Head-on collisions of dense granular jets.

We study head-on impacts of equal-speed but unequal-width incompressible jets in two dimensions with a focus on dense granular jets. We use discrete particle simulations to show that head-on impact of granular jets produces a quasi-steady-state where a fraction of the excess incident momentum from the larger jet is captured by an impact center that drifts steadily over time. By varying the dissipation in our discrete particle simulations and through additional analogous continuum jet impacts of different rheologies, we show that this central drift speed is remarkably dependent primarily on the total dissipation rate to the power 1.5, and largely independent of the dissipation mechanism. We finish by presenting a simple control volume analysis that qualitatively captures the emergence of the drift speed but not the scaling.

Still water: dead zones and collimated ejecta from the impact of granular jets.

When a dense granular jet hits a target, it forms a large dead zone and ejects a highly collimated conical sheet with a well-defined opening angle. Using experiments, simulations, and continuum modeling, we find that this opening angle is insensitive to the precise target shape and the dissipation mechanisms in the flow. We show that this surprising insensitivity arises because dense granular jet impact, though highly dissipative, is nonetheless controlled by the limit of perfect fluid flow.