The subject matter disclosed herein relates to compressors and, generally, to machines that use rotating elements to act on working fluids, with particular discussion about geometry in the region where one or more blades couple to the body of the rotating element.
As used herein, the term “compressor” describes machinery that acts on a working fluid, for example, to distribute the working fluid under pressure to a process line. This machinery can embody compressors (e.g., centrifugal compressors) and blowers, with artisans understanding that the difference between the two resides in the operating pressures of the fluid at the discharge. Examples of process lines may be found in various applications including chemical, water-treatment, petro-chemical, resource recovery and delivery, refinery, and like sectors and industries.
Compressors typically include a drive unit that is configured to rotate a rotating element (also “impeller”). Examples of the drive unit include steam turbines, gas turbines, and electric motors. The impeller may have a central body with a plurality of blades disposed thereon. In certain configurations, the blades are exposed. Other configurations enclose the blades on the impeller with a shroud or cover. This shroud secures to the impeller at the top of the blades.
In operation, rotation of the impeller draws a working fluid into the compressor. The blades are configured to accelerate the working fluid outwardly from the center of rotation, ejecting the working fluid from the impeller under pressure. The compressor directs the working fluid to a discharge. In most configurations, the discharge couples with a pipe that connects the compressor to the process line.
Engineers and designers expend great efforts to develop impeller designs to improve performance of the compressor. Structure for the blades is known among their design considerations to dramatically affect flow of the working fluid across the blades and the impeller in general. However, while this structure needs to be configured to maximize fluid dynamic concerns (aerodynamic for gasses and hydrodynamics for liquid) in order to benefit operation of the compressor, structural concerns including vibrations and loading often stand in tension with fluid dynamics because such structural concerns can lead to damage that reduces compressor efficiency and, ultimately, may lead to costly repair and maintenance on the compressor.
In the compressor industry, impellers for compressors undergo rigorous testing to confirm, inter alia, various mechanical and fluidic properties of the blades. It is often standard to employ computer modeling (including finite element analysis) to calculate resonant frequencies and to confirm fluid dynamics of the impeller design. It is also standard to implement physical tests on actual hardware. These physical tests may utilize accelerometers that mount to the blades to measure vibrations (and other physical phenomenon) that occur, for example, in response to one or more strikes to the blade from an impact hammer.
Analysis of these models and tests confirms that “open” impellers, or those that forego the shroud about the blades, are particularly susceptible to vibration. Without the shroud, the blades are effectively configured as tapered beams that are secured at only one end (to the impeller body). This structure provides little, if any, means to dampen vibration that propagates at the unsecured end. Aerodynamic demands on the blades, however, frustrate attempts to increase the physical dimensions (or other physical aspects) of the blades in a manner that could dampen vibration and improve mechanical performance.
This disclosure describes improvements to impellers and, generally, rotating elements, to address the competing interests between fluid dynamics and structural integrity of the blades. As noted herein, the embodiments below define geometry for a joint region at the root of the blade where the blade secures to the impeller body. This geometry includes a profile that is configured to enhance mechanical properties of the blade and to improve flow of the working fluid outwardly from the impeller. The profile can comprise an arc or fillet that forms a concave surface between the root of the blade and the impeller body. This fillet has a radius that varies along the chord length of the blade. In one implementation, the radius decreases from the leading edge of the blade to the trailing edge of the blade.
The improvements find use across various types and styles of impellers. As discussed below, use of the profile in accordance with the concepts herein is particularly beneficial to improve performance on “open” impellers and/or those impellers that have exposed blades. One particular type of open impeller, known as a splitter-type impeller, is configured with blades of different dimensions that populate the outer surface of the impeller. These configurations typically include one set of “main blades” that extend substantially along the axial length of the impeller body and one set of “splitter blades” that are shorter than the “main blades.” In conventional practice, one of the splitter blades is disposed between an adjacent pair of the main blades.
Reference is now made briefly to the accompanying drawings, in which:
Where applicable like reference characters designate identical or corresponding components and units throughout the several views, which are not to scale unless otherwise indicated. Moreover, the embodiments disclosed herein may include elements that appear in one or more of the several views or in combinations of the several views.
The embodiments below address vibration of blades in open impellers. These embodiments introduce a variably-dimensioned feature at the bottom, or root, of the blade to raise the resonant frequency of the blade. The variably-dimensioned feature has a profile exemplified, in one embodiment, by an arc or a fillet with a radius that decreases from the leading edge to the trailing edge of the blade. The fillet modifies the structure of the blade in a manner that raises the resonant frequency at the leading edge above the frequency that results from operation of the compressor at speeds within its normal operating range. During modeling and testing, an unexpected result of use of the fillet was to improve aerodynamic performance of the impeller by reducing the wake zone at the trailing edge of the blade.
