Flow characteristics within the scour hole around inclined circular bridge pier

Abstract

In the present study flow pattern and turbulence characteristics around an inclined circular bridge pier have been investigated experimentally in the presence of a scour hole and compare with vertical pier. An Acoustic Doppler Velocimeter (ADV) was used to observe the velocity components, turbulence intensities and Reynolds stresses in the vertical planes, at α = 0˚,30˚,60˚,90˚,120˚and 180˚. Run were conducted under the clear-water approach flow condition. Flow characteristics around a vertical pier in the presence of a scour hole will be compared with flow characteristics similarly observed around an inclined circular uniform pier by utilizing the observations made in radial planes at 0°, 90°, and 180°. Approaching to the pier i.e. while r is small and below the level of initial bed in the scour hole region the u component shows negative values, which indicates reversal of flow near the pier. The v component of the velocity is mostly small in this plane. Approaching to the pier, the w component of velocity has larger values in downward direction which is being considered as negative. This means there is dominancy of strong down flow in this region. In the plane at α = 180°, close to the pier i.e. while r is small, the u component shows a reversal of flow near the water surface also far away from the pier the value of w component is always positive at revealing that upward flow in the wake region. The local scour depth around inclined pier was found to be 7 % lesser than scour depth around vertical pier due to weaker value of turbulent characteristics in case of inclined pier. Results obtained are presented herein.