Experimental Investigation And Numerical Simulation Of Cavitation Inception In Flood-Discharge Tunnel With Orifices

The cavitation is an important factor in the design of hydraulic engineering. It has been studied for nearly a century by many scholars in the world, however, because of its complexity, a large amount of problems still need to be studied further. The orifice dissipator, as a new energy dissipation type, has been paid much attention since it was adopted in the Xiaolangdi project. In this dissertation, author summarized the existing results about the cavitation phenomena, its mechanism and method, studied the cavitation inception in the flood-discharge tunnel by experimental and numerical methods. The main contents and conclusions are as follows:1.Summarized the existing results about the cavitation phenomena, its mechanism and method. Analyzed the factors affecting the cavitation inception.2.Reveal the following important laws for the first time: a correlation exists among the maximum sound pressure level difference, the averaged sound pressure level difference and the relative energy of the cavitation noise for a given structure. It is very useful to unify the different noise index.3.Made the cavitation experiment of the flood-discharge tunnel with orifices in a pressure variable tank. The correlation among the maximum sound pressure level difference, the averaged sound pressure level difference and the relative energy of the cavitation noise was obtained. This correlation was used to determine the cavitation inception of the orifices and achieved good results.4.Simulate the time-averaged turbulent flow fields in the flood-discharge tunnel by using the axis-symmetric K turbulence mathematical model. The detailIII-2distributions of time-averaged parameters of the turbulent flow fields were obtained. The calculated pressure distributions were compared with the measured data and in reasonable agreement.5.Established a mathematical model to simulate the instantaneous flow fields and cavitation by combining the weakly compressible fluid theory and the Large Eddy Simulation method. Because the compressibility of fluid was taken into consideration, it is in better agreement with the true situation. It is valuable for simulating directly the cavitation in the prototype structures and studying the scale effects.6.Simulate numerically the cavitation in the flood-discharge tunnel with orifices for the first time. The Large Eddy Simulation method was used to give the detail flow feature. The calculated pressure distributions were compared with the measured data and in reasonable agreement. On the calculated instantaneous pressure distribution, the positions of cavitation inception were obtained. The predicted cavitation is in good agreement with the experimental results, which shows that the mathematical model given in this dissertation is reasonable.