| With the height of discharge structures increasing, the problem ofhigh-velocity flow cavitation has been concerned. Restricted byconstruction conditions, there are many irregularities in spillway dams,spillway tunnels and chute spillways of high-head discharge structures.When high-velocity flows over them, cavitation phenomena will occur.Cavitation erosion arises from the cavitating flow from underpressure tohigher pressure. In order to prevent the erosion due to the cavitation inhigh-velocity flow, an economic and effective measure is to set upaerators for generating forced aeration in underpressure cavitation regionsor upper locations liable to cavitation erosion. By far, the study ofaeration cavitation control by aeration has not well understood. But thereis lack of researches on the corresponding relations of each parameter inthe cavitaton region, which needs a further study.The aerated characteristics in cavitation erosion zone of high-velocity flows over surface irregularity---offset into flow areinvestigated in this thesis. Velocity Field and pressure Field in cavitationerosion zone with different air concentrations and flow velocities wereobserved in details by using DANTEC three-dimensional Particle ImageVelocimetry, PHOTRON High-speed Photography, SCANIVALEElectric Multipressure Scanivalve, and YE6267real-time Pressure DateAcquisition System etc. in the Hydraulics Laboratory at ZhejiangUniversity of Technology. The2D-structures of the cavitation erosionzone were experimentally investigated. The relationship between flowvelocity distribution and entrained air rate was obtained. And thevariation of pressure and cavitation number with air concentration andflow velocity were also obtained. The effect of shock wave andmicrojet due to cavitation bubble collapse, interaction between aerationbubbles and cavitation bubbles, the phenomenon of cavitation bubblecollape lighting in cavitation erosion zone were analyzed in this paper. |
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