| Dam-break wave is a kind of disastrous water flow phenomenon.When the dam breaks,the water in the reservoir leaks down,and the water level in the upstream of the dam site falls sharply while the water level in the downstream rises steeply,and the flow pattern changes sharply,forming the unique water flow fluctuation.Strong turbulence aerated flow will be generated in the process of dam-break wave from its generation to its interaction with structures.It is difficult for traditional ADV and PIV technologies to measure the aerated flow.Due to the limitation of measurement means,the flow field characteristics of strong turbulence aerated flow caused by dam-break are unknown.In this paper,the experimental technology combining PIV and BIV is used to break through the limitations of traditional ADV and PIV technology,and the flow field of strong turbulence aerated flow caused by dam break is measured in a noncontacting way.In view of the randomness of strong turbulent aerated flows,ensemble averaging is carried out through a large number of repeated experiments to obtain the overall robust mean value.The main research contents and results of this paper are as follows.According to the principle of PIV and BIV technology,combined with the actual situation of the laboratory,an experimental platform for generating dam-break wave is built.Through special experimental design,the synchronization of generating dam-break wave is improved.The results of repeated measurement show that the experimental results have sufficient repeatability and reliability,and meet the repeatability requirements when taking ensemble average.In the process of combining the measurement results of PIV and BIV technology,the bubble region identification method based on artificial neural network is proposed,which greatly reduces the complexity and time consumption of manual work.The corresponding identification software is developed based on MATLAB,which improves the technology combining PIV and BIV.Aiming at the movement process of dam-break wave caused by instantaneous total collapse under the downstream horizontal dry bed,the global view of its evolution process was captured by a high-speed camera,and the change of water level with time was obtained,which was compared with the theoretical solution.The results show that there is a certain deviation between the theoretical solution obtained from the nonlinear shallow water equation and the experimental results in the upstream of the gate at the initial stage,and the deviation decreases with the passage of time.The reason for the deviation of the water level in the theoretical solution is given by analyzing the characteristics of the upstream flow field.Combined with the technology of PIV and BIV,the movement process of the dam-break wave under the horizontal dry bed slamming against the downstream vertical wall was accurately measured.The internal flow field of the aerated movement when the dam-break wave slamming against the downstream vertical wall was obtained by taking the ensemble average method through several experiments.The maximum velocity of aerated dam-break wave,the run-up velocity of slamming vertical wall,the streamline and velocity distribution,turbulence intensity and other kinematics characteristics are presented.The results of the flow field reveal the physical phenomenon when the dam-break wave impact on the downstream vertical wall.The water first run-up and then turns back upstream.In the case of turning back,the main body of water wraps up the gas and forms a water-gas two-phase flow vortex.The turbulence intensity in the experimental results is higher at the location of that two vortices. |
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