the height of the blades.

On the other hand, because of the retention of the flow rate through each cylindrical section of the vein, an elevation of the outlet section in turn implies an enlargement of the inlet section of the fluid in the vane. Now it is observed that, for the compressor wheels representing the vast majority of the wheels designed according to the prior art, this constraint proves to be antagonistic with that, previously cited, which pushes to place the leading edges as close as possible of the axis of rotation of the wheel: in fact, on these wheels, the leading edges extend substantially in a radial direction, the flow of air at the inlet of the blade having a zero radial component or very weak.

On the other hand, it is observed that the antagonism designated here disappears if the leading edges extend in a direction close to that of the wheel axle: it is thus possible to have leading edges located close to the axis. wheel but long enough to provide a sufficient entrance section. In this case, the air flow extends substantially in a radial plane as soon as it enters the blading and, consequently, throughout the vein. We call here "radial" a rotating machine wheel whose geometry thus constitutes a fluid flow extending substantially in a radial plane and having a relatively low axial component.

The same reasoning applies to the case of a centrifugal pump.

In the case of a centripetal turbine, it may also be beneficial to use a radial type wheel, although the reasoning explained above, valid for the compressor or the centrifugal pump, is only partially transposable to the turbine. Indeed, if the turbine wheel must operate at low gas flow, it is not necessary that the vein is high output. On the contrary, it is rather advantageous that it is not exaggerated because it would lead to unnecessarily burden the turbine, the work provided by the fluid on the inside of the blading counting for a small part of the whole. In any case, it is not necessary, from the point of view of fluid mechanics, to place the trailing edges in a direction close to that of the wheel axle. It is therefore possible to have a turbine wheel similar to a radial-type wheel over most of it, but having a semi-axial or even totally axial fluid outlet.

In any case, we are aiming here for a wheel for which the fluid circulation extends substantially in a radial plane over a very large part of the surface of the flange.

One of the aspects limiting the rotational speed of a radial-type wheel is the mechanical stress generated at the location of the blades on the flange. This constraint comes mainly from the fact that the centrifugal forces applied on the blades deported forward tend to deform the flange rearward, and thus to stretch the front face. However, this phenomenon is very strongly aggravated, locally, by the concentration of stresses at the foot of the leading edges (for a compressor wheel or pump) or leakage (respectively for a turbine wheel) which are located towards the transition zone between the hub and the flange, configuration which s' typically observed in the case of a radial type wheel. This mechanical stress also comes from the moment generated at the foot of the blade due to the offset of the latter relative to the front face of the flange. Finally, it should be noted that, in the case of a radial wheel, the stress zone designated here is typically the area of the wheel which is the most stressed in fatigue.

However, it should be noted that, if the flange is generally shaped like a cone whose tip is oriented towards the front of the wheel, the centrifugal forces applied to the flange tend to straighten the flange towards the front, compressing its front, which offsets all or part of the stretching effect described above. Moreover, because of this inclination of the flange, the axial offset of the blades relative to the flange, and therefore the associated bending moment, are reduced compared to the case of a flat flange. This configuration makes it possible to push the speed limits of rotation of the wheel or to enlarge the wheel, and thus to obtain better performances.

Such a geometric layout, if it primarily aims to reduce the mechanical stresses in the most sensitive areas, can also be considered to optimize the deformation of the wheel. This secondary objective may aim in particular to ensure sufficient clearance vis-à-vis the body of the rotating machine, in terms of machining and assembly tolerances, thermal deformations, bearing movements and vibratory deformations. In this particular case, it is, contrary to what has been explained above, to choose a slightly larger cone angle than the one offering the best fatigue strength of the wheel.

