Patent Description:
A compressor stator vane unit comprises a base for engaging with a (semi-circle) slot in a compressor casing and an airfoil extending from the base for cooperating with airfoils of blade units on the compressor rotor. Engagement of the vane unit with the casing slot conventionally is realized through protrusions extending from transversal faces of the base which cooperate with longitudinal grooves in a side walls of the slot. A plurality of vane units may be slid into the slot for forming a stage of the compressor. To minimize relative motion, wear, and chatter of the vane units and slot, <CIT> teaches providing (i) blind-holes in longitudinal faces of the bases such that the blind-holes are aligned along their axes, and (ii) pins for assembling into two blind-holes in the bases of adjacent vane units in a stage thus connecting the two vane units (see <FIG>). <CIT> discloses a guide vane ring for thermal turbomachines, in particular aircraft engines, wherein guide vane feet of the guide vanes have grooves. Thereby, a ring element is positioned in a ring groove formed by the grooves of all the guide vane feet, which ring groove is open on one side for insertion of the ring element.

All vane units in a stage may so be connected through the pins to form a vane ring, or at least halve a ring in a first halve of the casing. A disadvantage of the prior art method is that the robustness of the vane ring is not very controllable. For instance, the tightness of the fit between adjacent vane units in the vane ring may vary, resulting in sub-optimal damping characteristics and thus in wear and chatter over time.

To overcome this technical problem, the invention provides a vane assembly according to claim <NUM>. Advantageously, the invention overcomes the variability in fitting the vane units in a vane ring, thus providing a more robust ring with improved damping characteristics. More in particular, the invention allows clamping the individual vane units on a single shared connecting part, the lacing bar, which thus functions as the robust back bone of the assembly.

In the assembly the through-holes of adjacent vane units together form a cavity, wherein the cavity and the lacing bar have distinct/dissimilar arcuate shapes (i.e. have different radii of curvature) for providing a predefined tension in a vane assembly. Advantageously, the dissimilar arcuate form factors of the cavity formed by the through-holes and the lacing bar enable the vane assembly to be constructed with a predefined and reproducible tension causing the vane units to be clamped on the lacing bar. As all units in the assembly are similarly clamped to a single shared back bone, the variability present in the prior art solution is drastically diminished. This reduced variability improves the damping characteristics and thus minimizes wear of the vane units. Advantageously, the cross section of the lacing bar can be dimensioned to create a predefined spring force when it is inserted in the assembled units. Moreover, the lacing bar - in contrast to the pin of the prior art - will be elastically deformed through bending upon insertion into and through the through-holes, thus providing the tension for reproducibly interconnecting the vane units in the assembly.

The through-holes in adjacent vane units within the assembly are straight and together form a polygonal cavity in, respectively through, which the lacing bar is insertable. Advantageously, in case of vane units with a rectangular base this overcomes the difficulty of machining the prior art blind-holes which are angled relative to the longitudinal base faces to accommodate the curvature of the casing slot. More sophisticated vane unit bases are trapezoidal allowing abutting the longitudinal base faces of adjacent units in the assembly, and (optionally) have adapted bottom faces congruent with the slot curvature.

The lacing bar comprises a predefined arcuate shape for providing a predefined tension in a vane assembly. Advantageously, the predefined arcuate shape of the lacing bar enables providing a predefined and reproducible tension. Moreover, the arcuate shape of the lacing bar enables easy and convenient assembly of vane units positioned in the slot and the lacing bar into a vane assembly.

In an embodiment, the arcuate shape of the lacing bar comprises a radius of curvature which deviates > <NUM>% to <NUM>% from an average radius of curvature of the through-holes (e.g. the polygonal cavity), preferably <NUM>% to <NUM>%, more preferably <NUM>% to <NUM>%. Advantageously, once assembled in the through-holes of the vane units and given the difference in radius of curvature of the lacing bar and polygonal cavity, the elasticity of the lacing bar provides the predefined tension in the vane assembly for clamping the vane units to the lacing bar. Moreover, this allows for the vane units in the vane assembly to be pushed tight with their base protrusions into the longitudinal grooves in the slot side walls. Consequently, this improves the damping characteristics of the vane assembly and minimizes wear.

In an embodiment, the lacing bar has a length corresponding with the length of a slot in the (half-) casing of a compressor. Such a lacing bar length allows connecting the vane units of (half) a vane ring into a single assembly. Advantageously, this allows for forming a single assembly from all, or half, the vane units of a vane ring. The single assembly can be fitted in a casing slot in a well-controlled fashion improving the damping characteristics and thus minimizing wear.

In an embodiment, the lacing bar comprises a plurality of lacing bar components. Advantageously, this allows advanced options to define the desired tension and adjust it to the specifics of the compressor specifications. Consequently, this improves the compressor specific damping characteristics of the vane assembly and minimizes wear.

