Numerical and experimental study of trajectory for free falling jets

Document Type : Research Article

Authors

1 Water Engineering, Department, University of Tabriz, Tabriz-Iran

2 University of Tabriz,, Department of Water Engineering

3 29 Bahman boulvard,

4 University of Tabriz, Department of Water Engineering

Abstract

The water flow over the dam spillways has a lot of energy and if this energy is not dissipated, the flowing water can cause irreparable damage to the dam and downstream structures. One way to dissipate this extra energy is to get water out of the jets into the plunging pool. Water-free jets often cause erosion and scouring downstream of the structure, affecting the abutments and the downstream channel. In the present study, the trajectory of free-falling jets is investigated numerically and experimentally. Ansys-Fluent software is used for numerical simulation and laboratory work is carried out in the hydraulic laboratory. The results showed that the domain of free falling jet in laboratory work is less than its calculated value using the projectile equations and the sample simulated using Ansys-Fluent software is due to air resistance. The equations of the projectile prediction and the simulated path in Ansys-Fluent have an error of 20.6% and 25.5%, respectively, compared to the laboratory data. Since none of the previously presented equations for calculating the path of falling jets were obtained using laboratory results and did not consider air resistance, therefore, they have errors in calculating the path of falling jets. In the present study, two equations have been presented to calculate the path of the free-falling jet, which have a relative error of 3.02% and 9.14%, respectively. These relationships significantly reduce the error of calculating the path of the free-falling jet. By reducing the outlet cross-section of the free-falling jet and increasing the head passing through the dam spillway, the free-falling jet reaches the ground at a greater distance from the dam body. Since none of the equations presented for calculating the trajectory of jets have been obtained using laboratory results and have not considered air resistance, so they have an average error of 21% in the estimation of trajectory jets. In the present study, in addition to providing equations to calculate the trajectory of a free-falling jet, the air resistance also entered the main equation of the projectile by fitting an equation (using laboratory data). The simulation results also showed that the water flow velocity with a 247% increase compared to the velocity at the end of the dam overflow, hits the ground, which requires more attention in the design of the stilling basin at the end of the dam.

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References

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Amirkabir Journal of Civil Engineering
Volume 56, Issue 9
2024
Pages 1125-1146

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