Abstract
The LANL Shear Campaign uses millimeter-scale initially solid shock tubes on the National Ignition Facility to conduct high-energy-density hydrodynamic plasma experiments, capable of reaching energy densities exceeding 100 kJ/cm3. These shock-tube experiments have for the first time reproduced spontaneously emergent coherent structures due to shear-based fluid instabilities [i.e., Kelvin-Helmholtz (KH)], demonstrating hydrodynamic scaling over 8 orders of magnitude in time and velocity. The KH vortices, referred to as “rollers,” and the secondary instabilities, referred to as “ribs,” are used to understand the turbulent kinetic energy contained in the system. Their evolution is used to understand the transition to turbulence and that transition's dependence on initial conditions. Experimental results from these studies are well modeled by the RAGE (Radiation Adaptive Grid Eulerian) hydro-code using the Besnard-Harlow-Rauenzahn turbulent mix model. Information inferred from both the experimental data and the mix model allows us to demonstrate that the specific Turbulent Kinetic Energy (sTKE) in the layer, as calculated from the plan-view structure data, is consistent with the mixing width growth and the RAGE simulations of sTKE.
Highlights
The Kelvin-Helmholtz (KH) instability, unlike RichtmeyerMeshkov and Rayleigh-Taylor instabilities, has been historically less studied in high-energy-density (HED) experiments due to the impulsive nature of the laser-drivers typically used in the experiments
We show that increasing the surface roughness significantly alters the morphology of the layer evolution, in the extreme, inhibiting the emergent structures from forming
We will demonstrate the necessity and efficacy of using the BHR turbulent mix model implemented in the RAGE hydrocode to simulate the layer width growth of the system
Summary
The Kelvin-Helmholtz (KH) instability, unlike RichtmeyerMeshkov and Rayleigh-Taylor instabilities, has been historically less studied in high-energy-density (HED) experiments due to the impulsive nature of the laser-drivers typically used in the experiments. HED shear experiments started with single-sided drive, single-mode sinusoidal perturbations or flow around a simple structure such as a ball and evolved into double-sided layer experiments and long duration single-sided flow experiments.. The construction of the National Ignition Facility (NIF) advanced the field by enabling the ability to field larger scale counter-propagating shear experiments with sustained flows.. The NIF has allowed multi-instability integrated mix experiments, which use an indirect Inertial Confinement Fusion (ICF) capsule platform to assess the impact of instabilities and mix on performance in ICF implosions. Studying isolated shear instability dynamics is important to studying mix and turbulence, as the instability is the dominant source of turbulence in mixing systems.. Planar mixing layers have been extensively studied in non-HED experiments and have formed the basis for the majority of turbulent mix models with variable compressible turbulent Setting up large flow velocities and sustaining them have been difficult until recently. HED shear experiments started with single-sided drive, single-mode sinusoidal perturbations or flow around a simple structure such as a ball and evolved into double-sided layer experiments and long duration single-sided flow experiments. The construction of the National Ignition Facility (NIF) advanced the field by enabling the ability to field larger scale counter-propagating shear experiments with sustained flows. The NIF has allowed multi-instability integrated mix experiments, which use an indirect Inertial Confinement Fusion (ICF) capsule platform to assess the impact of instabilities and mix on performance in ICF implosions.
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