Asymmetric hydraulic jump control in sudden expansion channels using a Jet system

Document Type : Research Paper

Authors

• afshin mahjoubi ¹
• Javad Ahadiyan ²
• Seyed Mohsen Sajjadi ²
• Seyed Mahmood Kashefipour ²

¹ 1. Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran. Center of Excellence of the Network Improvement and Maintenance, Ahvaz, Iran

² Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran. Center of Excellence of the Network Improvement and Maintenance, Ahvaz, Iran

Abstract

Keywords

• Cross and counterflow jets
• Asymmetric hydraulic jumps
• S and T-jumps
• Dissipating energy structures
• Sudden expansion

Main Subjects

• سازه‌های آبی

EXTENDED ABSTRACT

Introduction

The presence of a sudden expansion in open channels often leads to the formation of asymmetric hydraulic jumps. These jumps, while associated with turbulence, energy dissipation, and air entrainment, can be problematic due to their extended domain range. This can cause significant bed erosion, damage to structures, and endanger aquatic life. The cross-flow and counterflow jet system implemented in this research, positioned downstream of the sudden expansion section, aims to reduce pressure fluctuations and turbulence along the channel, promoting flow uniformity.

Material and Methods

The investigation focused on the influence of jet configurations (including the optimal case), jet diameter variations, different tailwater depths, and various Froude numbers on the downstream flow hydrodynamics. Interestingly, even with the active jet injection system, the β_L parameter exhibited lower dispersion and values for S-jumps compared to T-jumps. This suggests that the cross-flow and counterflow jet system performed particularly well as a dissipation structure, achieving more uniform flow under these critical conditions. The findings also revealed a significant decrease in the momentum parameter β_L.v_m² as flow progressed from the sudden expansion towards the canal end. This translates to a reduction in the momentum force acting on the channel bed. However, during the initial stages of wave formation (first or second cycles) observed in the witness model (without any flow control structure), the β_L.v_m² parameter reached its peak alongside the maximum β_L value. Overall, the results demonstrate that the cross-flow and counterflow jet system effectively controls asymmetric hydraulic jumps and promotes uniform velocity distribution throughout the downstream canal section in all tested configurations.

Results and Discussion

A comprehensive review of existing literature revealed a gap in research regarding the application of combined lateral cross-flow and counterflow jets for controlling asymmetric hydraulic jumps. This is particularly true for T-jumps, where existing studies are scarce, and the use of jet systems for their control has not been documented. Motivated by this gap, the present research aims to investigate the effectiveness of the cross-flow and counterflow jet system in controlling both S-type and T-type asymmetric hydraulic jumps. The underlying assumption is that this system will effectively dissipate the jump's energy and promote uniform flow conditions downstream. By extending the investigation to T-jumps, this study contributes valuable insights to a less explored area within the field of hydraulic jump control.

Asymmetric jumps inherently induce flow turbulence and generate long-wavelength waves with high localized velocities. S-type jumps exhibit longer wavelengths, while T-jumps may experience shorter wavelengths but significantly higher non-uniformity. Regardless of type, controlling asymmetric jumps is crucial in real-world scenarios to prevent severe damage to the downstream channel, whether prismatic or non-prismatic.

The configuration with the minimum number of jets achieved the most uniform flow distribution, while the jet diameter was found to be dependent on the type of jump (tailwater depth variation). The jump length was significantly reduced compared to the control model with the implementation of the jet system, albeit at the cost of a slight energy loss.

Conclusion

The cross-flow and counterflow jet injection system employed in this research acts as a barrier to the main flow, promoting the dispersion and uniformity of the velocity distribution downstream. This effectively eliminates waves and return flows. In the witness model (without jet injection), the return flow velocity for the S-jump was approximately twice that of the forward flow, while the T-jump experienced a return flow velocity four times stronger than the forward flow.

Author Contributions

All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.

Data Availability Statement

Data available on request from the authors.

Acknowledgements

The authors would like to thank all participants of the present study.

Ethical considerations

The authors avoided data fabrication, falsification, plagiarism, and misconduct.

Conflict of interest

The author declares no conflict of interest.