CFD Modeling of Sanitary Effluent Flow in Parshall Flumes Considering Surface Tension Variability

Resumo

This research aims to analyze the flow behavior of sanitary effluents in Parshall flumes through Computational Fluid Dynamics (CFD) simulations performed using ANSYS Fluent. The central hypothesis is that the surface tension of wastewater, which differs from that of pure water, significantly influences the hydraulic behavior of the flow, especially in critical regions of the flume. To represent wastewater in a simplified but technically grounded manner, water was used as the base fluid, with surface tension values varied across three scenarios: 0.030 N/m, 0.040 N/m, and 0.050 N/m, as recommended by the literature.The flume geometry was modeled according to technical standards, and the flow was considered two-phase (water–air), incompressible, and transient, with the interface between phases captured using the Volume of Fluid (VOF) method. Turbulence was modeled using the Shear Stress Transport k-omega (k-ω SST) model, chosen for its proven capability to capture strong shear zones and boundary layer behavior in transitional flows. Boundary conditions included a uniform velocity profile at the inlet, atmospheric pressure at the outlet, rough no-slip walls, and a free surface representing air–water interaction.The results revealed that lower surface tension values lead to greater surface instability, enhanced recirculation zones downstream of the throat, and increased air entrainment. These effects can compromise flow measurement accuracy, particularly in flumes equipped with ultrasonic or pressure-based level sensors. Variations were also observed in velocity profiles and stage-discharge curves, with higher surface tensions yielding smoother flow surfaces and more stable hydraulic conditions.It is concluded that surface tension is a non-negligible parameter in CFD modeling of wastewater flows in Parshall flumes. Its influence extends beyond surface aesthetics, impacting the internal flow structure and potentially altering hydraulic measurements. The study contributes to advancing CFD applications in sanitary engineering by proposing a realistic and computationally efficient approach for simulating effluent flows with varying physicochemical properties.