With the increasing of the tunnel operation life, various diseases of the tunnel are gradually highlighted, especially the lining cracking and leakage caused by the crystal blocking pipe of the drainage system, which brings serious hidden trouble to the safe operation of the tunnel. In order to solve the problem of crystal plugging of horizontal drainage pipe in tunnel, the transverse drainage pipe of the tunnel was taken as the research object, combined with the field survey data, and the indoor test was used to analyze the anti‐crystallization law of flocking drainage pipe at different velocities. The results showed that the flocking drainage pipes had an anti‐crystallization effect, and the anti‐crystallization efficiency could be increased by more than 50% compared with the ordinary drainage pipes, and the flow rate at 6.82 cm/s could reach more than 60%. At the flow rate of 5.46 cm/s, the crystallization on flocking drainage pipes at the later stage of the test remained basically unchanged and was less than that on ordinary drainage pipes. The change in the weight of crystals on the flocking drainage pipes was approximately sinusoidal, and the change period was different at different flow rates; among which, the change period of crystallization on the flocking drainpipe was shorter when the villi length was shorter at low flow rates.
The crystal plugging of tunnel drainage pipe seriously affects the safe and normal use of the tunnel. In order to obtain the mechanism of flocking drainage pipe anti crystal plugging based on the characteristics of flow field distribution, numerical simulation was used to optimize the parameters of flocking drainage pipe. The results show that: with the existence of fluff, the velocity in the lower part of the drainage pipe decreases by about 50%, and the velocity in the upper part increases by about 25~50%. With the increase of the length of fluff, the velocity funnel between fluffs gradually increases, the velocity distribution at the bottom of the funnel is basically unchanged, and the velocity in the upper part gradually increases. The velocity in the upper part of the flocked drainage pipe fluctuates above the fluff to a certain extent. The flow velocity in the lower part of the drainage pipe forms a flow velocity ladder in the longitudinal direction of the villus, and the width of the ladder is about 2/3 of the longitudinal spacing of the villus. The optimized parameters of 3-D flow field of flocked drainage pipe are helpful to the further improvement of indoor test, and provide theoretical basis for the mechanism of preventing crystal blockage of flocked drainage pipe.
The axial symmetric model has been widely used in the research and design of spiral case structure in hydraulic power station due to its convenience, however, instead of a continuous entity, the fixed guide vanes are discretely distributed around the vertical axis of the unit, and there are some different opinions on the simulation techniques for the fixed guide vane in the existing research. Commonly used processing methods for fixed guide vanes in the spiral case axial symmetry model are summarized and two new simulation techniques on the basis of existing research are proposed. Static analyses for a practical spiral case with cushion layer are conducted using 4 axial symmetry models and a 3-D FEM model. The influences of simulation techniques for fixed guide vanes on the stress and their distribution of steel liner, concrete and fixed guide vanes are investigated. The rationality and applicability of each simulation technique for fixed guide vanes are discussed.
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