Turbulent-like velocity fluctuations in two-dimensional granular materials subject to cyclic shear

Area of Science:

• Physics
• Soft Matter Physics
• Granular Dynamics

Background:

• Two-dimensional granular materials under cyclic shear display complex velocity fields.
• These fields exhibit turbulent-like characteristics, including vortices of various scales.
• Understanding the scaling behavior of these fluctuations is crucial for granular material science.

Purpose of the Study:

• To systematically investigate velocity fluctuations in 2D granular matter under cyclic shear.
• To analyze the influence of friction coefficients and shear amplitudes on these fluctuations.
• To characterize the scaling laws governing velocity power spectra and structure functions.

Main Methods:

• Experimental study of 2D granular matter with varying friction coefficients.
• Application of cyclic shear with a range of shear amplitudes.
• Analysis of transverse and longitudinal velocity power spectra (E(k)).
• Analysis of second-order velocity structure functions (S(2)ν(r)) in real space.

Main Results:

• Velocity fields show turbulent-like behavior with scale-dependent vortices.
• Power spectra scaling is influenced by inter-particle distance, unlike real turbulence.
• Structure functions exhibit power-law scaling, allowing deduction of spectral exponents.
• Deduced exponents increase with shear amplitude, showing no yielding transition.
• Friction coefficients have no significant effect on the observed fluctuations.

Conclusions:

• Turbulent-like collective particle motions in cyclically sheared granular materials are governed by both elasticity and plasticity.
• The findings provide insights into the fundamental dynamics of granular flows.
• The study highlights the distinct scaling behaviors compared to traditional fluid turbulence.