Cold Flow Experiments in a Sub-Scale Model of the Diffuser-Combustor Section of an Industrial Gas Turbine

Abstract

This paper describes the experimental facility and flow measurements in a sub-scale, 360-degree model of the diffuser-combustor section of an advanced developmental industrial gas turbine. The experiments were performed under cold flow conditions which can be scaled to actual machine operation through the use of a conventional flow parameter. Wall pressure measurements were used to calculate the static pressure recovery in the annular pre-diffuser. A five-hole probe was used to measure the complex three-dimensional flow in the dump diffuser. Mass-weighted average total pressures were calculated to examine the loss characteristics of the annular and the dump diffuser. The “sink” effect caused by the combustors induces a nonuniform velocity profile and pressure distribution at the exit of the annular pre-diffuser, thereby reducing the effectiveness of the annular pre-diffuser. The outer region of the dump diffuser effectively diffuses the flow while recirculation in other areas of the dump diffuser lowers diffuser effectiveness. Partially nonuniform flow distribution was observed at the entrance to the annular passage between the combustors and the combustor housing (top hat). The existence of circumferential flow in this annular passage tends to increase air flow uniformity into the combustor. Although a specific geometry was selected for the present study, the results provide sufficient generality for improving understanding of the complex flow behaviors in the reverse flow diffuser-combustor sections of industrial gas turbines.