Patent Application
20120027578
This present application relates generally to turbine diffuser design, which, as used herein and unless specifically stated otherwise, is meant to include all types of combustion turbine or rotary engines, including gas turbine engines, aircraft engines, and others. More specifically, but not by way of limitation, the present application relates to turbine diffuser design providing robust diffuser and CDC performance.
In general, a turbine engine includes a compressor that delivers a supply of highly compressed air to a combustor for combustion with a fuel. The resulting flow of hot gases from the combustor drives the turbines from which work may be extracted. Turbine engines may be configured with an axial compressor that is mechanically coupled by a common shaft or rotor to a downstream turbine, with a combustor positioned between the compressor and the turbine. Air leaves the compressor with a relatively high velocity and, conventionally, a diffuser is utilized for initially decreasing the velocity of the compressed airflow and minimizing subsequent pressure losses. The diffuser may include splitter vanes that divide the airflow into separate diffuser passages. A diffuser dump region or cavity receives airflow from the diffuser, and further deceleration occurs there before the air is directed to annular channels surrounding the combustor. As is conventional, the compressor is provided with an inner compressor discharge inner barrel and a compressor discharge casing (CDC). The CDC interconnects the inner barrel and a first-stage nozzle.
A primary source of loss and turbulence in diffusers is vortex generation as flow enters the diffuser dump cavity. The diffuser dump cavity has the highest diffusion gradient, leading to vortex formation. As the fluid flow moves forward, the vortex grows and begins interacting with the upstream sections of the diffuser. Vortex growth elevates the fluid flow upstream of diffuser dump region and results in high loss and poor pre-diffuser and CDC performance.
As a result, there is a need for improved systems and apparatus that trap the vortex and arrest its growth in the dump cavity of the diffuser, thus reducing overall losses and ensuring robust diffuser performance.
The present application thus describes a discharge diffuser that includes: a forward section and a dump cavity, the forward section being configured to direct discharge from the compressor to the dump cavity; an inner diffuser wall that defines an inner radial flowpath of the upstream section; and an outer diffuser wall that defines an outer radial flowpath of the upstream section; wherein at an aft lip of the inner diffuser wall, the discharge diffuser comprises an overhanging step.
The present application further describes a discharge diffuser that includes: a forward section configured to direct compressor discharge from the compressor to a dump cavity; wherein: the forward section includes an inner diffuser wall and an outer diffuser wall, the outer diffuser wall flaring outwardly to define a widening flowpath therethrough; the dump cavity comprises a region of increased volume positioned downstream of the upstream section, the dump cavity being configured to surround at least a portion of a combustor; and at an aft lip of the inner diffuser wall, the discharge diffuser comprises an overhanging step, the overhanging step including a step wall that, from the aft lip, slants radially inward and in an upstream direction so that the step wall undercuts a portion of the inner diffuser wall.
These and other features of the present application will become apparent upon review of the following detailed description of the preferred embodiments when taken in conjunction with the drawings and the appended claims.
These and other features of this invention will be more completely understood and appreciated by careful study of the following more detailed description of exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:
As an initial matter, to communicate clearly the invention of the current application, it may be necessary to select terminology that refers to and describes certain parts or machine components of a combustion turbine engine. Whenever possible, common industry terminology will be used and employed in a manner consistent with its accepted meaning. However, it is meant that any such terminology be given a broad meaning and not narrowly construed such that the meaning intended herein and the scope of the appended claims is unreasonably restricted. Those of ordinary skill in the art will appreciate that often a particular component may be referred to using several different terms. In addition, what may be described herein as a single part may include and be referenced in another context as consisting of several component parts, or, what may be described herein as including multiple component parts may be fashioned into and, in some cases, referred to as a single part. As such, in understanding the scope of the invention described herein, attention should not only be paid to the terminology and description provided, but also to the structure, configuration, function, and/or usage of the component, as provided herein.
