Turbulent mixing and atomization in a confined shear layer

Abstract

The influence of mean air velocity and shear-layer strength on turbulent mixing times and airblast atomization is investigated. Experiments carried out in a two-dimensional, two-stream wind tunnel have been developed to simulate the mixing region (i.e., shear layer with liquid injection) found in the primary zone of a gas turbine combustor. A turbulent mixing time defined as the ratio of length scale and fluctuating component of velocity (l/u^) is found to be an appropriate parameter to describe the mixing process. For a given value of shearlayer strength, these mixing times are found to be inversely proportional to the inlet mass average velocity. These mixing times are also shown to decrease with increasing shear-layer strength. Thus both shear-layer strength and inlet velocity have a strong influence on mixing time and, in relation to an actual combustor, on flame stabilization and combustion efficiency. Both of these parameters are also found to influence atomization quality, with Sauter mean diameter increasing with increasing shear-layer strength and decreasing with increasing velocity.