In an embodiment, the lacing bar components have end sections enabling engagement with a second lacing bar component for forming a combined vane assembly from a first and second vane assembly. Advantageously, multiple lacing bars may be used to assemble a plurality of vane assemblies into a vane ring, enabling easier mounting by maintenance staff.

In an embodiment, the end sections are selected from the group consisting of (i) slot & tongue end sections, (ii) hole & plug end sections, (iii) overlapping end sections, (iv) oblique end sections, and (v) flat end sections. Advantageously, the shape of the end sections is designed to promote contact between a first and second lacing bar component for improving the damping characteristics of a combined vane assembly. The interconnecting end sections are especially advantageous at the split line of two half-casings of an axial gas turbine compressor to engage and interlock the vane assemblies in each half to form a single integrated vane ring building a stage of the compressor.

In an embodiment, in cross-section the lacing bar and/or the lacing bar components comprise a plurality of members together forming the lacing bar, respectively the lacing bar component. Advantageously, the members allow advanced options to define the desired tension and adjust it to the specifics of the compressor specifications.

In an embodiment, each vane unit base comprises a plurality of through holes positioned between its longitudinal faces, and the vane assembly comprises a plurality of lacing bars, each lacing bar arranged in the assembly through a corresponding through hole of the plurality of through holes, for creating a predefined tension. Advantageously, this allows each vane unit to be clamped to more than one lacing bar (such as two, three, or four) further reducing the variability in connecting the vane units to a single robust assembly. Moreover, this allows for the vane units in the vane assembly to be pushed tight with their base protrusions into the semi-circular longitudinal grooves in the slot side walls. Consequently, incorporating a plurality of lacing bars improves the damping characteristics of the vane assembly and minimizes wear.

In an embodiment, the through-holes in the vane unit bases comprise a bushing or lining. Advantageously, the bushing and lining inside the through-hole improve the damping and wear characteristics of the assembly.

According to another aspect, the invention provides a method for assembling a vane assembly according to claim <NUM>.

Appreciate, however, that these embodiments may not be construed as limiting the scope of protection for the invention. They may be employed individually as well as in combination. The invention is explained in more detail below with reference to the schematic drawing. It is shown in:.

Those skilled in the art will appreciate that elements in the drawings are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help improve understanding of the various embodiments of the invention. Furthermore, the terms "first", "second", and the like herein, if any, are used inter alia for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. Moreover, the terms "front", "back", "top", "bottom", "up", "down", "over", "under", "proximal", "distal", and the like in the description and/or in the claims, if any, are generally employed for descriptive purposes and not necessarily for comprehensively describing exclusive relative position. Also, the term "engagement feature" may also constitute a "disengagement feature". Skilled artisans will therefore understand that any of the preceding terms so used may be interchanged under appropriate circumstances such that various embodiments of the invention described herein, for example, are capable of operation in other configurations and/or orientations than those explicitly illustrated or otherwise described.

Referring to <FIG>, perspective views of a vane assembly <NUM> according to the invention for use in axial gas turbine compressors are shown. <FIG> shows a vane assembly comprising three vane units <NUM> connected with a lacing bar <NUM>. Each vane unit <NUM> has a base <NUM> and an airfoil <NUM> extending from it for cooperating with airfoils of a blade unit on a compressor rotor. The vane unit bases have bottom faces for engaging the casing slot. Protrusions <NUM> extend from transversal faces of base <NUM> for engagement with a cooperating groove in a side wall of a casing slot (not shown) into which the vane units <NUM> are to be positioned. Between longitudinal faces of base <NUM>, through-holes <NUM> may be machined or cast for engagement with a lacing bar <NUM>. As shown in <FIG>, lacing bar <NUM> will be inserted into and through a through-hole <NUM> of base <NUM>. A vane assembly <NUM> is formed by lacing a plurality, such as two, three, four, or more, vane units <NUM> together through inserting a lacing bar <NUM> into and through the respective through-holes. <FIG> shows the possibility of providing a plurality of through-holes <NUM> (here two) in a vane unit base <NUM> for connecting the vane units <NUM> into a vane assembly <NUM>. Each of the plurality of through holes is positioned between the two opposing longitudinal faces of base <NUM>. In this embodiment a plurality of lacing bars <NUM>, such as two, three, or four, may be inserted into respective through holes. Advantageously, lacing the vane units <NUM> together into assembly <NUM> using a lacing bar <NUM> overcomes the variability in fitting the vane units in a vane ring, thus providing a more robust ring with improved damping characteristics.

