New Form of Mixing in Turbulent Sedimentation

Area of Science:

• Fluid dynamics
• Multiphase flow
• Particle dynamics

Background:

• Rayleigh-Taylor (RT) instability is a fundamental phenomenon in fluid dynamics.
• Sedimentation of particles in fluids is crucial in various industrial and natural processes.
• Understanding particle-fluid interactions is key to predicting suspension behavior.

Purpose of the Study:

• To investigate the sedimentation dynamics of finite-size inertial particles in an RT-like configuration.
• To characterize the distinct regions formed by falling particles.
• To identify and model a new regime of convective mixing.

Main Methods:

• Direct numerical simulations (DNS) of particle-fluid systems.
• Analysis of particle concentration profiles and layer dynamics.
• Development and validation of a 1D model based on hindered settling.

Main Results:

• Two distinct regions observed: a leading mixing layer and a uniform bulk region.
• The mixing layer extension shows anomalous, non-integer exponent acceleration.
• The bulk region moves at a constant velocity, independent of the mixing layer.
• A 1D hindered settling model accurately predicts dynamics across different density ratios.

Conclusions:

• A novel regime of convective mixing occurs at the front of sedimenting particle suspensions.
• The observed dynamics deviate from classical RT turbulence.
• The 1D model provides a robust framework for understanding hindered settling in this regime.