Patent Description:
Turbomachinery is used extensively in the oil and gas industry, such as for performing compression of a process fluid, conversion of thermal energy into mechanical energy, fluid liquefaction, etc. One example of such turbomachinery is a compressor, such as a centrifugal compressor.

<CIT> discloses a rotor structure for turbomachinery comprising a tie bolt. A first rotor shaft is fixed to a first end of the tie bolt and a second rotor shaft is fixed to a second end of the tie bolt. The rotor structure further comprises a plurality of impeller bodies arranged on the tie bolt between the two rotor shafts, wherein neighboring impeller bodies are connected to one another by means of hirth couplings. Each impeller body has on its radially-inner contour three axially extending portions that possess different bore diameters and axial lengths. The bore diameter of an intermediate axial portion is smaller than the bore diameters of the marginal axial portions.

A further rotor structure for turbomachinery of this type is disclosed in <CIT>.

As would be appreciated by those skilled in the art, turbomachinery, such as centrifugal compressors, may involve rotors of tie bolt construction (also known in the art as thru bolt or tie rod construction), where the tie bolt supports a plurality of impeller bodies and where adjacent impeller bodies may be interconnected to one another by way of elastically averaged techniques, such as involving hirth couplings or curvic couplings. As would be appreciated by the artisan, these coupling types use different forms of face gear teeth (straight and curved, respectively) to form a coupling between two components. As would be further appreciated by the artisan, these couplings and associated structures are typically subject to greatly varying forces (e.g., centrifugal forces) during operation of the turbomachine.

The present inventors have recognized that during operation of known turbomachinery, such as from an initial rotor speed of zero revolutions per minute (RPM) to a maximum rotor speed, (e.g., as may involve tens of thousands of RPM) different deflections (e.g., involving relative radial and/or axial growth) may develop at axial interface locations and this relative growth is undesirable. For example, high relative radial and/or axial growth at the axial interface locations could lead to increases in rotor vibration and could further lead to angular misalignments at the axial interface locations that can potentially lead to impaired contact patterns and increased levels of mechanical stresses and distortion at the hirth coupling interfaces.

In view of the foregoing considerations, disclosed embodiments make use of innovative structural features designed to reliably and cost-effectively accomodate or otherwise control or regulate relative radial and/or axial growth between corresponding interface locations, which may be effective for reducing rotor vibration over the life of a given turbomachine. The ability to control relative radial and/or axial growth between corresponding interface locations may be further effective to reduction of angular misalignments at the axial interface locations, which in turn would be effective to establish reliable contact patterns and reduced levels of mechanical stresses and distortion (e.g., angular distortion) at the hirth coupling interfaces.

<FIG> illustrates a fragmentary cross-sectional view of one non-limiting embodiment of a disclosed rotor structure <NUM>, as may be used in industrial applications involving turbomachinery, such as without limitation, compressors (e.g., centrifugal compressors, etc.).

In one disclosed embodiment, a tie bolt <NUM> extends along a rotor axis <NUM> between a first end and a second end of the tie bolt <NUM>. A first rotor shaft <NUM><NUM> may be fixed to the first end of tie bolt <NUM>. A second rotor shaft <NUM><NUM> may be fixed to the second end of tie bolt <NUM>. Rotor shafts <NUM><NUM>, <NUM><NUM> may be referred to in the art as rotor shafts. A plurality of impeller bodies <NUM>, such as impeller bodies <NUM><NUM> through <NUM>n, may be disposed between rotor shafts <NUM><NUM>, <NUM><NUM>. In the illustrated embodiment, the number of impeller bodies is six and thus n=<NUM>; it will be appreciated that this is just one example and should not be construed in a limiting sense regarding the number of impeller bodies that may be used in disclosed embodiments. The embodiment illustrated in <FIG> involves a center-hung configuration of back-to-back impeller stages; it will be appreciated that this is just one example configuration and should not be construed in a limiting sense regarding the applicability of disclosed embodiments.

The plurality of impeller bodies <NUM> is supported by tie bolt <NUM> and is mechanically coupled to one another along the rotor axis by way of a plurality of hirth couplings, such as hirth couplings <NUM><NUM> through <NUM>n-<NUM>. In the illustrated embodiment, since as noted above, the number of impeller bodies is six, then the number of hirth couplings would be five. It will be appreciated that two additional hirth couplings <NUM><NUM> and <NUM><NUM> may be used to respectively mechanically couple the impeller bodies <NUM>n,<NUM><NUM> respectively proximate to the first and second ends of tie bolt <NUM> to rotor shafts <NUM><NUM>, <NUM><NUM>.

