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3d Numerical Simulation For Local Scour Around Square Piers By Fluent

Congress: 2015

Keyword(s): Sub-theme 15: Water law,
AbstractThe scour mechanism is the modern world's one of the most favorite environmental topics. Many researchers have been interested to investigate the phenomenon of scour around bridge piers and abutments for about sixty years. There are different approaches to solving engineering problems; however they still need to be developed. As there are many uncertainties involved in this phenomenon, scour prediction is complex and difficult because of the turbulence effects. However, it is necessary to do so for the protection of bridges and other infrastructure, especially during design planning stages. Scour prediction requires expertise and experience in several fields of engineering, as well as an understanding of the behavior of flowing water and its interactions with structures and soils. To investigate the transport of bed material under steady and unsteady flow conditions an experimental system was test in Hydraulics Laboratory of Civil Engineering Department of Dokuz Eylül University that supported with TÜBİTAK project no: 106M274. The experiments were carried out in the rectangular flume with 18.6 m long, 0.80 m wide and 0.75 m depth. The slope can be adjustable in horizontal. In 2009, a series of local scour around bridge pier experiments were conducted according to TÜBİTAK project no: 109M637. The uniform graded material with D50=1.68 mm is used for tests. The geometric standard deviation is 1.35 mm which implies that the sediment can be assumed as uniform and specific gravity is 2.65. Local scour around bridge piers in both steady and unsteady flow conditions were measured. The main goal of these experiments was to examine maximum scour depth and area of scour hole around different types of piers in unsteady flow conditions. In this paper local scouring around square piers caused by flood hydrograph propagation was numerically investigated by computer program ANSYS FLUENT using Eulerian two phase flow (water and sediment) model. Numerical simulations were conducted to investigate the time dependent dimensions scour hole, the maximum scour depths, the flow velocity values on stream lines around piers and turbulence flow models effects in the scour hole area. And also experimental findings and empirical expressions in literature were compared with these obtained from the ANSYS FLUENT software. The three dimension geometry configuration system was generated with ANSYS meshing generator. The grids near the pier are denser because of more complex region of the flume. Sediment layer region was adapted while the data was setting in solution set up in FLUENT. Wall boundary conditions were set to at the walls which include rigid bed (flume side walls and pier wall). At the wall boundaries no slip boundary condition was set; it means that all velocity components were zero. The side walls and pier wall were assumed to smooth. On the other hand the roughness height of the bottom wall was specified according to D50 of the sediment. At the inlet, the flow unsteady hydrographs which had been presented before were used. The velocity was set to X direction by using user defined function UDF macro. A logarithmic velocity profile occurred at the end of the inflow section while the hydrograph was passing. At the downstream outlet, the outflow boundary condition was set. It means that the normal gradients of all dependent variables were set zero for exit. The water surface of the flume was open channel flow but it was modelled as a symmetry plane where a zero-gradient condition is used for the velocity components parallel to the free surface, while the gradients of k, ε and velocity components perpendicular to the free surface are set to zero. Density and viscosity of the water was set default values for 20 C; 998.2 kg/m3 and 0.001003 kg/ms respectively. The properties of the second fluid phase sediment was defined by kinetic theory. In the flume domain all velocity components were zero as initial conditions. The sediment region was adapted with 26 cm thickness for initial flat sediment surface. The volume fraction of the sediment was patched to adapted region before the calculation started. The scour profile along to the pier and maximum scour depths were investigated. And also velocity profiles and vortex cores were investigated by the simulations. The maximum scour depths and Numerical results have a good agreement with the experimental results. The model simulation especially achieves giving the results on maximum scour depths. Ali, K. Karim, O. (2002) Simulation of flow around piers, J. Hydr. Res. 40, 161-174. FLUENT Incorporated (2009) FLUENT 14.0 USER’S GUIDE. USA Zhao, Z. and Fernando, H.J.S. (2007) Numerical simulation of scour around pipelines using and Euler–Euler coupled two-phase model. Environ Fluid Mech 7:121–142.
2011 IWRA - International Water Resources Association - - Admin