Experimental study of the hydraulic and aeration characteristics within the vortex drop shaft spillway

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This study focuses on a novel type of vortex drop shaft spillway, addressing the lack of comprehensive research on its hydraulic and aeration characteristics. A combination of experimental and theoretical methods was employed to investigate these characteristics in detail. The results reveal that the relationship between the swirl angle and the Froude number (Frx) remains unclear. However, a positive correlation was observed between the water layer thickness, flow velocity, and Frx. Analytical formulas derived for the swirl angle and water layer thickness showed a small relative deviation from experimental data, and the maximum relative differences are about 4% and 8%, respectively. Furthermore, a linear negative correlation was identified between vortex cavity length, relative aeration rate (β), and Frx. An empirical relationship between β and Frx was established. When Frx ranges from 0.064 to 0.89, the aeration concentration along the shaft gradually decreases, while it increases along the outlet tunnel. At lower Frx values, the transverse aeration concentration in the upper layer of the outlet tunnel is highest at the center and lower at the sides. In the lower layer, the concentration is higher at the sides and lower at the center. The aeration concentration near the wall of the outlet tunnel is more than 4%, which can effectively reduce the cavitation damage in the outlet tunnel. These findings deepen the understanding of the hydraulics and aeration mechanism in the vortex drop shaft spillway, offering theoretical support for its application and further development.