Patent Application
20080044278
Embodiments of the invention are directed to a system that can improve engine performance by minimizing vane tip clearances while reducing the risk of significant component damage in the event of vane tip rubbing. Aspects of the invention will be explained in connection with one possible system, but the detailed description is intended only as exemplary. Embodiments of the invention are shown in
According to aspects of the invention, an abrasive material can be attached to compressor rotor disc and is positioned such that, in the event of vane tip rubbing, the abrasive material will come into contact with the vane tip. In one embodiment, as shown in
The abrasive material 34 can be any suitable abrasive. The abrasive material 34 can be, for example, cubic boron nitride, silicon carbide, silicon nitride, alumina, zirconia, diamond, or mixtures thereof. Ideally, the abrasive material 34 has a Mohs hardness of at least about 9. The abrasive material 34 can be attached to the base 32 in any suitable manner. Because the insert 30 is relatively small, the abrasive material 34 can be electroplated to the base 32. In contrast, it would not be feasible to electroplate an abrasive coating onto a large rotor disc. Alternatively, the abrasive material 34 can be applied to the base 32 by a thermal spray process. The abrasive material 34 can have any suitable thickness. In one embodiment, the thickness of the abrasive material 34 can be about 0.005 inches.
The abrasive insert 30 can be attached to the rotor disc 28 in any of a number of ways. Preferably, the insert 30 is removably attached to the disc 28 to facilitate removal and replacement of the insert 30 during field service. For instance, the insert 30 can threadably engage the disc 28. Alternatively, as shown in
Referring to
Each slot 36 can receive a respective one of the abrasive inserts 30. When installed, the abrasive material 34 of the insert 30 can be exposed along with the outer peripheral surface 38 of the rotor disc 28. The insert 30 and/or slot 36 can be configured such that the abrasive material 34 can extend beyond the outer peripheral surface 38 of the rotor disc 28 in the radial direction. In one embodiment, the base 32 of the insert 30 can be substantially flush with the outer peripheral surface 38 of the rotor disc 28, and the entire abrasive material 34 can protrude beyond the outer peripheral surface 38 of the rotor disc 28.
The insert 30 and the slot 36 can be configured for substantial mating engagement. Preferably, the insert 30 engages the slot 36 so as to be retained therein. The slot and the insert 30 can be configured to provide restraint in the axial, radial and/or circumferential directions. In one embodiment, the base 32 of the insert 30 and the slot 36 can be configured as a dovetail or “fir tree.” In such case, the engagement between the insert 30 and the slot 36 can substantially circumferentially restrain the insert 30. In addition, such an arrangement can radially restrain the insert 30, which is subjected to centrifugal forces during engine operation. It will be readily appreciated that there are numerous configurations for the insert 30 and/or slot 36 that can achieve radial and/or circumferential restraint.
Movement of the insert 30 can also be restrained in the axial upstream and the axial downstream directions. In one embodiment, the base 32 can include a protrusion 40 that extends generally transverse to the rest of the base 32. The protrusion 40 can be located at one end of the base 32. The protrusion 40 can engage a portion of the slot 36, such as a recess, notch or step 42 therein, to restrain the insert 30 in one of the axial directions. Restraint in the opposite axial direction can be achieved in a similar manner or in a different manner. For instance, an end 44 of the slot 36 can open to a cavity 46 in the rotor disc 28 that receives a compressor blade 48. Thus, when the insert 30 and the compressor blade 48 are installed, an end 50 of the insert 30 can be substantially adjacent to the compressor blade 48 such that axial movement of the insert 30 in the axial direction toward the compressor blade 48 is obstructed by the compressor blade 48 itself. The end 50 of the insert 30 can also be the end that includes the protrusion 40.
Referring to
It can be envisioned that an abrasive material can be attached to the vane tip instead of the rotor disc. In such case, the abrasive material would wear the rotor disc; however, such a system can have a number of drawbacks. First, the rotating disc is subjected to centrifugal loads during engine operation. These additional forces significantly raise concerns of portions of the rotor disc liberating upon contact with the abrasive material, which can cause significant engine damage. Further, the friction between the abrasive material and the rotor discs can heat treat the rotor disc material, thereby adversely affecting the properties of the material. Attaching an abrasive material to the tip of a vane, particularly a shrouded vane, is complex, costly and the performance is not expected to be as good.
If the abrasive material is attached to the stationary vane tip, then any rubbing between a vane tip (even a single vane) and the rotor disc would result in a 360 degree groove being formed in the abradable outer peripheral surface of the rotor disc. Consequently, there would be overly large clearances in areas where such clearances are not needed. On the other hand, if the abrasive material is attached to the rotor disc in accordance with aspects of the invention, then the only areas affected are those in which a vane tip clearance problem arises. For instance, if a vane tip rubbing event occurs between the rotor disc and only one of the plurality of blades, then only that blade would be worn away. The other blades would not be worn away unless and until they contact the rotor disc.
Moreover, there are a number of reasons as to why it is more important to protect the rotor disc as opposed to the vanes. First, rotor discs are substantially more expensive than the airfoils. Second, it is relatively easy to replace a vane whereas the removal and replacement of the rotor discs is a time consuming, labor intensive and expensive task. Third, there is a possibility of increased warranty claims because turbine engine service agreements commonly guarantee the rotor disc over a longer period than the vanes.
The foregoing description is provided in the context of one possible system for including an abrasive material on a disc. The system can be used on one or more of the discs in the compressor section of the engine. While well suited for the compressor section of a turbine engine, aspects of the invention can be readily applied to the turbine section of the engine as well. Thus, it will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention as defined in the following claims.