Turning first to
The blade 104 has a blade body 116 that extends axially along the longitudinal axis 112. The blade body 116 has a root 118 (also “base 118”) proximate the annular body 102 and a top 120 disposed radially outwardly of the root 118. In “open” impellers, the top 120 is exposed and, thus, likely to vibrate during operation of a compressor. The blade body 116 also has a first edge 122 and a second edge 124, one each disposed proximate the first end 106 and the second end 108 of the annular body 102. In one example, the profile extends annularly around one of the first edge and the second edge of the blade. The blade body 116 may terminate at the outer peripheral edge 114 with the second edge 124 terminating and/or formed integrally with the outer peripheral edge 114 of the annular body 102. The edges 122, 124 area also referred to as the “leading edge 122” and as the “trailing edge 124” of the blade body 116, the determination of which is based on the direction of flow of a working fluid F across the impeller 100. In one embodiment, the first or leading edge 122 is spaced apart from the first end 106 of the annular body 102.
As also shown in
The geometry includes a profile that varies in a direction along the longitudinal axis 112. At a high level, the profile forms a curved or concave surface between the root 118 of the blade body 116 and the outer surface 110 of the annular body 102. The dimensions of the profile, and in one example the concave surface, may decrease, for example, along the longitudinal axis 112 in a direction along the longitudinal axis 112 from the first end 106 of the annular body to the second end 108 of the annular body 102. This configuration can result in higher operating efficiencies for a compressor that uses the impeller 100 because the blade body 116 exhibits a higher resonant frequency with the variably-dimensioned feature that forms the concave surface with the larger dimensions found at the leading edge 122. The profile also configures the blade body 116 to meet other structural and aerodynamic requirements necessary for use in a compressor. In practice, these requirements often conflict with one another. Structural concerns, for example, need the blade body 116 to be of stout geometry to minimize vibration and tolerate high stresses. On the other hand, aerodynamic concerns favor geometry that reduces the “footprint” of the blade body 116 in the flow of the working fluid F to minimize drag and/or to optimize other fluid dynamics of the working fluid F that passes across the blade body 116 during operation of a compressor.
Referring now to
Values for the radius R of the fillet 128 change (or vary) along the blade body 116 between the leading edge 122 (
The radius R may decrease linearly, or in near linear manner, from the first value to the second value. However, this disclosure does contemplate step-wise changes that apply an increment to decrease the value of the radius R from the leading edge 122 (
In practical implementation, values for the radius R of the fillet 128 may satisfy an aspect ratio (also, “fillet ratio”) and a thickness ratio. The fillet ratio relates the values for the radius R in accordance with Equation (1) below:
where Rf is the aspect ratio, V1 is the first value of the radius R at the leading edge 122 (
where Rt is the thickness ratio, V1 is the first value of the radius R at the leading edge 122 (
The thickness of the blade body 116 can also correspond with the values for the radius R. In general, the thickness of the blade body 116 decreases radially from the root 118 to the top 120. This construction forms the blade body 116 in a manner that minimizes drag of the working fluid F (
As also shown in
The blades 252, 254, 258 can have an axial length, typically measured as the straight line distance between the leading edge 222 and the trailing edge 224 of the blade body 216. This distance is often referred to as the “chord length” or the “meridional length” of the blades 252, 254, 258. As noted above, in splitter-type impellers, the axial length of the first main blade 252 (the “first axial length”) and the second main blade 254 (“the second axial length”) are the same. In some embodiments, the axial length of the third blade 258 (“the third axial length”) is often axially shorter than the first axial length and the second axial length.
As also shown in
The compressor 266 has an inlet 268 with an inner wall 270 that defines a flow area 272. The inner wall 270 can form part of a component commonly referred to as an “inlet guide blade housing cover” or “inlet housing” that has a first end and a second end. In the present example, the first end of the inlet housing forms an opening to receive working fluid during operation of the compressor 266. At the second end, the inlet housing couples with a volute 274 that has an outlet 276 (also, “discharge 276”). Examples of the discharge 276 are configured to couple the compressor 266 with industrial piping, conduits, and like flow-related structures. As also shown in
Use of the variably-dimensioned fillet 128 (
wherein fi is the frequency, Ω is the operating speed (or “rotation speed”) of the compressor, and n is the Engine Order. The first resonant frequency 302 corresponds with blades (e.g., blades 252, 254 of
In view of the foregoing, the embodiments of this disclosure may comprise one or more clauses alone or in any suitable combination. Examples of such clauses follow below:
A1. An impeller, comprising an annular body with a longitudinal axis, the annular body having a first end with a first diameter and a second end with a second diameter that is larger than the first diameter; a blade disposed on the annular body and extending axially along the longitudinal axis, the blade having a root proximate the annular body and a top disposed radially outwardly of the root, wherein the blade and the annular body form a joint region that extends along the root of the blade, the joint region having a profile that varies in a direction along the longitudinal axis from the first end of the annular body to the second end of the annular body.
