Numerical investigation of flow field characteristics over vertical drops with sudden contraction for different contraction ratios

Vertical drops are widely implemented in hydraulic structures such as irrigation canals, wastewater collection systems, and stepped spillways to dissipate flow kinetic energy while enhancing aeration and promoting dissolved oxygen levels. Depending on local topography, these structures serve to reduce the kinetic energy of falling water and to regulate the flow velocity within canals and irrigation networks. In this study, a three-dimensional numerical simulation was performed to investigate the flow pattern over a vertical drop featuring a sudden contraction under various contraction ratios. The simulation employed the RNG k-ε turbulence model in conjunction with the volume of fluid (VOF) method to capture free surface dynamics. The computational model was validated against experimental data, yielding acceptable levels of accuracy based on average percentage error (APE) and root mean square error (RMSE) metrics. Moreover, results indicate that a reduction in the contraction ratio leads to an increase in the falling jet thickness and hydraulic jump height, accompanied by a decrease in the water jet length. These changes promote enhanced energy dissipation, which is critical for reducing the kinetic energy of the flow in hydraulic structures such as irrigation canals, wastewater collection systems, and spillways. The findings suggest that optimizing the contraction ratio is an effective design parameter for improving energy dissipation efficiency and overall hydraulic performance.

کلیدواژه ها:

Vertical drop ، Contraction ratio ، Falling jet ، Free surface ، Sudden contraction