Investigation of flow characteristics and energy dissipation over new shape of the trapezoidal labyrinth weirs

Abstract

Labyrinth weirs are mainly used to increase the discharge capacity. The current study adds a new performance to labyrinth weirs as an energy dissipator. The labyrinth weirs' zigzag shape and flow behaviour could benefit energy dissipation. Therefore, the present study aims to investigate the hydraulic characteristics and energy dissipation of the compound labyrinth weir. Sixteen models were used for different sidewall angles (α°) of 6–35 and 90 (linear weir for comparison). The results demonstrated the highest values of the compound coefficient of discharge, Cdc, for a sidewall angle of 35°, and the lowest value of the compound coefficient of discharge for a sidewall angle of 6°. The Cdc increased initially at low H՛t/P՛ values, and the Cdc showed a decreasing trend for higher values of H՛t/P՛. For sidewall angles (α°) ranging from 6 to 35, the compound coefficient of discharge Cdc does not significantly change as it approaches a value of H՛t/P՛ = 1.0. Furthermore, for the range of the relative critical head (yc/P՛) between 0.07 and 0.95, the results showed that the compound labyrinth weirs could dissipate the energy of flow by 93%, 92%, 89%, 85%, 83%, 79%, and 75% for α° = 6, 8, 10, 12, 15, 20°, and 35, respectively. The amount of improvement in energy dissipation over a compound labyrinth weir was better than a linear weir by 17%, 15%, 14%, 12%, 11%, 10%, and 8% for α° = 6, 8, 10, 12, 15, 20, and 35, respectively. The residual energy (E1/Emin) at the base of downstream compound labyrinth weirs was closer to the minimum potential amount of residual energy as yc/P՛ increased. For a given value of yc/P՛, the relative residual energy at the base of compound labyrinth weirs increased as the sidewall angle (α) increased. An empirical equation has been provided to predict the compound coefficient of discharge when relative energy dissipation data is available.