One important aspect of condition-based maintenance is the current condition of the machine. Machine condition can be determined from physical inspections, but only at long intervals as these inspections lead to lost revenue while the gas turbine is not operating.
Machine condition data also comes from monitoring of measured parameters during gas turbine operation. This typically includes a sparse number of gas turbine cycle pressure and temperature measurements, rotor vibration measurements, and bearing lubricant conditions.
While this information is valuable, it is often not enough to fully understand the health of individual components within the gas turbine system. For example, knowing the compressor discharge conditions and the shaft power of the unit can allow for an estimation of compressor efficiency, but it does not provide any more detail regarding the most likely stages of the multi-stage compression system that may be suffering reduced efficiency.
Ideally, a significant increase in the number of sensors could provide the fidelity of information required for more accurate diagnostics. However, this sensor density is reserved for much more expensive research and development units, not for production units.
As an alternative, it is possible to use a high-fidelity engine performance model to help the engineer see inside of the machine. Generally speaking, the engine performance models are owned and exercised by the same engineering teams that design and manufacture the gas turbine units.
These gas turbine performance models are used to perform preliminary design of new turbine concepts. During detail design, these same models are increased in fidelity to provide a system-level prediction of the total gas turbine performance while more specialized engineers make changes to individual component performance such as individual compressor or turbine stages.
Read more in the July-August 2015 issue of Turbomachinery International magazine
(David Ransom, P.E., is Manager of the Propulsion & Energy Machinery Section within the Fluids & Machinery Engineering Department at Southwest Research Institute (SwRI). David has 18 years’ experience in various turbomachinery topics including rotordynamics, secondary flows, fluid-thermal systems, seal and bearing systems, and machinery performance measurement.)
(Jacob Delimont, Ph.D., is a Research Engineer in the Propulsion & Energy Machinery Section within the Fluids & Machinery Engineering Department at SwRI. His research interests include the areas of heat transfer, fluid mechanics, thermodynamics, and microparticle impact modeling. For more information on NPSS, visit www.SwRI.org)