EXPERIMENTAL HEAD LOSS DETERMINATION AT INCLINED WEDGE WIRE FISH PROTECTION SCREEN

摘要

For downstream migrating fishes the turbines of hydroelectric power stations are almost insuperable barriers. A possibility for fish protection is the installation of wedge wire screens placed in front of the turbine intake to guide the fishes to a suitable bypass. In order to determine the head loss of an inclined screen of suitable shape an experimental investigation has been carried out. The paper contains a description of the experimental set-up, the results and a comparison with former investigations. The experiments were performed in a rectangular flume at different incoming flow velocities (0.5 to 0.9 m/s) and screen declinations (20°to 90°. The water depth of the incoming flow was adjusted to 0.4 m, the width of the flume is 0.977 m. The screen is not scaled and Reynolds similarity is assumed. It was found that the head loss increases with increasing flow velocity and decreasing screen declination. The measured head loss does not agree with the results of calculations based on well known formulas for inclined rakes. The difference originates in the neglect of the bearing profile influence which dominates the head loss at a screen declination smaller 45°. To consider the bearing profile a new formula has been developed consisting of two terms for the rake and bearing profiles respectively. The formula also contains shape factors for each profile which were determined in this experimental investigation. For a validation of the formula experiments at screens of different shape should be carried out in the future.