Patent Application
20070081894
This invention relates generally to the field of turbo-machinery, and more particularly to the field of vibration damping in a rotating airfoil of a turbine.
It is well known that the rotating blades of turbo-machinery such as gas turbine engines may be excited into undesirable modes and magnitudes of vibration by forces exerted on the blade during operation of the machine. Left unchecked, such vibration can cause a blade to fatigue prematurely or even to fail catastrophically.
U.S. Pat. No. 5,820,343 describes an airfoil vibration-damping device that attaches to the airfoil platform and extends into a cooling air passage along a radial length of the airfoil. The damping device includes a plurality of bearing surfaces that make contact with the walls of the cooling air passage to dampen vibration of the airfoil during operation of the turbine in which the airfoil is used.
The invention is explained in following description in view of the drawings that show:
The blade assembly 10 of
Referring now to
A wear feature, such as wear pad 32, is attached to the airfoil section 18 interior to the blade 14. In the illustrated embodiment, the wear pad 32 is cast as an extension of one of the interior walls 26. The wear pad 32 is designed for rubbing contact with an associated wear feature, such as wear pad 34 of damper 12 as illustrated in
Prior art U.S. Pat. No. 5,820,343 purposefully avoids the installation of a vibration damper through the airfoil cooling passage inlets by supporting the damper on the platform of the turbine blade. However, the present inventor has recognized a disadvantage of supporting the damper from the platform because of the high level of stress that is generated in the platform during operation of the turbine as a result of the centrifugal forces acting upon the weight of the damper. The present inventor has also recognized a need to provide a flow limiting orifice in certain blade cooling passages in order to limit the maximum cooling fluid flow rate that may occur in the event of a major breach in the cooling passage pressure boundary. The present inventor has advantageously solved both of these problems by using the mounting base 38 as both a support for the damper 12 and as an orifice plate for choking the flow of cooling fluid through the inlet end 24 of the cooling passage 22. The mounting plate 38 may be formed and installed, such as by welding, effectively to seal the inlet end 24 with the exception of one or more openings 40 that function as flow limiting orifices. In this manner the centrifugal forces acting on the damper 12 may be supported directly by the root section 20 of the blade 14, thereby reducing stress levels within the blade assembly 10 and reducing the required strength (and therefore size and weight) of portions of the blade 14. The openings 40 are sized to control a cooling fluid flow by allowing a desired flow rate of cooling fluid during normal operation while at the same time providing effective flow resistance to limit the cooling fluid flow rate in the event of an off-design breach of a cooling passage pressure boundary such as may be caused by impact damage to the blade assembly 10. The openings are illustrated in
As shown in
During operation of the gas turbine engine 16, a turbine blade may experience vibration in several different modes: chord-wise vibration; easy-wise vibration (perpendicular to the blade chord); torsional vibration; and breathing mode vibration (expansion and contraction of the volume of the blade). A finite element model or other type of analysis tool may be used to predict the movement of various points on the blade 14. The location of the wear pads 32, 34 advantageously may be selected to limit the displacement of a point 44 on the blade 14 that would otherwise experience a maximum displacement due to operation-induced vibration without the action of the damper 12. For example, if the blade 14 is predicted to experience an easy-wise mode of vibration that results in a sinusoidal displacement in the blade having a maximum displacement at a particular radial position (i.e. along the blade length perpendicular to the rotational centerline), then the wear pads 32, 34 may be located at that particular radial position. The wear pads 32, 34 are oriented at that radial location so that wear pad 32 is forced into wear pad 34 by the vibrational motion of the blade 14 with sliding contact between the faces of the rubbing wear pads. Reaction forces between the wear pads 32, 33 will limit the maximum displacement in the blade 14 and vibration energy will be absorbed in the process, thus resulting in a lowered peak stress within the blade assembly 10.
The shape, size and/or orientation of the wear pad surfaces may be selected to optimize the absorption of vibration energy and/or to minimize material wear on the pads. The embodiment illustrated in
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
