Probing of experimental boundary conditions for theoretical non-local models

Non-local phenomena in granular flows are evident in experimental data, but are difficult to explain with conventional granular theories. Recently, the concept of granular fluidity has been central in the development of new non-local constitutive equations, but experimental validation remains sparse. Specifically, the origin of the fluidity on a microscopic, single-particle level is still unproven. In this work, we present an experimental validation of the microscopic definition of the granular fluidity. Most importantly, we show that boundary conditions play a major role and influence the specific form of the granular fluidity model.