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We analyze the successive steps of the breakup morphology of a swirling liquid jet. Three-dimensional numerical simulations are carried out using the Volume of Fluid method with adaptive mesh refinement for axial Reynolds numbers of 50 and swirl numbers of 0.50 {less than or equal to} S {less than or equal to} 1 .55. We present fundamental flow features of the swirling jet in terms of time-averaged axial and azimuthal velocity profiles for the considered range of swirl numbers. The provision of a swirl induces helical disturbance at the interface of the jet, which exhibits an azimuthal mode number of m = 4. We identified that viscous forces are the most dominant force in the flow, which causes suppression of Kelvin-Helmholtz instability at the interface. In contrast, we found the existence of centrifugal instability, which destabilizes the helical rim developing at the interface. As a result, centrifugally induced corrugations in the form of tiny protrusions develop along each of the helical rims, which triggers Rayleigh-Taylor instability. Subsequently, these tiny protrusions get stretched in the radially outward direction and transform into twisting ligaments that break into droplets. We have elucidated the mechanism for the twisting of ligaments and its further disintegration into first-generation droplets, which has not been reported in previous studies.

We investigate the influence of the regular roughness of heated and cooled plates and adiabatic partition boards on the mean heat transport in a square Rayleigh-Benard (RB) convection enclosure by two-dimensional direct numerical simulations. The roughness is in the form of isothermal protrusions with a rectangular base and triangular tip. The protrusion height varies from 10% to 25% of enclosure height. With increased protrusion height, the large-scale circulation can not wash out the cavity between two consecutive protrusions. Thus, the overall heat transport of the enclosure impedes. We have inserted the partition boards between two successive protrusions with a gap between the conduction plate and the partition board to wash out the cavity. The partition board height varies from 20% to 99.8% of enclosure height. We have performed the simulations for the range of Rayleigh number 106 to 108 and at a fixed Prandtl number of 1. We observe a single large-scale elliptical roll with counter-rotating corner rolls for small partition board height. With an increase in partition board height, an elliptical large-scale roll breakdown into the number of large-scale rolls horizontally placed one beside the other. Finally, we observe multiple rolls stacked vertically when the partition boards almost touch the conduction walls. We found a maximum heat flux enhancement in protrusion with partitioned RB case approximately up to 4.7 times classical square RB for an optimal gap between conduction plate and partition board.

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