2018, Saeed Kamrani-Rad Graduated

Numerical simulation of temporal local scour pattern around a single cylindrical pier in clear-water condition

Abstract

There are many researches that studied the equilibrium depth of pier scour. On the other hand, the recent evaluation of damages to infrastructure due to floods has shown that the time-to-peak of a flood hydrograph is often shorter than what the scour process needs for the equilibrium depth to be reached. As a result, the modern trend in pier-scour research is the topic of time-evolution of local scour. Scour hole geometry, also known as scouring pattern, is another aspect of pier scour that has become appealing to researchers. Scour pattern can be used for damage assessments and schedules of future rehabilitation efforts. The numerical simulation of sediment transport processes is also a tool to be considered, as it is indeed more flexible and more cost-effective than experimental efforts. Owing to these facts, in the current research the numerical simulations of scour pattern evolution on beds constituting of sand and gravel have been done and verified using SSIIM 1 and experimental data. Experimental data; in a 2 (m) wide channel and a 0.2 (m) in diameter pier; used in these simulations presents the time evolution of scoured bed in a quantified manner which is suitable for comparing with the numerical simulations. To verify SSIIM 1, a sediment transport case in a horizontally contracted channel has been used.

The results have shown that the numerical method used in this research, in both cases, is capable of simulating the time evolution of general geometry of the scour hole in a fairly good manner. On the other hand, moving toward the downstream of the pier, a discrepancy with the experimental data can be seen in the compared profiles and scour depth. Especially in the case of sand used as bed material, the scour pattern moves toward the walls of the channel in the sides of the pier. Due to the fact that SSIIM 1 uses the RANS equations with the k-ε turbulence closure, it does not take into account the unsteady-flow structures behind the pier. The discrepancies seen in the downstream of the pier can be attributed to the unsteady-flow not being well computed.