Numerical analysis of roll waves in chutes

Uniform flow will become unstable when the channel slope is very steep. When this happens, the free surface will form a series of roll waves. This paper, using the Fluent software and applying the volume of fluid model to simulate free surface flow and the k – ε turbulence model, analyzes conditions for roll wave formation in free surface flow with the aim of predicting their occurrence in chutes. This study describes how the type of cross-section of the chutes influences the formation of roll waves. Hydraulic characteristics of the flow in the physical model of the flood control structure for Azad Dam spillway, which consists of a side spillway, chute, and flip, are three-dimensionally simulated. Numerical predictions were compared against the experimental data and results show that there is a good agreement between numerical and experimental results. Results indicate that an increase in side slope tends towards flow stability and the slower formation of rolling waves. Also, the rolling waves are expected to be generated for sections of the chute when the difference between the maximum dynamic pressure and the minimum dynamic pressure in those sections is above 9,000 Pa.