Patrick Wayne

Observation of the Development of Secondary Features in a Richtmyer–Meshkov Instability Driven Flow

Richtmyer–Meshkov instability (RMI) has long been the subject of interest for analytical, numerical, and experimental studies. In comparing results of experiment with numerics, it is important to understand the limitations of experimental techniques inherent in the chosen method(s) of data acquisition. We discuss results of an experiment where a laminar, gravity-driven column of heavy gas is injected into surrounding light gas and accelerated by a planar shock. A popular and well-studied method of flow visualization (using glycol droplet tracers) does not produce a flow pattern that matches the numerical model of the same conditions, while revealing the primary feature of the flow developing after shock acceleration: the pair of counter-rotating vortex columns. However, visualization using fluorescent gaseous tracer confirms the presence of features suggested by the numerics; in particular, a central spike formed due to shock focusing in the heavy-gas column. Furthermore, the streamwise growth rate of the spike appears to exhibit the same scaling with Mach number as that of the counter-rotating vortex pair (CRVP).

Effects Of Inclination Angle On A Shock-accelerated Heavy Gas Column

When a shock encounters a multiphase interface at an oblique angle, threedimensional (3D) flow effects are produced. Experiments using advanced optical diagnostics seek to elucidate the 3D nature of the flow as it transitions to turbulence. Planar laser-induced fluorescence (PLIF) images capture the development of flow instabilities in a shock-accelerated heavy gas column. Early time images show the counter-rotating vortex pair (CRVP) associated with the Richtmyer-Meshkov instability (RMI) both for normal planar and for oblique shocks, with the cores of the vortex pair parallel to the axis of the original gas column. For the oblique case, a shear-driven Kelvin-Helmholtz instability (KHI) also develops along the axis of the column due to 3D vorticity deposition. The influence of inclination angle of the column with respect to the shock direction on this secondary instability and thus upon the fully 3D flow, is assessed. The 3D data collected in these experiments is essential to the validation of numerical codes predicting a range of problems from scramjets to supernovae.

Oblique shock interaction with a laminar cylindrical jet

We present an experimental study of planar shock interaction with an initially cylindrical, diffuse density interface, where the angle α between the plane of the shock and the axis of the cylinder can be zero (planar normal interaction) or non-zero (oblique interaction). The interface is formed by injecting a laminar jet of a heavy gas mixture (sulfur hexafluoride, acetone, nitrogen) into quiescent air. The jet is stabilized by an annular co-flow of air to minimize diffusion. Interaction between the pressure gradient (shock front) and density gradient leads to vorticity deposition, and during the subsequent evolution, the flow undergoes mixing (injected material - air) and eventually transitions to turbulence. Several parameters affect this evolution, including the angle α, the Atwood number (density ratio), and the Mach number of the shock. For quantitative and qualitative characterization of the influence of these parameters, we use flow visualization in two planes that relies on planar laser-induced fl...

Experimental Studies of Shock Interactions with a Multiphase Medium

Both Rayleigh-Taylor instability (RTI [1, 2]) and Richtmyer-Meshkov instability (RMI [3, 4]) develop on a fluid (or gaseous) density interface undergoing sustained (RTI) or impulsive (RMI) acceleration. Misalignment between pressure and density gradients (baroclinicity) leads to vorticity production, and thus to interface perturbation, vortex formation, onset of secondary instabilities, and ultimately to turbulence