Patent Application
20050220615
This invention relates generally to rotary machine technology and, specifically, to the manufacture or modification of compressor stator blades.
In the past, natural frequency tuning of compressor stator blades has been accomplished by modifying the shape of the airfoil portion of the blade. It would be desirable, however, to be able to modify natural frequency of the airfoil of a compressor stator blade without having to modify the airfoil shape.
The present invention relates to a technique for natural frequency tuning of a compressor stator blade without modification of the airfoil portion (or simply, airfoil) of the blade. This technique enables the continued use of a customer's existing compressor stator blades when a need for frequency tuning arises. Alternatively, the frequency tuning technique described herein also may be employed in the manufacture of new compressor stator blades as well.
In an exemplary but non-limiting embodiment of the invention, material is removed from the base or mounting portion of the compressor stator blade via the formation of, for example, a single groove extending fully across the width of the base. It should be understood, however, that the invention is not limited to the formation of a single uniformly shaped groove. For example, multiple grooves could produce the same desired result. In addition, the depth and/or width of the one or more grooves may also vary. Thus, by the judicious removal of material in the stator blade base or mounting portion, the foundation stiffness of the airfoil portion of the blade is changed, which in turn also changes the natural frequency of the airfoil.
Accordingly, in its broader aspects, we have provided a method of tuning a compressor stator blade, having a base portion and an airfoil portion, to achieve a desired natural frequency, comprising a) identifying the natural frequency of the compressor stator blade; b) determining a different target natural frequency for the compressor stator blade; and c) removing material from the base portion of the compressor stator blade in an amount and in a configuration that achieves the target natural frequency.
In another aspect, we have provided method of tuning a compressor stator blade so as to achieve a desired natural frequency, wherein the stator blade has an airfoil portion and a base portion that is substantially rectangular, with a pair of relatively longer side surfaces, a pair of relatively shorter end surfaces a top surface and a bottom surface; the method comprising a) identifying the natural frequency of the compressor stator blade; b) determining a different target natural frequency for the compressor stator blade; and c) removing material from the base portion of the compressor stator blade in the form of a groove that is shaped to achieve the target natural frequency.
In still another aspect, we have provided a compressor stator blade comprising an airfoil portion and a base portion, the base portion having a substantially solid rectangular shape; and at least one groove cut across a width dimension of the base portion, the groove having dimensions selected to obtain a predetermined natural frequency for the airfoil portion.
The invention will now be described in detail in connection with the drawings identified below.
With reference initially to
It will be appreciated by those skilled in the art that the amount of material removed from the base or mounting portion is dependent upon the desired natural frequency. Thus, the width “W” of the groove and the depth “D” of the groove may be altered as necessary to achieve the targeted natural frequency. In addition, the sides 44, 46 of the groove 34 need not be straight or parallel, and the depth “D” of the groove may also vary across the flat base 48 of the groove. For example, surfaces 44, 46 may be oppositely curved (either convex or concave), and the depth D may vary linearly or non-linearly across the length and/or width of the groove. The desired frequency may also be achieved by forming one or more additional grooves of the same or different size and shape.
The removal of material from the stator blade base or mounting portion for purposes of tuning the natural frequency of the airfoil is a concept that may not only be retrofitted into existing compressor stator blades, but also used in the initial design and manufacture of compressor stator blades. The ability to utilize the invention in existing compressor stator blades provides a relatively quick hardware solution to a frequency related issue as compared to the normal cycle for the production of a new stator blade with a modified airfoil shape.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
