investigate relationship to determine the distance between the first and second aerator over the chute overflow based on the minimum air concentration (Case study of Kurdistan Azad Dam)

Document Type : Original Research

Authors
M. Arami Fadafan1 1
E. jafari nodoushan 2
M. Azhdary Moghadam 3
1 Ph.d. Graduated, Department of civil Engineering, Faculty of Engineering , Shahid Bahonar University of Kerman, Kerman, Iran
2 Department of Civil Engineering, Bijar Branch, Islamic Azad University,Bijar,
3 Department of Civil Engineering, University of Sistan and Baluchestan, Zahedan, Iran
Abstract
The increase of population and demand for water, agriculture and energy cause a rapid increase in construction of the dam has been. Moreover, the increase of dam height to increase storage and estimate the need for water cause increase the velocity of water over the spillway has been. Spillways, chutes and bottom outlets are important hydraulic structures for dam safety. Due to high velocities combined with low pressures, cavitation damages may occur on chute bottom and cause major damages or endanger the dam stability. Damage experience for flows in spillway tunnels and chutes indicates that damage becomes significant when water velocities exceed 30m/s, this velocity or head can be considered as the borderline for high velocity or high head flows. Introducing air to high-speed flow is necessary to prevent pressure reduction and its events such as cavitation. It is possible to protect spillway surfaces from cavitation damages using aerator devices. Usually, the air entering the flow is not reached to the bed chute. It is necessary to install the first aerated according to topographic conditions and cavitation index at the appropriate location. By determining the process of changing the air concentration of the bed, the distance between the two aerators can be determined. The air in the flow causes the compression and damping that cause Bursting bubbles. In result, the damage caused by cavitation is reduced. So cavitation investigations will be necessary and need to reduce and prevent cavitation damages. The length of the flow jet has a fundamental role in determining the distance between two aerators. With increases, the length of the jump, the contact surface of the upper and lower layers of the jet is in more contact with the air and affects the amount of air entering the flow. The absorbed air is removed from the flow after the Jet collision. By determining the minimum concentration of air in the bed, an optimal distance between the two aerations can be selected to prevent cavitation damage. Select the minimum air concentration of bed is based on the relationship provided by Wood (1983). It means that the concentration of average air in the stream is higher, which causes the flow of bulking and requires taller walls for the sides of the shut Which is not economically feasible. The variation in the air concentration of the bed can only be considered as a function of the length of the jump flow and the upstream heights. Creating a suitable duct for providing A negative cavity pressure Lead to the better performance that causes increases the distance between aeration. So use of aerators in suitable places and the entrance of air to water flow is a most effective way to reduce this damage, therefore in this study, an equation has been derived to estimate the distance between two aerators base on 1200 data of 90 experiments with R2 more than 0.84. results this study have been compared and investigated for aerator of Azad dam.

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[1] Totten, G.E., Sun, Y.H., Bishop, R.J., 1999 Hydraulics System cavitation,
[2] Chanson, H., 1988 Study of Air Entrainment and Aeration Devices on Spillway Model, PHD Thesis, University of Canterbury, Christchurch, New Zealand, March.
[3] Kramer, K., 2004 Development of Aerated Chute Flow, PHD Thesis, Mitteilungen 183, Versuchsanstalt für Wasserbau Hydrologie und Glaziologie der Eidgenössischen, Technischen Hochschule Zürich,
[4] Lesleighter, E.J., 1988 Cavitation in Hydraulic Structures, Prototype Correlation of Hydraulic Structures, Colorado Springs, Colorado, 74-94.
[5] Kells, J.A., Smith, C.D., 1999 Reduction of Cavitation on Spillways by Induced Air Entrainment, Canadian Journal of Civil Engineering, vol. 18, pp. 358-377.
[6] Rutschmann, P., 1988 Belüftungseinbauten in Schussrinnen, VAW Mitteilung 97, Versuchsanstalt für Wasserbau, Hydrologie und Glaziologie, ETH, Zürich, (in German).
[7] Falvey, H.T., 1983 Prevention of Cavitation on Chutes and Spillways, Frontiers in Hydraulic Engineering, Massachusetts Institute of Technology, Cambridge, 432-437.
[8] Falvey, H.T., 1990 Cavitation in Chutes and Spillways, Engineering Monograph No.42, Bureau of Reclamation, Denver Office, Colorado, April.
[9] Dong, Z., Wu, Y. and Zhang, D., 2010. Cavitation characteristics of offset-into-flow and effect of
aeration. Journal of hydraulic research, 48(1), pp.74-80.
[10] Erfanain-Azmoudeh, M.H. and Kamanbedast, A.A., 2013. Determine the appropriate location of
aerator system on Gotvandoliadam’s spillway using Flow 3D. American-Eurasian Journal of
Agricultural & Environmental Sciences, 13(3), pp.378-383.
[11] Mahdavi Meymand, A., Ahadiyan, J. 2015. Evaluation of Statistical, Empirical, Neural Networks and Neural – Fuzzy Techniques for Estimation of Spillway Aerators. Irrigation Sciences and Engineering,
38(3), pp. 51-61. (In Persian)
[12] Rutschmann, P., 1986 Volkart, P., Wood, I.R., Air Entrainment at Spillway Aerators, 9th Australasian Fluid Mechanics Conference, Auckland, 8-12 December.
[13] Ferrando, A.M., Rico, J.R., 2002 On the Incipient Aerated Flow in Chutes and Spillways, Journal of Hydraulic Research, Vol. 40, No. 1.
[14] Chanson, H., Study of air Entrainment and Aeration Devices, Journal of Hydraulic Research, Vol. 27, No. 3, 1989.1
[15] Chanson, H., 1991 Aeration of a Free Jet above a Spillway, Journal of Hydraulic Research, 29(5).
[16] Kramer, K., Hager, W.H., 2006 Minor, H-E., Development of Air Concentration on Chute Spillways, Journal of Hydraulic Engineering, ASCE, 132(9), 908- 915.
[17] Hager, W.H., 2006 Uniform Aerated Chute Flow, Journal of Hydraulic Engineering, ASCE,117(4) 528-533.
[18] Chanson, H., 1993 Self-Aerated Flows on Chutes and Spillways, Journal of Hydraulic Engineering, ASCE, 119(2). 220-243.
[19] Kökpinar, M.A., Gögüs, M., 2002 High-Speed Jet Flows over Spillway Aerators, NRC Research Press, Canadian Journal of Civil Engineering., 29(), 885-898.
[20] Pfister, M.U., 2007 Schussrinnenbelüfter, Lufttransport Ausgelöst Durch Interne Abflussstruktur, PHD Thesis, Versuchsanstalt für Wasserbau, Hydrologie und Glaziologie, Eidgenössischen Technische Hochschle Zürich.
[21] Tan, T.P. 1984 Model studies of aerators on spillways. Department of Civil Engineering Report Univercity of Canterbury, Christchurch, New Zealand.
Modares Civil Engineering journal
Volume 19, Issue 5
November and December 2019
Pages 73-83