Evaluation Effect of Changing the Cycle Arc Angle on Discharge Coefficient of Arced Labyrinth and Arced Piano Key Weirs

Piano-Key weirs (PKW) and labyrinth weirs (LW) are nonlinear weirs that can increase the passing over flow magnitudes for a given width without increasing the water head. Arced configuration of this weir, improve the flow direction to the cycles And reduce inequality entering of flow to the various cycles. Arced labyrinth(ALW) and Arced piano key(APK) weirs are especially well used for spillway rehabilitation where larger probable maximum flow have required modification or replacement of the spillway. In the current paper, a total of 308 experiments were conducted on 15 laboratory models for analyzing the variations of APKW and ALW Hydraulic Performance through altering the geometric parameters, i.e. cycle arc angle(θ), weir height(P), crest shape, Magnification cycle(Lc-cycle/w), cycles width ratio(w/P), apex length(A) and compared with the LW, PK and linear weirs. By increasing the cycle arc angle and modifying this weirs, increased efficiency so that The average and maximum difference in discharge coefficient of ALW (θ=40o) than LW weirs are 12 and 21 percent, respectively and this difference are 25 and 40 percent between the APK (θ=40o) and PK weirs, respectively. Modified arc weirs are more efficient than their unmodified weirs. But with increasing Ht/P, values of their discharge coefficient connected to each other. Finally, by increasing the cycle arc angle, the superiority of piano key weirs are more than the labyrinth weirs.