Improvement of turbine blade lifetime assessment by more accurate estimation of the thermal boundary conditions

Cristhian Maravilla Herrera,Sergiy Yepifanov,Igor Loboda

doi:10.1177/1687814017698613

Abstract

The known studies in the area of gas turbine lifetime prediction do not result in the algorithms for on-line engine monitoring. This article introduces and investigates a new method for developing “light” mathematical models to estimate static thermal boundary conditions for gas turbine hot elements. In contrast to the previous developments, these models allow on-line lifetime monitoring of such elements. The blade of the high-pressure turbine of a two-spool free turbine power plant was chosen as a test case. The models of blade boundary conditions were developed based on well-known thermodynamic relations and a steady-state nonlinear physics-based model of this engine. Many candidate models are analyzed in the article, and the best models are selected by their accuracy and robustness to engine faults using instrumental and truncation errors as criteria. The instrumentation errors are induced by measurement inaccuracy of gas path variables used. For the analysis of the model robustness, the truncation errors are computed. They appear when performance of an engine deviates from a baseline due to normal degradation of the engine and because of its faults. The gas path parameters under healthy and faulty engine health conditions are simulated by the thermodynamic model. These simulated quantities are used as the input data to perform the comparison of the candidate models. The final accuracy analysis shows that the proposed method improves the estimates of the thermal boundary conditions. As a result, prediction of an engine lifetime becomes significantly more accurate. The article also determines the positive effect of the compressor discharge temperature sensor. When it is installed in addition to a standard gas path measurement system, the accuracy of the measurement-based lifetime prediction grows drastically.

Highlights

Lifetime monitoring is an effective way to realize condition-based maintenance of gas turbine engines.[1,2,3] The usage of gas path parameters for the on-line thermal analysis of critical engine elements is an integral part of such monitoring
A turbine blade has been chosen as a test case for the proposed method
The necessary intermediate unmeasured parameters were defined via internal polynomial functions

Summary

Introduction

Lifetime monitoring is an effective way to realize condition-based maintenance of gas turbine engines.[1,2,3] The usage of gas path parameters for the on-line thermal analysis of critical engine elements is an integral part of such monitoring. This article focuses on estimating static thermal boundary conditions, which are necessary to calculate the engine lifetime Since these conditions are not measured, they are presented by models that employ measured engine parameters as the input data. For the group of critical groups ga, the results show that the use of physics-based models to calculate the thermal boundary conditions reduces the errors of the temperature at the critical point tr from 1.03% to 0.59%. It is of particular interest to know how its installation influences the accuracy of thermal stress and lifetime estimates To this end, all the previous calculations were later repeated considering that the temperature after compressor TSÃ1 = TCÃ is a measured parameter. If TCÃ is measured, the errors in the prediction of tr for the group of critical points ga reduce from 102.8% to 45.95% for the case of the physics-based models

Findings

Discussion

Conclusion