Patent Description:
Centrifugal compressors generally consist of at least two main components: an impeller and a diffuser. The impeller includes a hub which it is mounted to a drive shaft so as to be rotated therewith. Vanes (i.e., blades) of the impeller extend from the hub and are arranged to redirect an axially-directed inbound gas flow radially outwardly, toward the diffuser located downstream of the impeller. Stresses may however be imparted on the impeller, often in or near the hub. Such stress concentrations may adversely affect the life of the impeller. At the same time, vane bulk is generally regarded as being detrimental to aerodynamic properties of the flow passed from the impeller to the diffuser, thus rendering oversizing approaches undesirable in solving the issue of stress concentration. As such, there continues to be a need for improvement.

<CIT> discloses a method for adjusting the curved surface of a ruled-surface compressor impeller blade.

Kim Changhee et al. DOI: <NUM>/J. <NUM> discloses a study on the performance of a centrifugal compressor considering running tip clearance.

<NPL>) discloses the development of a high-flow centrifugal compressor stage.

<CIT> discloses a backswept titanium turbocharger compressor wheel.

<CIT> discloses a centrifugal compressor impeller with blades having an S-shaped trailing edge.

Sagar Pakle et al. DOI: <NUM>/j. <NUM> discloses the design of a high-performance centrifugal compressor with a new surge margin improvement technique for high speed turbomachinery.

Li Ziliang et al. DOI: <NUM>/J. <NUM> discloses a numerical investigation of flow mechanisms of a tandem impeller inside a centrifugal compressor.

In one aspect, there is provided an impeller for a centrifugal compressor as claimed in claim <NUM>.

The impeller as defined above and herein may further include, as defined by the dependent claims, the following additional features.

Wherein a <NUM>% chord position is defined at the leading edge and a <NUM>% chord position is defined at the trailing edge, the trailing edge thickness value being a thickness value at the <NUM>% chord position, the thickness value at the <NUM>% chord position is between <NUM>% and <NUM>% of the maximum thickness value.

The vane thickness has a thickness value at a <NUM>% chord position of between <NUM>% and <NUM>% of the maximum thickness value.

The thickness value at the <NUM>% chord position is of between <NUM>% and <NUM>% of the maximum thickness value.

In another aspect, there is provided a centrifugal compressor for a turbine engine, as claimed in claim <NUM>.

<FIG> illustrates a gas turbine engine <NUM> of a type preferably provided for use in transonic flight, generally comprising in serial flow communication a fan <NUM> through which ambient air is propelled, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section <NUM> for extracting energy from the combustion gases. Although the engine <NUM> is a turbofan gas turbine engine <NUM>, it should be understood that the present technology is also applicable to other types of gas turbine engine. Of particular interest to the instant application, the compressor section <NUM> includes at least one centrifugal compressor assembly <NUM>, including generally an impeller <NUM> and a diffuser <NUM> downstream of the impeller <NUM>.

Referring to <FIG>, the centrifugal compressor assembly <NUM> includes impeller <NUM> fixed to a central shaft <NUM> and rotatable with the shaft <NUM> about a central axis <NUM> within a stationary impeller shroud <NUM> of the compressor assembly <NUM>. The impeller <NUM> comprises a central hub <NUM> defining a bore <NUM> therethrough that is collinear with the axis <NUM>. The impeller <NUM> also comprises a plurality of vanes <NUM> disposed around the hub <NUM> and bore <NUM>, and extending radially outwardly thereof to define a radial periphery of the impeller <NUM>. The vanes <NUM> and the surrounding shroud <NUM> are shaped to redirect an incoming axially-flowing fluid flow <NUM>, radially outward by about ninety degrees, forcing the fluid flow <NUM> radially outwardly relative to the hub <NUM>, and increasing the velocity of the fluid flow <NUM>. Although it is not essential, the hub <NUM> and the plurality of vanes <NUM> form in some embodiments a unitary piece. An annular fluid path is thus defined through the compressor assembly <NUM>, along and through the vanes <NUM>, between an inner surface <NUM> of the impeller shroud <NUM> and an outer surface <NUM> of the hub <NUM>.

Still referring to <FIG>, the diffuser <NUM> includes a diffuser case <NUM> defining a circumferential inlet space <NUM> surrounding a periphery of an outlet space <NUM> of the compressor assembly <NUM>. As best seen in <FIG>, the diffuser <NUM> includes a series of angled passages <NUM> are defined through the diffuser case <NUM> from the inlet space <NUM>, each passage <NUM> being defined between adjacent diffuser vanes or vane islands <NUM> (<FIG>). The diffuser <NUM> can be a vane type diffuser or may comprise a plurality of diffuser pipes. Alternate diffuser geometries are also possible, including for example a diffuser with a vaneless inlet space. Although it is not essential, the diffuser case <NUM> is in one particular embodiment a unitary machined part.

