An investigation into the applicability of commonly used evaluative expressions in swirl atomizers for cryogenic conditions

Abstract

The objective of this thesis was to determine the validity of the expression developed by Rizk and Lefebvre in their seminal 1985 paper ???Internal Flow Characteristics of Simplex Swirl Atomizers??? for use in applications using cryogenic fluids as well as its common modifications. Since the hybrid rocketry applications of swirl atomizers most often involve such fluids, it is vital to determine whether a commonly used analytical expression remains valid in those circumstances. A computation fluid dynamics (CFD) simulation was performed, first using water as a working fluid to determine a baseline of accuracy that could be expected, then using liquid oxygen as a working fluid to determine the accuracy of the expression to a cryogenic case. In addition, experimental data from several papers using both room temperature and cryogenic fluids were examined; both to expand the data from which to draw a baseline and to expand the data from which to analyze the performance of cryogenic working fluids. The CFD simulation was run at a pressure of 1 kPa with a geometry similar to those commonly used in hybrid rocket applications. While the results diverged significantly from those of the analytical expressions, the water and liquid oxygen cases showed similar divergence, indicating a similar level of accuracy in prediction. As a secondary result, the low suitability of these expressions for analysis of atomizers significantly larger than those used in the initial development of the relation and at lower pressure was shown. The experimental data provided a baseline of ??20% accuracy of the expressions with regard to the empirical results for the room temperature fluids. Using that baseline, it was shown that the analysis of the case with a cryogenic fluid was accurate to within a similar tolerance.