Flow Characteristics of an Annular Intercooler-Diffuser for Gas Turbines

Abstract

Benefits of intercooling in power generating gas turbines can be maximized by reducing stagnation pressure loss in the intercooler flow path without adversely affecting the flow pattern in compressors. The intercooler-diffuser isolates the low pressure compressor from the intercooler, recovers the static pressure by decelerating the compressor discharge flow, and uniformly supplies low speed air to the intercooler for effective heat exchange. An experimental investigation was carried out to obtain data in a conceptual design with two sections: an outwardly canted prediffuser and a dump. The test-section was a one-fourth scale model of a typical industrial gas turbine. The diffuser flow is described in terms of the pressure recovery and loss coefficients, velocity vectors, static and stagnation pressure distributions, and the mean velocity and turbulence intensity profiles. The flow resistance by the intercooler was simulated to assess its effects on the upstream diffuser flow. The airflow rate was varied to obtain data at full and part-load operations. The inlet conditions corresponded to naturally developed axisymmetric annulus flow. Results show high stagnation pressure loss and distorted velocity profiles in the dump because of flow recirculation next to the casing. Pressure recovery was confined to the prediffuser and a tail-section downstream of the dump where the flow reattached. Results show that the diffuser flow was practically unaffected by the intercooler and by operation at part-load.

Flow Development in an Annular Contraction

“…In case of compressors, a constant area curved duct with its radius decreasing in the flow direction is used. Brichford et al (1994), Bailey et al (1997), and Sonoda et al (1997 have conducted experiments to determine flow characteristics of these passages, and to evaluate effects of upstream and downstream flow conditions. Flow development in an interstage turbine passage was investigated by Dominy et al (1996).…”

“…In this "S" shaped annular diffuser of area ratio 1.5, the passage radius increased in the flow direction. Another configuration includes a contoured wall annular intercoolerdiffuser investigated recently by Agrawal et al (1998).…”