Characteristics of Supercritical Flow Below a Sluice Gate in a Horizontal Channel

In the supercritical flow below a sluice gate, the determination of the position of the jump is important for hydraulic design of a horizontal apron, and the clarification of the water surface profile with boundary-layer development below a gate is necessary. A method for analytical calculation of the boundary-layer thickness and the water depth has been proposed in the developing flow region (Ohtsu and Yasuda, 1994). Also, it is important to obtain the energy loss of the supercritical flow below the gate.

Recently, it has been shown that the development of the boundary layer and the fluctuation of the water surface at the toe of the hydraulic jump have important effects on the characteristics of the air entrainment and the velocity fields in jumps (Takahashi and Ohtsu, 2017; Takahashi and Ohtsu, 2009). However, the effect of the development of the boundary layer on the free-surface fluctuation of a supercritical flow has not yet been clarified.

In this paper, the characteristics of the supercritical flow below a sluice gate in a horizontal rectangular channel are investigated both analytically and experimentally. For the developing flow, the method for calculation of the boundary-layer thickness and the water depth is examined. The relationship between the head loss and the energy thickness is presented by using an energy equation for the boundary layer. The results of the analysis are validated by the experiments performed. For the developed flow downstream of the critical point, the experimental investigation reveals the position of the section where the velocity characteristics are equal to those of the uniform open channel flow. Furthermore, the free-surface fluctuation is demonstrated.

References

Ohtsu, I. and Yasuda, Y. (1994). Characteristics of supercritical flow below sluice gate. Journal of Hydraulic Engineering, 120(3), 332–346.

Takahashi, M. and Ohtsu, I. (2009). Effect of inflow condition on air entrainment characteristics in hydraulic jump. Proceedings of the 33rd IAHR congress, Vancouver, BC, Canada, 4917–4924.

Takahashi, M. and Ohtsu, I. (2017). Effects of inflows on air entrainment in hydraulic jumps below a gate. Journal of Hydraulic Research, 55(2), 259–268.