Patent Application
20100303604
When the radial pressure gradient in the fluid stream of a turbine is minimized or eliminated, turbine stage efficiency can be significantly improved. Typical turbine inefficiencies may include noise production from several fluid dynamic sources, including wake cutting, high velocity fluid, and turbulent flow fields, including secondary flow vortices. The noise generally results from reflecting and turbulent wave fields incident upon the several stationary and moving blades downstream from a blade set that receives irregular pressure differentials and converts them into secondary flow vortices. As explanation, when a pressure gradient incident on a rotating blade set is intense enough, transient or sustained separation of fluid flow may occur in the vicinity of the trailing edges of the blades. This separation of fluid flow can result in secondary flow vortices directed downstream at stationary and moving blades, thus producing high-intensity noise instead of directing the fluid energy into the output shaft for power generation.
What is needed, therefore, is a system designed to reduce radial pressure gradients incident upon rotating blades and thereby direct the fluid energy into the output shaft instead of into the creation of noise.
Embodiments of the disclosure may provide a turbine having a working fluid. The turbine may include at least one set of rotor blades mounted radially symmetrically about a rotating shaft, wherein each rotor blade has a hub and a tip, and at least one stator axially-spaced from the at least one set of rotor blades and mounted radially symmetrically about the rotating shaft, wherein the at least one stator defines a plurality of radially-spaced vanes having inner and outer end walls that define end wall passages, wherein the end wall passages have a profile shaped to direct a working fluid to a plane substantially tangent to the inner and outer end walls.
Embodiments of the disclosure may further provide a stator for a turbine. The stator may include an inlet and an outlet, wherein the outlet is adjacent to at least one rotor blade having a hub and a tip, and a plurality of inner and outer end walls extending from the inlet to the outlet and defining a plurality of end wall passages having inner and outer radial limits, wherein the end wall passages have a profile configured to direct a working fluid to a plane substantially tangent to the inner and outer radial limits, wherein the plurality of inner and outer end walls are configured to substantially eliminate the radial pressure gradients incident between the hub and the tip of the at least one rotor blade, thereby attenuating the resultant acoustic signature.
Embodiments of the disclosure may further provide a method of reducing turbine acoustic signature. The method may include introducing a working fluid into a turbine having at least one stator adjacent to and axially-spaced from at least one rotor blade, wherein the stator comprises a plurality of radially-spaced vanes, each vane having an inlet and an outlet and defining a profile of an end wall passage including an inner and outer end wall, receiving the working fluid through the inlet of the end wall passage, channeling the working fluid through the profile of the end wall passage, and directing the working fluid out the outlet of the vane and substantially tangent to the inner and outer end walls, thereby substantially decreasing the radial pressure gradient incident between a hub and a tip of the at least one rotor blade, and thereby attenuating the resultant acoustic signature.
The present disclosure is best understood from the following detailed description when read with the accompanying Figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the present disclosure, however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure may repeat reference numerals and/or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and/or configurations discussed in the various Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Finally, the exemplary embodiments presented below may be combined in any combination of ways, i.e., any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure.
Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Further, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope.
According to an exemplary embodiment of the present disclosure, to reduce noise and thereby increase turbine efficiency, the end walls and airfoils of a turbine may be designed to reduce or eliminate radial pressure gradients and their potential secondary flow vortices which may excite downstream blade and vane rows into the production of noise. In particular, by channeling reflecting and turbulent flow waves into a continuously-flowing shape through the end walls and airfoils, the fluid flowpath of the working fluid becomes generally linear in the desired direction of flow. Consequently, with a generally linear flowpath, the working fluid may be channeled directly into the succeeding rotor row with a minimal hub to tip velocity differential. Thus, the fluid energy may be directed into the shaft to create work, rather than into the generation of inefficient noise.
The rotor blades 102 may each be provided with a root 108 configured to couple the blades 102 to the rotating shaft 106 which rotates around a central axis of the turbine 100. The stator vanes 104 may be in a fixed arrangement, typically mounted circumferentially to the outer casing 110 of the turbine 100 and extending inwardly therefrom.
In exemplary operation, a fluid, such as steam, air, products of combustion, or a process fluid such as CO2 or other fluid may be used as the working fluid. In an embodiment using steam, the fluid may include injected into the turbine 100 and follow a plurality of channels or passageways, depicted by the arrows 112, thus channeling itself through the various stages of rotor blades 102 and stator vanes 104. As the steam passes through the various stages of the turbine 100, the stator vanes 104 may be configured to direct the fluid into contact with the subsequent set of rotor blades 102, thereby causing the shaft 106 to rotate and produce work.
