| Bridges are significant component of the ground transportation infrastructure, which is imperative even in the present era of high speed aviation. In modern times, many bridges incorporate large steel girders supported by piers imbedded in ground. The huge cost and above all jeopardy of human life associated with bridge failure, has elevated the problem to be of national importance. It is for this reason the study of the erosion or scouring of the river bed is so important to guarantee the integrity of the bridge structure hereby ensuring public safety.;Scour means the lowering of the riverbed by water erosion such that there is a propensity to expose the bridge foundation, hereby making them inept of taking the colossal load of the bridge.;The objective of this study was to develop a simulation model to predict the final shape and size of scour-pit under the flooded bridge deck. A computational methodology has been developed in C++ code and implemented in STAR-CD, a commercial CFD application software, using a BASH script in UNIX environment. For the evolution of the scour-pit shape and depth, a single-phase (re)moving boundary formulation has been developed, based on the computational fluid dynamics analysis of the flow fields around the flooded bridge deck and the shear stress at the bottom-wall, using the High Reynolds number k -- epsilon turbulence model with standard wall function, based on Reynolds-Averaged Navier-Stokes (RANS) turbulent flow model. The "scouring tool" was assumed to be the flow forces (shearing stresses) in excess to bed material resistance (critical shear stress), corresponding to the scoured bottom-wall material structure. Starting with constant critical shear stress, all along the bed, the study was then expanded to incorporate the slope correction factor that took the model one step nearer to reality. Comparison with limited experimental data obtained from Turner-Fairbanks Highway Research Center, McLean, VA, USA, revealed larger discrepancies than anticipated; however, the developed iterative scouring methodology works well with the commercial CFD software and has potential for further enhancement, by including other flow parameters as well as material properties, influencing the complex scouring process, in addition to the shearing stresses. The advantage and thus the muscle, of the developed scouring methodology, lies in its simplicity based on physical reasoning and its easy expandability that makes it possible to perform extensive what-if parametric studies, including further enhancements based on physical reasoning or available data. |
