Experimental evaluation of free and submerged flow over piano key weirs

The piano key weirs (PKWѕ) are type of nonlinear weirs which can increase the discharge for a given width without the increase in head water .In piano key the length of weir crest in both upstream and downstream can be incresead and therefore can be considered to be a suitable substitution for the labyrinth weirs, with a relatively small footprint In this study, in order to evaluate the Hydraulic performance of PKWs of free & submerged flow, totally 554 experiments are conducted on 11 physical models. Results showed that in the free flow the PK₁.₄ (inlet over outlet key width; wi /w₀=1.4) in the head water ratio of 0.5≤H₀/P≤1 and the PK1.25 in H₀/P≥0.1 as compared with other weirs, has higher Hydraulic performance. In the case of constant values for the wi/w₀ ratio and changing of the floor slope from 1:1.5 to the curve (a quarter of the circle; PKC) the discharge coefficient of these weirs increased about 3 percent. In the condition of submerged flow the value of the submerged upstream head over the free flow of upstream head (H*/H₀) increased by decreasing the submerged upstream head ratio (H₀/P). For the PK1 weir and in the submergence values lower than 0.48, the downstream depth had no effect on upstream depth of weir, and H*=H₀. The modifying of PK₁ causes a decrease the modular submergence range in this weir and occurrence of the full submergence with a little delay. Modifying of PKC₁, lead to an increase in the modular submergence range and no change in the full submergence.