Distribution of homogeneous particles on the bottom due to settlement in a uniform low-velocity turbulent flow

Abstract

The cross-sectional size of the flow does not influence the pattern of distribution of sediment.Submountain and mountain rivers carry a great amount of suspended silt quite dangerous for diversion plants and irrigation systems. In order to fight the silt, waterworks facilities are equipped with special structures, i.e., desilting basins, characterized by a large volume and a high building cost. However, they are widely used in the world practice because they solve a very important problem of protecting structures from silting and of waterway linings and turbine equipment from abrasive wear.Absence of desilting basins or presence of inappropriately designed desilting basins in a waterworks facility influences substantially the labor and technical cost of cleaning of the facility from deposited silt, the repair of conduit linings and turbine equipment, the losses in the produced electric power, and the productivity of the irrigated lands. An alternative to desilting basins has not been invented yet.In this connection, the development of a reliable method for design (hydraulic computation in the first turn) of desilting basins is an important part of the solution of the mentioned problems. The most critical aspects are correct determination of the size of the smallest dangerous particles of suspended silt, substantiation of the appropriate degree of desilting of the water flow (or the probability of silt deposition), and correct determination of the size of the basin.It should be noted that the problem can be solved successfully only in the case of reliable determination of the effective length of chambers of the desilting basin, which should ensure settling of the required amount of suspended particles of specified coarseness.In desilting basins of hydropower plants (HPP) and irrigation systems with flow velocities v = 0.2 -0.5 m/sec the flow is turbulent and its velocity has pulsation components. In this connection, the horizontal path of settling of particles homogeneous with respect to hydraulic size, which pass the inlet (initial) cross-section at the same height, is a random variable. In other words, these particles settle from the flow over some length rather than at one point. Knowledge of the law and of the main parameters of the distribution of particles on the bottom during the deposition will make it possible to determine reliably the effective length of deposition of this or that amount of particles and thus design the desilting basin appropriately.Today we have several methods for designing desilting basins for HPP and determining their sizes.The method of Velikanov presented in [1] is based on the law of distribution of averaged vertical pulsation velocity components that act on the particles during settling. The method gives considerably overestimated lengths for desilting basins [4].The methods of D. Ya. Sokolov, V. B. Dul 'nev, are based on the experimental data of D. Ya. Sokolov. However, the latter has studied a limited circle of problems and his method contains assumptions some of which have not...

Distribution of settled homogeneous particles in Dufour-type continuous flushing settling basins

“…The computational values characterizing the agreement between the test curves and the normal distribution law show that the probability of the hypothesis accepted fluctuates within 0.63 -0.97 for 19 tests and is lower for only three tests, which proves its correctness. Figure 3 presents the experimental distributions and the unleveled theoretical curves of normal distribution at a standard deviation ó¢ computed by (2). Figure 4 also gives leveled theoretical curves of normal distribution of probability density; in Fig.…”