A2. The impeller of claim A1, wherein the profile is configured in accordance with an aspect ratio between a first dimension of the profile proximate the first end of the annular body and a second dimension of the profile proximate the second end of the annular body, and wherein the aspect ratio is configured so that the profile increases from the first end to the second end.
A3. The impeller of claim A1, wherein the profile forms an arc with a radius, and wherein the radius has a first value proximate the first end and a second value proximate the second end, and wherein the first value is larger than the second value.
A4. The impeller of claim A1, wherein the blade has a first side and a second side disposed annularly apart from the first side, and wherein the joint region is formed on both the first side and the second side of the blade.
A5. The impeller of claim 1, wherein the blade has a first edge and a second edge, one each disposed proximate the first end of the annular body and the second end of the annular body, and wherein the profile extends annularly around one of the first edge and the second edge of the blade.
A6. The impeller of claim 5, wherein the annular body has an outer peripheral edge at the second end, and wherein the second edge of the blade terminates at the outer peripheral edge.
A7. An impeller, comprising an annular body having a frusto-conical shape with a longitudinal axis; a first blade disposed on the annular body, the first blade having a first blade body with a root proximate the annular body, the first blade body extending axially along the longitudinal axis; and a first fillet disposed at the root of first blade body and the annular body, the first fillet having a radius with a value that varies along the longitudinal axis.
A8. The impeller of claim A7, wherein the frusto-conical shape finals a first end of the annular body with a first diameter and a second end of the annular body with a second diameter that is larger than the first diameter, wherein the value of the radius of the first fillet has a first value at the first end and a second value at the second end, and wherein the first value is larger than the first value.
A9. The impeller of claim A8, wherein the first fillet is configured in accordance with an aspect ratio between the first value and the second value, and wherein the aspect ratio is configured so that the value of the radius decreases from the first value to the second value.
A10. The impeller of claim A8, wherein the first fillet is configured in accordance with a thickness ratio between the first value of the radius and a thickness of the blade as measured at the root, and wherein the thickness ratio is configured so that the radius decreases from the first value to the second value.
A11. The impeller of claim A7, further comprising a second blade disposed on the annular body and annularly adjacent the first blade, the second blade having a second blade body with a root proximate the annular body, the second blade body extending axially along the longitudinal axis; and a second fillet disposed at the root of the second blade body and the annular body, the second fillet extending axially along the second blade.
A12. The impeller of claim A11, wherein the second fillet has a radius that is the same the radius of the first fillet.
A13. The impeller of claim A1, wherein the radius of the second fillet remains constant along the longitudinal axis in the direction from the first end to the second end of the annular body.
A14. The impeller of claim A13, wherein the first blade has a first axial length and the second blade has a second axial length, each of the first axial length and the second axial measured in a direction along the longitudinal axis, and wherein the second axial length is the same as the first axial length.
A15. The impeller of claim A11, further comprising a third blade disposed on the annular body and annularly adjacent to both the first blade and the second blade, the third blade extending axially along the longitudinal axis, wherein the third blade is axially shorter than the first blade and the second blade.
A16. A compressor to provide a working fluid to a process line, comprising an impeller comprising an annular body having a plurality of blades formed integrally therewith, wherein the plurality of blades comprises a first blade that forms a first concave surface with the annular body that extends along at least part of the first blade, and wherein the first concave surface has a radius that decreases along the first blade in a direction from the first end to the second end of the annular body.
A17. The compressor of claim A16, wherein the plurality of blades comprises a second blade that is annularly offset from the first blade, wherein the second blade forms a second concave surface with the annular body that extends along at least part of the second blade, and wherein the radius of the second concave surface is the same as the radius of the first concave surface.
A18. The compressor of claim A17, wherein the first concave surface and the second concave surface extend around the periphery of the first blade and the second blade, respectively.
A19. The compressor of claim A17, wherein the plurality of blades comprises a third blade disposed annularly between the first blade and the second blade, wherein the third blade forms a third concave surface with the annular body, and wherein the radius of the third concave surface is different from the first concave surface and the second concave surface.
A20. The compressor of claim A19, wherein the radius of the third concave surface remains constant along the third blade in the direction from the first end to the second end of the inlet housing.
As used herein, an element or function recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or functions, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the claimed invention should not be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.