FR2749038A1 - RADIAL TURBINE WHEEL - Google Patents

Abstract

The invention relates to a radial turbine wheel, comprising: - a wheel body (2) of generally frustoconical or equivalent shape having a small base (3), a large base (4), and a side surface (5); and - vanes (6) emerging radially from the lateral surface (5) of said wheel body (2). According to the invention, the wheel comprises: - an axial extension (7) of the small base (3) of the wheel body (2) extending beyond a transverse plane (8) at the end of the blades (6) ); - at least part of the lateral surface (5) formed by a web (9); and - an axial hub (10). Said part of the lateral surface (5) constituted by a web (9) and said axial hub (10) defining an axial annular recess (11) of the large base (4) of the turbine wheel.

Description

RADIAL TURBINE WHEEL

  The invention relates to a radial turbine wheel.

  The invention more specifically relates to a radial turbine wheel of small diameter (of the order of one hundred millimeters), subjected to high rotational speeds (of the order of 50000 revolutions / min), and to high operating temperatures (above 1000oC). In these ranges of speeds and temperatures, the refractory materials currently used to produce

  radial turbine wheels are limited.

  One reason is that the radial turbine wheels rotating at the speeds mentioned above include areas having peak stress distributions relative to the average level of stress in the wheel. These peaks of stress make it necessary to choose materials capable of supporting them in any

  security (in the statistical sense of Weibull's law).

  Thus, it is a small part of the wheel that imposes to choose a material having very characteristics

  higher than those required for the rest of the wheel.

  It is known to modify the shapes of the wheels for

  reduce the level of stress in these areas.

  It is known that the shape of these wheels has a great influence on the distribution and on the maximum level of

observed constraints.

  In the wheel shapes currently used, the refractory materials having the mechanical properties likely to respond to these peaks of stress are few

numerous.

  The use of carbon-carbon is known for the production of axial turbine wheels. It is a refractory material having good mechanical properties at high temperature. However, carbon-carbon is a very expensive material, difficult to shape for radial turbine wheels. In addition, this difficulty increases with radial turbine wheels of small diameter. In addition it is an anisotropic material which makes its use difficult Many achievements are known radial ceramic turbine wheels Si3N4. Again, the manufacture of such ceramic turbine wheels is complicated and expensive. In particular, the ceramic is not easily machinable. In addition, the proposed profiles have, in operation, very high peaks of stress.

  especially in the vicinity of the turbine wheel axle.

  For example, a Si3N4 wheel having a diameter of 112 mm has a peak stress greater than 230 MPa for a speed of the order of 90000 revolutions / min at a temperature of

the order of 1200 C.

  The pressure forces due to the aerodynamic loads of the blades are very low compared to the centrifugal stresses of the interest of using

low density.

  The object of the present invention is to propose a turbine wheel having a profile that substantially limits the peaks of stress. As a result, new low-density refractory materials, which are less expensive and more easily shaped, and which until now have been rejected because of their insufficient mechanical properties, can be used for the production of turbine wheels in the temperature ranges. and of

  speeds mentioned at the beginning of the description.

  For this purpose the invention relates to a radial turbine wheel comprising a generally frustoconical or equivalent wheel body having a small base, a large base, and a lateral surface, vanes emerging radially from the lateral surface of said wheel body, according to the invention, the turbine wheel comprises an axial extension of the small base of the wheel body extending beyond the transverse end plane of the blades, at least a portion of the lateral surface constituted by a web, and a axial hub, said part of the lateral surface constituted by a web and said axial hub defining an axial annular recess of the large base

of the turbine wheel.

  The axial hub is advantageously an axial sleeve

  hollow through which passes the axis of the turbine.

  In one embodiment, the turbine wheel comprises radial stiffening ribs located in the axial annular recess, and extend between the

sail and the axial sleeve.

  According to the invention the turbine wheel can be

  especially in dense graphite or glassy carbon.

  Other advantages and features of this

  invention will result from the following description in

  reference to the accompanying drawings, in which: FIG. 1 is a diagrammatic representation in longitudinal section of a radial turbine wheel according to a

  first embodiment of the invention.

  FIG. 2 is a schematic diagram comparing the observed stresses, as a function of the level considered on the spoke, on a dense graphite turbine wheel and on a dense graphite turbine wheel.

  according to the first embodiment of the invention.

  FIG. 3 is a diagrammatic representation in longitudinal section of a radial turbine wheel according to a

  second embodiment of the invention.

  FIG. 4 is a schematic diagram comparing the stresses observed on two vitreous carbon turbine wheels according to the second embodiment of FIG.

embodiment of the invention.

  The invention relates to a radial turbine wheel 1 comprising a wheel body 2 of generally frustoconical or equivalent shape having a small base 3, a large base 4, and a lateral surface 5, and vanes 6 emerging.

  radially of the lateral surface 5 of the wheel body 2.

  According to features of this invention, the turbine wheel comprises an axial extension 7 of the small base 3 of the wheel body 2 extending beyond the transverse plane 8 of the end of the vanes 6, at least a portion of the lateral surface. 5 constituted by a web 9, and a hub 10. The part of the lateral surface constituted by the web 9 and the hub 10 together define an axial annular recess 11 of the large base 4 of the radial turbine wheel 1. In the embodiment shown in Figures 1 and 3, the hub 10 is an axial sleeve 14 to

  through which the axis 12 of rotation of the turbine passes.

  In an embodiment not shown, the hub is solid and then constitutes the axis of rotation of the

turbine.

