Mechanical Engineering ETDs


Dell Olmstead

Publication Date



An experimental study was performed to elucidate the fundamental physics of shock-induced mixing for a simple three-dimensional interface. The interface studied consists of a gravity stabilized SF6-based heavy gas jet that produced a circular column with a diffuse interface into the surrounding air. The effects of density gradient (Atwood number, A), shock strength (Mach number, M), and column inclination angle (theta) were examined. Concentration was measured using Planar Laser Induced Fluorescence (PLIF) of an acetone vapor tracer mixed with the heavy gas jet and illuminated by a pulsed Nd-YAG laser. Shocks with Mach numbers of 1.13, 1.5, 1.7, and 2.0 were used for inclinations of 0 degrees (planar normal shock wave), 20 degrees and 30 degrees. Columns with Atwood numbers of 0.25, 0.4, and 0.60 were tested at Mach 1.7 for inclinations of 0 degrees and 20 degrees. The oblique shock-accelerated cylindrical interface produced a typical Richtmyer- Meshkov instability (RMI) consisting of a primary counter-rotating vortices. The streamwise extent of the vortex pair in the centerline plane (cross-section) images of the column is proportional to the square root of A divided by the square root of M, regardless of oblique shock angle for theta < 20. A heretofore unseen manifestation of Kelvin-Helmholtz (K-H) waves on the upstream edge of the column appear for oblique shock acceleration. The upstream edge K-H waves were observed in images from a vertical plane through the center of the column. The wavelength of the upstream edge K-H waves is proportional to theta divided by the product of M and the square root of A. This upstream edge K-H instability (KHI) caused earlier onset of secondary instabilities in the primary RMI vortices seen in the centerline plane images. The combination of more rapid onset of secondary instablities in the RMI and upstream edge KHI accelerated transition to turbulence and thus reduced the time to achieve well-mixed flow. Time to reach well-mixed flow was inversely related to Atwood number, and had a weak correlation with Mach number for M>1.13. Transition to turbulent, or well-mixed flow, was determined by analyzing the second-order structure function of intensity (I2(r)) in the PLIF images.


Shock, Richtmyer-Meshkov, Kelvin-Helmholtz, mixing, supersonic

Degree Name

Mechanical Engineering

Level of Degree


Department Name

Mechanical Engineering

First Committee Member (Chair)

Vorobieff, Peter

Second Committee Member

Mammoli, Andrea

Third Committee Member

Marios, Pattichis


National Nuclear Security Agency

Document Type




Appendix (63 kB)