The concept of understanding and predicting the behavior of flow characteristics such as velocity, pressure, and energy in the presence of bubbles and droplets of various morphologies has always fascinated researchers. Flow aeration has been a challenging topic contributing to drag force, flow morphology, and cavitation, which was successfully investigated through numerical studies. Subsequently, it has resulted in the development of numerical models that can predict and simulate the self-aerated flow more accurately with less cost and in a shorter time frame. This study presents a numerical model that utilizes drag coefficient, disperse phase diameter, and interfacial area concentration to provide a novel idea of drag force in the presence of bubbles and droplets in flow. As part of enhancing the numerical model's precision, a dynamic calibration parameter for drag coefficient is incorporated which captures the macro-and microflow characteristics as over- and subgrid effects. Additionally, bubbles and/or droplets lead to a variable eddy viscosity that implemented in the numerical model as modified mixture viscosity. Furthermore, this numerical model is implemented on a stepped spillway, a well-known structure that causes aeration, to validate its accuracy and present a better understanding of the flow velocity changes, pressure differences, aeration, and energy. Finally, this numerical model predicts the self-aeration with consistent precision to experimental data that can be used alternatively to create, investigate, and optimize the design of complex geometries like stepped spillways.
