Study On The Pulsating Pressure Characteristics Of A Full-section Aerated Water Flow

China is richful in hydropower resources,since the reform and opening up,the high dam of release structures is more and more.High speed flow's cavitation destruction of structures can not be ignored,so it is urgent to study the effective measures of reducing erosion which is attracted scholars' attention.Nowadays the most widely used measure is aerator to reduce erosion.Mainly based on the hydraulic model tests to study the hydraulic characteristics of fluctuating pressure of aerator flow and the aerator of chute on its whole section.There are four ways of aeration including natural aeration,sill aeration,side sill aeration and combined aeration facilities,five flow and lots of air hole types.Accoding to the controlling variables and the analysis of measured data's summary,the results show that in the different flow areas downstream the natural aeration and forced aeration facility,the flow air concentration and fluctuating pressure characteristics are quite different.The contents and results of research are:(1)From the theory of bottom cavity and lateral cavity analysis,we use the the calculation formula to summarize that for the same experimental conditions the bottom cavity length showed a inverse relationship with single wide flow and ventilation hole number.The lateral cavity length showed a positively proportional relationship with the Froude number and vent radius.(2)According to the distribution of the gas concentration and the fluctuating pressure at the same operating condition along the length,it is found that the variation trend of the two is consistent in the region of the water flow in the different forced aeration facilities.In this region,the phenomenon of strong water flow fluctuation is caused by the increase of the concentration of gas behind the aeration facility.The main factors that affect the fluctuating pressure is flow velocity and also include the air concentration.From the distribution of the pressure fluctuation along the side wall,the effect of aeration at the combined aeration facility is better than that of the single bottom and side aerator.(3)From the distribution of the pressure fluctuation along the bottom board,in the impact area,the building which suffer from the maximum instantaneous pressure load of flow especially in the bottom board or combined aeration facility.In the reflection area and stable area,the flow velocity is the main factor leading to increase the fluctuation of flow.The fluctuating pressure turbulence degree has a positive proportional with the number of air holes and air hole area.(4)From fluctuating pressure's time domain process,root-mean-square values,deviation coefficient,coefficient of kurtosis,the main frequency etc.The test results indicate the maximum fluctuating pressure of surface on the steep channel can be reflected by a formula and the measured maximum fluctuating pressure is about 3 times of its root-mean-square values,respectively.Under the test conditions,the main frequency of each district is less than 11 Hz,and the dominant frequency is mainly concentrated in the 0-10Hz which belongs to the low frequency range,At the same time,the distribution of the fluctuating pressure in the downstream and the stable region is close to the normal distribution.These results may provide some useful theoretical and experimental basis to the actual engineering application of these aeration facilities at the steep channel.