Model for airblast atomization

The objective of fuel injection modeling activities is generally to give support to the atomizer design effort to achieve improved spray quality. In gas turbine combustors, enhanced atomization is essential for satisfactory performance because droplet sizes can have direct impact on almost all key aspects of combustion. A model that includes the integration of the submodels of airflow, fuel injection and atomization, and droplets turbulent dispersion has been formulated. The model was applied to an airblast atomizer that incorporated a short prefilming device. The predictions were validated against two-component phase Doppler interferometry data of that atomizer. The results of the present investigation demonstrate the capability of the developed model to predict satisfactorily the airflow field and spray characteristics. The results also indicate the need for detailed measurements in the near field of the atomizer in order to quantitatively verify the modeling of the initial atomization processes in this region. CD d FN g P t U u V P a Nomenclature = drag coefficient = droplet diameter, m = atomizer flow number, m2 = gravitational acceleration, m/s2 = kinetic energy of turbulence, m2/s2 = static pressure, Pa = film thickness, m = velocity of carrier phase, m/s = fluctuation velocity of carrier phase, m/s = velocity of droplets, m/s = axial distance, m = dynamic viscosity, kg/ms = density, kg/m3 = surface tension, N/m I. Introduction T HE development of gas turbine combustors depends largely upon understanding the flow and combustion processes within the combustor. In order to accurately simulate the combustor flowfield, analytical approaches are required to account for various flow processes in addition to the details of the combustor configuration. It is equally important to establish a wide base of benchmark quality data needed for model validation. Most of the combustor performance parameters are directly related to the quality of the spray produced by the fuel injector.l The initial drop sizes formed at the injector exit and their trajectories coupled with the combustor primary zone aerodynamics significantly influence the evaporation and combustion characteristics of the spray. Fuel injection calculation concepts currently in use include empirical methods that readily provide a global picture of the whole spray as well as more complex models that account for the detailed spray dynamics.2'3 Spray correlations provide a convenient means of calculating such parameters as mean drop size and spray angle. However, it is difficult to develop a design method based only on empirical data because each correlation was derived for a certain application and may not