Patent Application
20090285690
This disclosure relates to a blade and disk interface and, more particularly, to forming an undercut at the blade and disk interface to reduce stresses.
Gas turbine engine components, such as turbine blades, turbine vanes, compressor blades, compressor vanes, or other components typically operate in a relatively high stress and high temperature environment. The stresses and temperature may result in damage to the component from corrosion, erosion, deformation, or the like.
One example of a high stress area is an interface between a blade component and an associated disk component that supports the blade component for rotation about an engine axis. For example, a disk body for a turbine or compressor includes a plurality of slots with one blade component being secured within each slot. Typically, the blades have a dove-tail formation at one end that is slid into the slot from one side of the disk. The dove-tail formation includes a blade bearing surface that contacts a disk bearing surface formed as part of a surface that defines the slot. When the gas turbine engine is operation, the blades slide radially outward within the slot due to centrifugal loading. This relative movement generates stresses at certain interfaces between the blade and the disk, such as crush stresses, shear stresses, hoop stresses, etc.
One proposed solution utilizes an undercut in the slots to reduce stresses by minimizing contact area between the blade and disk at high-stress contact areas. A surface of the slot defines an angle that is formed between a line extending along a blade and disk bearing interface and a line tangent to the undercut. In one example, this angle is 14 degrees; however, it has been known to have this angle approach up to 60 degrees.
Traditionally, angles between 3 to 60 degrees have been recommended as providing the most significant stress reduction. Angles in excess of 90 degrees are disfavored because such high angles weaken the disk. This can cause cracking, which can result in pre-mature wear or failure. However, as gas turbine engines are configured to operate under higher speeds and more severe conditions, stresses at the blade and disk interface continue to be analyzed for further stress reduction opportunities.
An example blade and disk assembly includes a blade body and a disk body having a slot to receive the blade body. The blade body has a blade bearing surface. The slot has a disk bearing surface that contacts the blade bearing surface at a bearing interface. The slot has an undercut surface that is spaced apart from the blade body. An angle between the disk bearing surface and a line tangent to the undercut surface is at least 70 degrees.
In another aspect, the undercut surface transitions directly from the disk bearing surface to form an undercut in the slot.
In another aspect, the line tangent to the undercut surface is defined at a location where the undercut surface transitions from the disk bearing surface.
In one example, the angle is 70 degrees or greater and is less than 90 degrees.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.
The blade body 36 includes a blade bearing surface 40 that extends at an oblique angle to a surface 42 that extends outward of the slot 34. The blade bearing surface 40 comprises a linear surface that faces a surface that defines the slot 34.
The slot 34 is defined by a disk bearing surface 50 that is positioned opposite from the blade bearing surface 40. The disk bearing surface 50 comprises a linear surface that contacts the blade bearing surface 40 at a bearing interface during engine operation. An exaggerated gap is shown at the bearing interface for clarity purposes.
It is known that a high stress concentration area is formed at an interface between a transition edge 52 of the blade body 36 and a corresponding surface of the slot 34. In order to reduce stresses at this contact interface, an undercut 60 has been formed within the slot 34. The undercut 60 comprises a curved surface and transitions directly from the disk bearing surface 50 at each edge. As such, the undercut surface is spaced apart from the blade body 36 by a gap.
In this configuration, an angle A is defined between a line L1 extending along the bearing interface as the blade bearing surface 40 contacts the disk bearing surface 50, and a line L2 that is tangent to the undercut 60 at a point where the disk bearing surface 50 transitions to the undercut surface. This is shown in greater detail in
In one example, this angle A is at least 70 degrees.
Traditionally, angles larger than 60 degrees have been disfavored due to potential weakening of the disk body 32 at the undercut location. However, analysis has been performed, and it has been found that increasing the angle A to 70 degrees provides significant reductions in stresses.
As shown in
Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.
The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.