However, if the fluid flow directed at the rotor blades 102 is composed of a heightened hub-to-tip pressure gradient, the rotor blades 102 may become agitated and create noise, or they may produce secondary flow vortices, potentially exciting downstream blades 102 or vanes 104 whose vibrations will also create noise. According to one aspect of the present disclosure, to reduce or eliminate the production of noise, the passageways 112 of the vanes 104 may be profiled in a manner that directs the fluid flow in a generally uniform pressure toward the rotor blades 102.
Referring now to
In particular,
When fluid flows in the end wall passage 202 the flow is considered “attached” if it flows continuously in one direction in the space defined between the outer section 204 and the inner section 206. Although the velocity profile of the flow will generally proceed in an equivalent direction, it may change depending on whether the flow is laminar or turbulent. In typical operations, there will be a small boundary layer of slower flow adjacent to each profile 208, 210, but the flow in this boundary layer will be in the same direction as the flow in the rest of the space. If the boundary layer gets too thick that the flow within it reverses, a phenomenon called “hub separation” may occur, potentially creating eddy currents.
In turbines, the flow being accelerated through the end wall passage 202 generally flows in a direction tangent to the circumference at the point in the end wall passage 202 where it turns from the axial direction and is thereby accelerated. The flow continues “straight” in space, but the boundary profiles 208, 210 both curve inward or downward, tending to bunch up the flow at the outer profile 208 (locally curving toward it) and flow away from the inner profile 210 (locally curving away from it). As can be appreciated, this results in an uneven velocity flow distribution, and is the type of behavior that the present disclosure is designed to prevent or remedy.
During turbine 100 operation, a pressure gradient incident across the tip 212 and hub 214 of a rotor blade 102 may also generate “hub separation.” For example, the centrifugal acceleration of the working fluid in a turbine 100 generally forces, or “stirs,” the fluid away from the hub 214 and creates a substantially higher pressure near the tip 212 of the rotating blade 102 than at the hub 214. However, suppressing the pressure at the hub 214 may potentially cause a negative reaction, typically in the form of a significant potential pressure rise across the hub 214 sections of the blade 102. Blade 102 reaction may be characterized by the pressure drop across the blade 102 row divided by the pressure drop across the end wall passage 202. Since this pressure rise at the hub 214 cannot generally be supported, the hub 214 sections of the blade 102 may “separate,” resulting in a radial pressure gradient flowing out of the end wall passage 202.
The result of this pressure gradient on the rotating blade 102 is that secondary flow vortices may potentially develop and excite or vibrate downstream objects, such as rotor blade 102 and stator vane 104 rows. The excitation or vibration of rotor blade 102 and/or stator vane 104 rows may produce high-intensity noise representing fluid energy that is inefficiently wasted as noise production instead of being directed into the output shaft 106 for generation of power.
According to one exemplary embodiment of the present disclosure, the profiles 208, 210 may be configured to provide a constant and equalized pressure gradient across the rotating blades 102, thereby reducing or eliminating secondary flow vortices. Particularly, the specific profiles 208, 210 of the end wall passages 202 may be configured to mimic the tangential fluid flow exiting the stator vane 104 and make the exiting pressure substantially uniform as it extends from the hub 214 to the tip 212 of the subsequently located rotating blade 102. Uniform pressures incident on the rotating blades 102 minimize and/or prevent hub 214 “separation” that would normally result in the production of downstream noise, as described above.
The curvature, or shape, of the end wall 202 profiles 208, 210 may be derived via axial and radial projections, upstream from the rotating blades 102, from a pair of lines of revolution about a centerline of the turbine 100. Referring to
According to the present disclosure, with a substantially tangential fluid flow exiting the end wall 202, the incident pressures on the rotating blades 102 from the hub 214 to the tip 212 may be substantially uniform, and thus reducing or completely eliminating any secondary flow vortices. Particularly, using a profiled end wall 202 may direct a working fluid onto the rotating blades 102 such that the pressure at the hub 214 is equal to the pressure at the tip 212. By reducing the hub 214 to tip 212 pressure gradient incident on the rotating blades 102, as explained above, a reduction of downstream turbine 100 acoustic signature may result, thereby increasing turbine 100 efficiency.
The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the detailed description that follows. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.
