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Experimental Investigation of Free Surface Dynamics and Pressure Fluctuations in a Closed-Conduit Hydraulic Jump

Author(s): Yee-Meng Chiew, Adel Emadzadeh

Linked Author(s): Yee Meng Chiew

Keywords: Hydraulic jump, closed conduit, water surface profile, pressure fluctuation


A hydraulic jump may occur in a closed conduit such as shaft spillways, culverts, etc. when the upstreamsuper-critical flow meets a downstream sub-critical flow. If the sub-critical conjugate depth is less than theheight of the conduit, a free surface will be present, causing the formation of a hydraulic jump, similar to thoseformed in open-channel flows. However, if the downstream sub-critical conjugate depth exceeds the closedconduit height, the flow may fill the conduit completely resulting in a pressurized hydraulic jump known as aclosed-conduit jump. These jumps are characterized by large vertical surges and low frequency pressurefluctuations that lead to significant vibrations and transient hydraulic loads, resulting in the destabilization ofhydraulic structures. While hydraulic jumps in open-channel flows have received extensive attention in theresearch fraternity, comparatively less information is available on the characteristics of turbulence, pressurefluctuations and energy dissipation in closed-conduit jumps. Consequently, this paper aims to present newexperimental data on the flow field and pressure fluctuations associated with such hydraulic jumps in view oftheir relevance on the stability of hydraulic structures. The present experiments are concerned with closedconduit jumps in a regular rectangular duct. Free surface fluctuations, if present, are measured using a highspeed camera synchronized with a series of pressure transducers mounted on the conduit bed. Water surfacedynamics and pressure fluctuations are investigated as a matter of concern in the design of stilling basins andother hydraulic structures. The experimental results show that high pressure fluctuations persist at thedownstream end of closed-conduit jumps. Moreover, the mean depth calculated from pressure measurementsis smaller than that deduced from the water surface profile obtained using high-speed images, probably due tothe presence of air in the flow. (2596, 67, 366)


Year: 2017

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