Flow characteristics downstream stepped back weir with bed water jets

Abstract

The development of hydraulic jump downstream weirs creates local scour that may affect the overall stability of the structure or even cause complete failure. In this study, an experimental work was carried out to present a new technique using bed water jets installed to the classical smooth apron to present stilling basin with specific characteristics motivated to dissipate the hydraulic jump energy. Five rows of bed water jets were implemented to explore their presence on the energy dissipation efficiency, the hydraulic jump characteristics, and the vertical and longitudinal flow velocity distributions downstream of the weir apron toe under skimming flow regime in stepped back weirs. Three different arrangements of bed water jets were used in addition to the reference case of a non-jetted system. The sum of jets discharge from the three activated rows were constant of 12 Lit/s. The tested total discharges were 120, 150, and 180 Lit/s. Each discharge was examined with three tailwater depths of 20, 25, and 30 cm. Initial Froude numbers ranging from 1.15 to 4.99 were applied under relative jet discharges ranging from 0% to 10% of the total discharge. The results showed that by activating the middle 3 rows, the average hydraulic jump energy dissipation efficiency can be improved by up to 70.8%, and the average jump lengths can be decreased by up to 48% compared to the non-jetted system. Using stepped back weir increased the energy dissipation efficiency and decreased the jump length by about 40% and 31%, respectively compared to 1:2 sloped back weir for similar flow conditions. Finally, possible future research directions were suggested.