Evaluation of Circular Orifice Effect on Discharge Coefficient of Piano-Key Weirs using FLOW-3D

One of an effective and economical solution in order to weir efficiency is using nonlinear weirs, Which can cause  the increase of the flow over weir by changing in geometric plan and increasing in weirs length in fixed widths of the channel . in this research, the hydraulic performances of  the piano-key weirs has been simulated by FLOW-3D and also it has been validated by the laboratory data. In the following, the discharge coefficient (Cd) has been measured and evaluated with the creation of single and double circular orifice on the heel of weir ( , For the different water head and in relation to without dimension parameters    .
Findings shown with the expansion orifice diameter, discharge coefficient of combined weir -with the maximum opening  - is increasing between 0.5 to 6% in comparison to without orifice piano-key weir., besides, with the rise in the high of single orifice ,which has a fixed diameter, the discharge coefficient is reducing between 0.5 to 3%. From the other side, the usage of double orifices decreases the discharge coefficient in comparison to the single type at the same opening size, in a way that by increase in the distance of orifices, at first, it faces to the rising trend and then by reaching to   it starts revising. Finally, an equation is provided for the estimation of the discharge coefficient by benefiting without dimension parameters with   .