Turning now to <FIG>, the vanes <NUM> will now be described in more detail with regard to a vane 32a of the vanes <NUM> of the impeller. It should be understood that the present description of the vane 32a is consistent, mutatis mutandis, with a remainder of the vanes <NUM> of the impeller <NUM>. The vane 32a has a pressure side <NUM> and a suction side <NUM>, opposite from one another. The pressure and suction sides <NUM>, <NUM> extend from the outer surface <NUM> of the hub <NUM>, thereby defining a root of the vane 32a formed at the junction between the outer surface <NUM> of the hub <NUM> and the pressure and suction surfaces <NUM>, <NUM> of the vane 32a. The vane 32a extends from its root to an outer free end of the vane 32a, which is spaced apart from the outer surface <NUM> to define a height of the vane at a given chord position. The vane 32a also has a leading edge <NUM> and a trailing edge <NUM>. The leading and trailing edges <NUM>, <NUM> extend from the root to the free end of the vane 32a, at the junctions between the pressure surface <NUM> and the suction surface <NUM>. The leading edge <NUM> forms an upstream end of the vane 32a. As best seen in <FIG>, in some embodiments, the pressure and suction sides <NUM>, <NUM> converge so as to define the leading edge <NUM>. The trailing edge <NUM> forms a downstream end of the vane.

The true chord <NUM> of the vane 32a is defined as the chord line that extends between the leading and trailing edges <NUM>, <NUM>, following the pressure and suction sides <NUM>, <NUM> of the vane airfoil, and measured at the hub <NUM> (i.e. at the junction between the pressure or suction side of the vane and the outer surface <NUM> of the hub <NUM>). According to the claimed invention, in <FIG>, the chord <NUM> is shown as extending at the root of the vane 32a, intermediate the pressure and suction sides <NUM>, <NUM>. A vane thickness is defined between the pressure side <NUM> and the suction side <NUM>. The vane thickness is measurable transversely to the chord <NUM> between the pressure and suction sides <NUM>, <NUM>, at the root of the vane 32a. The vane thickness includes a trailing edge thickness value, measured at the trailing edge <NUM>, and a maximum thickness value located at a point on the vane upstream from the trailing edge. The maximum thickness value is greater than the trailing edge thickness value. From <FIG>, it can be appreciated that the portion of the vane 32a having the maximum thickness value is substantially upstream of the trailing edge <NUM>, and in fact the maximum thickness value is disposed within the upstream half of the vane. As will be seen, the vane 32a of the impeller <NUM> has a vane thickness that reduces non-negligibly over a downstream portion of the vane 32a.

As best seen in <FIG>, at the trailing edge <NUM>, the pressure and suction sides <NUM>, <NUM> are spaced apart by a distance 58a corresponding to the trailing edge thickness value of the vane 32a at the hub <NUM>. At the outer free end of the vane 32a, away from the hub, the pressure and suction sides <NUM>, <NUM> are spaced apart by a distance 58b which may, at the trailing edge <NUM>, be less than the trailing edge thickness value 58a at the hub, such as in the one embodiment shown. In this one embodiment, a second vane thickness of the vane 32a measured at the free end is substantially constant over the downstream portion of the chord <NUM>. In other embodiments, the second vane thickness may vary over the downstream portion of the chord <NUM>.

Turning now to <FIG>, a graph is provided so as to describe the vane thickness of the vane 32a in more detail by means of specific examples of vanes 32b consistent with various embodiments of the present technology. The graph depicts vane thickness as a function of a chordwise position of the vanes 32b. At several estimated true chord positions <NUM> of each one of the vanes 32b (i.e., locations on the vane expressed as percentages of the chord <NUM>) estimates of normalized thickness values <NUM> (i.e., measured thickness values expressed as percentages of the maximum thickness value) are plotted. Each of the curves <NUM>, <NUM>, <NUM> depicted in the graph of <FIG> therefore represents a vane 32b in accordance with a different embodiment of the present technology, although only the curve <NUM> is according to the claimed invention.

It is however to be understood that each of these curves is exemplary in nature, and that other vane thickness profiles can be used without departing from the scope of the present invention, which is solely defined by the claims. In the graph of <FIG>, the <NUM>% chord position <NUM> of the true chord positions <NUM> corresponds to the leading edges <NUM> of the vanes 32b, and the <NUM>% chord position <NUM> of the true chord positions <NUM> corresponds to the trailing edges <NUM> of the vanes 32b.

In the graph, vane thicknesses of the vanes 32b are respectively depicted by curves <NUM>, <NUM> and <NUM>. In some embodiments, at the <NUM>% chord position <NUM>, the vane thickness has vane thickness value being a minimum thickness value <NUM> of the vane 32a. In some such embodiments, at the <NUM>% chord position <NUM>, the vane thickness has vane thickness value corresponding to less than <NUM>% (and in one particular embodiment about <NUM>%) of the maximum thickness value (shown at <NUM>).

From the graph, it can be appreciated that the vane thickness reduces over at least a downstream <NUM>% of the chord, i.e., downstream from a <NUM>% chord position <NUM> to the <NUM>% chord position at the trailing edge <NUM>.

