Response to perturbations for granular flow in a hopper.

Area of Science:

• Physics
• Fluid Mechanics
• Granular Materials

Background:

• Dense granular flow in conical hoppers typically exhibits radial velocity profiles.
• Circular symmetry is a key assumption in modeling unperturbed granular flow.

Purpose of the Study:

• To experimentally investigate the response of dense granular flow to symmetry perturbations in a conical hopper.
• To validate numerical models and commonly used constitutive relations for granular flow.

Main Methods:

• Particle tracking velocimetry (PTV) was employed to measure flow at the hopper's outer boundary.
• Experiments involved perturbing the system's symmetry by tilting the conical hopper.
• Numerical models based on continuum descriptions guided the experimental design and analysis.

Main Results:

• Experimental evidence of secondary, azimuthal circulation was observed in response to tilting.
• The onset and suppression of circulation were found to be dependent on tilt angle and wall friction.
• For large tilt angles, velocity fluctuations increased independently of circulation onset.

Conclusions:

• Perturbing the symmetry of a conical hopper induces azimuthal circulation in dense granular flow.
• Experimental results provide a basis for discriminating between different granular constitutive relations.
• Wall friction plays a significant role in suppressing or enabling secondary circulation.