Effect of Water Cushion on Dynamic Pressures at Impingement Area

Year 2021, Volume: 34 Issue: 1, 45 - 52, 01.03.2021

Cüneyt Yavuz

https://doi.org/10.35378/gujs.657473

Cited By: 2

Abstract

A free-fall water jet released from a spillway may cause significant scour on the downstream river reaches due to high dynamic pressures. Energy dissipators are generally used at the downstream of a spillway to disperse the energy of the water jet. In case of low air concentration, the jet may hit the river bed with high dynamic pressure heads that can cause significant scour adjacent to the dam body. The scour can cause significant stability problems on the dam body. To prevent the phenomenon, water cushion can be a practical tool to reduce the jet impact at the impingement area. In this study, the effectiveness of the water cushion is inspected by measuring the dynamic pressure variations against different discharges and varying water cushion levels. The results of the experimental study show that dynamic pressure reduction is reversely proportional to the water cushion level until a certain discharge. Then, water cushion level changes become meaningless, especially for small discharges.

Keywords

Water jet, Dynamic pressure, Impact assessment, Water cushion, Scour

Thanks

This experimental study is conducted on Laleli Dam and Hydroelectric Power Plant model built for DSIM Projects in Middle East Technical University Hydromechanics Laboratory.

References

• [1] Azmathullah, H.M., Deo, M.C., & Deolalikar P. B., “Neural networks for estimation of scour downstream of a ski-jump bucket”, Journal of Hydraulic Engineering, 131(10):898-908, (2005).
• [2] Hoffmans, G.J., “Jet scour in equilibrium phase”, Journal of Hydraulic Engineering, 124(4):430-437, (1998).
• [3] Hoffmans, G. J., Scour manual, Routledge, (2017).
• [4] Mason, P.J., & Arumugam K., “Free jet scour below dams and flip buckets”, Journal of Hydraulic Engineering, 111(2):220-235, (1985).
• [5] Mason, P.J., “Effects of air entrainment on plunge pool scour”, Journal of Hydraulic Engineering, 115(3):385-399 (1989).
• [6] Manso, P.A., Bollaert, E.F., & Schleiss A.J., “Influence of plunge pool geometry on high-velocity jet impact pressures and pressure propagation inside fissured rock media”, Journal of Hydraulic Engineering, 135(10):783-792, (2009).
• [7] Melville, B.W., & Lim S.Y., “Scour caused by 2D horizontal jets”, Journal of Hydraulic Engineering, 140(2):149-155, (2013).
• [8] Puertas, J., & Dolz J., “Plunge pool pressures due to a falling rectangular jet”, Journal of Hydraulic Engineering, 131(5):404-407, (2005).
• [9] Castillo, L.G., & Carrillo J.M., “Scour, velocities and pressures evaluations produced by spillway and outlets of dam”, Water, 8(3):68, (2016).
• [10] Bollaert, E.F., “Physics of rock scour: the power of the bubble”. In Scour and Erosion, ASCE Library, 21-40, (2010).
• [11] Pagliara, S., Hager, W.H., & Minor H.E., “Hydraulics of plane plunge pool scour”, Journal of Hydraulic Engineering, 132(5):450-461, (2006).
• [12] Bos, M.G., “Discharge measurement structures”. Wegeningen: International Institute for Land Reclamation, ILRI, (1989).
• [13] Naylor, R.H., “Galileo's theory of projectile motion”, Isis, 71(4):550-570, (1980).
• [14] Kawakami, K., “A study on the computation of horizontal distance of jet issued from ski-jump spillway”, In Proceedings of the Japan Society of Civil Engineers, 1973(219):37-44, (1973).
• [15] Data Acquisition (DAQ) Software, Online: http://turkey.ni.com/, (2019).