Effects of dimensionless parameters on air-entraining vortices

Proceedings of the Institution of Civil Engineers - Water Manag

2017

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A challenge when designing water intake structures in rivers, channels and reservoirs is to reduce the entrainment of air through free air-core vortices. Entrained air can cause discharge reduction, vibration and cavitation in the waterconveying system. This study firstly investigates flow boundary effects at the critical submergence of an intake, which is the depth up to which air entrainment occurs. The friction effect of a boundary section close to the free surface dominates the boundary blockage effect and retards the occurrence of the air-entraining vortex. Potential flow solution methods overpredict the critical submergence of an intake under the influence of boundary friction, so a design criterion is presented to correct this. Furthermore, previous work shows that Froude similarity is not always reliable for predicting critical submergence at prototype intakes. In the second part of this study, kinematic similarity -the equality of the ratios of intake velocity to the velocity at the imaginary critical spherical sink surface between the model and prototype intakes -is proposed and validated against experimental results. In addition, a theoretical explanation of the equal intake velocity concept is given using kinematic similarity.

Section: Water Managementsupporting

confidence: 57%

Section: Water Managementmentioning

confidence: 99%

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Scale and flow boundary effects for air-entraining vortices

Proceedings of the Institution of Civil Engineers - Water Manag

2017

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“…The available test results are given in the studies by Denny (1956), Jain (1977), Yıldırım and Kocabaş (1995), Kocabaş and Yıldırım (2002), and Taştan and Yıldırım (2010). In their experiments, there exist a sump, small, and large diameter pipe intakes, a dead-end wall, a blockage effect of the boundaries (incomplete CSSS), imposed circulation, still water and cross-flow, etc.…”

Section: Scale Effectsmentioning

confidence: 96%

“…use a different diameter intake or the easy way is to change or adjust Q) Figure 1 Variations of S c /D with similarity numbers [test results are from Denny (1956), Jain (1977), Yıldırım and Kocabaş (1995), Kocabaş and Yıldırım (2002), and Taştan and Yıldırım (2010)]. …”

Section: Scale Effectsmentioning

confidence: 99%

Effects of Froude, Reynolds, and Weber numbers on an air-entraining vortex

Journal of Hydraulic Research

Yıldırım

2014

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The present study highlights the need for using both the kinematic and dynamic similarities in scaled models of the critical submergence of vertical vortices at intake structures. A semi-theoretical approach, which is based on the principle of flow continuity, is used in combination with published experimental data. The present study shows that only the kinematic similarity is needed to model the ratio of the critical submergence to the diameter of the intake. For intakes that have an identical ratio of the intake velocity to the velocity at the critical spherical sink surface (CSSS), the ratio of the critical submergence to the diameter of the intake is identical regardless of the flow and the geometrical conditions. The new finding is that dynamic similarity is not required for the prediction of the ratio of the critical submergence to the intake diameter, provided that the ratio of the intake velocity to the velocity at the CSSS is kept the same.

Critical submergence for isolated and dual rectangular intakes

2016

Sādhanā

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This study examined critical submergence for isolated and dual rectangular intakes. It is shown that the critical submergence for an isolated intake can be predicted by disregarding whole boundary blockages on the complete imaginary critical sink surface that is the combination of imaginary complete critical cylindrical and hemi-spherical sink surfaces. It is proposed that this theory can be applied to the rectangular intakes located in general geometrical and flow conditions (i.e., intake in still water, circulation imposed flow, non-developed cross-flow, multiple intakes, etc.) and that it does not require computation of blockages caused from flow boundaries. The concept of complete sink surface (disregarding whole boundary blockages) developed for an isolated intake was also applied to dual rectangular intakes. The agreement between available test data and theoretical results was found to be satisfactory.