Radial Diffuser Vane for Centrifugal Compressors
A turbo machine comprising a rotor assembly comprising at least one impeller, a bearing connected to the rotor assembly, wherein the bearing is configured to rotatably support the rotor assembly, and a stator comprising at least one diffuser connected to an exit portion of the at least one impeller, wherein the at least one diffuser comprises a plurality of diffuser vanes, wherein at least one of the plurality of diffuser vanes comprising a camber line defined by a function comprising an inflection point.
This is a national stage application under 35 U.S.C. §371(c), PCT application number PCT/EP2010/061788 filed on Aug. 12, 2010, the disclosure of which is hereby incorporated in its entirety by reference herein.
BACKGROUND OF THE INVENTIONEmbodiments of the present invention relate generally to compressors and, more specifically, to diffuser vanes for centrifugal compressors.
A compressor is a machine which accelerates gas particles to, ultimately, increase the pressure of a compressible fluid, e.g., a gas, through the use of mechanical energy. Compressors are used in a number of different applications, including operating as an initial stage of a gas turbine engine. Among the various types of compressors are the so-called centrifugal compressors, in which mechanical energy operates on gas input to the compressor by way of centrifugal acceleration, e.g., by rotating a centrifugal impeller (sometimes also called a “rotor”) by which the compressible fluid is passing. More generally, centrifugal compressors can be said to be part of a class of machinery known as “turbo machines” or “turbo rotating machines”.
Centrifugal compressors can be fitted with a single impeller, i.e., a single stage configuration, or with a plurality of impellers in series, in which case they are frequently referred to as multistage compressors. Each of the stages of a centrifugal compressor typically includes an inlet conduit (inducer section) for gas to be compressed, an impeller which is capable of imparting kinetic energy to the input gas and a diffuser which converts the kinetic energy of the gas leaving the rotor/impeller into pressure energy.
More specifically, as shown in the exemplary side-sectional view of
Of more interest for the present application is the diffuser section 106. Vaned diffusers 106 (i.e., those diffusers having a circumferential array of airfoils (diffuser blades 110) along the flow passage as best seen in
Reducing the distance taken by the fluid reduces the friction losses associated with the travel of the process fluid and thereby increases the efficiency of compressors which use vaned diffusers relative to compressors using vaneless diffusers. On the other hand, centrifugal compressor stages employing vaned diffusers 106 are also known for their reduced operating range as compared to their vaneless counterparts.
The operating range of a centrifugal compressor 100 including a vaned diffuser 106 is determined based, at least in part, on the shape of the diffuser blades 110 which are employed. The shape of a diffuser blade (or more generally any airfoil) can be expressed by its camber line, (i.e., a line drawn halfway between the upper surface of the diffuser blade and the lower surface of the diffuser blade), and the thickness distribution along the camber line. Two previously used diffuser blade shapes are shown in
Employing diffuser blades 200 having a straight camber line in a centrifugal compressor is problematic because, for example, the leading edge of the diffuser vane with that shape is relatively highly loaded and the compressor has a relatively low stall limit.
where, ro is the radius of the diffuser vane leading edge radial position, and α3 is the angle of absolute velocity at diffuser vane leading edge.
This diffuser blade shape also results in certain drawbacks when employed as part of a diffuser in a centrifugal compressor. For example, employing diffuser blades 208 having a conformal mapped camber line in a centrifugal compressor is problematic because the trailing edge of the diffuser vane with that shape is relatively highly loaded and the compressor has a relatively low choke limit.
Accordingly, it would be desirable to design and provide diffuser blades having shapes which improve the performance of centrifugal compressors and which address the aforementioned drawbacks of existing diffuser blade shapes.
BRIEF SUMMARY OF THE INVENTIONVarious devices, systems and methods according to exemplary embodiments of the present invention provide diffusers, e.g., as part of a turbo machine, with diffuser vanes having S-shaped camber lines. Such S-shaped camber lines are defined by functions having an inflection point along their length, or a portion of such curves. Using diffuser vanes having such shapes results in, among other things, an operational characteristic wherein a portion of the diffuser vanes disposed near a leading edge is substantially unloaded when operating at design conditions and wherein the load gradually increases to a maximum loading value towards a middle portion of the diffuser vanes.
According to an exemplary embodiment, a turbo machine includes a rotor assembly having at least one impeller, a bearing connected to, and for rotatably supporting, the rotor assembly, and a stator including at least one diffuser connected to an exit portion of the impeller, wherein the at least one diffuser includes a plurality of diffuser vanes, at least one of the plurality of diffuser vanes having a camber line defined by a function having an inflection point.
