EXPERIMENTAL AND NUMERICAL INVESTIGATION OF LOCAL SCOUR AROUND SQUARE BRIDGE PIER

Abstract

This study examines, local scour around square pier under unsteady flow conditions, caused by five different hydrographs. The experiments were conducted in the rectangular flume of 18.6 m length, 0.80 m width and 0.75 m depth, with uniform sediment bed material D-50 = 1.68 mm. Five experiment series were conducted with a plexiglass square pier b = 8.5 cm. The unsteady flow was generated by means of triangular hydrographs. The temporal variations of the equilibrium scour depths in front of the pier and the scour hole dimensions were recorded by two different cameras. The equilibrium scour depths at lateral sides and downstream of the pier were also measured. The hydrograph peak flow rates were found to be much more effective compared to hydrograph durations. The numerical solution was realized by using the software ANSYS FLUENT with RNG k-epsilon turbulence model. The numerical and experimental values were compared and interpreted, and acceptable accordance was observed between them. The calculated lengths and widths of the scour hole were found close to the measured ones. A comparison of the final elevations (t = 15 min.) for experimental and numerical results revealed that; the values of RMSE, MAE errors, and the determination coefficient R-2 were 0.53 cm, 0.48 cm, and 0.94 respectively. The R-2 values are 0.98 and 0.95 for the measured and calculated scour hole length (L) and width (W), respectively.