SUBJECT: Ph.D. Dissertation Defense
BY: Mohammad Mohaghar
TIME: Friday, March 8, 2019, 11:00 a.m.
PLACE: MRDC Building, 3515
TITLE: Effects of Initial Conditions and Mach Number on Turbulent Mixing Transition of Shock-driven Variable-density Flow
COMMITTEE: Prof. Devesh Ranjan, Chair (ME)
Prof. Ari Glezer (ME)
Prof. Cyrus Aidun (ME)
Prof. Suresh Menon (AE)
Prof. Donald Webster (CEE)


Many studies of mixing focus on the role played by instabilities and turbulence in an incompressible medium. However, compressibility and shock play a critical role in many practical applications. Some examples include the design of more efficient fuel pellets for inertial confinement fusion, development of energy-efficient scramjet engines, and so on. Understanding the mixing process in such complex flows presents a set of truly fundamental and open problems in fluid mechanics that still remain to be solved. The present work will quantify the effects of initial conditions (single- and multi-mode) and incident shock wave Mach numbers (M) on the perturbation growth and mixing rate, as well as to determine the critical value of Reynolds number and length scales necessary for turbulence transition to occur in these extreme mixing environments. The simultaneous density/velocity measurements will provide the first detailed turbulence statistics measurements (i.e. Reynolds stresses, density-velocity correlations and their spectra) for shock-accelerated variable density flows at M > 1.5. This work will help develop the capability to accurately predict and model extreme mixing, potentially leading to advances in the fields of energy, environment, aerospace engineering, and most pertinently, inertial confinement fusion devices. The technical objectives are to: 1. Quantify the effect of the initial conditions and the incident shock Mach number (M~1.55 and M~1.9) on the perturbation growth and mixing rate; and a critical value of Reynolds number and turbulent length scales necessary for mixing transition to occur in these flows. 2. Measure the change in growth rate upon interaction of the interface with incident shock and reshock for both initial conditions and Mach numbers. 3. Acquire simultaneous density-velocity measurements of shock-accelerated variable-density flows to allow for the direct measurement of several turbulence quantities for the first time (for M> 1.5).