Study of USBR VI Stilling Basin with Entropy Generation Index

Stilling basins are one of the most important parts of hydraulic structures to dissipate the kinetic energy of the flow. The dissipation of the energy is an essential problem in the design of any stilling basin. USBR VI stilling basin is one of the oldest basins designed for dissipating the pipe outlet flow. This basin looks like a box with the intermediate baffle and an endsill. In this paper, the effect of the USBR VI stilling basin geometry on the entropy generation has been studied numerically by solving the RANS equations with the RNG k-epsilon turbulence model. In this research, the entropy generation analysis is used for the first time in the USBR VI stilling basin. In this study, the total entropy generation is introduced as a design index for the USBR VI stilling basin and its results are compared with the characteristics of the flow field in the basin and the outlet flow from the basin. The effect of W/D ratio (Basin width to incoming flow depth to the basin) on the flow field, entropy generation rate, and total entropy generation is analyzed. The results showed that variations of the total entropy generation have a good agreement with variations of the total hydraulic head loss along the basin, mean and maximum velocity on the endsill and shear velocity near the downstream channel bed. By decreasing of the W/D ratio from 9.23 to 3.50, total hydraulic head losses is decreased from 89 to 39 percent. Also, in general, a large W/D ratio is beneficial for the best performance and highest energy dissipation.