滞砂防除に関する土砂水理学的研究 (第6報) : 渦動管排砂工の沈砂池への適用(農業生産工学)

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Intake water from head works has been in great demand from various sectors recently, the intake gate is not allowed to close even at a time of high water level. Therefore, it is necessory in a sand settling basin to allow water to pass and flush the sand at the same time, and to reduce the time for the sand flushing. In this sense, the one point sand flushing method using a sand flushing gate should be improved. The efficiency of the vortex tube is examined when set in a sand settling basin, as a linear sand flushing method instead of the one point sand flushing method which has been used. First, the efficiency of the two methods are compared by a basic hydraulic experiment. Second, an experiment is conducted on the basis of FROUDE'S similarity using the one-tenth model in scale of the supposed prototype sand settling basin. The prototype basin is 25m long, 6m wide, its bed slope is 0°, and the diameter of the vortex tube, D, is 0.6m. In the hydraulic model experiment the hydraulic efficiency of the vortex tube sand trap is analyzed by varying the slit width, b, the length of the vortex tube, l_1 (or that of the sand flushing tube, l_2), the depth of water, H (or discharge, Q), etc. The trapping efficiency of the sand flushing pipe is tested based on the multistage continuous method with the regulating gate of multiple-span, using sand of mean grain size d_m (=0.43mm). It is proved by the results of the experiments that the principal factor which determines the hydraulic quantities such as the velocity of inflow to the vortex tube, V, the mean velocity in the tube, V, the pressure head, p/w, the extractor discharge, Q_2,the speed of sand flushing, V_s, is the shape of a section of the vortex tube, especially the relative width of slit b/D. The dominant parameter of the spiral flow in the vortex tube is the FROUDE'S number. It is proposed how to evaluate the hydraulic quantities such as the inflow length of slit, l_1,the length of spiral flow, l_H, the effective vortex tube length, l_e, dominant FROUDE'S number, _dF_r, dimensionless mean velocity, V_x/V_<m2x>, etc. In the case in which the basin is filled with sediment, the depth of sediment, H_s, equals 2.5m; inflow, Q, equals 3.9m^3/sec; the diameter of the vortex tube is 0.6m; one span of slit regulating gate, l_g, equals 5m; the width of a slit, b, is 0.075m; a 5 span slit regulating gate is set into the vortex tube in the prototype; the result is that the sand flushing time, T_s, is about one hour with the canal discharge, Q_1,of 2.0-2.3m^3/sec, and with the extractor discharge, Q_2,of 1.6-1.9m^3/sec. These experiments prove that the vortex tube sand trap is very efficient in a sand settling basin. The possibility of the application of vortex tube sand trap to man made reservoirs is also discussed.
神戸大学の論文

滞砂防除に関する土砂水理学的研究 (第6報) : 渦動管排砂工の沈砂池への適用(農業生産工学)

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