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In this paper, the results of water flow modeling and computation of air distribution in chute spillways are described. The depth average flow solver of NASIR finite volume software was utilized for modeling of water flow in chute spillways. In this module, the shallow water equations modified for steep slopes are solved using cell-centre and cell-vertex schemes of finite volume method that suits unstructured triangular meshes. Using the computed velocity components and flow depth at each nodal point, the air entertainment parameters (air inception point, mean air concentration and vertical distribution of air concentration) are calculated by utilizing some empirical relations. The empirical relations for the air concentration were adopted by the pervious researchers using the measurements on large scale flow in chute spillways. In the present work, three modeling strategies were performed: 1) Solution of flow field and then calculation of air concentration parameter (as a post-processing operation after convergence of the water flow solution), 2) Coupled solution of the flow equations and air concentration relations considering the flow bulking and reduction of global friction parameters due to air entrainment and 3) Adding the air entrainment on density variation effects to the coupled solution of the flow equations and air concentration relations considering the flow bulking and reduction of global friction parameters due to air entrainment. In order to assess the quality of the results of the three modeling strategies, the readily available flow velocity and air concentration measurements on AVIMORE chute spillway were used for comparison considering the best experimental relations for simulating the entrainment of air into the flow on chute spillways. In order to provide better understanding of the velocity and air concentration, the vertical distribution profiles of these parameters were plotted from the multi-layer treatments of depth averaged computed results. Comparison of the computed velocity fields and air concentrations with the reported field measurements at the stations 503 and 505 of AVIEMORE chute spillway presents promising agreements. However, the accuracy of the 2nd and 3rd modeling strategies (in which the coupled solutions of water flow equations and air concentration relations are considered and the effect of air content on the reduction of global friction of the water flow is taken into consideration) was much better than that of the 1st modeling strategy (in which the air concentration relations are considered as post processing on water flow equation solution for depth and velocity fields). Furthermore, no significant differences were observed between the results of the 2nd and 3rd modeling strategies. Hence, it can be concluded that the effect of air concentration on density variation of the supercritical water flow does not play an important role on the results of the coupled solutions of water flow equations and air concentration relations.

Keywords: Modeling chute spillway flow, Vertical distribution of air entrainment from water surface, SWE for steep slope

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