The present paper overviews the works carried out on achieving desired temperature pattern factors at combustor exit in gas turbine engines. These pattern factors are very important from the point of engine performance and life of turbine blades and vanes. They are controlled by a number of geometrical parameters such as liner front-end air passages, primary air holes, atomizer characteristics and air swirl number and dilution zone geometrical configuration. Combustor inlet pressure, Mach number, velocity profile and fuel-air ratio are the major operating parameters that influence the pattern factors. Due to the design uniqueness and importance of pattern factors, it is always a challenge to assess the pattern factors over a wide range of mission points for a gas turbine combustor designed for combat aircraft.
A highly loaded full-scale annular combustor is studied in the air-flow facility for the effect of operating variables such as compressor discharge velocity and fuel-air ratio on the performance parameters. The combustor is designed to operate at high pressures and high exit temperatures that impose stringent limitations on its performance such as pressure loss, exit temperature profiles and combustion efficiency. The effect of excess air ratio on performance parameters is found to be marginal over the range tested. Increasing the excess air ratio decreases the pressure loss, exit pattern factors and combustion efficiency. The inlet Mach no. is found to influence the pressure loss strongly and exit temperature patterns marginally. Combustion efficiency is found to deteriorate with increase in Mach number. This will in turn affect the integrity and life of hot end components of the aero engine.
This paper presents the computational study carried out on an aero gas turbine combustor to assess important performance parameters. The CFD results are compared with experimental dataobtained from the full scale combustor tested at ground test stand simulating various operational conditions. The CFD predictions have agreed very well with the experimental data. The model is then extended to predict combustor exit temperature pattern factors, pressure loss, and combustion efficiency and exhaust gas constituents over a wide range of operating pressure and temperature conditions. The paper also presents the studies carried out on the effect of atomizer spray cone angle, particle size and fuel flow variations expected due to manufacturing tolerances in various flow passages as well as due to operational degradations on temperature pattern factors. The pattern factors are also analyzed on cold and hot day environment. The radial pattern factor (RPF) at mid height is found to increase as altitude increases from sea level to 12 km. Spray cone angle is found to have a predominant effect on temperature non-uniformity at exit, lower cone angle increasing both radial and circumferential pattern factors. The findings of this study are valuable inputs for engine performance estimation.
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