Experimental and numerical investigation of piano key weirs.

Piano Key Weirs (PKW) are useful overflow structures to increase discharge capacity per unit length of spillway crest for relatively small heads over the weir compared to a standard straight weir crest. PKW can be used as a side or frontal weir in many circumstances to regulate reservoir levels with small changes in water surface elevation. Nearly constant reservoir level has many advantages in optimum operation of water reservoirs for instance in maximizing hydropower production. There are several empirical formulations available in the literature to find the discharge over the PKW for a given head. However, because of large number of geometric parameters involved in the weir design, available experimental data gathered from different sources do not overlap showing significant variations indicating dependence on specific experimental conditions of each data source. There is a physical model at 1/30 scale used in this study involving three units of PKW which was constructed as a part of hydraulic model testing for the spillway of Aşağı Kaleköy Hydropower Plant which is under construction in Turkey. Head-discharge data was measured for the specific design available. Then, Flow3D was used to numerically solve flow over PKW for different configurations, one configuration being identical to that of the physical model, at the model scale. The experimental results are compared to numerical ones to validate the CFD code. It was noticed that CFD solution is very sensitive to mesh size and quality. After validation, Flow 3D was used to investigate various design configurations at prototype scale to maximize the discharge capacity of the PKW. Compared to the flat shape, having curved parapet walls increases the discharge capacity of the system by approximately 3%