Inception point of flow aeration on quarter-circular crested stepped spillway

Abstract

The aim of this study was to investigate the location of inception point of flow aeration (LIPFA) on quarter-circular crested stepped spillway (QCSS). The QCSS is a typical stepped spillway the crest geometry of which consists of a quarter circle. To this purpose, a series of experiments were programmed. Dimensional analysis showed that the slope of the downstream stepped chute, step size and flow discharge are the effective parameters in the LIPFA. In this study, three values of 0.1 m, 0.15 m and 0.2 m were considered for the crest radius of QCSS. The heights of stepped spillways were as 0.05 m, 0.08 m and 0.10 m and lengths of steps were as 0.05 m, 0.10 m, and 0.15 m. Considering the step size, the four slopes for the downstream stepped chute were obtained at 0.33, 0.50, 1.0 and 1.60. The slopes of stepped chute changes from 0.33 to 1.6. The number of steps was 8, 10 and 16. Results showed that as flow rate increases, the distance of the LIPFA from the crest increases as well. By half the size of steps, the length of the non-aerated area increases by more than sixty percent. With an increase of one hundred percent slope, the length of the aerated area increases by more than 20%. In general, the reducing of the slope of the stepped spillway leads to decrease the length of the area of non-aerated, and also refining the size of steps leads to scrolling the location of inception point of aeration to the downstream.