HYDRODYNAMIC SIMULATIONS OF EJECTA PRODUCTION FROM SHOCKED METALLIC SURFACES

1 online resource (108 pages) : PDF

2017

University of North Carolina at Charlotte

The phenomenon of mass ejection into vacuum from a shocked metallic free surfaces can have a deleterious effect on the implosion phase of the Inertial Confinement Fusion (ICF) process. Often, the ejecta take the form of a cloud of particles that are the result of microjetting sourced from imperfections on the metallic free surface. Significant progress has been achieved in the understanding of ejecta dynamics by treating the process as a limiting case of the baroclinically-driven Richtmyer-Meshkov Instability (RMI). This conceptual picture is complicated by several practical considerations including breakup of spikes due to surface tension and yield strength of the metal. Thus, the problem involves a wide range of physical phenomena, occurring often under extreme conditions of material behavior.We describe an approach in which continuum simulations using ideal gases can be used to capture key aspects of ejecta growth associated with the RMI. The approach exploits the analogy between the Rankine-Hugoniot jump conditions for ideal gases and the linear relationship between the shock velocity and particle velocity governing shocked metals. Such simulations with ϒ-law fluids have been successful in accurately predicting the velocity and mass of ejecta for different shapes, and in excellent agreement with experiments. We use the astrophysical FLASH code, developed at the University of Chicago to model this problem. Based on insights from our simulations, we suggest a modified expression for ejecta velocities that is valid for large initial perturbation amplitudes. The expression for velocities is extended to ejecta originating from cavities with any arbitrary shape. The simulations are also used to validate a recently proposed source model for ejecta that predicts the ejected mass per unit area for sinusoidal and non-standard shapes. Such simulations and theoretical models play an important role in the design of target experiment campaigns.

doctoral dissertations

Mechanical engineering
Mechanics
Aerospace engineering

Ph.D.

CFD
Compressible Flows
Ejecta
Fluid Mechanics
Richtmyer-Meshkov Instability
Shock Waves

Mechanical Engineering

Ramaprabhu, Praveen

Keanini, Russell
Weggel, David
Deng, Shaozhong

Thesis (Ph.D.)--University of North Carolina at Charlotte, 2017.

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Karkhanis_uncc_0694D_11488

http://hdl.handle.net/20.500.13093/etd:1318