Modeling of turbulence effect on liquid jet atomization

Recent experimental investigations and physical modeling studies have indicated that turbulence behaviors within a liquid jet have considerable effects on the atomization process. Such turbulent flow phenomena are encountered in most practical applications of common liquid spray devices. Most existing atomization models do not account for the turbulence effects. Only limited attempts have been made to model the subject effects on the liquid jet disintegration; however, they treat the turbulence either as an only source or a primary driver in the breakup process.; This doctoral research aims to model the effects of turbulence, occurring inside a cylindrical liquid jet, to its atomization process. The modeling effort enhances the predictions of the liquid jet breakup in more physically realistic operating conditions. In the course of this study, the two widely used atomization models, the Kelvin-Helmholtz (KH) instability of Reitz and the Taylor-Analogy-Breakup (TAB) of O'Rourke et al., portraying the primary liquid jet disintegration and the secondary droplet breakup respectively, are examined. Additional terms are formulated and implemented appropriately into these two models to account for the turbulence effect on the atomization process. In the primary breakup model, the turbulence inside the liquid jet is characterized by the turbulence scales and the initial turbulence quantities when incorporating into the Reitz model. Meanwhile, an additional turbulence effect acting on the parent drops is modeled and integrated into the TAB governing equation for the secondary breakup regime.; The proposed extension of atomization models is assessed with a computer code written for simple flow situations. The results for the flow conditions examined in this study indicate that the turbulence terms are significant in comparison with other terms in the models. In the primary breakup regime, the turbulent liquid jet tends to break up into large drops while its intact core is slightly shorter than the ones without the turbulence. In contrast, the secondary droplet breakup with the inside liquid turbulence consideration produces smaller drops as compared to the case without the turbulence. Overall, the results are consistent with experimental observations from other researchers. Finally, the present models are also programmed into an existing computational fluid dynamic (CFD) code, and simulations for several experimental flow conditions are performed. The computational results suggest that the existing KH and TAB models tend to under-predict the product drop size and the spray angle. On the other hand, the proposed models provide the predictions, which agree reasonably well with available measured data.; In summary, this research effort contributes to the improvement of the prediction in the liquid jet atomization processes. The additional terms, representing the turbulence effects on the jet breakup, can be incorporated easily into the two well-known atomization models. Suggested numerical schemes for solving the proposed models also are presented in this study. Therefore, the proposed enhancements can be implemented conveniently into existing CFD codes.