Effect of baffled outlet keys at Piano Key Weir on dissipating energy

The piano key weirs are used at storage dam’s crest and irrigation and drainage systems. Piano key weirs are the newest type of long-crested weirs that have most crest length in comparison to Labyrinth weirs with the same width, because they increase the discharge capacity. Using baffles at outlet of piano key weirs with the purpose of increasing energy dissipation, is a method that has been less investigated. ,. In this investigation the subject of dissipation of energy in such structures is taken into consideration, by considering the effective parameters. , The physical models based on two different design (N) were fabricated in order to investigate the effect of design of baffles. The baffles were fixed on weir outlet key consisting of two formation namely: N1 (rows of 2 & 3 baffles that have just crossed) and N2 (2 rows of baffles). Total number of 27 tests were carried out in the range of 5 to 135 lit/s discharge. The test results showed that the energy dissipation decreases with increasing discharge. The energy dissipation in model with formation (2-2) was about 1.16 percent more than model with formation (3-2) and about 8.6 percent more than model with no baffle. Also the trend of discharge coefficient in this type of weir was evaluated. This means that the maximum amount of theoretical discharge Coefficient method was 0.63 and using integral method was 2.54 in all experimental models.