Spatially Resolved Characteristics and Analytical Modeling of Elastic Non-Newtonian Secondary Breakup
Secondary atomization occurs when aerodynamic forces cause a drop to deform and fragment. This topic, while studied extensively for over a century, still contains issues that remain uncertain or neglected despite the current efforts of groups such as Cao et al. (2007), Aliseda et al. (2008), and Zhao et al. (2011). The current study consists of spatially resolved secondary atomization characterization and modeling predictions of initiation time and drop diameter at initiation time using a modified TAB (Taylor Analogy Breakup) model. The spatially resolved characteristics were obtained using both dual- and fiber-mode Phase Doppler Anemometry (PDA) systems, a departure from shadowgraphs used by Chou et al. (1998) and Zhao et al. (2011), and PIV used by Flock et al. (2012). Data were obtained at multiple flow rates and varying radial distances for a set downstream location. A viscoelastic xanthan gum solution was used and characterized with Carreau rheology and Zimm relaxation time. Experimental data shows that drop fragment size and fragment velocity vary with xanthan gum concentration. As fragment size increased, the corresponding velocity decreased. An increase in fragment size was also found to correspond to an increase in xanthan gum concentration. As the xanthan gum concentration increased, so did the initiation time and D/d0 value (deformed diameter/original undeformed diameter). The analytical model used here was developed from the TAB model (O’Rourke and Amsden, 1987) and incorporated changes to the drag coefficient equation (Park et al., 2002), Cd coefficient value (Marek, 2013), and breakup criterion. Computed initiation time was in good agreement with the measured data, but both the predicted drop diameter and velocity at initiation time were underpredicted for all cases.
Sojka, Purdue University.
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