As may be better conceptually appreciated in respective zoomed-in views <NUM> and <NUM> of non-limiting representative impeller bodies <NUM><NUM> and <NUM><NUM>, a radially-inner contour of an impeller body <NUM> of the plurality of impeller bodies may have at least two distinct axially-extending zones (e.g., Z1, Z3) each having a respective geometry configured to control relative radial and/or axial growth between corresponding interface locations along the rotor axis at which corresponding faces <NUM> (<FIG>) of a respective hirth coupling <NUM> mesh or otherwise engage with one another. Three distinct axially-extending zones are involved, such as a first axially-extending zone Z1, a second-axially-extending zone Z3 and an intermediate axially-extending zone Z2, which is disposed between first and second axially-extending zones Z1 and Z3.

The respective geometry of the at least two axially-extending zones may be characterized by a differing bore diameter size (e.g., D1, D2, D3). That is, the respective bore diameters of zones Z1, Z2, Z3 may each have different sizes relative to one another. The respective geometry of the at least two axially-extending zones (e.g., zones Z1, Z2, Z3) may be characterized by a differing axial length (e.g., L1, L2 L3). That is, the respective axial lenghts of zones Z1, Z2, Z3 may each have different lenghts relative to one another. The respective geometry of the at least two axially-extending zones may be characterized by at least one of the following: a differing bore diameter size, and a differing axial length. That is, a differing bore diameter size or a differing axial length, or both.

Because of cross-sectional shape resemblance, without limitation, first axially-extending zone Z1 may be conceptually analogized to the toe section in an stiletto-style shoe; second-axially-extending zone Z3 may be conceptually analogized to the heel section of the shoe; and intermediate axially-extending zone Z2 may be conceptually analogized to the shank section disposed between the toe section and the heel section of the shoe.

Accordingly, in view of the above-noted shape resemblance, first axially-extending zone Z1 may be referred to as an impeller toe section; second-axially-extending zone Z3 may be referred to as an impeller heel section; and intermediate axially-extending zone Z2 may be referred to as an impeller shank section. The respective geometry of such toe, shank and heel impeller sections may each be configured to control the relative radial and/or axial growth that, for example, can develop between the impeller heel section and toe section of certain adjacent impellers, such as between the toe section of impeller body <NUM><NUM> and the heel section of impeller body <NUM>n; or, in another example, can develop between the respective impeller heel sections of adjacent impellers at the midspan of tie bolt <NUM>, such as between the heel section of impeller body <NUM><NUM> and the corresponding heel section of impeller body <NUM><NUM>.

Without limitation, the respective geometries of such sections of the impeller bodies may be appropriately configured to appropriately balance mass distribution and in effect balance the mass moment of inertia about the axis of rotation of the impeller bodies so that in turn the respective resulting centrifugal forces that develop in the toe, shank and heel impeller sections are appropriately balanced (e.g., in the impeller body illustrated in the zoomed-in view <NUM>, the respective resulting centrifugal forces are schematically represented by arrows Fz1, Fz2 and Fz3).

The foregoing structural and/or operational relationships are conducive in disclosed embodiments to control the relative radial and/or axial growth that can develop between corresponding interface locations along the rotor axis at which corresponding faces <NUM> of a respective hirth coupling <NUM> mesh or otherwise engage with one another, such as between the corresponding impeller heel section and toe section of certain adjacent impeller bodies.

It will be appreciated that the zoomed-in views <NUM> and <NUM> shown in <FIG> of impeller bodies <NUM> illustrate a constant bore diameter in connection with zones Z1, Z2, Z3; it will be appreciated that such zones need not have a constant bore diameter. According to the invention, the respective geometry of intermediate zone Z2 is characterized by a varying bore diameter along rotor axis <NUM>. A maximum value of the varying bore diameter of intermediate zone Z2 is larger relative to the respective bore diameters (D1, D3) of the first and second axially-extending zones (Z1, Z3). That is, if one were to revolve the radially-inner contour of intermediate zone Z2 about the axis of revolution (e.g., rotor axis <NUM>), then a resulting surface of revolution need not be a cylindrical surface but, without limitation, could be at least one conical surface or another non-cylindical surface of revolution or combination of such surfaces.

By way of example, second axially-extending zone Z3 of the radially-inner contour of the impeller body may be located axially downstream relative to first axially-extending zone Z1 of the radially-inner contour of impeller body <NUM> and relative to an inlet eye <NUM> of impeller body <NUM>.

