Improved Spray Model for Viscous Annular Sheets in a Swirl Injector

Abstract

A modified sheet breakup model was applied to a thin, viscous liquid film generated by a swirl injector similar to that installed in a liquid propellant rocket engine combustor. The sheet breakup model consists of three steps: determination of the swirl injector characteristics for the prediction of initial sheet conditions at the injector exit as input, linear stability analysis for primary sheet breakup, and the Taylor analogy breakup model for final drop formation. Under atmospheric pressure, the liquid sheet breakup occurs under a long-wave regime, sometimes according to simple theoretical analysis. But in high ambient pressure conditions, like a liquid propellant rocket engine combustor, the sheet breakup regime changes from a long wave to a short-wave regime due to a high gas Weber number (We 2 > 27/16), although the same injector was used. The sheet breakup model was, therefore, modified to be applicable to both long- and short-wave regimes and validated by the comparison of breakup length and Sauter mean diameter to experimental results. In both experimental and computational results, the spray cone angle and breakup length decreased as the ambient pressure increased, even though the pressure difference of the injector was constant. Local Sauter mean diameters, predicted by computation, were smaller at high ambient pressures. The comparative results show that the computational model is able to accurately predict sheet breakup length, spray cone angle, local Sauter mean diameter, and overall spray shape. Therefore, the model can be used as a design tool, ahead of analyzing spray characteristics of an injector in both atmospheric and high ambient pressure conditions.