Experimental Study of Flow Field and Movement of Sediment over a Ramp

Abstract

Applications of hydraulic structures in low dams and diversion structures in countries like India, where sediment is a serious concern, demands a good expanse of research on the flow field and movement of sediment. The present study was focused on the non-uniformity in the velocity distribution along the flow direction and the movement of sediment over a ramp. The velocity distribution of the flow near and over the ramp was studied with the help of Acoustic Doppler Velocimeter. Experiments were conducted to study the mechanics and kinematics of movement of sediment particles. The movement of sediment particles over the smooth ramp was studied with the help of high-speed camera system. The particle velocity, acceleration, applied force and the angle of velocity vector were processed and analyzed from the captured images using digital image analysis techniques. The path of the movement of sediment particle was tracked. The vector results of the flow pattern indicated a very high amount of increase of the uplift velocity (y – component of the instantaneous flow velocity) component over a ramp. The sediment had very little movement for about 3.8 seconds at the beginning of the ramp and accelerated as it moved along the ramp in the downstream side. The path of the sediment movement over the ramp was found to be inclined by 25.6 to 35.7 degree to the horizontal axis which was almost parallel to the ramp (29.055 degree).

Sediment Movement over Type A Piano Key Weirs

“…For larger particles, and especially in case of PK1, the transition segment along the path of movement was observed. The slight movements in the upstream part of the key in these cases may look similar to what was observed earlier by Kumar et al (2019) for sediment movement over a ramp. But still, these movements are faster than what was observed for the ramp.…”

“…This additional shear stress is being utilized to counter the tangential component of the particle weight to move it over the slopping key. Finally, the ratio of vs max to Vmax obtained from CFD simulation of PK1 is found to be 0.69 and 0.78 for 2.0 and 2.58 mm particles, respectively, which is close to the value (vs max/Vmax = 0.73) found by Kumar et al (2019) for movement of 2.18 mm particle over a ramp.…”

“…The shear stress on the upstream smooth channel bed was obtained at a location of 0.1235 m upstream of the outlet key by observing the velocity profile over the bed using ADV and fitting it in the wellknown Prandtl-Karman logarithmic equation available for smooth bed (Carvalho et al 2010;Ferro 2003;Kumar et al 2019;Ramesh et al 2011). For each point, the mean flow velocity was obtained from the filtered data separated from 3000 raw samples (60 seconds of recording at 50 Hz) of instantaneous velocity.…”

“…For each point, the mean flow velocity was obtained from the filtered data separated from 3000 raw samples (60 seconds of recording at 50 Hz) of instantaneous velocity. The data filtration was processed in Explorer V software by fixing the minimum correlation (COR) to 70 and minimum signal-to-noise-ratio (SNR) to 15 (Kumar et al 2019;Sharma and Tiwari 2013;Voulgaris and Trowbridge 1998). The depth of flow, y was measured at 0.5 m upstream of the outlet key.…”