Research On Hydraulic Characteristics Of Stepped Energy Dissipater After Adding Aeration Facility

With the development of water conservancy projects,there are more and more high dam structures,and the problem of high-velocity flow damage to the discharge works is becoming more and more prominent.On one hand,the structure may be destroyed by cavitation erosion,on the other hand,when the discharged flow velocity increases,the flow energy will increase,and the scours of structure will more severe.Although the stepped spillway can effectively solve the above problems under certain conditions,when the flow rate is large,the water depth increases,the aeration concentration in the flow is low,and cavitation erosion will be occured.Therefore,adding air to the flow by aerators can increase the air concentration in the flow,which can prevent the structure from cavitation erosion in large flow.Based mainly on the model experiments,different aerators are set on the stepped spillway in order to study the aeration concentration and the pulsating pressure distribution characteristics on the step surface.The test flume without aerator and with three different aerators are selected for 6 different flow discharges in this experiments.The main research contents and conclusions are as follows:(1).According to analysis of water surface profile and velocity variation along the spillway,it is found that at the same flow rate,the water is aerated and it is forced water surface profile rise in the stepped spillway after the aerator.With the increase of aerator height,the cavity behind the aerator increases,and the more air is added,the increase of the water surface profile is more obvious.After adding side aerator on the two side walls,the water near the side wall is jetted,and more air is added,the water surface profile rise.At the same flow rate,the flow velocity of stepped spillway has little change along the flow path.Increasing the height of aerator or adding side aerator will increase the flow velocity and the influence of flow velocity decreases along the path.(2).According to the analysis of aeration concentration along the flow path and the energy dissipation rate,it can be seen that under the same flow rate,as the aerator height increases,the aeration concentration of the whole flow increases,and the energy dissipation rate of the stepped spillway increases.The aeration concentration of the flow near the side wall increases obviously after adding side aerators,the turbulence of flow is strong and the energy dissipation rate is increased.In the same aerator type,when the flow rate increases,the aeration concentration first increases to a certain extent and then decreases,and the energy dissipation rate also increases to a certain extent and then decreases.(3).The analysis of step surface pressure of stepped spillway under the same condition shows that in the convex corner of the step the flow pressure is most strongly impacted by the water flow,and the pulsating pressure is the largest in the process of water discharge.Because of the existence of vortices and sufficient aeration,the pressure at the junction of the vertical and plane of the step is the smallest,and the main frequency is less than 11 Hz under the test condition,which belongs to the low frequency band.