Hydraulic characteristics of swirling flow at shaft spillways with the marguerite-shaped inlets.

Hydraulic characteristics of swirling flow at shaft spillways with an innovative inlet, namely the marguerite-shaped inlet, is investigated based on model experimentation. Detailed measurements of head–discharge relationship, flow regimes, water free-surface profiles, flow circulation, discharge coefficient and threshold and critical submergence depths were performed for shaft spillways with marguerite-shaped inlets. Results indicate that the strength of swirling flow through a marguerite-shaped inlet is significantly lower than that of a simple shaft and a morning glory spillway. Marguerite-shaped inlets increase the developed crest length by at least 6 times the global size of the original shaft spillway. Therefore, they produce exceptional hydraulic performances in increasing the weir overflow length without changing the global size of the shaft spillway, thereby increasing the flow discharge up to 6, 4 and 1.5 times the simple shaft, morning glory and circular piano-key spillways, respectively. Finally, based on the detailed experimental data, different empirical correlations are derived for estimating the threshold and critical submergence depths and discharge coefficient of the marguerite-shaped inlets for different flow regimes using regression analysis. [ABSTRACT FROM AUTHOR]