Intrusive and non-intrusive two-phase air-water measurements on stepped spillways: A physical study

During the recent decades, a number of overflow embankment protection systems were implemented. One design is the Minimum Energy Loss (MEL) weir, developed to pass large flood events with minimum energy loss and low erosion. Several MEL weirs have successfully operated for decades in Australian catchments affected by heavy tropical and sub-tropical rainfalls with very flat gradients. Their historical performances are discussed and confirmed the design capability to pass large floods with small afflux and very small energy loss and little environmental impact including no significant erosion at the abutments. During a major flood, visual and quantitative observations were undertaken at the Chinchilla MEL weir. On the smooth converging chute, the observations showed that the inception of self‐aeration was a three‐dimensional process with a gradual change in free‐surface roughness, from a smooth glassy free-surface to a very-rough choppy surface. An optical technique (OF) was implemented to derive the contour maps of surface velocities based upon video movies taken from a sturdy tripod. The self-aerated flow velocity data were close to the backwater equation in the self‐aerated region, while highlighting regions of high- and low-velocities across the chute. The OF data showed large streamwise surface velocity fluctuations in the aerated flow region, consistent with the broad literature on self-aerated flow measurements. The ratio of transverse to streamwise surface turbulence intensity indicated a strong anisotropy of the free-surface turbulence.

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Environmental fluid mechanics of minimum energy loss weirs: hydrodynamics and self-aeration at Chinchilla MEL weir during the November–December 2021 flood event

Chanson

Apelt

2023

Environ Fluid Mech

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Self aeration and energy dissipation on a steep stepped chute: how does physical modelling compare to prototype observations?

Chanson,

2024

Environ Fluid Mech

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For the last five decades, a number of overflow stepped chutes were built because the staircase shape is conducive to reduced construction costs and increased rate of energy dissipation. The stepped chute operations are characterised by air‐water flows that are highly turbulent flows with a large rate of energy dissipation, in comparison to smooth chutes. Herein, physical measurements were performed in a large‐size 1 V: 0.80H stepped chute model, with a steep slope typical of modern concrete gravity dams. The results are compared to visual observations of prototype spillway operation under Froude similar conditions. The detailed two‐phase flow measurements were conducted to characterise finely the self‐aeration and air diffusion process downstream of the inception region of free‐surface aeration. The bubble count rate profiles scaled with the instantaneous void fraction variance, and the relationship was biased close to the stepped invert under the influence of large‐scale vortical structures. The rate of energy dissipation was carefully estimated based upon the two‐phase flow measurements and the results are compared to earlier results on similar steep invert slopes and prototype data estimates. At the downstream end of the stepped chute, the rate of energy dissipation ranged from 43 to 46%, i.e. more than twice that on a smooth-invert chute for a similar chute length and discharge range. Graphical abstract Characteristics of self-aerated stepped chute flows for dc/h = 1.3—(I) Prototype flow at Hinze Dam (Re = 4.0 × 107); (II) Air-water flow properties in the large-size laboratory model (1:15) stepped spillway (Re = 6.1 × 105)

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Modelling spillway and weir operation during major overflows. On optical measurements in prototypes: pros and cons

Chanson,

Shi

2024

Flow Measurement and Instrumentation

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Intrusive and non-intrusive two-phase air-water measurements on stepped spillways: A physical study

Cited by 10 publications

References 38 publications

Environmental fluid mechanics of minimum energy loss weirs: hydrodynamics and self-aeration at Chinchilla MEL weir during the November–December 2021 flood event

Environmental fluid mechanics of minimum energy loss weirs: hydrodynamics and self-aeration at Chinchilla MEL weir during the November–December 2021 flood event

Self aeration and energy dissipation on a steep stepped chute: how does physical modelling compare to prototype observations?

Modelling spillway and weir operation during major overflows. On optical measurements in prototypes: pros and cons

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