Modeling the Mangla Dam Spillway for Cavitation and Aerators Optimization

Mohammad Rafi, Akhtar Ali, Ghulam Qadir, Rafaquat Ali

Asian Development Bank, Manila, Philippines.
WAPDA Model Study Cell, Irrigation Research Institute, Irrigation Secretariat, Lahore, Pakistan.
Water Resources Division, National Engineering Services of Pakistan (NESPAK), Lahore, Pakistan.

DOI: 10.4236/jwarp.2012.412121                

Abstract

This study evaluated the effects of increased reservoir conservation level by 40 ft (12.2 m), on spillway velocities; it’s discharging capacity and associated cavitation risk. The study optimized the aerators size and shape to avoid cavitations. The mathematical model was used to estimate the flow velocities and cavitation risk, when scale model study assessed the spillway discharging capacity and optimized the performance of the aerators for modified conditions. The mathematical model simulations showed increased flow velocities and damage index for modified conditions. The damage potential was 2 - 3 times higher with modifications and falls within the major to catastrophic region. The scale model study showed that discharging capacity of the spillway can effectively be restricted to original design by raising spillway crest by 5.0 ft (1.52 m). The scale model study also showed that the two aerators near sluice and at the chute with an air duct pipe of 3.0 ft diameter can improve the free surface flow profile reducing the risks of cavitation. Simulations for several configurations demonstrated clearer affect of aerators ramps on flow trajectory and gate opening. It also depicted that the height of the ramp of sluice aerator has a positive effect on the flow performance to about 7.5 inches (19 cm), when further increase in the ramp height reduced the flow performance.

Keywords

Spillway; Model Studies; Discharging Capacity; Cavitation Risk; Aerators Optimization

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	H. T. Falvey, “Cavitation in Chutes and Spillways,” Engineering Monograph No. 42, A Water Resources Technical Publication, United State Department of Interior, Bureau of Reclamation, Denver, 1990.
[2]	H. Chanson, “Air Bubble Entrainment in Free-Surface Turbulent Shear Flows,” Academic Press, London, 1997, 401 p.
[3]	M. Brocchini and D. H. Peregrine, “The Dynamics of Strong Turbulence at Free Surface. Part 1. Description,” Journal of Fluid Mechanics, Vol. 449, 2001, pp. 225-254. doi:10.1017/S0022112001006012
[4]	D. Colgate, “Hydraulic Model Studies of Amaluza Dam Spillway,” US Bureau of Reclamation Report No. GR-25-76, 1976.
[5]	A. J. Paterka, “The Effect of Entrained Air on Cavitation Pitting,” Proceedings of the Joint Meeting of the International Association for Hydraulic Research, American Society of Civil Engineers, Minneapolis, 1953.
[6]	V. M. Semenkov and L. D. Lentyaev, “Spillway with Nappe Aeration,” In: H. T. Falvey, Cavitation in Chutes and Spillways, Engineering Monograph No. 42, A Water Resources Technical Publication, United State Department of Interior (USBR), Bureau of Reclamation, Denver, 1973.
[7]	D. Colgate and R. Elder, “Design Considerations Regarding Cavitation in Hydraulic Structures,” Proceedings of 10th Hydraulic Division Conference of American Society of Civil Engineers, Urbana, 16-18 August 1961.
[8]	Borden, D. Colgate, J. Legas and C.E. Selander, “Documentation of Operation, Damage, Repair and Testing of Yellowtail Dam Spillway,” US Bureau of Reclamation Report REC-ERC-71-23, 1971, 76 p.
[9]	K. Kramer, “Development of Aerated Chute Flow,” Doctoral Thesis ETH No 15428, Technical University of Darmstadt, Dipl-Ing, 2006.
[10]	National Engineering Services Pakistan (NESPAK), Associated Consulting Engineers (ACE), Barqaab Consulting Services (BCS), Binnie, Black and Veatch, UK (BBV), MWH Americas Inc., “Sedimentation Studies of Mangla Dam Raising Project,” Vol. 1. Project Report Water and Power Development Authority (WAPDA), Pakistan, 2004.
[11]	F. M. Henderson, “Open Channel Flow,” MacMillan Company, New York, 1966.
[12]	P. Novak and J. Cabelka, “Models in Hydraulic Engineering, Physical Principles and Design Applications,” Pitman Publication, London, 1981.
[13]	M. Takahashi, C. A. Gonazalez and H. Chanson, “Self-Aeration and Turbulence in a Stepped Channel: Influence of Cavity Surface Roughness,” International Journal of Multiphase Flow, Vol. 32, No. 12, 2006, pp. 1370-1385. doi:10.1016/j.ijmultiphaseflow.2006.07.001