COMPRESSOR IMPELLERS
An impeller includes a hub having a direction of rotation, a plurality of impeller blades extending from the hub, each blade having a downstream end, an upstream end, a leading surface facing the direction of rotation of the hub, and a trailing surface facing opposite to the direction of rotation of the hub. The impeller further includes a secondary flow reducer extending towards the downstream end and the upstream end of the at least one of the plurality of impeller blades, the secondary flow reducer defining first and second surfaces intersecting one of the leading surface and the trailing surface of the at least one of the plurality of impeller blades as well as a third surface between the first and second surfaces.
1. Technical Field
Embodiments of the present invention relate generally to compressors and, more specifically, to secondary flow of process fluid proximate to compressor impeller blades.
2. Description of Related Art
A compressor is a machine which increases the pressure of a process 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 process fluid input to the compressor by way of centrifugal acceleration, e.g., by rotating a centrifugal impeller (sometimes also called a “rotor”) by which the process 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 for the flow of process fluid to be compressed, an impeller including blades which are capable of imparting kinetic energy to the input process fluid and a diffuser which converts the kinetic energy of the process fluid flowing away from the rotor into pressure energy.
The flow of the process fluid from the inlet to the diffuser may be categorized as primary or secondary. Primary flow is desirable and may be considered to be efficient progression of the process fluid through the compressor. Conversely, secondary flows are undesirable and may require the compressor to perform additional work to achieve the demanded pressure rise in the process fluid. Secondary flows are potentially troublesome not only during a compression process, stage or stages, but also, thereafter, when downstream components of the compressor are exposed and potentially compromised or otherwise prevented from performing optimally by such flows.
While a large percentage of the process fluid may move by way of a primary flow through the compressor, at least some portion of the process fluid may move by way of a secondary flow, particularly process fluid in close proximity to the impeller blades. For example, some portion of the process fluid flow may form a boundary layer near the face of an impeller blade and slow down relative to other portions of the process fluid being compressed. As another example, some portions of the flow may migrate transversely to a desired flow across the impeller blades. These portions may cause or be part of a secondary flow.
To address the problem of secondary flow, there has been a focus on the design of impeller blade shapes. As a result, blade shapes have evolved to the point where proposed changes oftentimes result in only incremental gains in compressor efficiency and/or performance. Moreover, these changes are oftentimes difficult and expensive to implement particularly where the design of other compressor components must be changed to accommodate the proposed changes to the shape of the impeller blades. Consequently, there may be a resistance to proposed change in compressor design, particularly in the design of impeller blade shape. Therefore, what is needed is a solution to the problem of secondary flows which is more readily accepted for integration to both new and existing impeller blade designs and further which may preserve the overall shape of a given impeller blade design.
SUMMARY OF THE INVENTIONAccording to an embodiment, an impeller includes a hub having a direction of rotation, a plurality of impeller blades extending from the hub, each blade having a downstream end, an upstream end, a leading surface facing the direction of rotation of the hub, and a trailing surface facing opposite to the direction of rotation of the hub. The impeller further includes a secondary flow reducer extending towards the downstream end and the upstream end of the at least one of the plurality of impeller blades, the secondary flow reducer defining first and second surfaces intersecting one of the leading surface and the trailing surface of the at least one of the plurality of impeller blades. The secondary flow reducer further defines a third surface between the first and second surfaces.
According to another embodiment, a turbo machine includes a rotor assembly including at least one impeller, a bearing connected to, and for rotatably supporting, the rotor assembly, and a stator. The at least one impeller includes a hub having a plurality of impeller blades. At least one of the impeller blades includes a plurality of ribs for reducing a secondary flow proximate to the at least one impeller blade.
According to another embodiment, a method of configuring an impeller blade surface to provide reduced secondary flow can include the steps of identifying an ideal streamline of the impeller blade surface and adding a rib to the blade surface coincident with the streamline, the rib defining first and second surfaces intersecting the surface and defining a third surface between the first and second surfaces.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:
The following description of embodiments of the present invention refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to the terminology and structure of a turbo machine that has a stator and a rotor. However, the embodiments to be discussed next are not limited to these systems, but may be applied to other systems.
Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.
To provide some context for the subsequent discussion relating to the reduction of secondary flows within a compressor according to these embodiments of the present invention,
The multistage centrifugal compressor operates to take an input process gas from duct inlet 52, to accelerate the process gas particles through operation of the rotor assembly 48, and to subsequently deliver the process gas through various interstage ducts 54 at an output pressure which is higher than its input pressure. The process gas may, for example, be any one of carbon dioxide, hydrogen sulfide, butane, methane, ethane, propane, liquefied natural gas, or a combination thereof. Between the impellers 46 and the bearings 50, sealing systems (not shown) are provided to prevent the process gas from flowing to the bearings 50. The housing 42 is configured so as to cover both the bearings 50 and the sealing systems, so as to prevent the escape of gas from the centrifugal compressor 40.