<FIG> provides side views of assembly <NUM> from a transversal (<FIG>) and longitudinal (<FIG>) perspective. <FIG> provides a cross sectional view along the line A-A of <FIG>. As the compressor casing of gas turbines usually comprises two semi-circular portions that are fitted together to encircle the rotor, the stator vanes units are assembled in vane ring segments for forming the stages of the compressor. A semi-circular slot in the two casing portions is arranged for engaging with the vane bases <NUM>, such that the airfoils <NUM> extend radially inward towards the shaft of the compressor rotor. The vane units are thus positioned on a semi-circle as is indicated in <FIG> with the slight curvature of the bases <NUM> in vane assembly <NUM>. Lacing bar <NUM> has an arcuate shape too, for easy assembly into the through-holes of the plurality of vane units <NUM> in assembly <NUM>.

Vane unit bases <NUM> may be machined or cast in a rectangular form. This however results in an inferior matching of adjacent vane units <NUM> and of the vane units and the casing slot. Hence, the vane units <NUM> are formed trapezoidal to match the longitudinal faces of adjacent vane units <NUM>. Moreover, the units may have adapted bottom faces congruent with the slot curvature.

The through-holes <NUM> in the vane bases <NUM> together form a cavity when the vane units <NUM> are positioned adjacent to each other in assembly <NUM> in the semi-circular slot. Consequently, the cavity has an arcuate shape. The cavity has an arcuate shape distinct from that of lacing bar <NUM>. Thus, the radius of curvature of the arcuate shape of lacing bar <NUM> may be larger, equal (as long as the arcuate shape is distinct), or smaller than the (average) radius of curvature of the cavity formed by the through holes of a number of adjacent vane units <NUM>. Hence, the arcuate shape of lacing bar <NUM> may comprises a radius of curvature which deviates > <NUM>% to -<NUM>% from that of the through holes, preferably <NUM>% to <NUM>%, more preferably <NUM>% to <NUM>%. Preferably, the radius of curvature of the arcuate shape of lacing bar <NUM> is smaller. The through-holes are straight for easy machining and/or casting. In this later case, the through-holes <NUM> of adjacent vane units build a polygonal cavity into which lacing bar <NUM> is insertable, as can be seen in <FIG>. The difference between the radius of curvature of the arcuate shape of lacing bar <NUM> and the average radius of curvature of the polygonal cavity, results in an elastic bending deformation of lacing bar <NUM>, as indicated by the forces F<NUM> and F<NUM> in <FIG>. The elastically bend lacing bar <NUM> improves the damping characteristics of the vane assembly. Hence, wear of the vane bases <NUM> and casing slot is reduced. Advantageously, arranging the lacing bar and the through holes in the respective bases such that the lacing bar is elastically deformed, respectively bend, when inserted into and through the through-holes causes each individual vane unit to be clamped onto the lacing bar.

The forces F<NUM> and F<NUM> may be chosen in accordance with the specification of the compressor. The tension provided by lacing bar <NUM> is dimensioned by selecting, amongst others, an appropriate difference in radius of curvature, material, cross-sectional size and form factor, and/or configuration of lacing bar <NUM>. Thus, preferably all parts and features of the vane assembly <NUM> and its components (i.e. vane unit <NUM>, base <NUM>, through hole <NUM>, lacing bar <NUM>) are dimensioned in such way that the curvature of the bottom faces of the combined vane units in the vane assembly closely matches the curvature of the mounting slots in the compressor casing. Advantageously, the vane assembly can then be mounted in the slot without elastic stresses between the assembly and the casing. As a result the internal stresses on the lacing bar <NUM> remain unchanged and well-defined, and thus the clamped vane units on the lacing bar back bone remain robustly secured. Moreover, inserting the vane assembly in the slot is more convenient for operating personnel.

<FIG> shows different embodiments of lacing bar <NUM>. As an example, lacing bar <NUM> may be cylindrical (5A), may have a rectangular (5B), such as a square, or a polygonal (5C & 5F) cross section, such as a hexagon or cross. Moreover, lacing bar <NUM> may comprise a plurality of members <NUM> for tuning the resilient characteristics of the lacing bar. As an example, a cylindrical lacing bar may be formed by two halves (5D), four quarters (5E) or any number of pie-shaped members. As another example, a cross shaped lacing bar <NUM> may comprise a plurality of rectangular members (5F). To further tune the characteristics of lacing bar <NUM>, and thus the tension and damping achieved in assembly <NUM>, the lacing bar members <NUM> may comprise different materials. Preferably, the material of lacing bar <NUM> and/or lacing bar members <NUM> is chosen from the class of ferritic-martensitic stainless steels, and is close to the composition of the material from which the vane units <NUM> are manufactured. Alternatively, austenitic stainless steels, duplex steels, or other materials, and combinations thereof, may be used to benefit from different thermal expansion characteristics.

