Experimental Studies of Air Extraction for Cooling and/or Gasification in Gas Turbine Applications

This paper describes an experimental study on how the flow field inside the dump diffuser of an industrial gas turbine is affected by air extraction through a single port on the shell around the dump diffuser. A sub-scale, 360° model of the diffuser-combustor section of an advanced developmental industrial gas turbine was used in this study. The experiments were performed under cold flow conditions which can be scaled to actual machine operation. Three different conditions were experimentally studied: 0%, 5%, and 20% air extraction. It was found that air extraction, especially extraction at the 20% rate, introduced flow asymmetry inside the dump diffuser and, in some locations, increased the local flow recirculations. This indicated that when air was extracted through a single port on the shell, the performance of the dump diffuser was adversely affected with an approximate 7.6% increase of the total pressure loss, and the air flow into the combustors did not remain uniform. The global flow distribution was shown to be approximately 35% nonuniform diametrically across the dump diffuser. Although a specific geometry was selected, the results provide sufficient generality for improving understanding of the complex flow behavior in the reverse flow diffuser-combustor sections of gas turbines under the influence of various air extractions.