Liquid Jet Atomization


A liquid jet of diameter 200 μm injected at 200 m/s undergoes turbulent atomization in a quiescent ambient. Liquid properties: ρl=850 kg/m3l=1.7e-4 Ns/m2; Gas properties: ρg=25 kg/m3g=1.8e-5 Ns/m2.

The likely substitution of jet fuel and diesel by renewable fuels, such as the hydrotreated alternatives, is bound to have an impact on the general combustion performance of the devices burning them. In this project the atomization characteristics are studied using an algebraic volume-of-fluid solver (interFOAM). The first aspect of this work focuses on the breakup of the small spectrum of ligaments, which from previous experimental and computational work is found to universally precede the formation of droplets.  In this work, this ligament breakup process is idealized as the Rayleigh-Plateau mechanism [Rayleigh, Proc. Roy. Soc. London, 1879], and it is used to study fuel property effects on various breakup characteristics. The fuels considered correspond to the traditional JP-5 and diesel fuels and their potential renewable substitutes, as well as a single species fuel, hexene, which represents an extreme in the fuel property range. The solver is compared to the instability growth rate from theoretical predictions and previous numerical simulations, as well as droplet sizes reported in experiments, yielding good agreement. Results show that breakup times increase with increasing Ohnesorge number (Oh = μl/(σlρlR0)1/2 ) and exhibit a strong demarcation point occurring at Oh = 0.1. This point is interpreted as representing a boundary between the viscous and inviscid domains occurring in the dynamics governing the last stages of ligament deformation prior to pinch off. This boundary point also characterizes satellite drop sizes, where for Oh > 0.1, these satellite droplets show a noticeable sensitivity to the Ohnesorge number, while for Oh < 0.1 this sensitivity is weak. Additionally, a prediction for break-up time is proposed, tbreak,M = (1/ωV ) ln(1.87R00), which matches the simulation data for all fuels to within 8%. It is also observed that the length of the liquid bridge, which characterizes the central section of the domain in the last stage of ligament deformation, is approximately constant for all fuels, and is equal to 5R0.

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