Study On The Hydraulic Characteristics Of The Irregular Bottom Sill Of The Open Channel

With the rapid development of water conservancy in China,the construction of high dams is increasing.More attention has been paid to hydraulic problems caused by high-speed flow.One of the most important problems is the cavitation damage caused by high-speed water flow.The most cost-effective way to reduce cavitation damage is to set aeration and erosion reduction measures.At present,there are many types of aeration and corrosion reduction measures in engineering,such as aeration,flip bucket,aeration drop,aeration tank or combination.Based on the model tests,for the specific convex aerator and concave aerator on the bottom of the flume,and compared with the linear aerator,the hydraulic elements of them are studied and analyzed in this paper.The characteristics of the cavity,the concentration of aeration and the pulsating pressure after the three aerators are analyzed,and the advantages and disadvantages of the three kinds of aerators are summed up.The main contents and conclusions are as follows:(1)The cavity length and cavity backwater depth of the three types of aerators are investigated by the control variable method.The relationship of cavity length,cavity backwater depth,the unit discharge,and Froude number are compared and analyzed.The relationship between the unit discharge q and cavity backwater depth d is fitted.Test results show that the cavity length of the linear aerated is the largest compared with the other two aerators under the same flow;both the convex aerator and the concave aerator can weaken the cavity backwater.(2)The variation of air concentration in the flow area near the flume floor and near side wall for three kinds of aerators are measured and analyzed.When x < 80 cm,and under the same flow discharge,for the flow area near the flume floor,the air concentration for the convex aerator is the biggest and it is the smallest for the concave aerator.For the flow area near the side wall,the air concentration for the linear aerator is the biggest and it is the smallest for the convex aerator.After x=80cm,the difference of air concentration among the three types is very small,and the rule is not obvious.(3)The amplitude characteristic,probability density distribution and frequency density of pulsating pressure at the flume floor for three kinds of aerators are compared and analyzed.For the amplitude of pulsating pressure under the same flow rate,it is the biggest for the linear aerator and it is the smallest for the concave aerator;the amplitude of the pulsating pressure of the three types of aerators increase with the increase of the flow rate.The probability density distributions of fluctuating pressure of three kind aerators basically agree with normal distribution.According to the analysis of the pulse pressure spectrum characteristics of the three types of aerators,it is found that the dominant frequency of the linear aerator under the same flow is the largest,which varies within14-15 Hz,and the pressure frequency for all three kinds of aerators belong to the low frequency range.When flow discharge is changed,the dominant frequency for each aerator is basically unchanged.