Numerical modeling of air concentration in skimming flow regime on the stepped spillways

In the present study، the flow field on stepped spillways in the skimming flow regime was modeled using free surface models of VOF and Mixture developed in Fluent software. Standard k-ε، RNG k-ε، Realizable k-ε and RSM turbulence models were used to resolve the Reynolds stresses. The results of concentration and velocity distribution were compared with those from an experimental study carried out by Chanson and Toombes in 2002a using a physical model set up in the hydraulic Laboratory at the University of Queensland. Comparing the results of VOF and Mixture models shows that the results obtained from the numerical modeling using the above-mentioned turbulence models، are in relative adaptation to each other and laboratory results. In general، the model of Standard k-ε yields worse results for concentration distribution in high discharges، but it acts like the other models in lower discharges. The results of velocity distribution obtained from Standard k-ε turbulence model using both methods of VOF and Mixture are more suitable results. The air and water flow pattern formed in models of Mixture and VOF are the same، but convergence time of the Mixture model is shorter than that of VOF model. RSM turbulence model privileges the longest convergence time and the Standard k-ε model has the shortest convergence time in both models of VOF and Mixture. In addition، among different meshes، the Tri pave discordant mesh brings about the best results.