Study On Turbulent Characteristics And Abrasion Mechanisms Of High-velocity Sediment-laden And Aerated Flow

The turbulent characteristics of high-velocity sediment-laden and aerated flow are more other than the clear water flow of single-phase and current of low speed. In a special circulating system with high velocity flow, some flow parameters such as boundary shear stress and pulsation pressure are measured. An investigation is made on the turbulent characteristics of the three-phase flow of water, air and sand. The mechanism of silt abrasion is studied. Specific contents are summarized as following:1. The research results of turbulent flow, sediment-laden, aerated flow and silt abrasion are introduced. The problems to be studied and the methods to be employed in this paper have been presented.2. The fundamental theory and equations for the pressure fluctuation are described and the wall pressure fluctuation is measured. Based on the experiment data, the characteristics of pressure fluctuations are analyzed in the three-phase flow of water, air and sand. The effects of air concentration and sediment content on the amplitude and frequency of pressure fluctuations are discussed.3. The definition and calculation of fractional dimension is introduced briefly. The pressure fluctuation signals are processed by reconstructing the phase space for sediment-laden and aerated flow. The correlation dimensions are calculated for sediment-laden flow, clear water and aerated flow. The results show that the correlation dimensions are different in different current conditions. It is indicated that sediment-laden and aerated flows are not completely stochastic, possessing its intrinsic order. Different correlation dimensions explain the differences of the dynamical mechanism and systematic complex level. Different pressure fluctuation signal sequences have different fractal characteristics.4. With the self-manufactured transducers, boundary stresses in clear water flow, aerated flow and sediment-laden flow are measured. Based on the experimental data, the relationship between shear stress and flow velocity, and the relationship between friction coefficient and air content are analyzed. The effect of air and sediment laden content on boundary shear stress is discussed. It is indicated that the higher the air concentration and the less sediment laden, the less the shear stresses.5. The surface material is liable to erosion wear with high- velocity sediment-laden flow, hi this paper, sand wear mechanisms are discussed and some effects of significant flow factors on material wear are analyzed; The possibility of preventing erosion wear with aeration is proposed; Based on test data, the formula for calculating the concrete material wall surface wear rate is derived. It is indicated that the wear rate is related to the air concentration, the strength of material, the flow velocity and the sediment content. It is shown that wear rate can be reduced with the help of flow aeration.6. Applying the k - e turbulence model, the distributions of air concentration are predicted for the air-water flow below an aerator. The validity of the numerical solution is demonstrated by the comparison between value measured and calculated.