Energy dissipation of flow over the type-B Piano Key Weir

Abstract

Piano Key Weir (PKW) is an evolution with an efficient implementation over conventional labyrinth weir, especially at low heads. It is used as the crest of spillways and specific flow regulation applications for overflow control structures. The effects of a PKW on the downstream flood regime have not yet been thoroughly studied; only a few studies have focused so far on the downstream characteristics of the PKWs. The consideration of energy-dissipation is the main component of downstream elements for all hydraulic structures. Therefore, there is a need to log and assess details on the energy dissipation of the PKWs. This paper presents the results of the experimental study to investigate the energy dissipation at the base of type-B PKW under free-flow conditions in a rectangular channel. According to the current study's findings, the type-B PKWs show a higher energy dissipation efficiency at low heads than other nonlinear or ordinary weirs, but dissipation efficiency decreases as the discharge or head over the weir increases. The energy dissipation was found to decrease with the increasing magnification ratio and relative width ratio; however, the energy dissipation was found to increase with increasing cycle number (for a constant-width channel). In addition, the sensitivity of the weir, i.e., using the steps at the outlet key instead of the slopping floor, increases the efficiency of energy dissipation for low head discharges about 6.43% while decreasing by 2.05% for higher head discharges.