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<p>The objective of this study was to investigate the influence of overflowing nappe flow on energy loss, scouring, and air bubble count while varying the physical scale with different levels of pooled water depths and overflow flow depths. The experiments were conducted in flumes at two scales: small-scale (1:100) and large-scale (1:25). The tests were performed using three different non-dimensional pooled water depths (<i>Dp</i>* = 0.2, 0.3, 0.4) with three non-dimensional overflow depths (<i>Yc</i>*) for both scale setups. Optical visualization techniques were utilized to analyze air bubbles, their count, and sizes. The findings indicated a direct relationship between the quantity and size of air bubbles and <i>Yc</i>*, as increasing <i>Yc</i>* resulted in higher air bubble counts. Conversely, a reverse correlation was observed between the size/number of air bubbles and <i>Dp</i>* for all <i>Yc</i>* levels. The research demonstrated that the smallest size and the fewest number of air bubbles were observed at the highest <i>Dp*</i> value (0.4), while the largest size and the greatest number of air bubbles were found at the lowest <i>Dp</i>* value (0.2) in both small- and large-scale experiments. Furthermore, the study revealed significant variations in energy loss due to changes in overflow depths <i>Yc</i>* and <i>Dp</i>*. Increasing the <i>Yc</i>* from the lowest to the highest Yc* resulted in an approximate 15–22% increase in energy loss. On the other hand, increasing <i>Dp</i>* from the lowest (0.2) to the highest (0.4) led to a 22–29% decrease in energy loss. Regarding scour reduction, a comparison was made between geogrid cases (G1) with an aperture size of 6.5&#xa0;mm and cases without geogrid (NG). The study showed that by varying the <i>Dp</i>* from 0.30 to 0.4 in G1 cases, a substantial reduction in scour (approximately 57–78%) was achieved. It is worth noting that in the small-scale experiments, the exact quantification of air bubbles was not possible, indicating the significant influence of physical scale on air entrainment properties. The outcomes of present study are important to mitigate the energy of overflowing nappe flow by using geogrid and water cushion effect of pooled water during floods.</p>

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Investigation of Energy Loss, Number and Size of Air Bubbles Generated Due to Nappe Flow Impinging into Pooled Water by Varying the Physical Scale

  • 期刊论文

  • 发表日期：

    2025年4月9日

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  • Fakhar Muhammad Abbas,
  • Norio Tanaka,
  • Amina

摘要

The objective of this study was to investigate the influence of overflowing nappe flow on energy loss, scouring, and air bubble count while varying the physical scale with different levels of pooled water depths and overflow flow depths. The experiments were conducted in flumes at two scales: small-scale (1:100) and large-scale (1:25). The tests were performed using three different non-dimensional pooled water depths (Dp* = 0.2, 0.3, 0.4) with three non-dimensional overflow depths (Yc*) for both scale setups. Optical visualization techniques were utilized to analyze air bubbles, their count, and sizes. The findings indicated a direct relationship between the quantity and size of air bubbles and Yc*, as increasing Yc* resulted in higher air bubble counts. Conversely, a reverse correlation was observed between the size/number of air bubbles and Dp* for all Yc* levels. The research demonstrated that the smallest size and the fewest number of air bubbles were observed at the highest Dp* value (0.4), while the largest size and the greatest number of air bubbles were found at the lowest Dp* value (0.2) in both small- and large-scale experiments. Furthermore, the study revealed significant variations in energy loss due to changes in overflow depths Yc* and Dp*. Increasing the Yc* from the lowest to the highest Yc* resulted in an approximate 15–22% increase in energy loss. On the other hand, increasing Dp* from the lowest (0.2) to the highest (0.4) led to a 22–29% decrease in energy loss. Regarding scour reduction, a comparison was made between geogrid cases (G1) with an aperture size of 6.5 mm and cases without geogrid (NG). The study showed that by varying the Dp* from 0.30 to 0.4 in G1 cases, a substantial reduction in scour (approximately 57–78%) was achieved. It is worth noting that in the small-scale experiments, the exact quantification of air bubbles was not possible, indicating the significant influence of physical scale on air entrainment properties. The outcomes of present study are important to mitigate the energy of overflowing nappe flow by using geogrid and water cushion effect of pooled water during floods.