Further, as used herein, “downstream” and “upstream” are terms that indicate a direction relative to the flow of working fluid through the turbine. As such, the term “downstream” refers to a direction that generally corresponds to the direction of the flow of working fluid, and the term “upstream” generally refers to the direction that is opposite of the direction of flow of working fluid. The terms “aft” and “forward” may be used to describe relative position within the turbine engine. It will be appreciated that the compressor is generally referred to as residing on the “forward” side of the turbine engine while the turbine section resides on the “aft” side. Accordingly, as used herein, “forward” describes a position closer to the compressor and “aft” describes a position closer to the turbine. The term “radial” refers to movement or position perpendicular to an axis. It is often required to describe parts that are at differing radial positions with regard to an axis. In this case, if a first component resides closer to the axis than a second component, it may be stated herein that the first component is “radially inward” or “inboard” of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is “radially outward” or “outboard” of the second component. The term “axial” refers to movement or position parallel to an axis. Finally, the term “circumferential” refers to movement or position around an axis.
As shown by arrows in
Generally, the discharge diffuser 101 includes a dump cavity 110, which receives airflow from the forward section 101 (shown by arrows). It will be appreciated that within the dump cavity 110, air is directed into the annular channels surrounding the combustor.
The inner diffuser wall 102 terminates at an aft lip 113. As used herein, the aft lip 113 is the downstream or aft termination point of the inner diffuser wall 102, as indicated in
According to embodiments of the present application, the discharge diffuser 100 includes an overhanging step 116, which, as discussed more below, serves to minimize or trap or arrest the growth of vortices in this region. The overhanging step 116 generally includes a step wall 118 that slants radially inward and in an upstream direction, thereby undercutting an aft portion of the inner cavity wall 112, as shown in the cross-sectional views of
The step wall 118, as shown, may be planar, and, in cross-section, generally forms an angle 306 with a radial reference line, which is specifically illustrated in
The aft lip 113 of the inner diffuser wall 102 may include several preferred configurations. In one configuration, as shown in
In a preferred embodiment, the shape of the connection made between the step wall 118 and the inner cavity wall 112, as shown, includes a rounded, fillet region. As will be appreciated, this may prevent stress concentrations. Other configurations are also possible.
Further, it has been discovered through experimentation and computer modeling of flow patterns that certain dimensions are particularly more effective at controlling or limiting vortex formation than others.
It will be appreciated that the design of the diffuser 100 also facilitates uniform flow distribution across a transition piece 504 and prevents the formation of hot spots. The resulting flow field reduces overall losses and improves the diffuser 100 performance. Further, containment of the mitigated vortex 502 relieves the stringent need of having a uniform flow profile at the compressor, without negatively affecting performance. The reduced losses in the CDC may also allow a higher margin of loss during compressor or combustor design, providing significant performance and financial benefit.
Table 1 compares the performance of the conventional diffuser 400 with that of the diffuser 100. Four scenarios are considered, having different leakage levels set at the fourteenth stator (S14) of the compressor, the leak being between the airfoil at S14 and the CDC. 0.3% leak at S14 is the design point for the present example. The pressure loss is measured according to the following equation 1:
It should be noted that, typically, significant effort is invested in uniformly maintaining such low levels of leakage. The reduced losses in the diffuser 100 may impart some flexibility during compressor or combustor design and may further relax the stringent requirements for maintaining leakage levels.
Table 1 shows that the diffuser 100 lowers the pressure loss due to vortex growth compared to the conventional diffuser 400. It should be noted that the claimed diffuser design provides robust performance not only at design point, but also across various operating conditions. Thus, the diffuser 100, according to the embodiments of the present disclosure, restricts vortex growth and limits upstream flow interaction with the vortex, leading to substantial improvements in diffuser and CDC performance.
As one of ordinary skill in the art will appreciate, the many varying features and configurations described above in relation to the several exemplary embodiments may be further selectively applied to form the other possible embodiments of the present invention. For the sake of brevity and taking into account the abilities of one of ordinary skill in the art, all of the possible iterations is not provided or discussed in detail, though all combinations and possible embodiments embraced by the several claims below or otherwise are intended to be part of the instant application. In addition, from the above description of several exemplary embodiments of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are also intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof.
