Method for maintaining blade tip clearance

Claim 1

A method for maintaining long term performance efficiency between consecutive periodic seal replacement in a particular one of a plurality of substantially similar gas turbine engines each having an active clearance control system for selectably reducing the clearance between a plurality of rotating blade tips and a surrounding annular seal, including means, disposed adjacent a portion of the engine structure, for delivering a modulated flow of gas, said gas flow having a temperature substantially different from the engine portion, means, responsive to current engine operating conditions, for modulating the flow rate of the delivered gas relative to a baseline flow rate, the baseline flow rate being established at each seal replacement, wherein the method comprises the steps of: establishing, for the plurality of engines, an average clearance deterioration rate between the blade tips and the annular seal, the deterioration rate being determined as a function of accumulated engine usage since the most recent overhaul, selecting at least one level of accumulated engine operation intermediate two consecutive periodic seal replacements and determining, for the selected level, an average incremental change to the gas baseline flow rate required to restore the deteriorated clearance between the blade tips and the annular seal, the restored clearance being no less than the undeteriorated clearance immediately following seal replacement, and altering, by an amount equal to the average incremental change, the baseline gas flow rate of the particular one engine when the particular one engine achieves the selected level of accumulated engine usage.

Claim 2

A method for maintaining long term performance efficiency between consecutive periodic seal replacement in a particular one of a plurality of substantially similar gas turbine engines each having an active clearance control system for selectably reducing the clearance between a plurality of rotating blade tips and a surrounding annular seal, including means, disposed adjacent a portion of the engine structure, for delivering a modulated flow of gas, said gas flow having a temperature substantially different from the engine portion, means, responsive to current engine operating conditions, for modulating the flow rate of the delivered gas relative to a baseline flow rate, the baseline flow rate being established at each seal replacement, wherein the method comprises the steps of: establishing, for the plurality of engines, an average clearance deterioration rate between the blade tips and the annular seal, the deterioration rate being determined as a function of accumulated engine usage since the most recent overhaul, selecting at least one level of accumulated engine operation intermediate two consecutive periodic seal replacements and determining, for the selected level, an average incremental change to the gas baseline flow rate required to restore the deteriorated clearance between the blade tips and the annular seal, the restored clearance being no less than the undeteriorated clearance immediately following seal replacement, and altering, by an amount equal to the average incremental change, the baseline gas flow rate of the particular one engine when the particular one engine achieves the selected level of accumulated engine usage.