Patent Application
20070237629
The present invention relates to compressor rotors and stator casings and, more particularly, to rings set in dedicated grooves in the stator casing that define the outer flowpath and that can be easily replaced in the event of rotor airfoil tip rubbing.
With reference to
A common occurrence in gas turbine compressors is rotor blades rubbing on compressor casings for various reasons. Rubbing can be caused by a number of conditions such as improper alignment between the rotor 18 and the casing, casing joint slippage at the horizontal and vertical flanges, or transient thermal response differences between the casing 12 and rotating parts. The end result is airfoil 20 tip loss and/or casing flowpath wear. These conditions lead to a loss of compressor performance and surge margin. If rubs are severe enough, the casing and rotating airfoils have to be replaced. Typically, this will result in loss of service of the gas turbine for an extended period of time.
With continued reference to
In an exemplary embodiment of the invention, a flowpath ring is securable in a machined groove of a compressor stator casing. The flowpath ring includes a connector section engageable with the machined groove where the connector section is shaped corresponding to the machined groove. A flowpath section is disposed radially inward relative to the connector section and includes a clearance surface disposed facing a compressor rotor blade and defining a blade flowpath when secured in the compressor stator casing machined groove.
In an another exemplary embodiment of the invention, a gas turbine compressor includes a stator casing having airfoil grooves each supporting a plurality of stator airfoils. A rotor supports a plurality of rotor blades for rotation relative to the stator casing. A plurality of the noted flowpath rings are secured in respective ring grooves in the stator casing.
It would be desirable to facilitate repairs in rotor flowpaths due to rotor airfoil tip rubbing. In this manner, optimum clearances can be restored while recovering performance and surge margin. Also, clearances can be made tighter in order to increase performance and surge margin.
By utilizing easily replaceable rings installed in the casing where the rotor blades may rub the casing, flowpath repairs can be effected rapidly and efficiently. Additionally, replaceable rings (or flowpath rings) can reduce the rate of heat transfer into the casing, thereby changing the transient and steady state matching of the rotor and casing thermal growth. This allows for a passive clearance controlling design feature that permits tighter clearances between the rotor blades and the casing, adding to overall engine performance and surge margins.
With reference to
A rotor 18 supports a plurality of rotor blades 20 for rotation relative to the stator casing 12. As noted, gas turbines attain optimum performance when the clearance, designated by reference numeral 22, between rotating airfoils and the stator casing 12 is maintained at an optimal distance, which is generally very small (e.g., 40-80 mils at steady state temperature). A common occurrence during the operation of a gas turbine compressor is rubbing or contact between tips of the rotor blades 20 and the stator casing 12. The end result is rotor tip loss and/or casing flowpath wear, which can lead to a loss of compressor performance and surge margin. Moreover, if rubs are severe enough, the stator casing 12 and rotor blades 20 may require replacement, resulting in loss of service of the turbine for an extended period of time.
With reference to
A plurality of flowpath rings 26 (
The flowpath rings 26 can be used to optimize tip clearance by using an abradable coating 34 formed on the clearance surface 32 of the flowpath rings 26. Preferably, the clearance surface 32 includes a groove 36 or the like in which the abradable coating 34 is disposed. Examples of abradable coatings that can be used for this application are aluminium silicon alloy/polymer composite, nickel/graphite composite, aluminium bronze/polymer composites. By using the abradable coating 34, the rotor blades 20 can serve to carve/cut the coating during the clearance pinch-point to attain an optimal steady state running clearance.
With reference to
Moreover, in order to further minimize flowpath gas leakage behind the rings 26, a seal 40 (
Since the flowpath rings are replaceable, flowpath repairs due to rotor blade tip rubbing can be quickly facilitated in a reliable and cost effective manner. Thus, even on units with heavy rubbing, original performance and compressor surge margin can be restored. Moreover, the cycle time and associated cost to replace the flowpath rings is considerably less than to replace casings. Additionally, the flowpath rings 26 allow for a better thermal match between rotors and compressor casings, allowing a designer to better match the thermal responses and thereby run with tighter clearances. As noted, the compressor casing flowpath rings can be coated with an abradable material to allow closer clearances and an improvement in compressor performance. As would be appreciated by those of ordinary skill in the art, the flowpath rings can be installed in new units as a performance enhancement feature, particularly if combined with abradable coatings. Since the flowpath ring grooves can be machined into a stator casing in the same manner as stator slots with similar tolerance control, the flowpath rings can be accommodated with minimal cost and cycle impact on the casing.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
