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This study deploys Large Eddy Simulations of turbulence to investigate secondary flows and near-wall turbulence characteristics induced by surface-mounted longitudinal ribs in a channel flow. The systematic variation of the Reynolds number (R e τ , based on friction velocity and channel height) between 300 and 950 and the rib aspect ratio (W / h , W and h represent the width and height of the rib, respectively) between 1 and 3 are considered, where the rib height h of 0.1 H (H is the channel height) and rib spacing of 8 h are held constant. The near-wall flow physics are also examined across varying Reynolds numbers while maintaining a constant inner-scaled rib geometry. The impact of the roughness function is evaluated in relation to the strength of the near-wall secondary flow. Additionally, the effects of increasing R e τ on the variations of extrinsically averaged Reynolds stresses in the wall-normal direction are analyzed. Some of the Reynolds stress contours show a correlation with the vortex cores on the secondary flow plane. The presence of ribs does not significantly influence the average streak spacing near the wall. The production and dissipation rates of turbulent kinetic energy (TKE) remain nearly constant above y / H = 0.4 (y is the wall-normal direction) irrespective of the value of R e τ and the rib aspect ratio. The numerical flow visualization and TKE budget analysis reveal that secondary vortices primarily form near the ribs. The TKE budget also shows that the narrow production zone is balanced by dissipation at low R e τ , expanding significantly at high R e τ . [ABSTRACT FROM AUTHOR]

Comprehension of the mechanics leading to the outcomes of the drop–drop collisions is essential for several industrial applications, including design of combustion chambers, development of spray drying techniques, agricultural spraying, and spray coating. In the broader context of several areas of applications, the stretching separation as well as transition between the reflexive and the stretching separation are required to be analyzed thoroughly. In this study, collision dynamics of two drops of equal size undergoing head-on and oblique collisions are studied using three-dimensional (3D) numerical simulations. The outcomes of collisions resulting in permanent coalescence, reflexive separation, and stretching separation are analyzed for a set of Weber numbers and impact parameters. The reflexive separation is an outcome of head-on collision for small values of the impact parameter. The stretching separation occurs owing to oblique collisions where the value of the impact parameter is larger. An accurate mass transfer mechanism coupled with the three-dimensional multi-phase simulations is deployed to study the collision outcomes of the evaporating drops for head-on and oblique collision scenarios. Simulations are performed for various levels of superheat between the drops and their surroundings to understand the effect of increasing mass transfer. The velocity field during the collision processes are altered when mass transfer due to evaporation plays an important role. The evolution of energy budgets and liquid volumes for all three collision regimes are presented for various levels of superheat considered in this study. [ABSTRACT FROM AUTHOR]

The splashing phenomenon associated with the impact of a liquid drop on a liquid pool is investigated in this study using the volume of fluid method. The different outcomes of this phenomena largely depend on the height (/depth) of a liquid pool and the impinging drop velocity. The impingement angle, drop shape, fluid properties, and other non-isothermal effects also play a role, but we have eliminated those dependencies by considering no variation in these parameters. The different phenomena that are observed when a drop impacts a liquid pool are controlled by (i) crater depth and wave-swell (rim of the crater) expansion, (ii) wave-swell retraction followed by crater side retraction, and (iii) crater base retraction. During splashing, a deep crater is produced in the receiving liquid after the drop impact. At its rim, a crown-like cylindrical liquid film is ejected out of the crater. Small droplets are normally shed from this rim. It is seen that the depth of the pool has dramatic effects on the dynamics of the crown formed during splashing. When observed even more comprehensively, the physical attributes of the crown, such as crown height and crown radius, are found to strongly relate to the velocity of the falling drop. Finally, we try to demarcate the regions of splashing with and without the formation of secondary droplets on the regime map of Weber number–dimensionless pool depth. [ABSTRACT FROM AUTHOR]