Experimental study on the hydraulic characteristics of the two-stage energy dissipation in low Froude Number flow

In this study, the problem of energy dissipation under low Froude number flow conditions is investigated based on the shape of a single stage stilling basin vs. a two-stage stilling basin. Tests on a physical model were conducted to study the hydraulic and energy dissipation structure characteristics of these two types of basins in low Froude number flow. The results of these experiments reveal that under low Froude number flow conditions, the large fluctuation area of the original single stilling basin is changed in the two-stage stilling basin into an adaptive area, while the adaptive area of the downstream tail water level increases significantly, and the fluctuation of the outlet water level decreases. In addition, the streamline in the single stilling pool is sparser and the velocity gradient and vorticity smaller than those of the two-stage stilling basin, while the Reynolds stress is significantly larger. The flow in the two-stage stilling basin is more stable, and the Reynolds stress zoning is more obvious than that in the single stage stilling basin. The surface rolling zone is markedly larger than the bottom rolling zone as well. Compared with the single stage stilling basin, the energy dissipation rate of the two-stage stilling basin is significantly improved, which is beneficial to the anti-scour protection of downstream riverbeds and the shore.