The vane assembly <NUM> may be assembled with a lacing bar (<NUM>) having a length corresponding with a length of the slot in the compressor casing for connecting the vane units (<NUM>) of (halve) a vane ring into a single assembly (<NUM>). Alternatively, lacing bar <NUM> may comprise lacing bar components <NUM> that in lengthwise combination form lacing bar <NUM>. The lacing bar components allow for easier insertion into the through holes, especially when the assembly is performed "in the field". In order to maintain the integrity of the damping characteristics of vane assembly <NUM>, the lacing bar components <NUM> comprise end sections <NUM> allowing two adjacent components to engage for forming a single assembly <NUM> from a first and second assembly. To this purpose end sections <NUM> may be formed such that two adjacent components interlock inside the cavity formed by through-holes <NUM>. Several examples of appropriately formed end sections <NUM> are depicted in <FIG>, as well as in <FIG>. The latter figure shows end sections <NUM> from the type (i) slot & tongue end sections (6A), (ii) hole & plug or pin end sections (6B), (iii) overlapping end sections (6C), (iv) oblique end sections (6D), and (v) flat or butt end sections (6E).

Under practical circumstances, lacing bars <NUM> will preferably connect <NUM> to <NUM> vane units <NUM> into a vane assembly <NUM>. The length of a vane unit is typically between <NUM> and <NUM>. Thus, the length of a lacing bar <NUM> (or lacing bar component <NUM>) ranges from <NUM> to <NUM>. Alternatively, the lacing bar <NUM> could extend up to the length of the casing slot, which in dependence of the specification of the compressor ranges between about <NUM> and about <NUM> (semi-circle) for casing diameters of utility gas turbines in the range of <NUM> to <NUM>. The typical diameter for lacing bar <NUM> ranges between <NUM> and <NUM>, preferably between <NUM> and <NUM>. This dimension may be chosen in relation to the actual geometry of the vanes unit bases <NUM>.

The through-hole <NUM> may have a circular cross-section and forms a circumferential polygonal cavity in the vane units <NUM> of vane assembly <NUM>. Alternatively, through-holes <NUM> may have differently shaped cross-sections, such as a polygonal cross-section. Preferably, lacing bar <NUM> will have a cross-section congruent with the cross section of through-holes <NUM>. Thus, preferably it has a circular cross-section. It may, however, have other cross sections, for instance polygonal, such as square, rectangular, hexagonal, etc. Optionally, lacing bar <NUM> or lacing bar components <NUM> may be composed of one or more members <NUM>, for instance a plurality of pie-shaped members, that fill the desired cross section of the lacing bar or lacing bar component.

Preferably, the tension created by the assembly of the lacing bar <NUM> into the vane assembly <NUM> will be in the range of <NUM> N to <NUM> N. The designed tension is realized through many factors, including but not limited to,.

Although the invention has been elucidated with reference to the embodiments described above, it will be evident that alternative embodiments may be used to achieve the same objective. The scope of the invention is therefore not limited to the embodiments described above.

As an example, through-holes <NUM> may be lined, for example with a bushing or other appropriate lining component or coating. Advantageously, the lining improves the damping and wear characteristics of vane assembly <NUM>, thus improving the effective operational life of the gas turbine compressor in which the invention is implemented.

Claim 1:
A vane assembly (<NUM>) comprising a plurality of vane units (<NUM>) and a connecting part comprising a lacing bar (<NUM>), wherein each of the circumferentially arranged vane units comprises at its outer periphery a base (<NUM>), wherein longitudinal base faces of adjacent vane units circumferentially oppose each other, the bases (<NUM>) being trapezoidal allowing the abutting of the adjacent longitudinal base faces, each base (<NUM>) having a through-hole (<NUM>) extending between opposing longitudinal faces of the base and wherein in the assembly the through-holes (<NUM>) of adjacent vane units are straight and together form a circumferential polygonal cavity, wherein the lacing bar (<NUM>) is formed such that it is insertable into and through the through-holes (<NUM>) for coupling at least two adjacent vane units (<NUM>) into the vane assembly (<NUM>),
wherein, when assembled, the lacing bar (<NUM>) is arranged through the through-holes of the plurality of vane units, wherein the cavity and the lacing bar (<NUM>) have dissimilar arcuate shapes, and wherein a difference between a radius of curvature of the arcuate shape of the lacing bar (<NUM>) and an average radius of curvature of the polygonal cavity results in an elastic bending deformation of the lacing bar (<NUM>) when inserted, such that each individual vane unit (<NUM>) is clamped onto the lacing bar by means of a force-fit, the force-fit being created by radially inwards and outwards directed bending forces (F1, F2) induced in inner and outer areas of contact between the lacing bar and the straight through-holes (<NUM>), the radial forces being predefined by selecting an appropriate difference in radius of curvature, material, cross-sectional size and/or
form factor between the
force-fit components of the vane assembly (<NUM>).