  In the first embodiment shown in FIG. 1, only a part of the lateral surface 5 is constituted by a web 9. The turbine wheel then has a solid muzzle 13 pierced axially for mounting on the axis of the turbine. , extending beyond the transverse plane 8 of end of the blades 6 on the side of the small base 3, and thus forming the extension 7, and extended to the opposite by a radial expansion formed by a web 9 and by a hollow axial sleeve 14 extending towards the large base 4 of the wheel

of turbine.

  Advantageously but without limitation, the thickness

  the sail decreases from the axis to the periphery of the wheel.

  Advantageously but not exclusively, the turbine wheel according to the first embodiment is made of dense graphite. FIG. 2 represents a curve 20 of the stresses calculated at different levels of the radius of a full turbine wheel made of graphite and without axial extension of the small base (not shown) rotating at 50000 revolutions / minute and a curve 21 of the stresses calculated at different spokes of a graphite turbine wheel according to the

  representation of Figure 1 rotating at the same speed.

  The particular shape of the wheel of FIG. 1 makes it possible to decrease by more than 50% (from 88 MPa to 42 MPa) the

  maximum stress compared to the full turbine wheel.

  As taught in the prior art, this maximum stress is located near the axis of rotation. Dense graphites have a maximum tensile strength of about 65 MPa for the most common

  and of the order of 85 MPa for those of higher quality.

  The profile of the radial turbine wheel according to the first embodiment thus makes it possible to use, in complete safety (in the Weibull law sense), dense graphite for the realization of radial turbine wheels rotating at speeds of 1 ° C. order of 50000 rpm. This material has the advantage of its low density, ease of machining, its low cost, its mechanical properties increasing with temperature (an increase of 30% at the temperatures envisaged compared to the values at ambient temperature). The radial turbine wheel according to the first embodiment therefore allows a reduction of the order of 50% of the maximum stresses. In addition, combined with a material such as graphite, it makes it possible to produce radial turbine wheels at costs compatible with large series. Such a turbine wheel can be advantageously used in closed cycle or open cycle turbine-generator hybrid vehicles. At the expected operating temperatures, since such a graphite turbine wheel would be used in an oxidizing atmosphere, it is necessary to protect it with an antioxidant coating, for example SiC. Similarly, the graphite being relatively porous, it may be envisaged to coat the graphite radial turbine wheel of PyroCarbone to prevent diffusion of the fluid.

  motor through the turbine wheel.

  The profile of the first embodiment can be used with any other material than graphite, in particular

  for example ceramics or equivalent.

  In the second embodiment shown in FIG. 3, the entire lateral surface 5 consists of a web 9. The turbine wheel then comprises a web 9 forming the lateral surface 5, a hollow axial sleeve 14 coming from the small base 3 and extending towards the large base 4 of the turbine wheel, and a plurality of radial stiffening ribs 15 located in the axial annular recess 11 defined by the web 9 and the sleeve 14. The ribs 15 ' extend between the web 9 and the axial sleeve 14. This type of shell profile with ribs 15 is made to allow the use of materials whose manufacturing methods require

limited thicknesses.

  Advantageously, but not exclusively, the radial turbine wheel according to the second embodiment is in

vitreous carbon.

  FIG. 4 represents two curves 30 31 of the stresses calculated at different radii of a glassy carbon turbine wheel according to the representation of FIG. 3 rotating at 50000 revolutions / minute. One of the curves relates to a vitreous carbon radial turbine wheel having a shell 3 mm thick with 16 radial ribs of 3 mm equidistribution, the other 31 of the curves relates to a vitreous carbon radial turbine wheel having a 3mm thick shell with 32 ribs

radial 2 mm equiparts.

  The maximum tensile strength / bending of the vitreous carbon is of the order of 180 MPa at ambient temperature, the maximum stresses calculated on the radial turbine wheels according to the second embodiment are therefore well

below this maximum.

  The second embodiment of the present invention therefore makes it possible to use lightweight materials whose nominal manufacturing thicknesses are limited, but

  which are inexpensive and can easily be molded.

  Glassy carbon, like graphite, has properties

  mechanical increasing with temperature.

  Of course, the invention is not limited to the embodiments described and shown, but it is capable of many variants accessible to those skilled in the art without departing from the invention. In particular, it is possible, without departing from the scope of the invention, to replace the materials used with any other equivalent material.

Claims (5)

  A radial turbine wheel comprising: a wheel body (2) of generally frustoconical or equivalent shape having a small base (3), a large base (4), and a lateral surface (5); and vanes (6) emerging radially from the side surface (5) of said wheel body (2); characterized in that it comprises an axial extension (7) of the small base (3) of the wheel body (2) extending beyond a transverse plane (8) end of the blades (6); at least a portion of the lateral surface (5) constituted by a web (9); and an axial hub (10); said part of the lateral surface (5) constituted by a web (9) and said axial hub (10) defining an axial annular recess (11) of the large base (4) of the turbine wheel.   2. turbine wheel according to claim 1 characterized in that the axial hub (10) is a hollow axial sleeve (14) through which passes the axis (12) of the turbine. 3. turbine wheel according to claim 1 or 2 characterized in that it comprises radial stiffening ribs (15) located in the axial annular recess (11), and extending between the web (9) and the hub axial (10).   4. Turbine wheel according to any one of   Claims 1 to 3 characterized in that it is dense graphite.   Turbine wheel according to claim 3   characterized in that it is glassy carbon.