Enhancing Industrial Design: A Comparative Study of CFD and Physical Modeling for Vortex Drop Structures

Computational fluid dynamics (CFD) and physical modeling are frequently used in tandem during the project design and evaluation to maximize confidence that the system will perform as designed. In some cases, this can facilitate a comparison of methods. This paper presents a comparative analysis of CFD and physical modeling for six proposed vortex drop shafts that are part of the I-35 Capital Express Central Drainage Tunnels project. The study aims to evaluate the reliability of CFD as a design tool by benchmarking its performance against physical models, with a focus on replicating hydraulic behaviors. Using the k-omega SST turbulence model, the research examines critical aspects such as flow patterns, air entrainment and detrainment processes, and overall hydraulic efficiency in these structures. The analysis delves into key parameters affecting CFD accuracy, including the impact of mesh resolution, turbulence schemes, outlet boundary conditions, and surface roughness. By investigating these factors, the paper highlights how precise numerical setups can influence the ability of CFD to reproduce physical model results effectively. The study focused on air entrainment and detrainment phenomena, which are essential for the proper functioning and safety of vortex drop shafts. However, these phenomena were excluded from the final simulations due to discrepancies caused by the bubble size in the air entrainment model. Further study by Flow Science has provided insights into refining the setup, suggesting that adjustments to bubble size in Flow-3D could improve alignment between CFD and physical model results. The paper also provides a detailed account of the design evolution of the drop structures, tracing the transition from initial conceptual ideas to finalized designs. This progression explores efforts to reduce swirling in the deaeration tunnel, a feature where physical models indicated it likely does not impact performance significantly. This progression showcases the iterative process of using CFD and physical modeling to refine hydraulic performance metrics and ensure optimal operational efficiency. The study evaluates these design changes by assessing their impact on hydraulic efficiency and structural performance, demonstrating the importance of integrating both modeling approaches for engineering success. Finally, the research seeks to address a fundamental question: Can CFD serve as a reliable and efficient alternative to physical modeling for drop structure design in industrial applications? While CFD performs effectively in the approach channel, vortex generator, and drop shaft, uncertainties remain in highly turbulent flow zones, such as at the bottom of the structure. However, in the deaeration tunnel, CFD seems reliable for bulk flow patterns. The findings suggest that CFD models should always be performed for vortex drops, with physical models added only where CFD blind spots-such as air entrainment and detrainment-are crucial. By synthesizing findings from numerical simulations and physical tests, the paper underscores the potential of CFD to complement or even replace traditional physical modeling in specific scenarios. The insights gained from this study emphasize the value of combining advanced simulation techniques with physical validation, offering a roadmap for future design and optimization of hydraulic structures.