Dynamics of shear-thinning droplet under pulsating flow

The breakup of non-Newtonian droplets under steady flow has been investigated extensively. However, non-Newtonian droplets under unsteady or pulsating flows have not been studied. This is relevant for kerosene gel droplets, which are shear thinning in nature and may be subjected to thermo-acoustic instabilities in the rocket combustion chamber. The investigation focuses on the shear-thinning droplet dynamics and breakup subjected to pulsating (sinusoidal) airflow of different amplitudes and frequencies. The volume of fluid multiphase model tracks the liquid–gas interface, and the governing equations are solved using the finite volume method. The shear-thinning behavior is modeled using a power law. Simulations are carried out for a Weber number (We=13) for which the droplet with power law index, n=0.67, does not show a breakup in a steady flow. However, a breakup is exhibited when subjected to a pulsating flow for the same We based on the mean gas speed except for the lowest amplitude (A=0.25) and frequency (f=500 Hz) investigated. Parametric investigations for different n show that the droplet breakup time significantly increases for n>0.8 for the pulsating flow of different amplitudes and frequencies. It is also observed that the change in frequency or amplitude changes the temporal evolution of the droplet viscosity for a constant n. Also, for the same A and f, the droplet with the lower value of n (<0.8) has a higher acceleration as compared to a droplet with a higher value of n (>0.8).