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<p>Stilling basins with sudden expansions are commonly used downstream of spillways to dissipate energy via a hydraulic jump. However, the resulting asymmetric (S-type) jump generates intense pressure fluctuations that can threaten the stability of the basin floor and any control structures within it. Unlike previous floor-mounted pressure measurements, this study experimentally investigates the hydrodynamic pressures on the upstream face of the first row of cross-beams used to control an S-jump in a channel with an expansion ratio of 0.67. Pressure measurements were taken at five lateral locations on the beam for three optimal beam configurations under Froude numbers of 7.4, 8.7, and 9.5. The results demonstrate that the cross-beam system effectively reduces the root mean square (RMS) of pressure fluctuations on the basin floor by 36–61% relative to an uncontrolled S-jump. Critically, dynamic pressure peaks were consistently recorded at normalized lateral positions <i>x</i>/<i>w</i> = 0.33 and 0.67, coinciding with the asymmetric jet’s lateral impingement zones, identifying these as priority zones for structural reinforcement. Notably, extreme positive pressures on the first beam are 4–8 times larger than the RMS fluctuations, highlighting the importance of direct beam-surface measurements for fatigue assessment. The maximum dimensionless pressure fluctuation coefficient (<i>C</i>ₚ′ₘₐₓ) for the optimal configuration reached values of 0.13, 0.14, and 0.12 for Fr = 7.4, 8.7, and 9.5, respectively. These direct pressure measurements on the cross-beam surface provide valuable guidance for the design of cross-beam dissipators and the assessment of slab stability in expanding stilling basins subject to asymmetric inflow conditions.</p>

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Pressure fluctuations of horizontal beams as control structures of asymmetric hydraulic jump

  • 期刊论文

  • 发表日期：

    2026年5月15日

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  • Saeed Hajialigol,
  • Shokoofeh Sharoonizadeh,
  • Hossein Azizi Nadian,
  • Javad Ahadiyan,
  • Maryam Shahabi,
  • Seyed Mohsen Sajjadi,
  • Manousos Valyrakis

摘要

Stilling basins with sudden expansions are commonly used downstream of spillways to dissipate energy via a hydraulic jump. However, the resulting asymmetric (S-type) jump generates intense pressure fluctuations that can threaten the stability of the basin floor and any control structures within it. Unlike previous floor-mounted pressure measurements, this study experimentally investigates the hydrodynamic pressures on the upstream face of the first row of cross-beams used to control an S-jump in a channel with an expansion ratio of 0.67. Pressure measurements were taken at five lateral locations on the beam for three optimal beam configurations under Froude numbers of 7.4, 8.7, and 9.5. The results demonstrate that the cross-beam system effectively reduces the root mean square (RMS) of pressure fluctuations on the basin floor by 36–61% relative to an uncontrolled S-jump. Critically, dynamic pressure peaks were consistently recorded at normalized lateral positions x/w = 0.33 and 0.67, coinciding with the asymmetric jet’s lateral impingement zones, identifying these as priority zones for structural reinforcement. Notably, extreme positive pressures on the first beam are 4–8 times larger than the RMS fluctuations, highlighting the importance of direct beam-surface measurements for fatigue assessment. The maximum dimensionless pressure fluctuation coefficient (Cₚ′ₘₐₓ) for the optimal configuration reached values of 0.13, 0.14, and 0.12 for Fr = 7.4, 8.7, and 9.5, respectively. These direct pressure measurements on the cross-beam surface provide valuable guidance for the design of cross-beam dissipators and the assessment of slab stability in expanding stilling basins subject to asymmetric inflow conditions.