Bradley Motl

Experimental validation of a Richtmyer-Meshkov scaling law over large density ratio and shock strength ranges

A universal scaling law for the Richtmyer–Meshkov instability is validated with experimental results covering a wide range of density ratios and shock strengths. These results include the first membraneless, gas-phase, interface experiments for A>0.5 and M>1.5. The shock-accelerated, sinusoidal interface experiments are conducted in a vertical shock tube with a large square cross section and cover the experimental parameter space: 0.29<A<0.95, 1.1<M<3, and 3.1×104<Re<1.4×107. Results provide growth-rate data for comparison with computational fluid dynamics simulation codes and verify the nondimensional time and amplitude parameters chosen for scaling are the correct ones. Correct scaling is obtained by including a growth-reduction factor that accounts for diffusion at the interface. Planar imaging techniques are used to diagnose the instability development for a nearly single-mode interface, and results are reported for eight scenarios (including three distinct gas pairs) that span the linear and nonlinea...

Richtmyer-Meshkov Parameter Study

The growth of an interfacial perturbation after acceleration by a shock wave, known as the Richtmyer-Meshkov instability (RMI), plays an important role in the compression of an ICF target. Experiments studying the RMI are performed in a vertical shock tube by observing the growth of the interface between a pair of gases after acceleration by a planar shock wave. A near 2D, sinusoidal, membraneless interface is created in a shock tube by oscillating rectangular pistons at the stagnation plane between the two gases. The interface is visualized by seeding one of the gases with acetone, smoke, or atomized oil and observing the fluorescence or Mie scattering from a planar laser sheet. The results presented here span a range of Atwood numbers, 0.30<A<0.95, and shock wave strengths, 1.1<M<3. Numerical simulations of the experimental conditions are performed and compared with the experiments using the 2D hydrodynamics code Raptor (LLNL).

Experimental study for ICF-related richtmyer-meshkov instabilities

Abstract Richtmyer-Meshkov experiments for a membrane-less, sinusoidal gas interface are carried out in a vertical shock tube for a pre-shock Atwood number (A = (σ2 – σ1)/(σ1 + σ2)) of approximately 0.68 at M = 1.26 and M = 2.05. The perturbation amplitude is obtained by analyzing a time sequence of pre-shock and post-shock images. The Mikaelian and Dimonte & Schneider models both predict the observed growth in the perturbation amplitude, with better agreement obtained for the data at M = 1.26.