Experimental Study On Energy Dissipation Characteristic Of Stepped Spillway

Stepped spillway is a widely used pattern in the energy dissipation and flood dischargeof hydraulic engineering, due to obvious advantages on energy dissipation ratio of steppedspillway over smooth spillway and constructing convenience in most cases. Energydissipation characteristic of stepped spillway has been a hot issue and many researches wereperformed by many scholars. At present energy dissipation ratio is generally used in the studyon energy dissipation characteristics of stepped spillway, but it is unable to represent theenergy dissipation status in detail and has complex laws with parameters of stepped spillway,such as hydraulic parameters and water power parameters. In fact, smooth spillways also havedefinite energy dissipation ratio actually. Only different part about energy dissipation ratiobetween smooth spillway and stepped spillway has practical significance.Model experimentation and numerical simulation are developed on study of energydissipation characteristics of stepped spillway in this paper. Energy dissipation ratio of puresteps is put forward in this paper. For investigation of energy dissipation ratio of pure steps,hydraulic models of stepped spillway under three gradients and step heights were conductedsystematically. Calculating results indicate that the discrepancy between the energydissipation ratio of pure steps under different discharges and step heights are both less than5%and energy dissipation ratio of pure steps follows good linear rules with the length of flowpath. Unit flow path energy dissipation ratio of pure steps under different discharges and stepheights can be regarded as a constant, and has a10.4%increase while dam gradient decreasesfrom55°to32°.The proportion of energy dissipation created by steps in the total energydissipation, which is called relative energy dissipation, increases with the unit discharge anddecreases with the increase of step amount. With better regularities than that of energydissipation ratio, these two parameters are suitable for analyses of energy dissipationcharacteristics.On the other hand, through the numerical simulation of stepped spillway using thestandard k-ε model, distribution laws of velocity gradients were extracted and analysis ofenergy dissipation in the flow field was made. Furthermore study of turbulent kinetic energyand turbulent dissipation rate indicates that turbulent kinetic energy increases as unitdischarge and step amount increase, so as to turbulent dissipation rate. The maximum of turbulent kinetic energy and turbulent dissipation rate exist both in the area of the sharp cornerof step. In addition, for smaller unit discharges, main areas of energy dissipation are sharpcorner of step and eddy; when unit discharge increases main areas transfer to “virtual floor”and sharp corner of step. The paper also analyses the fundamental cause of the decrease inenergy dissipation ratio with the increase in the unit discharge.