On the wheels according to the invention, most of the front face extends substantially along a cone whose tip is oriented forward and whose angle at the top is between 154 and 170 °, but it is very common that the peripheral circle and the central circle, circles delimiting the area of implantation of the blading, are located outside this characteristic area. Indeed, the profile of the front face is generally rectified peripherally to guide the output velocity of the fluid in a radial plane. Furthermore, because the hub is generally thicker than the flange in the axial direction, the portion of the front face close to the wheel axis is generally a form of fillet, constituting the contour of the hub; however, because of the need to maximize the length of the fluid flow in the radial direction, it is common that the implantation of the leading edges (in the case of the compressor or centrifugal pump) or leakage (in the case of the turbine) is in this area, and this even if the leading edges (respectively leakage) extend in a direction close to that of the wheel axis. Apart from these two portions, or between the inner and outer circles, which is almost always more than 70% of the extent of the front face, the Applicant has found that it was particularly interesting to tilt the profile of the front panel in the specified range. Finally, in certain configurations, the front face of the flange may be slightly curved over a very large part of the wheel adopting nowhere the exact shape of a section of cone of revolution.

Overall, very satisfactory results are obtained when the front face of the flange substantially describes a cone whose apex angle is between 160 ° and 166 °. It is thus possible to use this configuration to give very good performance to a rotating machine operating at low fluid flow.

It is possible, taking into account the two contradictory effects described above, to look for the configuration that makes it possible to minimize the fatigue load in the areas concerned. The equilibrium thus defined depends on the different geometrical characteristics of the wheel, and in particular on the height of the blades, but we have observed that it is in most of the cases considered, it is rather insensitive and the minimization of the quasistatic stress is reached when the front face of the flange substantially describes a corner cone at the apex close to 164 °. However, a slightly lower angle provides even more compression in the identified areas, and may therefore sometimes be a better choice for fatigue performance.

According to a particular embodiment, some of the blades, of a fractionation subassembly, extend from an intermediate circle between the central circle and the peripheral circle. Such blades, also called "splitters", subdivide the space between the blades that extend from the central circle. The invention is particularly advantageous in such a configuration, because the leading edges (in the case of a compressor or a pump) or leakage (in the case of a turbine, respectively) of these intermediate blades are typically located on a radial wheel, in the transition zone between the flange and the hub, or in an area where the bending deformation of the flange tends to concentrate.

In special cases, the inner circle and the outer circle have a difference in diameters of at least 85% of the difference in diameters between the central circle and the peripheral circle.

In a particular arrangement, the flange and the hub are in one piece.

The invention also relates to a turbine, characterized in that it comprises a wheel as described above.

The invention also relates to a compressor, characterized in that it comprises a wheel as described above.

The invention also relates to a turbocharger comprising a turbine and a compressor, the turbine and the compressor each comprising at least one wheel, the wheels being coupled in rotation, characterized in that at least one of the wheels is a wheel such as as previously described. Brief description of the figures

The invention will be better understood and other features and advantages will appear on reading the description which follows, the description referring to the appended drawings among which:

- Figure 1 is a perspective view of a wheel according to a first embodiment of the invention;

- Figure 2 is a sectional view of the wheel of Figure 1;

FIG. 3 is a view similar to FIG. 2 of a wheel according to a second embodiment of the invention;

- Figure 4 is a sectional view of a turbocharger comprising two wheels according to the invention;

- Figure 5 is a longitudinal sectional view along the line V-V of Figure 6 of a centrifugal compressor according to the prior art;

- Figure 6 is a sectional view along the line VI-VI of Figure 5; - Figures 7 to 10 are views similar to Figure 2 of wheels according to the prior art.

