Flow Interactions in the Combustor-Diffuser System of Industrial Gas Turbines

Abstract

This paper presents an experimental/computational study of cold flow in the combustor-diffuser system of industrial gas turbines to address issues relating to flow interactions and pressure losses in the pre- and dump diffuses. The present configuration with can annular combustors differs substantially from the aircraft engines which typically use a 360 degree annular combustor. Experiments were conducted in a one-third scale, annular 360-degree model using several can combustors equispaced around the turbine axis. A 3-D computational fluid dynamics analysis employing the multidomain procedure was performed to supplement the flow measurements. The measured data correlated well with the computations. The airflow in the dump diffuser adversely affected the prediffuser flow by causing it to accelerate in the outer region at the prediffuser exit. This phenomenon referred to as the sink-effect also caused a large fraction of the flow to bypass much of the dump diffuser and go directly from the prediffuser exit to the bypass air holes on the combustor casing, thereby, rendering the dump diffuser ineffective in diffusing the flow. The dump diffuser was occupied by a large recirculation region which dissipated the flow kinetic energy. Approximately 1.2 dynamic head at the prediffuser inlet was lost in the combustor-diffuser system; much of it in the dump diffuser where the fluid passed through the narrow gaps and pathways. Strong flow interactions in the combustor-diffuser system indicate the need for design modifications which could not be addressed by empirical correlations based on simple flow configurations.

One-Dimensional Numerical Analysis of Cross-Sectional Area Variation Effects on Flow through the Gas Turbine Diffuser

“…Using thermodynamic relationships and expressed boundary conditions, Mach number can be obtained through following non-linear relationship, as well as try and error [3]:…”

“…From among most important of these conditions is appropriate air speed so that high air velocity would not be resulted in blowing out the flame. To obtain the appropriate air conditions, in the path of inlet gas to the gas turbine combustion chamber, a divergent diffuser is used [1][2][3]. In Figure (1), one 25MW gas turbine is shown.…”

Design methodology for a lean premixed prevaporized can combustor

“…The experim ental work of Kline et al (1959), Reneau et al (1967, and Sovran & Klomp (1967) on faired diffusers provides designers with a means of selecting an optim al geom etry and predicting its performance. These ex perim ents do not take into account the inlet conditions th a t combustor diffusers must accommodate such as high levels of turbulence, Reynolds and Mach num ber effects, compressor exit velocity profile non-uniformities, and swirl (Little & M anners, 1993;Agrawal et al , 1996). Nonetheless, the experim ental d a ta discussed above provides a suitable prelim inary design despite its lim itations.…”