Research On The Characteristics Of Fluctuating Pressures And The Mechanism Of Its Scouring In The Scour Pit

Energy dissipation of ski-jump type is very important in the hydroelectric power engineering. In the macroscopic view, the scouring by jet fluids on the rocky river beds results from the combined action of the impulsive forces of the incident fluids and the scour resistances of the river bedrocks. According to above two sides, the characteristics of pressure fluctuations in the scour pit and the mechanism of scouring by jet fluids are researched in this thesis.As far as the impulsive forces of the incident fluids are concerned, based on the mainly researching results of the oblique-submerged turbulent impinging jet, the diflusive characteristics for a submerged turbulent impinging jet, the pressure features at the bottom of the scour pit and the cause of generating fluctuating pressures are analysed. According to the model experiments, fluctuating pressures and their distribution at the bottom of the scour pit by submerged turbulent impinging jet are discussed by use of the methods of mathematical statistice and spectrum analysis. The wave equation of the fluctuating pressures at the bottom of the scour pit is generalized.As far as the scour resistances on the rocky river beds are concerned, the lifting conditions considered resisting forces for rock blocks in the scour pit are investigated. The vibration naturals for rock blocks are obtained through modal analytical module of finite element software-Ansys. By leading-in the model for transient flow, the mechanism of fluctuating pressure transmission in cracks of the bed rock and the cause of generating fluctuating uplift are discussed. A predicting formula for the maximum fluctuating uplift on rock blocks in a scour pool is deduced. A statistical relational expression considered resistance forces about vibration displacement and fluctuating uplift forces of rock blocks is put forward. The regularities of distribution about dynamic stress by fluctuating pressures of the rock masses at the bottom of the scour pit are gained through transient dynamic analysis. The predicting formula considered resistance forces for the limiting scour depth is obtained.These results in this thesis have reference value for the hydraulic design and the scouring.