DETAILED DESCRIPTION

A wheel 2 of a rotary machine according to a first embodiment is shown in FIGS. 1 and 2. The wheel 2, for example that of a compressor, comprises a hub 20 arranged to mount the rotating wheel about an axis of rotation. wheel A, a flange 21 in one piece with the hub 20 and extending substantially in a plane perpendicular to the wheel axis A, and blades 22 mounted on a front face 210 of the flange 21 so as to protrude a front side of the wheel 2. To be rotatably mounted, the wheel 2 comprises at the hub 20 a bore 201 for receiving a shaft, not shown. All the elements of the wheel 2 are in one piece, the wheel 2 being made for example by molding a metal alloy or a synthetic material, or by machining a block of such material. The flange 21, as seen in section in Figure 2, has a greater width near the hub 20 at the periphery, for reasons of mechanical strength and to minimize the overall deformation of the wheel. The blades 22 have a blade shape, of substantially constant thickness, and substantially perpendicular to the front face 210. Some blades 22 extend from a leading edge 221 whose base is located on a circle J, near from the hub 20, to a trailing edge 222 located at the periphery 24 of the wheel 2 on the front face 210. Other blades 22 of a fractionation subassembly, interposed between those of the preceding group, have an edge driver 223 located on or beyond a circle N of intermediate diameter placed between the circle J and the periphery 24. The leading edges 221, 223 are substantially parallel to the wheel axis A.

The front face 210 comprises a first zone C in the form of a rounded fillet of connection extending from the central circle J, passing through the feet of the leading edges 221, at the intersection of the leading edges 221. and from the front face 210, to an inner circle K, followed by a second zone D of substantially conical shape extending from the inner circle K to an outer circle L, then by a third zone E extending from the outer circle L to a peripheral circle M at the periphery 24 of the wheel 2, the generatrix of the front face 210 on this outer zone E being of rounded shape and tangential to the perpendicular to the wheel axis A to periphery level 24. On this wheel, with particular reference to FIG. 2, the diameter of the central circle represents 18.5% of the diameter of the peripheral circle. The outer circle L is defined in this case as the circle to which a second cone S of angle = 170 ° at the apex P2 is tangent to the front face 210. The diameters of the inner circle K and the outer circle L respectively represent 29 % and 90.5% of the diameter of the circumferential circle M. The angle a at the top of the first cone R which contains the inner and outer circles K and L is 164 °. In other words, on the second zone D, the angle between a generatrix of the first cone R and a radial plane is 8 °. Thus, the difference in diameter between the inner and outer circles K and L represents 74% of the difference in diameter between the peripheral circle M and the central circle J. Any cone tangent to the front face 210 in any circle located on the front face 210, between the inner circle K and the outer circle L has an apex angle less than or equal to 170 °.

This wheel according to the invention has been compared and whose geometric characteristics are listed above at an identical wheel except that it comprises a plane front face from the inner circle. In the case of these two wheels, the critical stress point being located at the base of the leading edge of the intermediate length intermediate blade, therefore relatively far from the hub, the gain provided by the balancing associated with the optimum inclination the flange of the wheel according to the invention is very consequent. Here, the optimization of the inclination of the flange, obtained with the characteristics described above, has made it possible to obtain a reduction of about 55% of the stress at the critical point, in other words to increase by approximately 50% the speed maximum fatigue mission profile of the compressor.

According to a second embodiment of the invention, a centripetal turbine wheel 2 ', as shown in FIG. 3, the front face 210' has a profile evolving continuously between the central circle J ', of diameter Di, and the peripheral circle M ', of diameter De. The outer circle L' is defined as coinciding with the peripheral circle M ', and the inner circle K' of diameter (De-2X), such that X = 0.7 ^{De Di.} The first cone R ', containing the inner circles K' and outer L 'has an apex angle of 1 60 °. The second most open cone S 'is the cone of greater angle at the top which is tangent to the front face 210' between the inner and outer circles, K 'and L'. In this configuration, the second cone is tangent to the front face 210 'at the outer circle L'. The angle β at the apex P2 'of the second cone S' is 166 °.

