EXPERIMENTAL RESEARCH OF FACILITIES OF ENVIRONMENTAL PROTECTION OF HYDROSYSTEM TAILRACES FROM EROSION

During operation of hydrosystems, a number of environmental problems, associated with the water-race conjugation by the transition from a protected part of the apron to the loose erodible bed, appears. By significant flow velocities, an erosion pool develops which can lead to loss of the hydrosystem stability. For the environmental protection of the tailrace facilities by the operation of hydrosystems, devices characterized by deployment and installation mobility are required. Effective hydrodynamic controllers of the near-bottom flow rate can be developed based on the theory of a profile, flowed round by fluid. The constructive design of such devices may be fulfilled based on the profiles made of flexible materials. To determine the parameters of the flexible profiles, it is necessary to determine experimentally the regularities of the flow distribution in the tailrace in different operating modes of gates and its influence on the depth of erosion. Experimental research of the tailrace bed erosion was performed on a scale model of the overflow weir of Cheboksary hydropower station in the hydraulic flume. For the open flows having non-deformable bed, a basic criterion of dynamic similarity is the Froude number. Work of the stream, by erosion of the bed formed with viscoplastic soil, was investigated on the basis of the dimensional theory. The regression dependence of the model diameter on the value of the soil adhesion was obtained. To measure the flow velocity in the model flume, a measuring system was developed based on heat-loss anemometers with an analog-digital converter and computer data logging. During the homing experiment we tested representativeness, accuracy, reliability, uniformity, variability, distribution of the recorded data. Check of the reproducibility of the experiment results was carried out by the Cochran criterion. Adequacy of the received data was evaluated by Fisher's fitting criterion. Comparison of experimental measurements of kinematic characteristics obtained on a laboratory model, with actual values, showed good convergence. The nature of erosion in different operating modes of gates was studied. On the basis of measurements, we constructed lines of equal depths and isotachs for each flow rate and set the maximum depth of erosion. The model device for controlling the bed erosion in the hydrosystem tailraces based on the down-dropped airfoil was tested. The tested airfoils were installed in the hydraulic flume in the place of the flow descent from the model weir apron. The test of the model device was carried out with the most unfavourable operation mode for gates in relation to erosion and extreme water flow. A reduction of the maximum depth of the erosion pool during work of the airfoil was established.