As may be better appreciated in <FIG>, mutually opposed axial sides of first and second axially-extending zones Z1, Z3 of adjacent impeller bodies <NUM> may define respective notches <NUM> configured to receive a radially-outward portion <NUM> of the corresponding faces of the respective hirth coupling <NUM> that mesh with one another. Since the respective notches <NUM> defined by the mutually opposed axial sides of first and second axially-extending zones Z1, Z3 of adjacent impeller bodies <NUM> are subject to controlled relative radial and/or axial growth, this feature is effective to inhibit misalignments and/or mechanical stresses that otherwise could develop between the corresponding faces of the respective hirth coupling.

As suggested above, an axial side of the first axially-extending zone Z1 of impeller body <NUM>n proximate to the first end of tie bolt <NUM> is mechanically coupled to first rotor shaft <NUM><NUM> by way of a further hirth coupling (e.g., hirth coupling <NUM><NUM>). In this case, as illustrated in <FIG>, the axial side of the first axially-extending zone Z1 of impeller body <NUM>n and a corresponding axial face of first rotor shaft <NUM><NUM> define respective notches <NUM> for supporting a radially-outward portion <NUM> of the corresponding faces of further hirth coupling <NUM><NUM>. Since the respective notches defined by the axial side of first axially-extending zone of impeller body <NUM>n and the corresponding axial face of first rotor shaft <NUM><NUM> are subject to controlled relative radial and/or axial growth, this feature is effective to inhibit misalignments and/or mechanical stresses that otherwise could develop between the corresponding faces of hirth coupling <NUM><NUM>.

The foregoing structural and/operational relationships are equally applicable to the axial side of first axially-extending zone Z1 of impeller body <NUM><NUM>, which is proximate to the second end of the tie bolt and which is mechanically coupled to second rotor shaft <NUM><NUM> by way of another hirth coupling (e.g., hirth coupling <NUM><NUM>). Accordingly, to spare the reader from pedantic and burdensome repetitive details, the foregoing structural and/operational relationships will not be disclosed again.

In operation, disclosed embodiments include structural and/or operational relationships (e.g., distinct axially-extending zones in the radially-inner contour of respective impeller bodies configured to balance mass distribution about the rotor axis) designed to control relative radial and/or axial growth between corresponding interface locations, thereby reducing rotor vibration over the life of a given turbomachine. Additionally, in operation disclosed embodiments offer superior and reliable contact pattern and reduced annular distortion at hirth coupling interfaces.

Claim 1:
A rotor structure (<NUM>) for a compressor, the rotor structure (<NUM>) comprising:
a tie bolt (<NUM>) that extends along a rotor axis (<NUM>) between a first end and a second end of the tie bolt (<NUM>);
a first rotor shaft (<NUM><NUM>) fixed to the first end of the tie bolt (<NUM>);
a second rotor shaft (<NUM><NUM>) fixed to the second end of the tie bolt (<NUM>);
a plurality of impeller bodies (<NUM><NUM>-<NUM>n) disposed between the rotor shafts (<NUM><NUM>,<NUM><NUM>), the plurality of impeller bodies (<NUM><NUM>-<NUM>n) supported by the tie bolt (<NUM>) and mechanically coupled to one another along the rotor axis by way of a plurality of hirth couplings (<NUM><NUM>-<NUM>n-<NUM>),
wherein a radially-inner contour of an impeller body (<NUM>) of the plurality of impeller bodies (<NUM><NUM>-<NUM>n) has at least two distinct axially-extending zones (Z1,Z2,Z3) each having a respective geometry configured to balance mass distribution about the rotor axis (<NUM>) and control relative radial and/or axial growth between corresponding interface locations along the rotor axis (<NUM>) at which corresponding faces (<NUM>) of a respective hirth coupling (<NUM>) of the plurality of hirth couplings (<NUM><NUM>-<NUM>n-<NUM>) mesh with one another,
wherein the radially-inner contour of the impeller body (<NUM>) comprises a first axially-extending zone (Z1), a second-axially-extending zone (Z3) and an intermediate axially-extending zone (Z2), which is disposed between the first and second axially-extending zones (Z1,Z3),
characterised in that the respective geometry of the intermediate zone (Z2) is characterized by a varying bore diameter (D2) along the rotor axis (<NUM>), wherein a maximum of the varying bore diameter (D2) of intermediate zone (Z2) is larger relative to the respective bore diameters (D1,D3) of the first and second axially-extending zones (Z1,Z3).