A more detailed illustration of an impeller 46 is provided in
A detailed view of the trailing surface 76 of a pair of impeller blades 60 is shown in
As shown in
As may be further appreciated from
A streamline may be unique with respect to other streamlines on the same surface, for example, a streamline proximate to hub 62 may be different from a streamline proximate to shroud 64. As another example, a single secondary flow reducer 80 may define more than a single streamline, for example, a secondary flow reducer 80 may branch into two interconnected streamlines.
The secondary flow reducers 80 in
In a test involving the simulated operation of impeller blade 60 including the secondary flow reducers shown in
In the graph of
A more detailed view of a secondary flow reducer 80 is shown in
In the embodiment shown in
As also shown in
In the embodiment of
As further shown in
In addition to improving the flow of process fluid, another benefit associated with secondary flow reducers according to embodiments of the present invention is the ease of integration with various impeller blade designs. Specifically, and as may be appreciated from
Thus, according to an embodiment shown in
The above-described 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. An impeller comprising:
- a hub having a direction of rotation;
- a plurality of impeller blades extending from said hub, each said blade having a downstream end, an upstream end, a leading surface facing said direction of rotation of said hub, and a trailing surface facing opposite to said direction of rotation of said hub; and
- a secondary flow reducer extending towards said downstream end and said upstream end of said at least one of said plurality of impeller blades, said secondary flow reducer defining a first surface and a second surface intersecting one of said leading surface and said trailing surface of said at least one of said plurality of impeller blades and a third surface between said first and second surfaces.
2. The impeller of claim 1, further comprising at least one of the plurality of impeller blades with at least one secondary flow reducer on said leading surface and said trailing surface, the flow reducer being designed following an ideal streamline.
3. The impeller of claim 2, wherein said ideal streamline is substantially parallel to lines associated with the endwalls of the at least one of the impeller blades.
4. The impeller of claim 1, wherein said first surface and said second surface intersect said trailing surface of said at least one impeller blade and extend opposite to said direction of rotation of said hub to said third surface thereby forming a rib on said trailing surface.
5. The impeller of claim 1, wherein said at least one secondary flow reducer comprises a plurality of secondary flow reducers on said trailing surface.
6. The impeller of claim 5, wherein said third surface of each said plurality of secondary flow reducers is congruent to said trailing surface thereby preserving an overall shape of said at least one of said plurality of impeller blades.
7. The impeller of claim 5, wherein said plurality of secondary flow reducers is evenly distributed across said trailing surface.
8. The impeller of claim 6, wherein, for each of said plurality of secondary flow reducers, a curvilinear line defined by said intersection of said first surface with said trailing surface is congruent to a curvilinear line defined by said intersection of said second surface with said trailing surface.
9. A turbo machine comprising:
- a rotor assembly including at least one impeller of claim 1;
- a bearing connected to, and for supporting the rotor assembly; and
- a stator.
10. A turbo machine comprising:
- a rotor assembly including at least one impeller;
- a bearing connected to, and for rotatably supporting, the rotor assembly; and
- a stator,
- wherein said at least one impeller includes:
- a hub having a plurality of impeller blades; and
- a plurality of ribs on at least one of said plurality of impeller blades for reducing a secondary flow proximate to said at least one impeller blade.
11. A method of configuring an impeller blade surface to provide reduced secondary flow, said method comprising:
- identifying an ideal streamline of said impeller blade surface; and,
- adding a rib to said blade surface coincident with said streamline, said rib defining first and second surfaces intersecting said blade surface and a third surface between said first and second surfaces.
12. The impeller of claim 6, wherein said plurality of secondary flow reducers is evenly distributed across said trailing surface.
13. The impeller of claim 2, wherein said first surface and said second surface intersect said trailing surface of said at least one impeller blade and extend opposite to said direction of rotation of said hub to said third surface thereby forming a rib on said trailing surface.
14. The impeller of claim 3, wherein said first surface and said second surface intersect said trailing surface of said at least one impeller blade and extend opposite to said direction of rotation of said hub to said third surface thereby forming a rib on said trailing surface.
15. The impeller of claim 2, wherein said at least one secondary flow reducer comprises a plurality of secondary flow reducers on said trailing surface.
16. The impeller of claim 3, wherein said at least one secondary flow reducer comprises a plurality of secondary flow reducers on said trailing surface.
17. The impeller of claim 4, wherein said at least one secondary flow reducer comprises a plurality of secondary flow reducers on said trailing surface.
Type: Application
Filed: Jun 11, 2014
Publication Date: May 5, 2016
Inventors: Alberto SCOTTI DEL GRECO (Firenze, Florence), Libero TAPINASSI (Firenze, Florence)
Application Number: 14/895,224