Spatial-temporal behaviors of low-Stokes-number particles forming coherent structures in high-aspect-ratio liquid bridges by thermocapillary effect

We investigate experimentally coherent structures of low-Stokes-number particles in the thermocapillary liquid bridge as a closed system. Such coherent structures in thermocapillary liquid bridges have been known as particle accumulation structures (PASs) realized in traveling-wave-type convection. We discover the PAS in the flow of m=1 in an azimuthal wave number in the liquid bridge of O(10-3m), whose spatial structure is different from those hitherto indicated in previous research, with the particles heavier than the test liquid. The coherent structures by the particles suspended in the liquid bridge are illustrated in the laboratory frame and in the rotating frame of reference. Individual particles of Stokes number St=O(10-5) are tracked to indicate their spatial-temporal behaviors forming the coherent structures. We unveil that two major coherent structures are simultaneously emanated inside the liquid bridge of Γ=1.6 in aspect ratio. Their Poincaré sections are illustrated, which well reproduce qualitatively the predictions of Barmark et al. [Phys. Rev. Fluids 6, 084301 (2021)10.1103/PhysRevFluids.6.084301].