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Mapping and Predicting Air Flows in Gas Turbine Axial Compressors

[+] Author Affiliations
Robert J. McKee

Southwest Research Institute, San Antonio, TX

Paper No. GT2003-38745, pp. 91-98; 8 pages
  • ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference
  • Volume 4: Turbo Expo 2003
  • Atlanta, Georgia, USA, June 16–19, 2003
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 0-7918-3687-8 | eISBN: 0-7918-3671-1
  • Copyright © 2003 by ASME


Determining the airflow through a gas turbine’s axial compressor is not a simple or one step process as many factors affect flow and there is seldom a flow meter or a means to directly measure airflow rate. Speed of the compressor, inlet pressure and temperature, and resistance or backpressure at the compressor’s outlet all affect the amount of airflow. The type of gas turbine, single or twin spool, the magnitude of power produced, the use of bleed or bypass valves, the power turbine speed, and operating conditions all have influences on the amount of airflow. Despite this, there are several reasons why an estimate of airflow is useful for understanding and describing the behavior and performance of gas turbines. The amount of airflow compared to fuel flow determines the composition and condition of the exhaust gases and is directly related to the turbine’s power output, heat rate, and waste heat recovery potential. A predicted airflow rate and the corresponding axial compressor discharge pressure can be used to identify deterioration in performance and to estimate emission characteristics of a unit. This paper presents an approach based on easily obtained gas turbine data, such as the design point data, test stand data, or manufacturer’s curves for the compressor. Compressor performance curves may be obtained from the manufacturer or by mapping compressor output during normal operations. A great deal of information has been presented in the literature about the performance of gas turbines and axial compressors but this paper focuses on methods that are sufficiently simple and direct that users can obtain an estimate of their unit’s airflow, References 1, 2, and 3. Some manufacturers provide computer data bases or on-line control panel estimates of gas turbine airflow but in these cases, the user has no idea what causes a change. Detailed performance curves for axial compressors are usually not available, however, through the methods presented in this paper, a reasonable approximation of the operating curves can be developed and used to estimate axial compressor airflow over the full range of normal operations. The methods described are based on tracking and mapping a compressor’s operations over a period of time and relating compressor output to other performance parameters and known conditions (design point) in order to establish a normally expected airflow rate.

Copyright © 2003 by ASME



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