Abstract: The layout form of trapezoidal pier and suspension grid in stilling basin is optimized through comparative analysis of the hydraulic characteristics and energy dissipation effect in the presence and in the absence of trapezoidal pier and suspended grid in stilling basin via physical model test. Results show that under the condition of water flow of low Froude number, the trapezoidal pier-suspended grid joint energy dissipator could generate uniform water depth distribution, smaller fluctuation range of pressure distribution gradient along the stilling basin floor and time-averaged pressure distribution coefficient, and better overall stability. The kinetic energy correction coefficient basically maintained in the range of 1 < α< 2, which can effectively improve the velocity distribution at the section of pool entrance. The energy dissipation rate increased from 52.25%, 70.37% and 75.89% to 56.74%, 75.95% and 79.22%, respectively. With the trapezoidal pier at about 0.35 L away from the head of stilling basin with staggered double row when the height of suspension grid is the same as that of tail ridge and arranging in single rows at equal spacing in the trapezoidal pier-suspension grid stilling basin, the overall flow pattern improves obviously, the flow rate at the outlet of stilling basin reduces to 0.4 m/s, and the energy dissipation rate increases to 59.63%, 76.12% and 79.37%. The research results offer an idea for the underflow energy dissipation of similar projects.

Key words: water flow of low Froude number, trapezoidal pier-suspended grid, hydraulic characteristics, layout form, time-averaged pressure distribution coefficient