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Blast shocks in quasi-two-dimensional supersonic granular flows.
J F Boudet1, J Cassagne, H Kellay
1Centre de Physique Moléculaire Optique et Hertzienne, Université Bordeaux 1, UMR 5798 CNRS, 351 cours de la Libération, 33405 Talence, France.
Physical Review Letters
|April 7, 2010
Summary
Impacts in granular materials create expanding holes, similar to blast shocks in gases. This study models this phenomenon, revealing two distinct growth stages: an initial blast and a slower acoustic-like expansion.
Area of Science:
- Physics
- Granular Mechanics
- Fluid Dynamics
Background:
- Understanding granular material dynamics is crucial for various industrial and geological processes.
- Blast shock phenomena in gases are well-studied, but analogous behaviors in granular media are less understood.
Purpose of the Study:
- To investigate the dynamics of hole formation and expansion in a flowing granular layer after sphere impact.
- To compare the observed dynamics to blast shock phenomena in gases and develop a predictive model.
Main Methods:
- Experimental setup involving a thin, dilute, fast-flowing granular layer impacted by a small sphere.
- Detailed observation and analysis of the resulting matter-free hole growth.
- Development and validation of a theoretical model incorporating inelastic grain collisions.
Main Results:
- The impact generates a rapidly expanding hole with dynamics mimicking blast shocks in gases.
- Hole growth exhibits two stages: an initial rapid blast phase followed by a slower phase governed by the medium's sound speed.
- A simple model accurately predicts the observed dynamics, accounting for inelastic collisions.
Conclusions:
- Granular impacts can generate blast-like shock phenomena.
- The developed model provides a framework for understanding shock wave propagation and relaxation in granular systems.
- This system offers a unique platform for studying the transition from strong shocks to acoustic disturbances.
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