Experimental Study On The Influence Factors Of The Bottom Aeration Facility On The Hydraulic Characteristics Of The Steep Channel

With the extensive application of aeration and erosion reduction facilities in engineering,the prevention and reduction of cavitation damage by aerated water flow has been widely recognized.However,because of aeration,the turbulent features of high-speed water flow become more complicated.The amount of air aerated in the flow is a key factor in cavitation reduction by aeration.In one hand,it will directly affect the result of cavitation reduction,and in other hand it will affect the aeration flow characteristics.Therefore,it is particularly important to study the changes of air amount in the flow which affects aerated water flow's hydraulic characteristics.Based mainly on the hydraulic model experiments and the theoretical analysis,for the aerator set on the steep chute with different vent areas,the aeration flow hydraulic characteristics affected by the amount of air entrainment,compared with flow characteristics of self-aeration without aerator in the same other flow conditions,are investigated.The influence of the amount of aeration on hydraulic characteristics along the flow course is mainly discussed.The main conclusions are as follows:The installation of an aeration bottom facility will result in the bulging of the surface line after the aerator,the uplift height of flow water surface after the aerator mainly depends on the boundary conditions of aerator and chute together with flow conditions.The reasonable choice of aerator is very important for flow aeration and flow patterns.The experiment results show that for the aerator with different vent areas and just for the natural aeration from flow surface without aerator,in the flow reach after the impact point of flow on the chute floor,flow velocity is not much different from each other in the same flow discharge.The average pressure at the impact point after aerated cavities is increased by 1 time for the flow with aerator compared with the natural aeration conditions.The coefficient of variation of the pulsating pressure is several times higher than that of natural aeration.Therefore,the impact problem of pressure on the bottom plate caused by the aerator should be paid attention to.The power of pulsation pressure after forced aeration is more evenly distributed in the frequency domain.There is no obvious dominant frequency and formation of peaks with relatively concentrated energy is in only 15 Hz ~ 45 Hz.Under the same conditions,increasing the flow discharge does not cause significant changes in the hydraulic flow characteristics along the course of the flow,but as the flow discharge increases,the value of each hydraulic element corresponding to the same position also increases.Low-frequency,large-scale vortex turbulence constitutes most of the fluctuating pressure energy of the chute.Along the flow course in the impact region,the amplitude and power of the pulsation pressure are the largest.The probability density distribution of pulsation pressure in this area is with positive bias characteristics.The probability distribution of pulsation pressure throughout the region is of a peak state.The pulsation pressure amplitude of the bottom plate is larger than that of the side wall,and the pulsation pressure of the bottom plate is more evenly distributed in the frequency domain.In general,the turbulence intensity of the water flow in the impact zone after the aerated cavities was the highest,the turbulent action on the bottom plate is the strongest,and the pulsating pressure values are more evenly distributed in the time and frequency domains.Increasing the area of the vent hole can increase the amount of air in the water flow.The increase in the amount of air entrainment will cause the water flow to expand,and the surface line will increase.However,the increase of air entrainment does not have a significant impact on the flow velocity and time average pressure.The amplitude and variation level of pulsating pressure show a tendency to increase with the increase of the amount of air entrainment in the impact zone.But the increase in the amount of air entrainment does not affect the probability density distribution of pulsating pressure.The greater the amount of air entrainment is,the more uniform the distribution of pulsating pressure in the frequency domain.The results of this paper are a good complement to the study of hydraulic characteristics of aerated water flow.It provides a useful reference value to further study the effects of the amount of air entrainment on the flow hydraulic characteristics.