High-fidelity simulation of liquid atomization in quiescent environment and supersonic flows.


The atomization of liquid fuel in both quiescent environment and supersonic flows is essential to a wide variety of applications. Since it is challenging to obtain high-level details of the time-dependent, 3D, and chaotic multiphase flow features in experiment, high-fidelity simulation is an important alternative to reveal the complex flow physics involved, such as liquid breakup and shock-interface interaction. The goal of this dissertation is to develop rigorous numerical methods for both incompressible and compressible interfacial multiphase flows, and to investigate liquid jet atomization in both quiescent environment and high-speed gas flows through high-fidelity simulations. To achieve this goal, simulation is first performed for the breakup and oscillation of a dripping water droplet in quiescent air. The drop formation and dynamics are essential elements of the more complex counterpart, liquid jet atomization. The pinching process plays an important role in initiating the shape oscillation of the drop. The interplay between the shape oscillation and the falling motion induces a complex transient flow inside and outside of the drop. Furthermore, modeling and simulation are conducted to investigate the injection and breakup of a cylindrical gasoline surrogate jet in a quiescent gas under the Engine Combustion Network spray G conditions. The spray G benchmark was developed to advance the study of gasoline direct injection engines. A momentum-conserving volume-of-fluid (VOF) method is used. To account for the effect of the internal flow in the injector, in particular that the liquid flow at the nozzle inlet is not aligned with the nozzle axis, a finite injection angle is invoked at the inlet. The injection angle is found to have a strong impact on the breakup dynamics and the statistics of the droplets generated. Finally, the study is extended to developing numerical methods for simulation of liquid breakup in a supersonic flow. An All-Mach approach is employed and the advection of conservative variables are conducted consistently with the VOF. To suppress numerical oscillations near discontinuities in the flow, numerical diffusion is introduced based on the Kurganov-Tadmor method. The new method is tested by different compressible multiphase flow problems. The numerical results are validated against theory and experiments and a good agreement is achieved.

Direct numerical simulation. Atomization. Multiphase flow. Fuel injection. Supersonic flow. Volume-of-fluid method.