We investigate the occurrence of spontaneous convection in a coaxial cylinder highly filled with monodisperse spheres. To analyze the flow field noninvasively, initial pulses consisting of colored particles are placed at equal intervals. By analyzing the spatiotemporal distribution of these pulses, we obtained axial velocity profiles for both the surface and subsurface regions. Our advection-diffusion equations with steady advection terms incorporate experimentally obtained axial velocity profiles in the surface layer, while the rest of the components are estimated using azimuthal symmetry and volume conservation. The validity of our model is confirmed by comparing experimental data with numerical solutions for both the spatiotemporal distribution and cross-sectional profile of the colored particles.

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• Granular flows
• Non-Newtonian fluids