Perpustakaan Digital ITB

In almost all of the studies on the circular hydraulic jump (CHJ), gravity had been considered as a significant variable that affects the formation of the jump. Most recently, gravity was deprived of being important in the origin of the CHJ, which challenged researchers in this field of fluid mechanics. This study addresses in detail the physical concepts behind this intriguing phenomenon occurring in the radial outspreading of a vertically downward free-surface liquid impinging jet upon a horizontal plate. The aim is to find out whether gravity plays any role in the origin of the CHJ. Accordingly, the jump evolution is investigated in two cases: first, the initial formation of the CHJ in which the subcritical flow downstream from the jump is approaching the outlet boundary (developing jump). Second, the final evolution of the CHJ in which a steady-state flow is circumventing an obstacle at the edge of the impinged plate and falling uniformly down from the outlet boundary (developed jump). The results indicate the existence of two different flow regimes in the jump formation: gravity- and capillary-dominant flow regimes. In general, the role of gravity in the formation of developing or developed jumps cannot be eliminated; however, its importance lies in the fact of which regime dominates the flow. Intensification of gravitational effects is observed when capillary waves are dampened by increasing viscosity, density, or volume flow rate as well as by decreasing surface tension. Finally, a generalized scaling relation for the jump radius is obtained considering both capillary and gravitational effects in the critical flow condition. In contrast to the previous results, this generalized scaling relation predicts more accurately the radius of both a developing and a developed jump.