Abstract
Air-water flows appear in both natural and man-made situations. In spite of the notable progress verified during last four decades, there are still significant challenges to establish definite, solid guidelines to simulate these flows. When dealing with flows past hydraulic structures, the high Reynolds number promotes a wide range of scales; further, the small scales associated to the bubble size contribute to the macro-behavior of the flow. This issue requires either a detailed resolution of the flow at the “bubble-to-bubble” scales, or the use of indirect approaches which take into account the sub-grid interactions. The issue significantly complicates when air entrainment needs to be simulated. Here, we introduce a framework for the multi-scale modeling of air entrainment in hydraulic structures. First, we present Scale-Resolving Simulations (SRSs), which were started in 2015-2017, continued in 2020, and evolved to an interesting extent recently for flows past stepped spillways. The SRS model uses the Spalart-Allmaras-Detached Eddy Simulation model, and no sub-grid model is included for the dispersed air phase. Then, we move to a Reynolds-Averaged Navier-Stokes (RANS) approach for the same flow. The RANS is based upon a three-phase mixture formulation; further, a criterion using a balance between a disturbing energy and stabilizing energy allows for determining the regions where air is entrained or detrained. The combination has produced good results for stepped spillways as well as impinging jets and other flows. The RANS model provides information about air concentrations and correctly predicts the flow bulking, which causes notable numerical shortcomings in many other codes. Both methodologies show very good agreement with experimental data. Future lines of research for both types of models are discussed during the presentation.
Bio
Dr. Fabián A. Bombardelli is the former the Gerald T. and Lillian P. Orlob Endowed Professor in Water Resources (2017-2022), at the Department of Civil and Environmental Engineering of the University of California, Davis (UC Davis). Bombardelli is a leader in the development of theoretical and numerical models for multi-phase flows, as well as in their observation in the laboratory and the field. He currently serves as the Editor in Chief of the Journal of Hydraulic Engineering, of the American Society of Civil Engineers (ASCE), and of RIBAGUA, the International Journal of Water of Iberoamerica, IAHR. Bombardelli received a degree in Hydraulic Engineering from the National University of La Plata, Argentina; a Magister (Master) degree in “Numerical Simulation and Control” at the University of Buenos Aires, also in Argentina; and a PhD by the University of Illinois, Urbana-Champaign (UIUC), under the supervision of Prof. Marcelo Garcia. Prior to his move to the States, he was a Researcher in Numerical Models at the National Water Institute for seven years.
Bombardelli is widely known for his contributions on bubble plumes, sediment transport in open channels, the Basset force, flow in stepped spillways, and for the application of the phenomenological theory of turbulence to hydraulics; in addition, he has developed applied research on water bodies in California. He has also worked as a consultant for the government of Argentina and for the United Nations in Peru, in 2011 and 2013, proposing systems of cascades for the very polluted Matanza-Riachuelo, Buenos Aires. He has delivered seminars and keynote lectures in many universities and conferences worldwide. His research has been supported by the US Army Corps of Engineers, the National Science Foundation, FEMA, the California Departments of Water Resources (DWR) and Pesticide Regulation, and other state and federal agencies and private organizations