Research On Aeration Characteristics Of Stilling Basin With Sudden Expansion And Drop Sill

As a new type of energy dissipater used in high-head and large unit-wide flow projects,the stilling basin with sudden expansion and drop sill is not only friendly to the ecological environment,but also can significantly reduce the internal hydraulic indicators of the stilling basin.It has been well applied in many projects.Due to the existence of lateral sudden expansion,the water flow enters the stilling basin,the geometry of the flow field changes suddenly,and the water flow loses the constraint of the solid side walls on both sides,and a vertical axis is formed on both sides of the main flow.The vortex is a typical ternary mixed flow state,and the internal water flow structure of the stilling basin is more complicated than that of the stilling basin without sudden expansion.Based on this,this paper uses theoretical analysis and model tests to study the flow pattern,aerated distribution characteristics and frequency spectrum characteristics of the aerated water flow in the stilling basin with sudden expansion and drop sill,aiming to explore the internal structure of aerated water flow and provide a reference for engineering design.The main research results and conclusions are as follows:(1)Based on the model test,the aerated water flow patterns of the stilling basin with sudden expansion and the stilling basin without sudden expansion were studied.It was concluded that the typical flow pattern of aerated water flow in the stilling basin with sudden expansion and drop sill is that the water jump is superimposed on the jet,and the jump head is split into two parts by the jet.The bubble jump zone is within the extension line of the vent,and the length is longer.Without sudden expansion,the ramp strength basin has been reduced,the length of the bubble suspension zone has been increased,and the bottom length has been reduced.The sudden expansion is the clear water return zone,which carries some bubbles.(2)Based on the model test,the aeration concentration distribution characteristics of the bottom of the stilling basin without sudden expansion and it with sudden expansion were studied.It was concluded that the aeration concentration of the bottom plate of the stilling basin without sudden expansion has a peak-decreasing curve distribution,and the aeration concentration of each longitudinal section is evenly distributed along the way;the aeration concentration of the bottom plate of the sudden-expansion stilling basin has a peak-rising curve distribution,The air-entrained concentration at the 1/4 midline is the largest,followed by the1/2 midline,and the air-entrained concentration near the side wall is the smallest.(3)Based on the model test,the aeration concentration distribution characteristics in the stilling basin without sudden expansion and it with sudden expansion were studied.It was concluded that in the direction of the water flow,the aeration concentration in the non-sudden expansion and sudden expansion slumping stilling basins attenuates along the way,and the maximum appears at the position of the head;in the direction of the vertical water flow,the bottom of each section of the jumping head is self-stable The aerated concentration first increases and then decreases when the water surface is reached,and then the aerated concentration of the cross-section increases with the increase in height;the aerated concentration of each cross-section of the no-sudden expansion slumping basin is uniformly distributed;the sudden expansion-type stumbling-off force The aeration distribution inside the basin is high in the middle and low on the two sides.(4)Based on the model test,the spectrum characteristics of aeration in the centerline of the bottom of the stilling basin without sudden expansion and it with sudden expansion were studied,including the amplitude characteristics,probability density distribution characteristics and power spectrum characteristics of the aeration pulsation.It was concluded that the aerated pulsation of the bottom of the stilling basin without sudden expansion and it with sudden expansion is obviously skewed,and the aerated pulsation energy has obvious the energy is mainly concentrated in 0?20Hz,and the dominant frequency is within 5Hz.