Hydraulic characteristics of water-wings for the middle-pier of a discharge tunnel*

Water-wings, induced by the middle-pier placed in the inlet of a discharge tunnel, have harmful effects on the operation of the discharge tunnel. Based on dimensional analysis and physical model tests, the hydraulic characteristics of water-wings were investigated and their causes were analyzed in this study. The results show that the height and length of the water-wings increased with the increase of three factors, i.e., the Froude number Frd of the outlet of the pressure section, the depth Hc of the water surface concave at the end of the middle-pier, and the impact length Li of the two flows after this end.