At the <NUM>% chord position <NUM>, the vane thickness has a thickness value of between about <NUM>% and <NUM>% of the maximum thickness value <NUM>, and more particularly between about <NUM>% and about <NUM>% of the maximum thickness value <NUM>. For instance, in the embodiments depicted by the curves <NUM>, <NUM> and <NUM>, the vanes have thickness values of approximately <NUM>%, <NUM>% and <NUM>% at the <NUM>% chord position, respectively.

At a <NUM>% chord position <NUM>, the vane thickness has a thickness value of between about <NUM>% and about <NUM>% of the maximum thickness value <NUM>. For instance, in the embodiments depicted by the curves <NUM>, <NUM> and <NUM> indicate thickness values of approximately <NUM>%, <NUM>% and <NUM>%, respectively.

At a <NUM>% chord position <NUM>, the vane thickness has a thickness value of between about <NUM>% and <NUM>% of the maximum thickness value <NUM>, and more particularly between about <NUM>% and <NUM>%. For instance, the curves <NUM>, <NUM> and <NUM> indicate thickness values of approximately <NUM>%, <NUM>% and <NUM>%, respectively.

At the <NUM>% chord position <NUM>, i.e. at the trailing edge of the vane, the vane thickness has a thickness value of between <NUM>% and <NUM>% of the maximum thickness value <NUM>, and more particularly between <NUM>% and <NUM>% of the maximum thickness value <NUM>. For instance, the curves <NUM>, <NUM> and <NUM> indicate trailing edge thickness values of approximately <NUM>%, <NUM>% and <NUM>%, respectively.

In the claimed embodiment, the maximum thickness value <NUM> is at a position upstream of a <NUM>% chord position <NUM>, or in other words within the upstream half of the vanes. For instance, the curves <NUM>, <NUM> and <NUM> are indicative of their respective maximum thickness values <NUM> being generally between a <NUM>% chord position and a <NUM>% chord position.

In light of the preceding, it can be appreciated that a chordwise reduction in thickness of the vanes <NUM>, 32a, 32b as disclosed herein can result in an impeller <NUM> having a greater life when compared to some conventional impellers. The reduction in thickness of the vanes <NUM>, 32a, 32b over at least the downstream <NUM>% of the chord <NUM> is arranged so as to impart the impeller <NUM> with a desired resistance to stress at the bore <NUM> under certain operating conditions. For instance, the reduction in thickness results in a distribution of a mass of the vanes <NUM>, 32a, 32b as they extend away from their root, yielding a desired inertial load at the root. Upstream of the reduction, a bulging <NUM> of the vanes <NUM>, 32a, 32b inclusive of the portion thereof having the maximum vane thickness value <NUM> yields a desired resistance to stress concentration typically borne by conventional impellers. It should also be understood that the vanes <NUM>, 32a, 32b are also arranged so as to impart the impeller <NUM> with certain desired aerodynamic properties. For instance, in some embodiments, the reduction in thickness of the vanes <NUM>, 32a, 32b over at least the downstream <NUM>% of the chord <NUM> is arranged such that, under certain operating conditions, the flow <NUM> is imparted with a desired maximum amount of disturbance upon moving downstream from the trailing edge <NUM>. In some embodiments, a geometry of the vanes <NUM>, 32a, 32b over at least the downstream <NUM>% of the chord <NUM> may be configured with respect to a shape of the corresponding diffuser <NUM>.

Claim 1:
An impeller (<NUM>) for a centrifugal compressor (<NUM>), the impeller comprising:
a hub (<NUM>) defining a rotation axis (<NUM>) about which the impeller (<NUM>) is rotatable; and
a vane (32a, <NUM>) extending from the hub (<NUM>) to an outer free end, the vane (32a, <NUM>) having a leading edge (<NUM>), a trailing edge (<NUM>), and a chord (<NUM>) defined therebetween, a pressure side (<NUM>) of the vane (32a, <NUM>) and a suction side (<NUM>) of the vane (32a, <NUM>) opposite the pressure side (<NUM>), the chord (<NUM>) extending between the leading and trailing edges (<NUM>, <NUM>) intermediate the pressure and suction sides (<NUM>, <NUM>) of the vane (32a, <NUM>), a vane thickness defined transversely between the pressure side (<NUM>) and the suction side (<NUM>),
wherein the vane thickness is measurable transversely to the chord (<NUM>) between the pressure and suction sides (<NUM>, <NUM>) at a root of the vane (32a, <NUM>), the root of the vane (32a, <NUM>) formed at a junction between an outer surface (<NUM>) of the hub (<NUM>) and the pressure and suctions sides (<NUM>, <NUM>) of the vane (32a, <NUM>);
wherein the vane thickness at the root reduces over at least a downstream <NUM>% of the chord (<NUM>),
and wherein a maximum thickness value (<NUM>) of the vane thickness at the root is within an upstream <NUM>% of the chord (<NUM>),
characterized in that the vane thickness at the root has a trailing edge thickness value (58a) at the trailing edge (<NUM>) of between <NUM>% and <NUM>% of the maximum thickness value (<NUM>) of the vane thickness at the root.