A set of elementary conditions makes it possible to characterize certain geometrical features peculiar to the invention and to distinguish it from the prior art. It is observed first of all that, on the wheels of centrifugal compressor or centripetal turbine other than those, rare, of radial type, the generating curve of the front face always has, by construction, a quarter-elliptical shape. This is the consequence of a triple geometric condition: firstly, the direction of the gas outlet on the compressor or the centrifugal pump and that of the gas inlet respectively on the centripetal turbine are by definition substantially radial; secondly, the circular symmetry associated with the rotational nature of the system and the need to arrange together the different fluid circulation channels imply that the direction of the gas inlet on the compressor or the centrifugal pump, and that of the gas outlet respectively on the centripetal turbine, are always axial; thirdly, for better efficiency, it is necessary to avoid that the curvature of the vein is too violent. Most commonly, this shape is quite close to a quarter circle. Figures 7 to 10 show compressor and turbine wheels in an extremely common design. The blades extend, as a whole, from a central circle J to a peripheral circle M. For each of these wheels respectively, two inner and outer circles, K and L, located on the front face, are considered between the circle central J and the peripheral circle M, the difference 2X in diameter between the outer circle L and the inner circle K being equal to 70% of the difference (De-Di) in diameter between the peripheral circle M and the central circle J, the positions of the circles K and L being such, moreover, that the apex angle of a first cone R passing through these two circles is maximum. In each of these configurations, the outer circle L coincides with the peripheral circle M. It is observed that the apex angle of the first cone R thus constructed is typically between 130 ° and 145 °, ie outside the characteristic angular range of the invention.

FIG. 4 shows a turbocharger 3 comprising a turbine 30 and a compressor 31 whose respective wheels 302, 312 are fixed on the same rotary shaft 32 via a bearing 33 placed between the body 31 1 of the compressor 31 and that of the turbine 301. The wheels 302, 312 are in accordance with the embodiment as previously described. Such a turbocharger 3 provides good efficiency for a low gas flow. The wheels made according to the invention being particularly large compared to conventional wheels, this turbocharger 3 operates at a lower speed of rotation of the wheels. As a result, a bearing 33 can be used with ball bearings.

The invention is not limited to the embodiments which have just been described by way of examples. The rotor shaft may be integral with the wheel.

Claims

1. A rotating machine wheel for a fluid, the wheel having a wheel axle (A) and having a hub (20) arranged to mount the rotating wheel about the wheel axle (A), a flange (21) fixed on the wheel hub (20) and extending substantially in a radial plane with respect to the wheel axle (A), the flange having a front face (210), blades (22) projecting from the front face (210), each of the blades extending at most between a central circle (J) and a peripheral circle (M) located on the front face (210), a blade at least extending to the central circle (J) and a blade at least extending to the peripheral circle (M), characterized in that there is an inner circle (K) and an outer circle (L) located on the front face (210) between the central circle (J) and the peripheral circle (M) having a difference in diameters of at least 70% of the difference in diameters between the central circle (J) and the circumferential circle (M), the inner circles (K) and outside (L) belonging to a first cone of revolution (R) whose tip (P1) is oriented forward and whose apex angle is between 154 ° and 170 °, and in that, whatever the circle on the front face (210) between the inner and outer circles (K, L), a second cone (S) having the axis of revolution of the wheel axis (A) and whose tip (P2) is oriented forward, tangent to the front face (210) on said circle has an apex angle less than or equal to 170 °.

Wheel according to claim 1, wherein the first cone (R) has an angle of 164 °.

A wheel according to claim 1 or 2, wherein the inner circle (K) and the outer circle (L) have a difference in diameters of at least 85% of the difference in diameters between the central circle (J) and the peripheral circle (M).

4. Wheel according to one of claims 1 to 3, wherein the blades of a fractionation subassembly of the blades (22) extend towards the periphery (24) from an intermediate circle (N) between the circle central (J) and the peripheral circle (M).

5. Wheel according to one of claims 1 to 4, wherein the flange (21) and the hub (20) are in one piece.

6. Compressor, characterized in that it comprises a wheel (2) according to one of claims 1 to 5.

7. Turbine, characterized in that it comprises a wheel (2 ') according to one of claims 1 to 5.

8. Turbocharger comprising a turbine (30) and a compressor (31), the turbine (30) and the compressor (31) each comprising at least one wheel (302, 312), the wheels being coupled in rotation (32), characterized in that at least one of the wheels (302, 312) is a wheel according to one of claims 1 to 5.