According to another exemplary embodiment, a method of manufacturing a turbo machine includes providing a rotor assembly including at least one impeller, connecting the rotor assembly to a bearing assembly to rotatably support the rotor assembly, and providing a stator assembly including at least one diffuser connected to an exit portion of the impeller, wherein the at least one diffuser includes a plurality of diffuser vanes, at least one of the plurality of diffuser vanes having a camber line defined by a function having an inflection point.
According to another exemplary embodiment, a diffuser includes an inner annular wall, an outer annular wall, a plate portion disposed between the inner annular wall and the outer annular wall, and a plurality of diffuser vanes disposed on the plate portion, at least one of the plurality of diffuser vanes having a camber line defined by a function having an inflection point.
The accompanying drawings illustrate exemplary embodiments, wherein:
The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.
To provide some context for the subsequent discussion relating to diffuser blades and diffuser blade shapes according to the exemplary embodiments,
The multistage centrifugal compressor 300 operates to take an input process gas from duct inlet 312, to accelerate the process gas particles through operation of the rotor assembly 308, and to subsequently deliver the process gas through various interstage ducts 314 (which include diffusers and diffuser blades described below) at an output pressure which is higher than its input pressure. The process gas may, for example, be any one of atmospheric air, carbon dioxide, hydrogen sulfide, butane, methane, ethane, propane, natural gas, or a combination thereof. Between the impellers 306 and the bearings 310, sealing systems (not shown) are provided to prevent the process gas from flowing to the bearings 310. The housing 302 is configured so as to cover both the bearings 310 and the sealing systems, so as to prevent the escape of gas from the centrifugal compressor 300. Those skilled in the art will appreciate that the centrifugal compressor 300 illustrated in
Turning now to the discussion of diffusers and diffuser blade shapes, a brief discussion of airfoils and airfoil terminology will assist the reader to better understand the exemplary embodiments. Looking at
According to exemplary embodiments, the camber lines of diffuser vanes are “5-shaped” which results in, among other things, more balanced loading between the leading and trailing edges of the vane as compared to the earlier described diffuser vane shapes and associated camber lines. An example of a diffuser vane 600 having an S-shaped camber line 602 according to an exemplary embodiment is provided as
Although described generally as “S-shaped” camber lines herein, diffuser blades or vanes according to these exemplary embodiments have camber lines which are more specifically defined by, for example, at least third order algebraic equations or functions. By way of contrast, the conventional diffuser vanes described above with respect to
y=ax3+bx2+cx+d
where a, b, c and d are constants. As will be discussed below, however, camber lines associated with diffuser blades according to other exemplary embodiments may be described by other types of functions.
Another S-shaped camber line 800 associated with a diffuser blade according to an exemplary embodiment is illustrated in
By employing S-shaped diffuser vanes as described above, the result is an unloading of the portion of the blade near to the leading edge at design conditions and a gradual load increase to a maximum loading towards the blade middle portion. An unloaded leading edge according to exemplary embodiments will suffer less flow separation at lower flow rates, thereby increasing the left operating limit of the compressor. These benefits associated with exemplary embodiments are shown by various simulation results described below and illustrated in
The results plotted in
Another simulation, the results of which are plotted in
To summarize, some of the efficiency benefits and advantages associated with using diffuser vanes or blades having S-shaped camber lines in centrifugal compressors include: higher efficiency toward the left (lower) operating range, thereby increasing the stall limit of the compressor, better or comparable efficiency at the design point relative to other designs and lower efficiency towards the choke limit relative to some designs (i.e., except conformal mapped camber line designs).
This simulation also showed a higher polytropic head raise for the S-shaped camber line diffuser according to an exemplary embodiment relative to the straight camber line diffuser and vaneless diffuser as shown in
Exemplary embodiments also include a method of manufacturing a turbo machine which can be expressed a shown in the flowchart of
In addition to manufacturing centrifugal compressors with diffuser vanes having S-shaped camber lines according to these various exemplary embodiments, it may further be desirable to retrofit existing centrifugal compressors having vaneless diffusers or diffusers with differently shaped diffuser vanes, with diffusers having S-shaped camber lines according to the exemplary embodiments to, for example, increase efficiency relative to vaneless diffusers or reduce the loss of range associated with existing vaned diffusers. Thus exemplary embodiments further contemplate the manufacture of diffusers themselves for retrofitting and/or repair of existing compressors.
As mentioned above, third order algebraic equations can be used to define camber lines according to some exemplary embodiments. However other types of equations, e.g., exponential equations, can also be used to define camber lines according to exemplary embodiments. For example, Sigmoid functions or Gompertz functions can also be used to define camber lines according to exemplary embodiments. Sigmoid functions, also known as logistic functions, can be expressed as:
while Gompertz functions take the form of:
y=ae[−be
Like the above described third order algebraic equations, these exponential equations also generate functions which have inflection points.
