Numerical method for shock driven multiphase flow with evaporating particles

Abstract

This work is done in part as a requirement towards the fulfillment of the master's degree. Four different chapters were explored in this work. Chapter 1 gives the overview of the various works that have been done in the field and the applications of this work. Chapter 2 discusses the details of the numerical methods developed for predicting the interaction of active, phase changing particles in a shock driven ow. The Particle-in-Cell (PIC) technique was used to couple particles in a Lagrangian coordinate system with a fluid in an Eulerian coordinate system. This method was implemented in the open source hydrodynamics software FLASH, developed at the University of Chicago. A simple validation of these methods is accomplished by com- paring particle properties at advance time qualitatively with the analytical solution and quantitatively with the experiments. Chapter 3 explores the parametric study of the multiphase hydrodynamics. Here, we are particularly interested in the effects of paricle size distribution and the particle radius during evolution of multiphase hydrodynamic instability. It is found that the distribution of particles sizes causes less vorticity deposition than a case which considers only single size of same median diameter. The large particles are found to have lower enstrophy production at early times and higher enstrophy dissipation at late times due to the advection of the particle vorticity source term through the carrier gas resulting in less net overall vorticity depositon. Furthermore, the particle evaporation is found to increase the vorticity deposition causing the interface to evolve faster. Chapter 4 expands upon the study done in the previous chapter to the third dimension. Further validation of the code is done to make sure that the results obtained in the third dimension are correct. Shock interaction of the particle sphere containing randomly selected particle radii, which follow a lognormal distribution of median 1 μm at, random locations within the sphere is studied. This simulation is run with about 1 million particles at 1:1 parcel to particle size, and resolution of 128 nodes in the circle. The qualitative study shows the initial particle lag making the interface width large at early time. After some time, the hydrodynamic growth is found to overcome the differences in the particle velocity relaxation time decreasing the interface width. A highly asymmetric gas field is seen with alternating patches of positive and negative vorticity in the vorticity field. Further analysis of the 3D data will be done in the future to characterise the particle turbulence characteristics in the shock driven condition. These turbulence data would be interpreted to get new insights on the behaviour of the cosmological dust during the shock interactions.