In this paper, a temporal instability model has been derived to explore the influence of slight multiple airflow movements for the power-law fuel annular jet. Adopting the method of linear approximation and considering two different disturbance modes, the power-law fuel jet dispersion equation has been obtained based on the initial and boundary conditions. The influence of dimensionless characteristic parameters for the annular jet is investigated. By solving the dispersion equation, it can be found that the para-sinuous mode is more likely to play a leading role. For low-speed cases, the outer crossflow gas promotes the instability of fuel annular jets more effectively, while the inner coaxial airflow has an obvious promotion impact on high-speed jets. Reducing the thickness of the fuel annular film will weaken the stable inertia of the fuel, make the fuel annular jet easier to break up, and enhance the primary breakup scale. Furthermore, increasing the outer or inner gas density can accelerate the annular spray breakup process, and also amplify the gain effect of airflows. Besides, pseudoplastic fluid annular jets are more unstable and more suitable as fuel for future use. These discussions aim for a better understanding of the power-law fuel annular jet breakup process with multiple airflows and provide theoretical guidance for practical applications.

An investigation has been performed to reveal the breakup mechanism of three-dimensional power-law cylindrical jets with different mode disturbances. It is observed experimentally that the asymmetric mode disturbances could prevail over the counterpart of symmetric mode under special conditions. The dispersion equation characterizing the instability of three-dimensional cylindrical jets of power-law fluids is deduced. The effects of the Weber number, generalized Reynolds number, power-law exponent, and gas–liquid density ratio on the jet instability are studied in detail. It is found that the maximum growth rates of asymmetric mode disturbances are usually larger than those of symmetric mode disturbances under high Weber numbers and low generalized Reynolds numbers, which implies that the former are more likely to be responsible for the breakup of power-law fluids. Meanwhile, the large gas–liquid interaction could trigger more short, unstable waves. Interestingly, with the increase of jet velocity, the interaction between liquid and gas phases plays an increasingly leading role on the breakup of power-law cylindrical jets, whereas the viscous force and the power-law exponent have less significant impacts. Theoretical analysis results give a better comprehensive understanding for the power-law jets.

As a kind of non-Newtonian fluid with special rheological features, the study of the breakup of power-law liquid jets has drawn more interest due to its extensive engineering applications. This paper investigated the effect of gas media confinement and asymmetry on the instability of power-law plane jets by linear instability analysis. The gas asymmetric conditions mainly result from unequal gas media thickness and aerodynamic forces on both sides of a liquid jet. The results show a limited gas space will strengthen the interaction between gas and liquid and destabilize the power-law liquid jet. Power-law fluid is easier to disintegrate into droplets in asymmetric gas medium than that in the symmetric case. The aerodynamic asymmetry destabilizes para-sinuous mode, whereas stabilizes para-varicose mode. For a large Weber number, the aerodynamic asymmetry plays a more significant role on jet instability compared with boundary asymmetry. The para-sinuous mode is always responsible for the jet breakup in the asymmetric gas media. With a larger gas density or higher liquid velocity, the aerodynamic asymmetry could dramatically promote liquid disintegration. Finally, the influence of two asymmetry distributions on the unstable range was analyzed and the critical curves were obtained to distinguish unstable regimes and stable regimes.