New directions for Rayleigh-Taylor mixing

Area of Science:

• Fluid Dynamics
• Computational Physics

Background:

• Rayleigh-Taylor (RT) instability is crucial for understanding gravitationally induced mixing in oceanography and inertial confinement fusion.
• Current engineering codes often rely on parameter calibration, making them interpolative rather than predictive.
• Reducing reliance on experimental data requires predictive computational science, necessitating error diagnosis in complex multi-physics problems.

Purpose of the Study:

• To validate engineering codes in an idealized Rayleigh-Taylor mixing layer setting.
• To investigate the impact of long-wavelength perturbations on RT mixing growth rates.
• To compare simulation results with experimental data and identify model inconsistencies.

Main Methods:

• Utilizing front tracking/large eddy simulations with increased mesh resolution.
• Inferring a self-similar power law for initial perturbation amplitudes from experimental data.
• Analyzing the effect of long-wavelength perturbations on the dimensionless RT growth rate parameter, α.

Main Results:

• Simulations show agreement with experimental data.
• The growth rate parameter α is non-universal, as revealed by advanced simulations.
• Long-wavelength perturbations have a maximum ±5% effect on the growth rate, contrary to predictions of larger effects.

Conclusions:

• Large predicted effects (factors of 2) on growth rates are inconsistent with experimental data.
• Inconsistencies in some models stem from their treatment of shortest-wavelength bubble dynamics.
• An alternative bubble merger model for shortest wavelengths aligns with experimental findings.