Patent Application
20140064933
The subject matter disclosed herein relates to compressor devices (e.g., centrifugal compressors) and, in particular, to diffusers and diffuser vanes for a compressor device.
Compressor devices (e.g., centrifugal compressors) use a diffuser assembly to convert kinetic energy of a working fluid into static pressure by slowing the velocity of the working fluid through an expanding volume region. An example of a diffuser assembly typically utilizes several diffuser vanes in circumferential arrangement about an impeller. The design (e.g., shapes and sizes) of the diffuser vanes, in combination with the preferred orientation of the leading edge and the trailing edge of the diffuser vanes with respect to the flow of the working fluid, often determine how the diffuser vanes are affixed in the diffuser assembly.
To add further improvement and flexibility to the design, some examples of a diffuser assembly incorporate variable diffuser vanes. These types of diffuser vanes move to change the orientation of the leading edge and the trailing edge. This feature helps to tune operation of the compressor device. Known designs for variable diffuser vanes rotate about an axis that resides in the lower half, i.e., closer to the leading edge than the trailing edge of the diffuser vanes.
The location for the axis of rotation permits the trailing edge to sweep through large angles and, thus, enables better tuning and optimization of compressor performance. However, although use of these variable diffuser vanes can improve performance, implementation of the conventional designs for variable diffuser vanes move (e.g., rotate) both the trailing edge and the leading edge with respect to the incoming working fluid. This feature can have a negative impact on the performance of the compressor. The change in position of the leading edge, which results from the change in angular orientation of the diffuser vane, can cause the flow of the working fluid to prematurely separate from the surface of the diffuser vane, thus reducing the effectiveness of the variable diffuser vane to tune performance of the compressor device.
This disclosure presents embodiments of a diffuser assembly that incorporates diffuser vanes with a trailing edge that changes position to improve flow performance of a compressor device. The diffuser vanes, however, maintain the position of the leading edge relative to the orientation of the working fluid. When implemented, e.g., in a compressor device, these embodiments prevent pre-mature flow separation of the incoming working fluid from the surfaces of the diffuser vane. At least this feature can provide better control and optimization of compressor performance over a large flow range.
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.
Broadly, the discussion below focuses on improvements in diffuser and diffuser assembly design to realize better performance in compressor devices, e.g., centrifugal compressors. In one aspect, these improvements address issues that arise as a result of re-orientation in the angular position of diffuser vanes inside the diffuser assembly. As set forth below, embodiments of the proposed diffuser assembly allow the trailing edge to be positioned as desired but maintains the orientation of the leading edge on diffuser vanes relative to the direction of flow of a working fluid that flows past the diffuser vanes in the diffuser assembly.
As shown in the detail of
The rotation axis 114 resides proximate the leading edge 104 and, for example, within 5% or less of the chord length L (as measured from the leading edge 104). Depending on the size and shape of the tip 112, other exemplary locations for the rotation axis 114 can be found within an area that the radius RTIP defines about the center axis 118. In one example, the rotation axis 114 is coaxial with the center axis 118 of the tip 112.
As best shown in
The pivot boundary 130 defines the circumferential location of the leading edges 104 of the diffuser vanes 100, e.g., relative to the impeller axis 128. Construction of the diffuser assembly 124 can affix the diffuser vane 100 to limit movement of the diffuser vanes 100 to rotation about the rotation axis 114. This configuration minimizes displacement of the leading edge 104 relative to the pivot boundary 130 and relative to one another. In one example, the rotation axis 114 on the diffuser vanes 100 align with the pivot boundary 130. However, in other examples, one or more of the diffuser vanes 100 can be spaced apart from the pivot boundary 130, e.g., aligned in a different circumferential location relative to the impeller axis 128. As shown in
As mentioned above, during operation of the diffuser assembly 124, the diffuser vanes 100 in the vane array 126 can rotate (or pivot) about the rotation axis 114, e.g., to change the angular position of the trailing edge 106. The angular position accommodates changes in the direction of the flow of the working fluid. The orientation of the leading edge 104, however, remains relatively unchanged with respect to the direction and/or orientation of the flow F of the working fluid. This feature provides a much more consistent point of impact for the working fluid on the leading edge 104 throughout the vane array 126. Thus, despite the change in position of the trailing edge 106, the position of the leading edge 104 changes very little and, in turn, the diffuser vanes 100 in the diffuser assembly 124 exhibit minimal flow separation of the working fluid from the surfaces (e.g., suction side surface 108 and the pressure side surface 110 of
Examples of the pivot members 134 can use a number of devices and mechanisms to rotatably secure the leading edge 104 of the diffuser vanes 100. The pivot members 134 can be an integral extension of the diffuser vanes 100 or may be fabricated such as by welding or it may be a separately attached piece of material. Pins and bearings can insert, for example, into the diffuser vanes 100 along the rotation axis 114. These elements provide a pivot and/or pivot point about which the diffuser vanes 100 can rotate. In one example, the diffuser assembly 124 can include a plurality of support devices, with one of the support devices secured to the bottom surface of each of the diffuser vanes 100. Examples of the support devices can couple with actuators, linkages, and other mechanisms to impart movement to the diffuser vanes 100 in the vane array 126. The support devices can align with the rotation axis 114 and/or be constructively offset to allow rotation of the diffuser vanes 100 about the rotation axis 114 as set forth herein.
Referring now also to
Generally the compressor device 200 undergoes extensive performance testing and tuning to optimize performance for a given application. Such tuning will modify operation, e.g., of the drive unit 208, to adjust the speed of the impeller 210, which effectively modifies flow parameters (e.g., pressure, flow rate, etc.) of the working fluid that exits the outlet 206. Performance of the compressor device 200 will also change in response to the orientation of the diffuser vanes. In one example, tuning will involve adjusting the orientation of the diffuser vanes, which can modify, among other things, the pressure of the working fluid at the outlet 206. Collectively, optimization of flow parameters will likely include incremental changes to several operating parameters of the compressor device 200 to achieve a collective combination, including orientation of the diffuser vanes, that allows the compressor device 200 to operate efficiently to achieve desired flow parameters.
Examples of the diffuser vanes 100 can be constructed of various materials and combinations, compositions, and derivations thereof. These materials include metals (e.g., steel, stainless steel, aluminum), high-strength plastics, and like composites. Material selection may depend on the type and composition of the working fluid. For example, working fluids with caustic properties may require that the diffuser vanes comprise relatively inert materials and/or materials that are chemically inactive with respect to the working fluid.
Geometry for the diffuser vanes 100 can be determined as part of the design, build, and fitting of the compressor device 200 for the application. The geometry can include airfoil shapes, e.g., the shape shown in
In view of the foregoing discussion, embodiments of the diffuser vane and diffuser assembly contemplated herein improve performance of compressors and related devices. For example, and as set forth above, the trailing edge of the diffuser vanes rotates about the leading edge, which effectively reduces flow separation of the working fluid from the surfaces of diffuser vanes. This feature improves performance of the compressor over a larger flow range because the leading edge remains oriented with the flow direction of the working fluid.
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.
