Flow field and sediment passing capacity of type-a piano key weirs

Abstract

In the present era, sedimentation and bed morphology near hydraulic structures is a great concern as it affects the flow configuration and reduces the discharge capacity. Experimental investigations were done to study the flow field in the vicinity of one cycle, two cycle, and three cycle piano key weirs (PK weirs) with noses to monitor the sediment passing capacity of the weir. The three dimensional (3D) velocities were measured close to the inlet and outlet keys using an acoustic Doppler velocimeter (ADV). The velocity fields near both the inlet and outlet keys were examined, and it was found that there were considerable increases in the vertical (v-component) and lateral (w-component) velocities. Added to this, it was seen that the mean vertical velocity was more in front of the outlet key as compared to the front of the inlet key while the mean lateral and longitudinal velocities were low. The maximum velocity was observed in front of the inlet key which resulted in an increase of sediment movement over the PK weir. Furthermore, 2.6%–5.2% of the total sediment passing over the upstream portion of the weirs are flushed over the inlet key by self-cleaning. The flow field over the keys could not be accurately estimated using an ADV, possibly due to the flow complexity so computational fluid dynamics (CFD) simulations were done to understand the complex flow field for all the three PK weirs using a CFD solver which needs less computational cost and space. The widely used standard k–ε turbulence model (an eddy-viscosity model) was applied in the current numerical investigations. The numerical investigation shows that the magnitude of the velocity components was increased because of the vertical contraction in front of the sloped keys owing to very high flow immediately downstream of PK weirs.