Late-Time Mixing Sensitivity to Initial Broadband Surface Roughness in High-Energy-Density Shear Layers.

Area of Science:

• Fluid dynamics
• Plasma physics
• High-energy-density physics

Background:

• Supersonic sheared mixing layers are crucial in astrophysics and inertial confinement fusion.
• Understanding their evolution is key to controlling complex physical phenomena.
• Previous experiments lacked control over initial conditions, limiting insights into mixing dynamics.

Purpose of the Study:

• To investigate the effect of initial surface roughness on supersonic sheared mixing layer evolution.
• To demonstrate control over the transition from ordered to random states in mixing layers.
• To validate turbulent-mix models against experimental data.

Main Methods:

• Conducted a large volume (8.5 cm^3) high-energy-density fluid shear experiment at the National Ignition Facility.
• Varied the initial surface roughness of tracer foils to alter layer conditions.
• Utilized simulations with a turbulent-mix model for comparison.

Main Results:

• Demonstrated the ability to significantly alter mixing layer evolution by controlling initial conditions.
• Transitioned the layer from a highly ordered system to a randomly ordered system.
• Observed faster mix layer growth indicative of strong mixing at high temperatures and near solid density.

Conclusions:

• Initial conditions, specifically surface roughness, play a critical role in supersonic sheared mixing layer evolution.
• Experimental results align well with simulations incorporating turbulent mix models.
• This work provides a pathway to control and understand mixing processes in high-energy-density regimes.