Turbulence characteristics and energy distribution in hydraulic jumps downstream of planar gate orifices: a particle image velocimetry experimental study

Abstract Hydraulic jumps formed by flow discharge through planar sluice gate openings represent a characteristic high-intensity turbulent phenomenon in hydraulic engineering. The turbulent structure exhibits directional asymmetry, intense energy dissipation, and complex spatial distribution, making it challenging to accurately characterize turbulence evolution and energy transfer. This study employs high-speed Particle Image Velocimetry to systematically measure flow fields in the jump region downstream of planar sluice gates under two conditions: free and submerged hydraulic jumps. By analyzing turbulence statistics, vortex intensity, Reynolds stress, and energy dissipation mechanisms, the study elucidates the generation, development, and dissipation patterns of turbulence in the jump region under different hydraulic jump types. Results indicate that a significant high-turbulence region forms at the gate bottom edge, where turbulent fluctuations exhibit directional asymmetry. Streamwise turbulent fluctuations substantially exceed vertical fluctuations, with intensities approximately three times greater. The shear layer at the bottom edge rotates opposite to vortices in the water layers above and below it, with positive streamwise vortices forming within the bottom edge shear layer. Under submerged hydraulic jump conditions, vortex numbers increase while their relative intensity decreases. Reynolds shear stress exhibits positive values at the gate bottom edge, transitioning to negative values beyond x / e = 3. Quadrant decomposition of Reynolds stress reveals that outward interactions (Q1) and inward interactions (Q3) dominate the flow field, differing markedly from boundary layer flows. Proper Orthogonal Decomposition analysis shows that first-mode energy accounts for approximately 85%–95% of total energy, indicating that large-scale vortex structures play a dominant role in the energy dissipation process. These findings provide a scientific basis for optimizing sluice gate structural design and downstream protection engineering.