Effect of swirl cup on characteristics of fuel spray in gas turbine combustors

Abstract

A systematic numerical study has been performed to understand the effect of the secondary venturi tip angle on the characteristics of a swirl stabilized spray combustor with a radial mixer swirl cup assembly in a nominal condition of 60 % of full load. Three variations of secondary venturi tip angles are made: converging, straight, and diverging angles. It is found that the variation of the venturi tip angle results in the significant changes of flow and spray characteristics in. gas turbine combustors, such as the size and location of recirculation zones downstream of the venturi tip, turbulent kinetic energy and drop size distribution affecting combustion efficiency and NOx emissions. Also, the flow characteristics of reacting cases are very different from those of nonreacting cases due to the considerable increase of axial momentum caused by the increase of temperature. In converging venturi case, it is found that the relative velocity between two flows through double swirler is very large, so that the strong shear layer is formed at the venturi tip. This strong shear layer induces high level of turbulent kinetic energy region. And, in converging venturi case, the aerodynamic secondary breakup of fuel spray occurs very intensively due to a large relative velocity between droplets and flows through the secondary swirler. Finally, the intense mixing and small drop size distributions result in less amount of NOx emission due to even temperature distribution formed in converging venturi case. Therefore, it is found that the converging venturi geometry is adequate for high efficiency and low emission industrial gas turbine engines.