Turbomachines, such as turbines, engines, and compressors, include pluralities of stationary vanes and rotating blades. These are typically arranged in alternating stacked airfoil rows disposed around and along the longitudinal axis of the machine, with the vanes affixed to the turbine casing and the blades affixed to a disk connected to a shaft. Efforts have been made to improve the efficiency of such machines by indexing or “clocking” the relative circumferential positions of airfoils in one row to the circumferential positions of airfoils in adjacent or nearby rows. Typically, such improvement is achieved by reducing the impact of vane wake on the rotating blades.
Some turbomachines, such as gas turbines, include a diffuser disposed adjacent the final stage of the turbine. Such a diffuser is configured to decelerate the exhaust flow, converting dynamic energy to a static pressure rise, and do so more efficiently when circumferential variation in the flow entering the diffuser is reduced. Known turbomachines and clocking methods do not address or consider the circumferential variation of the flow field entering the diffuser. In fact, some clocking methods may increase circumferential variation in order to provide efficiencies in other areas of the turbine, such as increased energy efficiency or decreased vibration and stress in the airfoils.
Embodiments of the invention relate generally to turbomachines and, more particularly, to the clocking of turbomachine airfoils to reduce airflow pressure variations entering a diffuser of the turbomachine.
In one embodiment, the invention provides a turbomachine comprising: a diffuser; a plurality of airfoil rows, including: a first airfoil row adjacent the diffuser, the first airfoil row being of a first type selected from a group consisting of: stationary vanes and rotating blades; a second airfoil row adjacent the first airfoil row, the second airfoil row being of a second type different from the first type; and a third airfoil row of the first type adjacent the second airfoil row, wherein at least one of the plurality of airfoil rows is clocked, relative to another airfoil row of the turbomachine, reducing variations in airflow circumferential pressure at at least one spanwise location in the diffuser adjacent the first airfoil row in an operative state of the turbomachine.
In another embodiment, the invention provides a method of reducing variation in airflow pressure entering a diffuser of a turbomachine, the method comprising: calculating airflow across at least three airfoil rows of the turbomachine, the at least three airfoil rows including: a first airfoil row adjacent a diffuser of the turbomachine, the first airfoil row being of a first type selected from a group consisting of: stationary vanes and rotating blades; a second airfoil row adjacent the first airfoil row, the second airfoil row being of a second type different from the first type; and a third airfoil row of the first type adjacent the second airfoil row; evaluating a pressure variation at at least one spanwise location of the diffuser; and determining whether the pressure variation is within a predetermined target.
In still another embodiment, the invention provides a method of reducing variation in airflow pressure entering a diffuser of a turbomachine, the method comprising: calculating airflow across at least airfoil rows of the turbomachine; evaluating a first pressure variation at at least one spanwise location of a diffuser of the turbomachine; changing a relative clocking position of at least one of the three airfoil rows; recalculating airflow across the at least three airfoil rows; evaluating a second pressure variation at the at least one spanwise location of the diffuser; determining whether the second pressure variation is less than the first pressure variation; and in the case that the second pressure variation is less than the first pressure variation, operating the turbomachine using the changed relative clocking position of the at least one airfoil row.
These and other features of embodiments of the invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which:
It is noted that the drawings are not to scale and are intended to depict only typical aspects of the invention. The drawings should not, therefore, be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements among the drawings.
Similarly, one skilled in the art will appreciate that rows 110, 120, 130, 140, 150, and 160, which will be referred to below as a first, second, third, fourth, fifth, and sixth row, respectively, are intended to describe relative ordering of the rows. That is, a turbine or other turbomachine according to various embodiments of the invention may include more than the six airfoil rows shown in
The airfoils and their shapes shown in
The pitch of the airfoils may be described as the circumferential distance between corresponding features of adjacent airfoils of the same row. For example, as shown in
As can be seen in
One of ordinary skill in the art will appreciate that clocked airfoil rows will generally have substantially the same pitch, but with an airfoil in one row offset in position from a corresponding airfoil in the row with respect to which it is clocked.
While known clocking techniques have been employed to address other causes of inefficiency or strain, such as the impact of vane wake on rotating blades, such techniques generally have focused on “upstream” airfoil rows located furthest from the diffuser. Applicants have found that the clocking of late stage airfoils—those nearer the diffuser—can significantly reduce the variation in the flow field entering the diffuser, thereby improving diffuser performance and aerodynamic robustness. In some embodiments of the invention, the clocking of such late stage airfoils includes clocking at least two of three adjacent airfoil rows nearest the diffuser.
For example, referring again to
The calculation of airflows across turbomachine airfoils typically relies upon computational fluid dynamics (CFD) to model turbulence. In some embodiments of the invention, this may include employing the Navier-Stokes or Reynolds-averaged Navier-Stokes solver equations—the basic governing equations for viscous, heat conducting fluids. Other solver equations may also be employed for any number of reasons, as will be appreciated by one skilled in the art.
The Navier-Stokes solver equations are a set of differential equations, including a continuity equation for the conservation of mass, conservation of momentum equations, and a conservation of energy equation. These equations employ spatial and temporal variables, as well as pressure, temperature, and density variables. One skilled in the art will recognize, of course, that other CFD equations and techniques may be used. Specifically, it should be noted that other solver equations may be employed and the use of other CFD equations, techniques, or solver equations is intended to be within the scope of the invention.
Returning to
As will be discussed below, one skilled in the art will recognize that, typically, pressure variation at the diffuser will not be eliminated entirely. As such, there will generally be some level of pressure variation at the diffuser that will be acceptable for a particular turbomachine. This may be, for example, a percentage deviation from an average pressure. Clocking airfoils according to embodiments of the invention will therefore typically seek to reduce pressure variation to a point equal to or less than such a targeted pressure variation.
At S3, the relative clocking position of at least one upstream row of airfoils of similar type is changed (e.g., where the airfoil row adjacent the diffuser is a blade row, the relative clocking position of an upstream row of blades is changed). For example, returning to
In other embodiments of the invention, changing the clocking at S3 may include changing the clocking of row 130 relative to row 150. One skilled in the art will recognize that other changes to the relative positions of upstream rows of airfoils in carrying out S3.
In any case, flow is recalculated at S4 using the changed clocking position and the pressure variation is reevaluated at S5.
At S6, it is determined whether the pressure variation at S5 is within a targeted pressure variation (e.g., 5% of the average pressure measured). If so (i.e., YES at S6), the changed clocking positions may be used in operation of the turbomachine at S7. If not (i.e., NO at S6), S3 through S6 may be iteratively looped until the pressure variation at S5 is found to be within the targeted pressure variation at S6.
The targeted pressure variation at S6 may be an absolute value (e.g., an amount of variation in p.s.i.), an amount of decrease in pressure variation (e.g., a decrease of 1%, 2%, 3%, etc.) with respect to the pressure variation at S2, or any pressure variation value less than the pressure variation at S2.
Returning to
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
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 related or 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.