Additionally, higher order polynomial functions, e.g., fourth order or higher, can also be used to obtain the same s-shape. Moreover, according to other exemplary embodiments, more complicated shapes (with multiple inflection points) can be custom designed for a particular application. One way to define such generalized curves is through Bezier Curves. A Bezier curve forming the s-shape of camber lines according to exemplary embodiments can be described as shown in
Devices, systems and methods according to exemplary embodiments provide diffusers, e.g., as part of a turbo machine 300, with diffuser vanes having S-shaped camber lines 408. Such S-shaped camber lines 408 are defined by functions having an inflection point. Using diffuser vanes 400 having such shapes results in, among other things, an operation characteristic wherein a portion of the diffuser vanes 400 disposed near a leading edge 402 is substantially unloaded when operating at design conditions and wherein the load gradually increases to a maximum loading value towards a middle portion of the diffuser vanes.
The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. Thus the present invention is capable of many variations in detailed implementation that can be derived from the description contained herein by a person skilled in the art. All such variations and modifications are considered to be within the scope and spirit of the present invention as defined by the following claims. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items.
Claims
1. A turbo machine comprising:
- a rotor assembly comprising at least one impeller;
- a bearing connected to the rotor assembly, wherein the bearing is configured to rotatably support the rotor assembly; and
- a stator comprising at least one diffuser connected to an exit portion of the at least one impeller, wherein the at least one diffuser comprises: a plurality of diffuser vanes, wherein at least one of the plurality of diffuser vanes comprising a camber line defined by a function comprising an inflection point.
2. The turbo machine of claim 1, wherein the function is y=ax3+bx2+cx+d, where a, b, c and d are constants.
3. The turbo machine of claim 1, wherein the function is one of a higher order polynomial function, a Sigmoid function, a Gompertz function, and a Bezier curve.
4. The turbo machine of claim 1, wherein the function is an exponential function.
5. The turbo machine of claim 1, wherein a portion of the at least one of the plurality of diffuser vanes disposed near a leading edge is substantially unloaded when operating at design conditions, and wherein a load gradually increases to a maximum loading towards a middle portion of the at least one of the plurality of diffuser vanes.
6. The turbo machine of claim 1, wherein each of the plurality of diffuser vanes is attached to one of a hub or shroud.
7. The turbo machine of claim 1, wherein the function is a Bezier curve.
8. A method of manufacturing a turbo machine, the method comprising:
- providing a rotor assembly comprising at least one impeller;
- connecting the rotor assembly to a bearing assembly configured to rotatably support the rotor assembly; and
- providing a stator assembly comprising at least one diffuser connected to an exit portion of the at least one impeller, wherein the at least one diffuser comprises: a plurality of diffuser vanes, wherein at least one of the plurality of diffuser vanes comprises a camber line defined by a function comprising an inflection point.
9. The method of claim 8, wherein the function is y=ax3+bx2+cx+d, where a, b, c and d are constants.
10. The method of claim 8, wherein the function is one of a higher order polynomial function, a Sigmoid function, a Gompertz function, and a Bezier curve.
11. The method of claim 8, wherein the function is an exponential function.
12. The method of claim 8, wherein a portion of the at least one of the plurality of diffuser vanes disposed near a leading edge is substantially unloaded when operating at design conditions and wherein a load gradually increases to a maximum loading towards a middle portion of the at least one of the plurality of diffuser vanes.
13. The method of claim 8, further comprising:
- attaching each of the plurality of diffuser vanes to one of a hub or shroud.
14. The method of claim 8, wherein the function is a Bezier curve.
15. A diffuser comprising:
- an inner annular wall;
- an outer annular wall;
- a plate portion disposed between the inner annular wall and the outer annular wall; and
- a plurality of diffuser vanes disposed on the plate portion, wherein at least one of the plurality of diffuser vanes comprises a camber line defined by a function comprising an inflection point.
16. The diffuser of claim 15, wherein the function is y=ax3+bx2+cx+d, where a, b, c and d are constants.
17. The diffuser of claim 15, wherein the function is one of a higher order polynomial function, a Sigmoid function, a Gompertz function, and a Bezier curve.
18. The diffuser of claim 15, wherein the function is an exponential function.
19. The diffuser of claim 15, wherein a portion of the at least one of the plurality of diffuser vanes disposed near a leading edge is substantially unloaded when operating at design conditions, and wherein a load gradually increases to a maximum loading towards a middle portion of the at least one of the plurality of diffuser vanes.
20. The diffuser of claim 15, wherein the function is a Bezier curve.
Type: Application
Filed: Aug 12, 2010
Publication Date: Aug 29, 2013
Inventors: Sen Radhakrishnan (Bangalore), Susanne Clary Svensdotter (Le Creusot), Libero Tapinassi (Florence)
Application Number: 13/880,817
International Classification: F01D 9/00 (20060101);