The dynamics of the diffusing interface separating two miscible fluids in a rotating Hele-Shaw cell is studied by intensive and highly accurate numerical simulations. We perform numerical experiments in a wide range of parameters, focusing on the influence of viscosity contrast and Korteweg stresses on the shape of the interfacial patterns. A great variety of morphological behaviors is systematically introduced, and a wealth of interesting phenomena related to finger competition dynamics, filament stretching, and interface pinch off are reveal. Our simulations exhibit miscible patterns that bear a strong resemblance to their immiscible counterparts for larger Korteweg stresses. The quantitative equivalence between such stresses and the usual immiscible surface tension is studied. The concept of an effective interfacial tension is considered, allowing the direct and precise calculation of the important fingering properties under miscible circumstances. Our results show excellent agreement with existing experiments and simulations for corresponding immiscible displacements. This agreement refers to a striking similarity between miscible and immiscible pattern morphologies, and also to an accurate prediction for the typical number of miscible fingering structures formed. Our findings suggest that the effective interfacial tension is both qualitatively and quantitatively equivalent to its immiscible counterpart.

SUMMARYInterfacial instability of a rotating miscible droplet with signiÿcant Coriolis force in a Hele-Shaw cell is simulated numerically. The in uences of the relevant control parameters are ÿrst discussed qualitatively by ÿngering patterns. More vigorous ÿngerings are found at higher rotational e ects, a lower viscosity contrast and a weaker e ective surface tension (Korteweg constant). For a time-dependent gap HeleShaw cell, a higher cell lifting rate makes the rotating droplet bear an inward straining ow, which leads to ÿngering enhancement. On the contrary, a higher pressing rate provides more stable e ects by additional squeezing outward ow. A quantitative analysis between the Coriolis e ects and tilting angles of ÿngers is addressed. For arbitrary combinations of all relevant control parameters, the values of tilting angles follow a nearly linear relationship with the Coriolis e ects. We estimate the correlation between the relevant control parameters (dimensionless Coriolis factor Re, viscosity parameter R, cell lifting rate a) and tilting angles (Â) of ÿngers that can be approximated as  = (0:0047 √ Pe=R+18:2a)Re for signiÿcant Korteweg stresses.

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